SY181025
DENTON CREEK DRAINAGE STUDY
PREPARED BY:
HALFF ASSOCIATES, INC.
1201 N. BOWSER RD.
RICHARDSON, TX 75081
PREPARED FOR:
CITY OF COPPELL, TEXAS
Denton Creek Drainage Study
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TABLE OF CONTENTS
EXECUTIVE SUMMARY ........................................................................................................................................... 5
I. INTRODUCTION .................................................................................................................................................. 8
A. Purpose ............................................................................................................................................. 8
B. Study Area ......................................................................................................................................... 8
C. Study Objectives ............................................................................................................................... 9
D. Flooding History .............................................................................................................................. 10
II. WATERSHED DESCRIPTION .............................................................................................................................. 11
A. Data Search and Collection ............................................................................................................. 11
Methods ...................................................................................................................................... 11
Data Sources ............................................................................................................................... 11
B. Field Reconnaissance ...................................................................................................................... 11
C. Geomorpholgy Evaluation .............................................................................................................. 12
Methodology ............................................................................................................................... 12
Stream Condition Assessment .................................................................................................... 12
Identified Areas of Concern ........................................................................................................ 12
Recommendations ...................................................................................................................... 14
D. Survey .............................................................................................................................................. 14
III. HYDROLOGY ................................................................................................................................................... 15
A. Methodology ................................................................................................................................... 15
Rainfall Data ................................................................................................................................ 15
Drainage Basin Delineation ......................................................................................................... 16
Drainage Area Parameters .......................................................................................................... 17
Channel Routing .......................................................................................................................... 20
Reservoir Routing ........................................................................................................................ 20
B. Results and Concusions ................................................................................................................... 20
Summary of Results .................................................................................................................... 20
Comparison with Effective Discharges ........................................................................................ 22
IV. HYDRAULICS ................................................................................................................................................... 23
A. 1D Steady state Model Development ............................................................................................. 23
Cross Sections ............................................................................................................................. 23
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Stream Reach Layout .................................................................................................................. 23
Manning’s Roughness Coefficients ............................................................................................. 24
Ineffective Areas ......................................................................................................................... 24
Levees ......................................................................................................................................... 24
Lateral Structures ........................................................................................................................ 24
Bridges and Culverts ................................................................................................................... 24
B. 1D/2D Unsteady State Model Development .................................................................................. 25
Model Development ................................................................................................................... 25
Unsteady Flow Data .................................................................................................................... 25
Results ......................................................................................................................................... 26
C. 2D Model Development .................................................................................................................. 29
Model Development ................................................................................................................... 29
Terrain Modification ................................................................................................................... 29
Manning’s n-value ....................................................................................................................... 29
Boundary Conditions ................................................................................................................... 29
Simulation Parameters ................................................................................................................ 30
Model Validation ......................................................................................................................... 30
Results ......................................................................................................................................... 31
V. DEVELOPMENT OF ALTERNATIVES ................................................................................................................... 38
A. Alternatives Analysis ....................................................................................................................... 38
Alternative 1- Bypass Channel .................................................................................................... 38
Alternative 2- Stream Barbs ........................................................................................................ 42
Denton Tap Grade Control Structure .......................................................................................... 45
Property Buyout Option .............................................................................................................. 46
No Action Option ........................................................................................................................ 46
B. Cost Estimates ................................................................................................................................. 46
VI. CONCLUSIONS ................................................................................................................................................ 47
VII. REFERENCES .................................................................................................................................................. 48
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LIST OF TABLES
Table 1: Conceptual Alternative Analysis Summary Table ........................................................................... 6
Table 2.1: Summary of ArcGIS Data ............................................................................................................ 11
Table 3.1: Precipitation for 1- to 500-year Rainfall Events ......................................................................... 15
Table 3.2: Drainage Area Comparison ........................................................................................................ 16
Table 3.3: Land Use ..................................................................................................................................... 17
Table 3.4: Initial and Constant Loss Parameters ......................................................................................... 18
Table 3.5: Drainage Area Parameter Comparison ...................................................................................... 19
Table 3.6: HEC-HMS Discharge Summary ................................................................................................... 21
Table 3.7: 100-Year Discharge Summary .................................................................................................... 22
Table 4.1: Hydraulic Structures ................................................................................................................... 25
Table 4.2: FEMA Water Surface Elevation Comparison .............................................................................. 26
Table 4.3: USACE Water Surface Elevation Comparison............................................................................. 27
Table 4.4: 1-D Steady vs Unsteady Comparison ......................................................................................... 27
Table 4.5: May 2015 Storm Event Calibration ............................................................................................ 30
Table 4.6: iSWM Allowable Velocities for Natural Channels ...................................................................... 31
Table 5.1: Alternative 1 Water Surface Elevation Comparison .................................................................. 40
Table 5.2: Stand Alone Channel Water Surface Elevation Comparison ...................................................... 41
Table 5.3: Alternative 2 Water Surface Elevations Comparison ................................................................. 44
Table 5.4: Summary of Cost Estimates ....................................................................................................... 47
LIST OF FIGURES
Location of Proposed Drop Structure ........................................................................................................... 6
Location of Proposed Alternatives ................................................................................................................ 7
Figure 1: Project Location ............................................................................................................................. 9
Figure 2.1: Erosion Hazard Zone (EHZ) Setback Limits ............................................................................... 13
Figure 4.1: 2-year Existing Velocity Map (River Station 36500 to 34000) .................................................. 32
Figure 4.2: 2-year Existing Velocity Map (River Station 35000 to 31500) .................................................. 33
Figure 4.3: 2-year Existing Velocity Map (River Station 31500 to 28500) .................................................. 33
Figure 4.4: 2-year Existing Velocity Map (River Station 16000 to 14800) .................................................. 34
Figure 4.5: 2-year Existing Velocity Map (River Station 14000 to 12700) .................................................. 35
Figure 4.6: 2-year Existing Velocity Map (River Station 13200 to 11950) .................................................. 36
Figure 4.7: 2-year Existing Velocity Map (River Station 9400 to 5400) ...................................................... 37
Figure 5.1: Alternative 1 2-year Velocity Map (River Station 17500 to 11500) .......................................... 39
Figure 5.2: Stream Barb Design Layout ....................................................................................................... 42
Figure 5.3: Aquilla Creek Bendway Weir, Waco, TX.................................................................................... 43
Figure 5.4: Alternative 2 Bankfull Velocity .................................................................................................. 44
Figure 5.5: Grouted Sloping Boulder Drop for Unstable Channels in Erosive Soils .................................... 45
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APPENDICES
APPENDIX A – Exhibits
Exhibit 1- Project Area Map
Exhibit 2- Drainage Area Map
Exhibit 3- Flow Change Locations
Exhibit 4- Hydrologic Soils Map
Exhibit 5- Land Use Map
Exhibit 6- Hydraulic Work Maps
Exhibit 7- Revised Existing 2-year Velocity Distribution Map
Exhibit 8- Alternative 1 Proposed Bypass Channel
Exhibit 9- Alternative 2 Proposed Stream Barbs
Exhibit 10- Alternative 3 Proposed Property Buyout & Erosion Hazard Zone
APPENDIX B – FLUVIAL-GEOMORPHIC ASSESSMENT OF THE DENTON CREEK: DCLID No. 1 DOWNSTREAM
TO THE ELM FORK
APPENDIX C – COST ESTIMATES
APPENDIX D – HEC-HMS OUTPUT
APPENDIX E – HEC-RAS OUTPUT
APPENDIX F – HYDROLOGIC PARAMETER CALCULATIONS
APPENDIX G – DIGITAL DATA
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EXECUTIVE SUMMARY
Denton Creek is a major tributary of the Elm Fork Trinity River in North Central Texas. The headwaters of
the stream are located near Bowie, TX. Denton Creek flows southeasterly through rural areas of
Montague, Wise and Denton Counties. Grapevine Lake, a US Army Corps of Engineers reservoir built
primarily for flood control and water supply, is located on Denton Creek near Grapevine Texas (Tarrant
and Denton Counties). Downstream of Grapevine Lake, Denton Creek flows easterly through urbanized
portions of Tarrant and Dallas County to its confluence with the Elm Fork Trinity River just north of Sandy
Lake Road. Only the lower portion of Denton Creek (below Grapevine Lake) is included in this study.
Over the past decade, several homeowners located along the creek have reported erosion problems to
the City of Coppell raising concerns over safety and long-term channel stability. Significant sedimentation
within the DCLID-1 portion of the creek has also been observed bringing into question the creeks flood
capacity and levee accreditation. Because of these concerns along with the flooding that occurred from
the May and June 2015 floods, the City of Coppell commissioned this study to identify solutions along
Denton Creek.
Field reconnaissance and geomorphology evaluations were performed for this study to determine
locations of significant erosion, the causes of sedimentation, and to determine stable channel design
parameters. Locations of concern were measured and documented within the Fluvial-Geomorphic
Assessment of the Denton Creek: DCLID No. 1 Downstream to the Elm Fork completed as part of this study
by Dr. Peter Allen and Dr. John Dunbar of Baylor University, along with Dr. Jeff Arnold of the United States
Department of Agriculture – Agriculture Research Service. Using the results of the evaluation, alternatives
were developed based on stable channel recommendations to address areas of concern due to channel
bank erosion and sedimentation. Field surveys of existing structures and cross sections along the channel
were performed. Detailed survey through the DCLID-1 portion of the creek was conducted using
conventional survey techniques as well as sonar equipment for locations along the creek with deep water
to accurately determine the extents of sedimentation along the levee portion.
This study is based on the most recent technical data available for Denton Creek including the existing
hydrologic and hydraulic models obtained from United States Army Corps of Engineers (USACE) Corridor
Develop Certificate (CDC) completed in May 2013. Updates were made to these models to reflect the
current conditions of the watershed. Land uses in the Denton Creek watershed below Grapevine Lake are
considered to be almost fully-developed. Therefore discharges developed and used for this study were
based on fully developed land uses.
A detailed hydraulic study was performed along Denton Creek for existing conditions by updating the 2013
USACE HEC-RAS model. This included the development of a one-dimensional (1D) steady state, two-
dimensional (2D), and a combined 1D/2D unsteady HEC River Analysis System (HEC-RAS) models. The
study determined peak water surface elevations for the existing conditions 1-, 2-, 5-, 10-, 25-, 50-, 100-,
and 500-year events. The 1D steady state model was developed to update the fully developed USACE
100- and 500-yr discharges, which incorporate releases out of Grapevine Lake during these events. The
1D/2D unsteady model was developed to evaluate the impacts of flow interactions between Denton Creek
and the Elm Fork. The full 2D model was developed to better evaluate velocities for the 1-year up to the
10-year storm event as well as flow interaction between the flood control channel and Old Denton Creek
within the DCLID-1.
The Conceptual Level Alternative Analysis focused on proposed improvements within public Right of Way
(R.O.W.) to reduce flood risk and increase channel stability (based on recommendations from the fluvial-
geomorphic assessment). Using the results of the geomorphology evaluation, alternatives were
developed based on stable channel recommendations to address areas of concern due to channel bank
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erosion and sedimentation. Several measures were evaluated to provide multiple benefits to the
surrounding areas while avoiding negative impacts downstream and/or upstream. The conceptual level
alternatives consist of:
• The construction of a new bypass channel
• Stream barbs (weir-like rock structures located along channel banks used to prevent erosive
velocities along the bank)
• Voluntary buyouts
• Grade control structures to prevent channel down-cutting
The two structural alternatives developed as part of this project were a bypass channel and stream barbs
to address erosion along Denton Creek. Alternative 3 addresses a nonstructural option in the form of a
voluntary buyout of the affected properties. Included in all three alternatives is replacement of the
existing storm sewer outfall headwall located approximately 2,400 feet downstream of DCLID-1 and a
grade control structure to be located just downstream of Denton Tap Road. Table 1 shows the total
conceptual level cost estimates for each alternative.
Table 1: Conceptual Alternative Analysis Summary Table
Alternative Alternative Description Cost
1 Denton Creek Bypass Channel $ 7,400,000
2 Stream Barbs $ 836,000
3.1 Property Buyout- Phase 1 (Initial) $ 5,300,000
3.2 Property Buyout- Phase 2 (Future) $ 34,600,000
Location of Proposed Drop Structure
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Location of Proposed Alternatives
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I. INTRODUCTION
A. PURPOSE
Based on historical observations of Denton Creek during the past decade, segments throughout the creek
have undergone significant erosion and sedimentation raising issues for both citizens and governing
bodies located near the creek. Sedimentation within the flood control channel of the Denton County Levee
Improvement District No. 1 (DCLID-1) has raised flood risk concerns due to higher Base Flood Elevations
(BFE) resulting in reduced freeboard for the DCLID-1 levees and other developed areas on fill. Downstream
of the DCLID-1, in the City of Coppell, stream bank erosion along the creek has impacted several residential
homes which are at risk for additional loss of property. The City has also raised concern about erosion
along the creek between Denton Tap Road and State Highway 121. The purpose of this study was to assess
the existing conditions of Denton Creek and to develop a channel improvement plan aimed at reducing
sedimentation, erosion, and flood risk within the City of Coppell. Halff Associates, Inc. (Halff) was also
separately contracted by the DCLID-1 to perform an assessment along Denton Creek within the district’s
limits. A copy of this report can be provided to the City once it is completed. The assessment for DCLID-1
will address sedimentation, Base Flood Elevation (BFE) issues, and current/future levee certification issues
within the flood control channel.
B. STUDY AREA
Denton Creek is a tributary to the Elm Fork Trinity River. The upper portion of Denton Creek, above the
Grapevine Lake Dam, originates near Bowie, Texas. The lower portion, downstream of the Grapevine Lake
dam to the confluence with the Elm Fork Trinity River is located in the cities of Grapevine, Carrollton and
Coppell. At the Grapevine Lake dam, the watersheds total drainage area is approximately 695 square
miles. Releases from Grapevine Lake into lower Denton Creek are controlled by the United States Army
Corps of Engineers (USACE) up to the emergency spillway elevation of 560 feet. Above this elevation,
releases from Grapevine Lake are uncontrolled. The total contributing area of the lower Denton Creek
watershed is 25.42 square miles. This study is focused on the lower portion of Denton Creek and all
references within the report to Denton Creek herein refer to Lower Denton Creek. A project location map
is shown in Appendix A, Exhibit 1 as well as below in Figure 1.
Denton Creek is approximately 11.25 miles in length and originates at the spillway of Grapevine Lake,
flowing generally east and south to its confluence with the Elm Fork Trinity River. The DCLID-1 segment
of Denton Creek extends from Denton Tap Road to approximately 4,700 feet downstream of MacArthur
Boulevard. The DCLID-1 levee begins approximately 3,200 feet downstream of Denton Tap Road and
extends to its termination near the IH-35E/SH 121 intersection. In 1986 the flood control channel and
levee was constructed within the DCLID-1 portion to provide additional flood conveyance and protection.
The existing Denton Creek (Old Denton Creek) within this section remains and intersects the flood control
channel at several locations between Denton Tap Road and the downstream limits of DCLID-1. The 1986
Gateway Reclamation project originally designed the flood control channel to convey the higher flows. As
part of the Plan of Reclamation for the project, inline weirs were constructed within the flood control
channel to convey low flows down the Old Denton Creek channel and not the flood control channel.
However, due to sedimentation within parts of the Old Denton Creek channel very little flow is conveyed
down those reaches. A majority of the low flow is conveyed down the flood control channel portion. As
a result concerns over BFE’s through the DCLID-1 portion have been raised due to reduced flood capacity.
The limits of this study extend from SH 121 to Denton Creek’s confluence with the Elm Fork Trinity River.
Denton Creek’s watershed is considered to be almost fully-developed below Lake Grapevine, therefore,
fully developed discharges were used for this study.
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This study is based on the most recent technical data available for Denton Creek. The study determined
updated fully developed conditions peak flood flows and water surface elevations. The current effective
flood mapping for Denton Creek is located on FEMA FIRM panels 48113C0135K and 48113C0155K for
Dallas County, Texas effective date July 4, 2014, and panel 48121C0705G for Denton County, Texas
effective date April 18, 2011. There are nine (9) structures crossing Denton Creek in the study area
including Grapevine Mills Parkway, Lakeside Parkway, State Highway 121, Denton Tap Road, MacArthur
Boulevard, two pedestrian bridges, and two sanitary sewer crossings. Figure 1 shows the project location
and limits.
Figure 1: Project Location
C. STUDY OBJECTIVES
Specific objectives of the Denton Creek Drainage Study for the City of Coppell include:
• Perform a geomorphological evaluation along the creek to assess stream conditions
• Update existing hydrologic models to determine discharges for the 1-,2-,5-,10-,25-,50-,100-, and
500-year storm events based on current hydrologic data
• Develop detailed one-dimensional (1D) and two-dimensional (2D) hydraulic modeling for
existing and proposed conditions
• Formulate alternatives and recommend a master plan of conceptual level improvements to
mitigate damages to structures caused by erosion
The Conceptual Level Alternative Analysis focused on improvements in public Right of Way
(R.O.W.)/easements that would result in stable channel conditions. Alternatives on or within private
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property were not considered. Several measures were evaluated to provide multiple benefits to the
surrounding areas while avoiding negative impacts downstream. The conceptual alternatives evaluation
considered include proposed construction of a new bypass channel, stream barbs (weir-like rock
structures located along channel banks used to prevent erosive velocities along channel banks), and grade
control structures to prevent channel down-cutting. A nonstructural alternative including affected
property buyouts was also considered.
D. FLOODING HISTORY
The maximum known flood for lower Denton Creek occurred in May of 1908, according to local reports
from residents. No specific data for this event exists along Denton Creek, however an estimated discharge
of 145,000 cubic feet per second (cfs) was recorded for the Elm Fork Trinity River at Sandy Lake Road. In
April of 1942 extensive flooding was recorded throughout the upper Trinity watershed with a measured
discharged of 90,700 cfs for the Elm Fork Trinity River at Sandy Lake Road. Since that time, the
construction of three major flood control reservoirs have drastically reduced flood risk for Lower Denton
Creek and the Elm Fork Trinity River: Grapevine Lake was constructed in 1952, Lake Lewisville was
constructed in 1954, and Lake Ray Roberts was constructed in 1975. In September of 1964 a storm event
approaching the magnitude of the 100-year intensity at the time in the City of Coppell resulted in a
discharge of 33,000 cfs for the Elm Fork Trinity River at Sandy Lake Road. This flow was primarily from the
uncontrolled areas below Lewisville Lake and Grapevine Lake. Prolonged heavy rainfall in May of 1989
caused both Lake Lewisville and Lake Grapevine to record peak elevations above the crest of their
uncontrolled spillways. This caused an uncontrolled release over the Grapevine Lake spillway down
Denton Creek and resulted in flooding along Denton Creek, Cottonwood Branch, and the Elm Fork Trinity
River. This event, coupled with increased development within the City of Coppell, led to the commission
of the City-Wide Storm Water Management Study completed by Halff for Coppell in January 1991. In May
and June of 1990, record rainfall caused the closure of Sandy Lake Road and units in the Wellington Place
Apartment complex on MacArthur Boulevard to flood. This flood was estimated by the USACE to be in the
range of a 25 to 50-year frequency storm event. The most recent flooding occurred in May and June of
2015. On May 29th rain gages at Grapevine Lake and Lewisville Lake recorded 4.17 and 4.1 inches of rainfall
respectively. Rainfall for June 17th and 18th measured 1.27 and 1.51 inches at Grapevine Lake and 2.32
inches on June 18th at Lewisville Lake. The 2015 rainfall caused flooding in Andrew Brown Park and the
Wellington Place Apartments in the City of Coppell.
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II. WATERSHED DESCRIPTION
A. DATA SEARCH AND COLLECTION
Methods
Halff collected pertinent data for the Denton Creek study from a variety of sources, including visual
observations, all of which was necessary to conduct the study. The data collected included recorded flood
complaints, digital spatial data, effective, and best available hydrologic and hydraulic models.
Coordination with the United States Army Corps of Engineers (USACE) was necessary for documentation
of previous hydrologic and hydraulic studies conducted on Denton Creek. The information collected from
the City of Coppell was used to provide guidance during the model development process and alternatives
analysis.
Data Sources
Digital spatial data was collected from the City of Coppell and other entities and used in analyzing existing
conditions. The existing hydrologic and hydraulic models were obtained from the USACE. This data,
provided in ERSI ArcGIS format, included stream centerlines, street centerlines, storm drain layout, 2014
aerial imagery, 2009 terrain surface data, soils data, existing land use data, zoning maps, and parcel data.
Table 2.1 below provides a list of the spatial data collected, the provider, and the date received.
Table 2.1: Summary of ArcGIS Data
Data Description Received From Date Received
Storm Drains Storm Drain Lines City July 2015
Street Centerlines City Streets DFIRM N/A
2014 Aerials Aerial Photography City October 2016
Topography 2009 TNRIS LiDAR Topography TNRIS October 2016
Creeks Stream Centerlines City October 2016
Parcels County Parcels City October 2016
Stream Centerlines 2009 DFIRM data DFIRM N/A
Floodplains 2009 DFIRM data DFIRM N/A
Base Flood Elevations 2009 DFIRM data DFIRM N/A
Cross Sections 2009 DFIRM data DFIRM N/A
Soils SSURGO NRCS N/A
Zoning Current City Zoning City July 2015
B. FIELD RECONNAISSANCE
Field reconnaissance along Denton Creek was performed to become familiar with the channel, hydraulic
structures, land use, vegetative cover, conditions of the floodplain, and problem areas within the
watershed. These visits included general observation of hydraulic structures as well as the surrounding
areas. Photos collected during field reconnaissance can be found in the geomorphology assessment in
Appendix B.
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C. GEOMORPHOLGY EVALUATION
Methodology
A fluvial-geomorphic assessment of Denton Creek was completed by Dr. Peter Allen and Dr. John Dunbar
of Baylor University’s Department of Geosciences, along with Dr. Jeff Arnold of the United States
Department of Agriculture (USDA) – Agriculture Research Service. The full report is provided in Appendix
B – Fluvial-Geomorphic Assessment of Denton Creek: DCLID No.1 Downstream to the Elm Fork. A
Summary of the report as well as pertinent data is provided in the following sections. The scope of the
geomorphic assessment included the following tasks:
• Analyze the current condition of the of the channel through visual survey
• Conduct a stability analysis using empirical and analytical methods including Capacity Supply
Analysis (CSA)
• Assess stable channel configurations
• Assess sediment contribution and source of sediment in supply reach.
• Physically measure erodibility of banks through submerged jet testing
• Measure the grain size in the supply reach upstream and assess incipient motion of bed material.
This assessment utilized multiple empirical methods to calculate sediment balance of the creek as well as
recommended stable channel design. Pertinent hydrologic and hydraulic data was provided by Halff for
use in this evaluation.
Stream Condition Assessment
A stream condition assessment was conducted between State Highway 121 and Denton Tap Road and
from the downstream limits of DCLID-1 to Denton Creek’s confluence with the Elm Fork Trinity River. Using
kayaks, the site visits were conducted between January and August of 2017. This assessment included
obtaining channel measurements, documenting locations of erosion/scour, and locating the position of
homes with respect to the creek. At several homes located along the creek, a variety of stream bank
protection methods such as gabion walls or concrete riprap were noted. However, the majority of homes
had no such protection. Soil samples were also obtained to determine grain size distribution and
erodibility of the bed material. The creek bed material is primarily fine sand which is characterized as
highly mobile at low flow depths. Hydraulic information such as flowrate, velocity, shear, water surface
elevations (WSEL), depth and stream power was provided by Halff to Dr. Allen and his Team for the
determination of the bankfull discharge on Denton Creek. Bankfull discharge is defined as the dominant
channel forming flow for a stream or river. For Denton Creek it was found to be less than the 1-year
frequency at approximately 1,080 to 1,740 cfs within the study reaches. Other information provided by
Halff included: 1-year and 100-year frequencies to assist in the evaluation of stable channel design. Based
on historical aerial photography the channel meander migration appears to be low with no apparent shift
in creek’s path since 1968. Based on the findings from the geomorphology evaluation, the releases form
Grapevine Lake are the dominant control on downstream channel morphology and ultimate control in the
downstream channel stability calculations.
Identified Areas of Concern
Based on the results of the stream condition assessment, several residential properties located along the
creek are noted to have lost portions of their backyards to bank erosion along the creek and are at risk for
further erosion and loss of land. In order to determine the limits of potential degradation, geotechnical
setback, and lateral migration of the creek with respect to these homes, two methods were utilized: The
City of Austin Method (2017) and the Cruden Method (1989). Using these two methods an Erosion Hazard
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Zone (EHZ) was determined from the toe of slope to evaluate the number of residential properties located
along the creek at risk of further erosion. There are a total of 46 residential properties that border the
creek. Based on the resulting the EHZ limits, it was found that 41 of these 46 properties are located within
the EHZ. Twenty one and a half (21.5) of these homes have implemented some form of bank protection.
Fifteen (15) site do not have bank protection and are experiencing serious erosion and/or stability issues.
Seven (7) of these homes were chosen for the property buyout option alternative due to the severity of
erosion and proximity to the creek. The remaining 4 homes located within the EHZ have no bank
protection and do not have erosion issues at this time but may be at future risk. Limits of the EHZ along
with the affected properties can be found in Appendix A, Figure 10. Figure 2.1 below shows an illustration
of the EHZ with respects to the location of the homes. The EHZ limits are based upon preliminary
calculations only and further geotechnical investigation would be required to itemize the list of affected
houses. This study did not have access to boring information and the depth to the Eagle Ford Shale was
not obtained.
Figure 2.1: Erosion Hazard Zone (EHZ) Setback Limits
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Recommendations
To determine stable channel design parameters the Capacity/Supply Ratio Method (CSR) was utilized. This
method balances the sediment transport capacity of a design reach with the sediment supply of an
upstream reach over the entire flow duration curve rather than for a single discharge. This method has
been used to determine channel modifications that promote sediment balance within the creek to achieve
long-term channel stability. The governing equation used for this method is provided below:
/
A CSR of one (1) denotes an equilibrium for the channel while less than one (1) indicates degradation and
more than one means aggradation of sediments is likely. Using this approach for the Denton Creek study
reach indicates a stable channel geometry design for Denton Creek would require a bottom width of
approximately 47-53 feet and a channel slope of 0.000438-0.000455 ft/ft. Exact dimensions for channel
geometry used for design may vary based on topography, horizontal/vertical limitations, and the need to
maintain positive drainage. The recommendations provided in the geomorphology evaluation are
primarily focused on providing a stable channel condition to help mitigate the adverse effects of erosion
and sedimentation along Denton Creek. Its purpose is to not address specific erosion concerns along the
creek, but rather provide recommended channel geometry for global stability.
D. SURVEY
Detailed channel surveys were completed by Halff Associates, Inc. in October 2016. Field survey cross
sections were measured every 300 feet along the main reach of Denton Creek from State Highway 121 to
Denton Tap Road and from the end of DCLID-1 to the confluence with the Elm Fork Trinity River. The old
Denton Creek channel that meanders through DCLID-1 was surveyed every 100 feet. The DCLID-1 flood
control channel was surveyed every 200 feet. Sonar technology was used within DCLID-1 to complete
surveying the flood control channel due to extended discharge releases from Grapevine Lake resulting in
flows too high for conventional survey methods. All of the survey was necessary to provide detailed data
for the channel and locate areas of deposition along the flood control channel. The datum used was North
American Datum 1983 (NAD 83), and the projected coordinate system used was State Plane Texas North
Central FIPS (4202). The North American Vertical Datum 1988 (NAVD 88) was used.
The topographic survey information for the cross sections included information about the channel bank
locations, toe and top of slope, and channel flow line information. This channel survey was spliced into
the existing hydraulic model cross section data in order to update the existing geometry. Using ArcGIS
version 10.2.2, two separate terrain models were created based upon the survey data and sonar data.
These terrain models were then merged together with 2009 Texas Natural Resources Information System
(TNRIS) Light Detection and Ranging (LiDAR) to create the overall terrain used for modeling purposes. Two
structures were surveyed; the weir locations in the flood control channel of the DCLID-1 segment of
Denton Creek and a sanitary sewer crossing in the lower reach at cross section 4378.
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III. HYDROLOGY
The purpose of the hydrologic study is to estimate peak flood discharge rates and hydrographs for a range
of frequencies at defined points along Denton Creek for use in the hydraulic study. Detailed hydrologic
models were created utilizing the existing land use conditions. For existing conditions, the 1-, 2-, 5-, 10-,
25-, 50-, 100-, and 500-year events were analyzed. Halff utilized the hydrologic models from the USACE
Corridor Development Certificate (CDC) Denton Creek Hydrologic and Hydraulic Model Update dated May
2013. Halff revised these models to reflect current terrain and storm sewer data obtained from the cities
of Coppell and Lewisville. The revised hydrologic data included updates to drainage areas, lag times, and
percent impervious. The watershed is considered to be fully-developed.
A. METHODOLOGY
A hydrologic model was created for the approximately 25.42 sq. mile watershed using HEC-HMS version
3.5. For rainfall loss estimation, the model uses the Initial Constant Loss method. The Modified-Puls
routing method was used where the necessary hydraulic model was available and lag methods were used
where appropriate throughout the rest of the model. The methodology and approach used in the CDC
study was generally keep consistent and utilized for this study. Where methodology differs when
applicable, is in the subsequent sections of this report.
Modeling parameters were developed using updated topographic data 2009 LiDAR, Natural Resources
Conservation Service (NRCS) Soil Survey Geographic database, City of Coppell and Lewisville storm sewer
data and fully developed land-use conditions. As part of the modeling process, basin delineation and
percent impervious information, lag times, and routing reach information were all included based on
standard engineering practices. Drainage areas provided by USACE were further revised to reflect current
conditions within the watershed including storm sewer and updated topography. This information was
geo-referenced and imported into the HMS model.
Rainfall Data
The National Weather Service (NWS) “Technical Paper 40 (TP40)” manual was used to determine rainfall
depth-duration data for the 1-, 2-, 5-, 10-, 25-, 50-, 100- and 500-year events. This is kept consistent with
2013 USACE CDC study for Denton Creek as well as the Elm Fork Trinity River. The data was used to
develop a series of 24-hour rainfall hyetographs with 1-minute intensity duration. Rainfall precipitation
data is provided below in Table 3.1.
Table 3.1: Precipitation for 1- to 500-year Rainfall Events
Time
Precipitation (IN)
1-YR 2-YR 5-YR 10-YR 25-YR 50-YR 100-YR 500-YR
5 Min 0.42 0.46 0.53 0.58 0.65 0.71 0.77 1.13
15 Min 0.88 1.04 1.22 1.36 1.56 1.71 1.87 2.49
1 Hour 1.51 1.87 2.34 2.67 3.15 3.52 3.89 4.75
2 Hours 1.83 2.25 2.93 3.43 4.03 4.54 5.03 6.17
3 Hours 2.00 2.48 3.27 3.88 4.55 5.13 5.70 7.01
6 Hours 2.32 2.97 3.92 4.66 5.48 6.19 6.91 8.57
12 Hours 2.67 3.44 4.66 5.53 6.47 7.33 8.24 10.36
1 Day 3.09 3.99 5.38 6.41 7.53 8.54 9.54 11.86
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Drainage Basin Delineation
The watershed area for Denton Creek was determined to be approximately 25.42 square miles (sq. mi).
The original drainage area delineation was completed in August 2006 as part of the USACE’s update of the
CDC model for Denton Creek. The CDC model delineation was based on topographic data, where available,
and USGS quad maps. Drainage area divides were located at hydraulic structures and at any point where
a substantial change in flow occurs along the reach. For this study, the drainage area delineation
developed by the USACE were revised by Halff using 2009 TNRIS LiDAR information and taking into
account streets, storm sewer and observed drainage patterns. HEC-HMS model junctions were placed at
any point where there is a substantial change in flow to define flow breaks along the reach. There are 30
total drainage sub-areas which contribute to Denton Creek ranging from 0.01 to 6.11 sq. mi. with an
average of 0.88 sq. mi. Table 3.2 shows the USACE and Halff revised drainage area comparison. A map
of the drainage basins is located in Appendix A, Exhibit 2 and flow change locations are provided in Exhibit
3.
Table 3.2: Drainage Area Comparison
USACE
Drainage Area
Halff
Drainage Area
Drainage Area
USACE
(sq. mi.)
Halff
(sq. mi.)
Difference
(sq mi)
Difference
(%)
SUB 1 DCLID_0010 0.2 0.28 0.08 41%
SUB 2 DCLID_0020 1.15 1.29 0.14 12%
SUB 3 DCLID_0030 0.16 0.08 -0.08 -50%
SUB 4 DCLID_0040 0.81 0.81 0.00 0%
SUB 5 DCLID_0050 0.02 0.02 0.00 16%
SUB 6 DCLID_0060 1.31 1.22 -0.09 -7%
- DCLID_0070* - 1.02 - -
SUB 8 DCLID_0080 0.77 0.50 -0.27 -35%
- DCLID_0090* - 0.08 - -
SUB 9 DCLID_0100 0.1 0.16 0.06 57%
SUB 11 DCLID_0110 0.02 0.01 -0.01 -41%
SUB 12 DCLID_0120 2.98 3.02 0.04 1%
SUB 13 DCLID_0130 0.12 0.13 0.01 7%
SUB 14 DCLID_0140 0.05 0.05 0.00 -9%
SUB 15 DCLID_0150 0.6 0.93 0.33 55%
SUB 16 DCLID_0160 0.25 0.25 0.00 0%
SUB 17 DCLID_0170 0.6 0.34 -0.26 -44%
SUB 18 DCLID_0180 0.09 0.10 0.01 11%
SUB 19 DCLID_0190 0.32 0.22 -0.10 -30%
SUB 20 DCLID_0200 0.56 0.62 0.06 12%
SUB 21 DCLID_0210 0.03 0.04 0.01 41%
SUB 23 DCLID_0230 0.72 0.76 0.04 6%
SUB 24 DCLID_0240 0.69 0.40 -0.29 -42%
SUB 25 DCLID_0250 0.14 0.42 0.28 200%
SUB 26 DCLID_0260 6.33 6.11 -0.22 -3%
SUB 28 DCLID_0270 0.51 0.42 -0.09 -17%
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USACE
Drainage Area
Halff
Drainage Area
Drainage Area
USACE
(sq. mi.)
Halff
(sq. mi.)
Difference
(sq mi)
Difference
(%)
SUB 27 DCLID_0280 1.29 1.34 0.05 4%
SUB 29 DCLID_0290 1.76 1.68 -0.08 -5%
SUB 30 DCLID_0300 3.19 3.12 -0.07 -2%
Cumulative 24.77 25.42 0.65 3%
*New drainage area as a result of further delineation of USACE drainage areas
Drainage Area Parameters
Hydrologic parameters such as drainage area, time of concentration, percent urbanization, and percent
impervious were computed for this study. Parameter calculations for revised existing conditions were
computed for drainage areas in the Denton Creek watershed, and are shown in Appendix F. Soils and fully
developed land use exhibits can be found in Appendix A, Figures 4 and 5, respectively.
In order to determine a percent impervious value for each drainage area, the revised existing conditions
hydrologic models used the zoning districts provided by the municipalities. City zoning and aerials were
used to determine a percent impervious and percent urban for each drainage area. The methodology to
use percent impervious and urbanization for each landuse and were kept consistent with the CDC model,
which was based on the year 2055. This data was obtained from the North Central Texas Council of
Governments (NCTCOG) ultimate land use conditions (fully developed) for the purposes of the CDC study.
Based upon drainage area redelineation, the total percent impervious was re-calculated for each drainage
area using ArcGIS to develop a composite impervious value for use in HMS. Table 3.3 provided below
shows the percent impervious and percent urbanization values used for this study.
Table 3.3: Land Use
Description
Percent
Impervious
(%)
Percent
Urbanization
(%)
Single Family 41 80
Multi-family 70 95
Mobile Homes 20 40
Group quarters 60 70
Commercial 95 95
Office 90 90
Retail 95 95
Institution 40 50
Hotel/motel 95 95
Institutional/semi-public 40 50
Education 40 50
Industrial 90 95
Transport 15 30
Roadway 35 80
Utilities 60 70
Airports 20 40
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Description
Percent
Impervious
(%)
Percent
Urbanization
(%)
Runway 100 100
Railroad 15 30
Communication 75 95
Parks/recreation 6 10
Parks 6 10
Under construction 15 20
Cemeteries 6 10
Flood Control 0 0
Vacant 0 0
Vacant 0 0
Residential acreage 25 30
Ranch land 0 0
Timberland 0 0
Farmland 3 5
Parking 95 95
Water 100 100
Water 100 100
Small water bodies 100 100
Transportation 35 80
The initial and constant loss method was used for loss rate estimation in this study. This method was used
for to remain consistent with the USACE 2013 CDC report. The values used are shown in Table 3.4. A
percent impervious and urbanization value was determined using ArcGIS based on the zoning for each
area. The percent impervious represents the percentage of the drainage area that is covered by
impervious material and is hydraulically connected to the basins network. The percent urbanization is the
percentage of the local area that has been developed and/or improved with channelization and/or a storm
collection network. A composite percent impervious and urbanization was then calculated for each
drainage area.
Table 3.4: Initial and Constant Loss Parameters
Storm
Frequency
(yr)
Initial Loss
(in)
Constant
Loss
(in/hr)
1 1.5 0.2
2 1.5 0.2
5 1.3 0.16
10 1.12 0.14
25 0.95 0.12
50 0.84 0.1
100 0.75 0.07
500 0.5 0.05
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Lag times and peaking coefficients are input parameters for the Snyder Unit Hydrograph method in HEC-
HMS and were calculated using the standard methodology. Snyder’s method was selected for consistency
with the USACE 2013 CDC report. Snyder Unit Hydrograph takes into consideration the length, length from
basin centroid, and slope. The flow path from the most hydrologic point of the basin to the outlet is the
length. Using the basin centroid location, the flow path from this point perpendicular to the original length
to the outlet is calculated. The slope is based upon the elevations at 85% and 10% on the total length from
the outlet. These parameters were calculated using ArcGIS. Percent clay and sand were calculated using
soils data from the National Resource Conservation Service (NRCS) Soil Survey Geographic (SSURGO)
database. Table 3.5 shows the Halff revised and USACE drainage area parameters comparison. The
differences reflect the revision based on updated topography and storm sewer.
Table 3.5: Drainage Area Parameter Comparison
USACE
Drainage Area
Halff
Drainage Area
Percent Impervious (%) Lag Time (hr)
USACE Halff Difference USACE Halff Difference
SUB 1 DCLID_0010 40 6.7 -33.3 0.24 0.39 0.15
SUB 2 DCLID_0020 23.5 60.3 36.8 0.53 0.57 0.04
SUB 3 DCLID_0030 41.88 39.9 -1.98 0.26 0.12 -0.14
SUB 4 DCLID_0040 66.66 38.7 -27.96 0.42 0.79 0.37
SUB 5 DCLID_0050 67.03 67.3 0.27 0.1 0.1 0
SUB 6 DCLID_0060 70.41 70.1 -0.31 0.48 0.78 0.3
- DCLID_0070 - 71.6 - - 0.58 -
SUB 8 DCLID_0080 86.91 81.2 -5.71 0.33 0.4 0.07
- DCLID_0090 - 87.6 - - 0.17 -
SUB 9 DCLID_0100 79.94 75.2 -4.74 0.16 0.13 -0.03
SUB 11 DCLID_0110 19.37 7.9 -11.47 0.19 0.36 0.17
SUB 12 DCLID_0120 40.73 43 2.27 0.88 1.2 0.32
SUB 13 DCLID_0130 20.05 80.9 60.85 0.2 0.2 0
SUB 14 DCLID_0140 15.61 26.2 10.59 0.14 0.15 0.01
SUB 15 DCLID_0150 19.41 68.5 49.09 0.38 0.45 0.07
SUB 16 DCLID_0160 73.08 55.3 -17.78 0.2 0.31 0.11
SUB 17 DCLID_0170 9.97 85 75.03 0.47 0.4 -0.07
SUB 18 DCLID_0180 86.21 45.5 -40.71 0.18 0.1 -0.08
SUB 19 DCLID_0190 48.15 60.2 12.05 0.22 0.34 0.12
SUB 20 DCLID_0200 59.96 77.5 17.54 0.36 0.44 0.08
SUB 21 DCLID_0210 26.06 23 -3.06 0.1 0.1 0
SUB 23 DCLID_0230 71.93 68.5 -3.43 0.44 0.71 0.27
SUB 24 DCLID_0240 36.88 37.2 0.32 0.28 0.33 0.05
SUB 25 DCLID_0250 39.95 59.5 19.55 0.26 0.36 0.1
SUB 26 DCLID_0260 50.82 67.9 17.08 1.75 2.05 0.3
SUB 28 DCLID_0270 23.67 47.4 23.73 0.38 0.37 -0.01
SUB 27 DCLID_0280 39.68 45.3 5.62 0.55 0.35 -0.2
SUB 29 DCLID_0290 46.38 64.8 18.42 0.24 0.59 0.35
SUB 30 DCLID_0300 33.59 31 -2.59 1.55 2.48 0.93
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Channel Routing
Two channel routing methodologies were used in this study: Modified-Puls and Lag Time. Lag Times were
used in the most downstream reach where the DCLID-1 sump outfall discharges into Denton Creek until
the confluence with the Elm Fork Trinity River. The lag time routing method was chosen due to
complexities at the Elm Fork confluence. Modified-Puls was used as the routing method for all other
reaches within the watershed.
Those reaches that were routed using Modified-Puls used the hydraulic model (HEC-RAS) to develop
storage discharge relationships for each reach. The development of the hydraulic model will be discussed
in detail in Section IV of this report. A range of discharge values were used in the steady state hydraulic
model to develop storage-discharge curves for each routing reach. The resulting storage-discharge curves
were input back into the HMS model for use in the Modified-Puls routing. The lateral weirs in the HEC-
RAS model, which will be discussed in Section IV of the report, were not optimized for the routing runs.
This process was iterated until discharge values converged; these storage-discharge curves were used in
the final routing. Lag routing was used in the downstream reaches of the watershed and set to 60 minutes
based on the existing CDC report.
Modified-Puls routing also requires a determination of the number of steps, or subreaches. The intent is
to set the number of steps such that the travel time through each subreach is equal to the timestep, in
this case 1-minute. The step calculation was accomplished using the equation shown below, where ! is
the total routing reach length and " is the average wave speed.
#
∆
The number of sub-reaches was calculated based on the 1-minute time step and average wave speed, in
this case the average channel velocity, was taken from the RAS model for each range of sections in the
routing reach. The average velocity was recalculated at each iteration to ensure consistency between the
storage-discharge relationships and the subreaches.
Reservoir Routing
There is one reservoir modeled in the Denton Creek HMS model. The DCLID-1 sump is located near the
downstream limits of the DCLID-1 to the north of the levee and outfalls into the flood control channel.
Due to the pumping operations of the pond a rating curve was used based on the CDC model. The initial
elevation was set at 436.0 ft. The Elevation-Discharge curve was the same as used in of the CDC model.
B. RESULTS AND CONCUSIONS
Summary of Results
The hydrologic analysis for Denton Creek was modeled using HEC-HMS version 3.5. Table 3.6 displays the
peak discharges for the existing 1-, 2-, 5-, 10-, 25-, 50-, 100- and 500-year events at several key locations
throughout the watershed. Detailed tables with peak discharges for each of the drainage areas, junctions,
routing reaches, etc. are provided in Appendix D of this report. The hydrologic modeling is based on fully
developed land use conditions. The 100- and both 500-year USACE discharge of 13,000, 36,200 and 55,500
cfs, respectively, are the calculated discharges that would be flowing over the emergency spillway plus
releases out of Grapevine Lake during these events. These discharges were calculated by the USACE as
part of the original CDC model for Denton Creek. The 13,000 and 36,200 cfs are effective FEMA discharges
for these events and were adopted by FEMA since the completion of Grapevine Lake in 1952. However
the 55,500 cfs is the new 500-year discharge developed by the USACE for the 2013 Denton Creek CDC
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which has not been adopted by FEMA. These discharge were used until the HMS discharges became
greater than these USACE discharges. Thus, these 100- and 500-year USACE discharges were modeled.
Table 3.6: HEC-HMS Discharge Summary
HEC-HMS
Element
Drainage
Area
(sq.
mile)
1-Year
Storm
Event
2-Year
Storm
Event
5-Year
Storm
Event
10-Year
Storm
Event
25-Year
Storm
Event
50-Year
Storm
Event
100-Year
Storm
Event
500-Year
Storm
Event
DCLID_J0020 1.57 2,200 3,200 4,300 4,900 5,800 6,500 13,000* 36,200*
DCLID_J0030 1.64 2,200 3,200 4,300 4,900 5,800 6,500 13,000* 36,200*
DCLID_J0040 2.45 2,200 3,200 4,300 4,900 5,800 6,500 13,000* 36,200*
DCLID_J0050 2.48 2,200 3,200 4,300 4,900 5,600 6,300 13,000* 36,200*
DCLID_J0060 3.70 3,200 4,600 6,200 7,100 8,100 9,100 13,000* 36,200*
DCLID_J0070 4.72 3,500 5,000 6,000 6,800 7,900 8,300 13,000* 36,200*
DCLID_J0080 5.22 3,600 5,200 6,300 7,000 8,100 8,500 13,000* 36,200*
DCLID_J0090 5.30 3,600 5,100 6,200 7,000 8,000 8,500 13,000* 36,200*
DCLID_J0100 5.46 3,600 5,000 6,200 6,800 7,900 8,400 13,000* 36,200*
DCLID_J0110 5.47 3,500 5,000 6,000 6,600 7,600 8,200 13,000* 36,200*
DCLID_J0120 8.49 4,400 6,400 8,200 9,200 10,000 10,800 13,000* 36,200*
DCLID_J0130 8.62 4,400 6,400 8,200 9,200 10,000 10,800 13,000* 36,200*
DCLID_J0140 8.67 4,400 6,300 8,200 9,200 10,000 10,800 13,000* 36,200*
DCLID_J0150 9.59 4,500 6,400 8,500 9,700 10,700 11,400 13,000* 36,200*
DCLID_J0160 9.84 4,400 6,300 8,400 9,600 10,600 11,400 13,000* 36,200*
DCLID_J0170 10.18 4,400 6,300 8,500 9,700 10,800 11,500 13,000* 36,200*
DCLID_J0180 10.28 4,400 6,300 8,500 9,800 10,800 11,600 13,000* 36,200*
DCLID_J0190 10.50 4,400 6,300 8,500 9,700 10,800 11,600 13,000* 36,200*
DCLID_J0200 11.13 4,400 6,300 8,600 9,900 11,000 11,800 13,000* 36,200*
DCLID_J0210 11.17 4,400 6,300 8,600 9,900 10,900 11,800 13,000* 36,200*
DCLID_J0230 11.93 4,500 6,300 8,700 10,100 11,200 12,100 13,000* 36,200*
DCLID_J0240 12.33 4,400 6,300 8,700 10,100 11,200 12,100 13,100 36,200*
DCLID_J0250 12.75 4,400 6,300 8,700 10,100 11,200 12,200 13,200 36,200*
DCLID_J0260 18.86 5,800 8,100 11,900 14,400 16,500 18,100 20,200 36,200*
DCLID_J0270 19.28 5,800 8,100 11,900 14,400 16,600 18,200 20,300 36,200*
DCLID_J0280 20.62 5,800 8,100 11,900 14,500 16,800 18,500 20,600 36,200*
DCLID_J0290 22.30 5,700 8,400 12,500 15,300 17,500 19,400 21,400 36,200*
DCLID_JOutlet 25.42 5,800 8,700 12,900 16,100 18,500 20,600 22,700 36,200*
* The 100- and 500-Year discharges are the calculated discharges by the USACE for releases out of Grapevine Lake
combined with flow over the emergency spillway during these storm events
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Comparison with Effective Discharges
The 100-year discharge developed as part of this study was compared to FEMA and USACE effective 100-
year discharge along Denton Creek. The FEMA discharges are from the 2014 effective FIS discharges for
Dallas County. The USACE discharges are from the 2013 CDC model. Table 3.7 compares the Halff revised
existing, USACE, and FEMA FIS 100-year discharge, where FIS discharges could be compared.
Table 3.7: 100-Year Discharge Summary
Location Description River
Station
100-Year Discharges
FEMA USACE Halff
(cfs) (cfs) (cfs)
17892 Approximate Beginning of Levee
Approximately 3,300 feet
downstream of MacArthur Boulevard 18826 20,600 22,000 20,600
MacArthur Boulevard
24519 Approximate End of Levee
Approximately 3,769 feet
downstream of Denton Tap Road 25499 21,300 21,000 20,300
Approximately 2,500 feet
downstream of Denton Tap Road 26688 21,300 21,000 20,200
Approximately 1,000 feet
downstream of Denton Tap Road 28217 21,300 13,500 13,100
Denton Tap Road
Halff revised existing discharges were slightly different than FEMA FIS effective discharges for Dallas
County. When compared with USACE discharges, Halff revised existing discharges are lower than the CDC
model. This is due to updated terrain and storm sewer configuration which were taken into consideration.
These differences reflect revisions to existing drainage areas and the resulting changes to the other
hydrologic parameters.
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IV. HYDRAULICS
The hydraulic analysis included the development of a detailed 1D steady, 1D/2D unsteady, and 2D
unsteady state hydraulic models for approximately 11.25 miles of Denton Creek. The 1D steady state
model was developed to better compare hydraulic results with the effective FEMA and CDC hydraulic
models which were both computing using steady state flows. It was utilized to account for releases from
Grapevine Lake. The 1D/2D unsteady model was developed to evaluate the effects of the time of inflow
hydrographs and attenuation of the flood wave. This model also includes a portion of the Elm Fork Trinity
River as a 2D storage area to accurately model flow interaction between Denton Creek and the Elm Fork
Trinity. The 2D unsteady model was developed to better evaluate velocity distribution through the creek
as well flow interaction between the DCLID-1 flood control channel and Old Denton Creek. Peak flows
computed from the detailed hydrologic model were input into the hydraulic model and water surface
elevations were computed for the 1-, 2-, 5-, 10-, 25-, 50-, 100-, and 500- year flood frequencies within the
1D steady and unsteady model only. The 2D model only uses frequencies up to the 10-year event. The 1D
steady state model revised existing (fully developed land use) floodplain can be seen in Appendix A, Figure
6.
A. 1D STEADY STATE MODEL DEVELOPMENT
The 1D steady-state hydraulic model was developed using HEC-RAS (Version 5.0.3). Cross section
geometry was determined using a combination of 2009 TNRIS LiDAR and survey data. The criteria used in
the Denton Creek hydraulic analysis is in accordance with the general FEMA, USACE modeling criteria, and
standard engineering practices. The 1D steady model was also used to model the USACE 100- and 500-
year discharges, which included releases out of Grapevine Lake. After the steady state model was
developed, the model was converted to a 1D/2D unsteady state hydraulic model in order to better model
the backwater effects from the Elm Fork Trinity River and the effects of flow interaction between the old
channel and flood control within DCLID-1. The 1D/2D unsteady flow model was also used for a more
accurate comparison to the 2D unsteady model discussed in later sections of this report.
Cross Sections
Stream cross sections were positioned along Denton Creek to define the geometry of the hydraulic model.
They were laid out generally perpendicular to the direction of flow and spaced generally in the same
locations as survey data and USACE cross section locations.
A Triangulated Irregular Network (TIN) was created utilizing mass points and break lines from 2010 LiDAR
data. Using HEC-GeoRAS, cross section data was extracted from the TIN and imported into HEC-RAS for
evaluation and filtering. Survey data was added into the HEC-RAS model where available. Cross sections
32331 through 36181 include the Westhaven Residential development geometry in the left overbank. The
current construction in Andrew Brown Park are not reflected in the geometry. The locations of the
hydraulic cross-sections are displayed on the floodplain work maps presented in Appendix A, Exhibit 6.
Stream Reach Layout
The HEC-RAS model includes a total of four (4) distinct reaches. The reaches include the following:
• Denton Creek Below DCLID-1 – Extends approximately 18,000 feet from the DCLID No. 1 sump
outfall to the confluence at Elm Fork Trinity River
• DCLID-1 Denton Creek Flood Control Channel – Extends approximately 11,100 feet from Denton
Tap Road to the DCLID-1 sump outfall
• Denton Creek above DCLID-1 – Extends approximately 7,200 feet from State Highway 121 to
Denton Tap Road
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• Denton Creek below Grapevine Lake – Extends approximately 21,200 feet from State Highway
121 to the emergency spillway of Grapevine Lake
Manning’s Roughness Coefficients
Channel roughness coefficients (Manning’s “n”) were assigned to channels and overbank cross sections
based on actual physical condition using information from field inspections of floodplain areas. A
horizontal variation in n-values was used across the channel instead of composite n-values. Manning’s
roughness coefficients for the channels ranged from 0.045 through 0.055 and overbank roughness
coefficients ranged from 0.025 through 0.12 for Denton Creek. Manning’s n-value breaks were placed at
the bank locations, places where the overbank n-value changed, and also at locations where there was a
noticeable shift in the grades. In general, all n-values were kept consistent with the USACE model unless
engineering judgment from field visits warranted changing them.
Ineffective Areas
Ineffective flow areas were set on some of the culvert cross-sections to transition flow in the area of the
bridge crossings. This approach followed the standard practice as outlined in the HEC-RAS Hydraulic
Reference Manual. Most structures are configured such that the approach channels are roughly the same
width as the culvert or bridge opening. Ineffective flow areas were placed on cross sections throughout
the model to represent areas of the cross-section that do not convey flood flows, or where water could
possibly be stored. Ineffective areas were used mainly at ponds and parks in development areas.
Levees
Levees were used throughout the model to represent the high ground downstream of Denton Tap Road
and DCLID-1 levee which runs along the left overbank of the Denton Creek flood control channel. The
DCLID-1 Levee begins approximately 3,200 feet downstream of Denton Tap Road and terminates near the
intersection of IH-35E and SH 121.
Lateral Structures
A lateral structure was used to model the high ground along Gun Club Road. This allows flow to leave the
Denton Creek System into the Elm Fork Trinity River floodplain. The lateral structure was maintained
consistent with the CDC hydraulics model.
Bridges and Culverts
As previously mentioned, there are a total of nine hydraulic structures along the stream reaches. No
bridges, except for the sanitary sewer crossing at river station 4282, were surveyed. The bridge data from
the USACE CDC model was used in the 1D models. Contraction and expansion coefficients were set at a
value of 0.3 for contraction and 0.5 for expansion for the cross sections upstream and downstream of the
structures. Table 4.1 provides a summary of the various hydraulic structures.
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Table 4.1: Hydraulic Structures
River Station Description Structure Type
4282 Sanitary Sewer Crossing Bridge
22146 MacArthur Boulevard Bridge
23825 Pedestrian Bridge Bridge
29267 Denton Tap Road Bridge
33100 Sanitary Sewer Crossing Bridge
34593 Pedestrian Bridge Bridge
36570 State Highway 121 Bridge
46076 Lakeside Parkway Bridge
50441 Grapevine Mills Parkway Bridge
B. 1D/2D UNSTEADY STATE MODEL DEVELOPMENT
Model Development
The 1D steady state model was converted to a 1D/2D unsteady state model in order to better model
backwater effects from the Elm Fork Trinity River and comparison to the 2D unsteady model results for
verification. This model was used to analyze potential impacts of the alternatives for the 100-year
frequency event. All hydraulic data and parameters in the 1D/2D unsteady state model was maintained
with 1D steady state model with some exceptions:
• The most upstream reach of Denton Creek that flows from the emergency spillway through
Grapevine Recreational Area Golf Course was removed from the geometry data. This was because
this portion of Denton Creek was well beyond the study area and scope of this project and did not
add any benefit to the purpose of this model.
• Ineffective areas representing ponds were changed to permanent. This is standard practice within
HEC-RAS unsteady models to improve model stability.
• A 2D mesh area was created to represent the Elm Fork Trinity River floodplain and connected to
the 1D river reach by two lateral weir connections. This allows flow to spill out of Denton Creek
into the Elm Fork floodplain, model backwater effects within the Elm Fork floodplain, and
accounts for storage ponds located near the Elm Fork.
Unsteady Flow Data
For the 1D reach within the unsteady model, inflow hydrographs were used from the Denton Creek HMS
model. Only basin runoff hydrographs were input to allow the unsteady model to route the inflow
hydrographs during simulation runs. Uniform lateral inflow hydrographs were selected as the inflow
boundary conditions for the model based on storm sewer outfall locations along the stream. The
exceptions were for Cottonwood Creek tributary and DCLID-1 sump outfall which were modeled as lateral
inflow hydrographs. Normal depth was used for the downstream boundary condition. The initial flow
condition for the model was set at 70 cfs due to normal low flow in Denton Creek ranges from 60-80 cfs
and to provide greater model stability. The boundary conditions for the 2D flow area connection for the
Elm Fork were modeled as normal depth values based on the slope within that reach.
Denton Creek Drainage Study
City of Coppell, TX
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Results
The 1D/2D unsteady existing conditions model was compared with both FEMA and USACE water surface
elevations. FEMA water surface elevations are obtained from the FEMA effective model, DFRIM BFEs, and
the Letter of Map Revision (LOMR) for the Westhaven Residential Development – Denton Creek prepared
by Kimley-Horn and Associates, Inc. in 2013 between cross section 32479 and 35888, which used FIS
discharges. Table 4.2 shows this study’s existing conditions and FEMA water surface elevations
comparison. Existing conditions were also compared with USACE water surface at the major road crossing
along Denton Creek shown in Table 4.3. Study water surface elevations are from the 1D/2D unsteady state
model, which does not take into consideration releases out of Grapevine Lake. Differences between
USACE and FEMA can be attributed to updated discharges, terrain, and survey. Revised existing conditions
water surface elevations were higher than BFEs along Denton Creek. These results also showed that levee
certification could be an issue with the current FEMA effective 500-year discharge of 36,200 cfs. Also, if
the new CDC 500-year discharge of 55,500 cfs becomes adopted by FEMA the DCLID-1 would no longer
comply with the level of protection outlined in the Plan of Reclamation. Table 4.4 shows the comparison
for 100-year water surface elevations between the 1-D steady and unsteady state models. Differences in
study water surface elevation results are because the 1D steady state model simulates water surface
profiles using peak flows only and the 1D/2D unsteady state model generates water surface elevations
based upon time varying flows. Due to this, typically unsteady flow water surface results are generally
higher than steady state results as is seen in the comparison. Adding the inflow hydrograph from the Elm
Fork Trinity River CDC model for the river also attributed to higher water surface elevations.
Table 4.2: FEMA Water Surface Elevation Comparison
Cross Section 100-Year WSEL (ft)
FEMA Halff Difference
17892 451.00 453.52 2.52
18335 452.00 453.53 1.53
18646 453.00 453.58 0.58
20397 453.30 454.27 0.97
21059 453.00 454.45 1.45
MacArthur Boulevard
22211 454.00 455.32 1.32
23506 454.00 456.01 2.01
24748 454.67 457.98 3.31
25168 455.30 458.76 3.46
25927 456.00 459.18 3.18
27603 457.77 460.02 2.25
28791 458.92 460.27 1.35
29206 458.86 460.22 1.36
Denton Tap Road
30531 460.17 460.56 0.39
32479 464.54 464.63 0.09
34218 465.28 465.28 0.00
35888 466.03 466.03 0.00
State Highway 121
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Table 4.3: USACE Water Surface Elevation Comparison
Location 100-Year WSEL (ft)
USACE Halff Difference
MacArthur Boulevard 455.85 454.45 1.40
Denton Tap Road 458.58 460.22 -1.64
State Highway 121 465.70 466.03 -0.33
Table 4.4: 1-D Steady vs Unsteady Comparison
100-Year WSEL Comparison (ft)
Cross
Section
1-D
Steady
1-D
Unsteady
Difference
(Unsteady
– Steady)
Approximate End of Levee (Along Denton
Creek)
17892 453.22 453.52 0.30
17991 453.24 453.53 0.29
18114 453.28 453.52 0.24
18223 453.28 453.53 0.25
18335 453.28 453.53 0.25
18479 453.28 453.54 0.26
18592 453.32 453.56 0.24
18646 453.35 453.58 0.23
18826 453.37 453.64 0.27
19071 453.42 453.69 0.27
19223 453.42 453.73 0.31
19421 453.33 453.78 0.45
19614 453.61 453.94 0.33
19742 453.7 454.00 0.30
19807 453.73 454.03 0.30
20012 453.81 454.1 0.29
20224 453.88 454.12 0.24
20314 453.93 454.15 0.22
20397 454.09 454.27 0.18
20579 454.34 454.42 0.08
20616 454.35 454.42 0.07
20728 454.39 454.46 0.07
20873 454.4 454.46 0.06
20944 454.43 454.47 0.04
21059 454.45 454.45 0.00
21169 454.59 454.54 -0.05
100-Year WSEL Comparison (ft)
Cross
Section
1-D
Steady
1-D
Unsteady
Difference
(Unsteady
– Steady)
21275 454.7 454.64 -0.06
21354 454.73 454.73 0.00
21416 454.75 454.75 0.00
21558 454.89 454.83 -0.06
21611 454.91 454.88 -0.03
21798 455.06 454.97 -0.09
21822 455.06 454.97 -0.09
22080 455.23 455.05 -0.18
MacArthur Boulevard
22211 455.63 455.32 -0.31
22424 455.83 455.48 -0.35
22616 456.02 455.59 -0.43
22795 456.15 455.67 -0.48
22997 456.37 455.82 -0.55
23063 456.43 455.89 -0.54
23198 456.40 455.86 -0.54
23229 456.36 455.77 -0.59
23413 456.45 455.81 -0.64
23506 456.73 456.01 -0.72
23628 456.94 456.14 -0.80
23802 457.75 456.42 -1.33
Pedestrian Bridge
23868 457.78 456.25 -1.53
24058 457.78 456.30 -1.48
24099 457.78 456.58 -1.2
24198 457.79 456.90 -0.89
24264 457.79 457.02 -0.77
24519 457.80 457.60 -0.20
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100-Year WSEL Comparison (ft)
Cross
Section
1-D
Steady
1-D
Unsteady
Difference
(Unsteady
– Steady)
24748 457.43 457.98 0.55
24947 457.54 458.09 0.55
25168 458.64 458.76 0.12
25356 458.65 459.03 0.38
25499 458.65 458.98 0.33
25558 458.65 459.07 0.42
25760 458.28 459.07 0.79
26087 458.84 459.37 0.53
26383 459.46 459.85 0.39
26688 459.47 459.9 0.43
26970 459.49 459.9 0.41
27041 459.52 459.91 0.39
27145 459.57 459.94 0.37
27672 459.68 460.02 0.34
27892 459.48 460.07 0.59
28217 460.03 460.18 0.15
28380 460.14 460.24 0.10
29050 460.22 460.27 0.05
29206 460.21 460.22 0.01
Denton Tap Road
29331 460.5 460.45 -0.05
29530 461.12 460.63 -0.49
30063 461.16 460.66 -0.50
30366 461.18 460.67 -0.51
30424 461.18 460.67 -0.51
30531 461.20 460.56 -0.64
30779 461.44 460.96 -0.48
31216 461.72 461.16 -0.56
100-Year WSEL Comparison (ft)
Cross
Section
1-D
Steady
1-D
Unsteady
Difference
(Unsteady
– Steady)
31611 461.79 461.21 -0.58
31797 462.33 461.28 -1.05
31949 462.21 461.03 -1.18
32105 462.15 464.22 2.07
32231 462.68 464.50 1.82
32586 462.96 464.67 1.71
32897 463.97 464.98 1.01
33087 464.37 465.08 0.71
Sanitary Sewer Crossing
33108 464.38 465.10 0.72
33400 464.50 465.13 0.63
33696 464.51 465.18 0.67
33852 464.58 465.21 0.63
34064 464.80 465.29 0.49
34218 464.78 465.28 0.5
34458 464.91 465.34 0.43
34585 465.07 465.40 0.33
Pedestrian Bridge
34638 465.15 465.37 0.22
34676 465.46 465.39 -0.07
35090 465.74 465.62 -0.12
35504 465.87 465.93 0.06
35681 465.98 465.89 -0.09
35888 465.99 466.03 0.04
36181 466.27 466.26 -0.01
36345 466.60 466.43 -0.17
State Highway 121
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C. 2D MODEL DEVELOPMENT
A 2D unsteady flow model using HEC-RAS v5.03 was developed to model the channel forming (bankfull)
discharge, 1-, 2-, 5-, and 10-year events from downstream of State Highway 121 to the Sandy Lake Road
crossing with the Elm Fork Trinity. The purpose of the 2D simulation was to evaluate the velocity patterns
within the channel and flow interactions between the DCLID-1 flood control channel and the old Denton
Creek channel. The 2D model was also used to evaluate each alternative as to how the existing velocity
patterns are impacted. Computational stability and volume balance were evaluated throughout the
process to ensure accurate results.
Model Development
A 2D mesh with a 20 foot grid cell size was created throughout the study area using a combination of 2009
LiDAR and survey topographic data. The limits of the mesh extend from State Highway 121 to Sandy Lake
Road. Breaklines were placed along locations of grade changes, channel centerlines, channel banks and
toes to better align grid cell faces with the direction of flow. This enforces an elevation at the faces of the
cells so that the water surface must be greater than the breaklines in order to flow into the next cell. After
the mesh was defined, a terrain, inflow hydrographs, Manning’s n-value polygon, and boundary
conditions were added.
Terrain Modification
The terrain used in the 2D analysis was based on a combination of 2009 LiDAR and survey data. To
generate an overall terrain that encompasses these two sources, a TIN was created from surveyed data
points within the channel and spliced into the 2009 LiDAR. This creates the overall terrain within the mesh
that reflects the detailed survey data within the channel bank limits and the LiDAR to define the overbank
geometry.
Manning’s n-value
Using ArcGIS, a Manning’s n-value polygon was created based on landuse data and cover type. The
polygon contains the different land use and n-values within the mesh area. The n-values were maintained
consistent with the 1D model and range from open space to heavy tree cover. One variation between the
1D and 2D model n-values is areas where buildings and structures are located. In the 2D model building
locations were assigned a high n-value (0.3) to account for flow conditions in the presence of the structure.
Streets and roads within these areas were assigned a lower n-value (0.02). This approach provides greater
detail in model results when flow occurs in these areas than does the composite values typically used in
the 1D model.
Boundary Conditions
The boundary conditions used within the 2D model were based on the inflow hydrographs and normal
depth. Similar to the 1D unsteady model, the inflow hydrographs allow flow to enter the mesh at specified
locations and normal depth allows flow to leave the mesh if water surface elevations exceed the mesh
boundary elevations. Inflow hydrographs were obtained from the Denton Creek HEC-HMS model and are
consistent with the 1D unsteady model inflow hydrographs. Normal depth values were set with the slope
within that reach. Inflow hydrographs were placed at along the boundaries of the 2D mesh at locations
where flow enters the channels.
Denton Creek Drainage Study
City of Coppell, TX
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Simulation Parameters
A three second time step was selected as the computational time interval to satisfy the Courant Equation.
The Courant Equation, shown below, takes into consideration the velocity of the flood wave (or average
channel velocity), computational time-step, and average cell size. The Courant number normally is set to
one (1). Therefore, the Courant Equation was solved for the time step used in the simulation which yielded
a recommended time step of three seconds.
% ∗ ’(
’) * 1.0 . max 3.0
Model Validation
The validation of the 1D/2D unsteady model and 2D unsteady model was determined using the May 2015
storm event gage data only. No high water marks were captured or surveyed as part of this event. There
are two USGS stream gages within the study area. One gage is located at the downstream face of State
Highway 121 (SH 121) along Denton Creek and the other is at the Carrollton Dam just downstream of
Sandy Lake Road along the Elm Fork Trinity River. Table 4.5 shows the results from the May 2015 event
model simulations. The 2D model was able to reproduce the gage data at the Carrollton Dam (the 1D/2D
unsteady model does not extend to the Carrollton Dam). Reproduction of gage date at SH 121 was not
successful in either the 1D/2D unsteady or the 2D unsteady model. The differences between the gage
data and model water surface elevations at SH 121 is thought to be because the gage datum may not
have been calibrated or was out of its original location during the event. Survey data shows a flowline
elevation of 444.59 feet at the downstream end of State Highway 121 whereas the gage datum near this
location is 439.11 feet. This is a 5.48 feet difference in elevation between flowlines, which may be the
cause for the differences in water surface elevations at this location. The measured discharge at this
location was also much lower than the revised model discharge at this location. The measured discharge
at the gage was closer to the 1-year frequency storm discharges calculated as part of this study. However,
after investigating the rainfall data during this event, the precipitation depths indicate that this event was
closer to the 10-year frequency storm event which is consistent with reported values for this event.
Therefore, recalibration of this gage by the USGS maybe needed. Additionally, the Wellington Place
Apartments reported flooding to the City of Carrollton during the same event. The models were able to
reproduce flooding at this location for this flood event. Based on the reproduction of results at the
Wellington Place Apartments and the 2D model reproducing water surface elevations within 0.2 feet of
the USGS gage station at the Carrollton Dam for the May/June 2015 flood event, the model is considered
validated.
Table 4.5: May 2015 Storm Event Calibration
Gage Location
Gage
Flowrate
(cfs)
Halff
Flowrate
(cfs)
Gage
WSEL
(ft)
1D
WSEL1
(ft)
2D
WSEL
(ft)
Carrollton Dam 26,600 32,404 444.51 N/A1 444.34
SH 121 3,300 4,597 458.64 461.08 463.70
1The 1D model does not extend to the Carrollton Dam gage
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Results
The 2D model output was reviewed using HEC-RAS version 5.03 to identify locations along the stream
where erosive velocities occur. Additionally, locations where velocities were low (2 fps or less) were also
identified as areas of probable sedimentation. Information on flow patterns derived from utilizing the
particle tracer feature in RAS Mapper was also gained in the 2D model for the interaction between the
flood control channel and old channel within DCLID-1 as well as with the Elm Fork Trinity River. In these
cases the 2D modeling allows the underlying terrain to determine flow patterns at locations where spill
out of the main channel occurs. This is often a limitation of 1D modeling where flow takes an alternative
path that does not follow the direction of the main channel.
Based on the findings of the geomorphology evaluation, the bed material for Denton Creek downstream
of DCLID-1 to the confluence with the Elm Fork Trinity River is primarily fine sand which can be transported
easily even at low flows. The 2D model results show several locations along the creek where channel
velocities are above maximum permissible velocities based on the Integrated Stormwater Management
(iSWM) Technical Manual Hydraulic Section for Open Channel Design provided below in Table 4.6. The
iSWM Technical Manual was developed and maintained by NCTCOG of which the City of Coppell is a
member. Locations of notable interest are provided below in Figures 4.1 to 4.4. The 2-year storm event
velocities used as the design frequency for bank stability evaluation. Existing 2D velocity maps can be
found in Appendix A, Exhibit 7.
Table 4.6: iSWM Allowable Velocities for Natural Channels
Denton Creek Drainage Study
City of Coppell, TX
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Figure 4.1, 4.2 and 4.3 below show the 2-year existing velocity results along an approximately 8,000 foot
stretch of Denton Creek located upstream of Denton Tap Road. Within this area, there are velocities
upwards of 6 feet per second (fps). Based on the results of the geomorphological evaluation, these high
velocities easily erode the fine grained sand within this section of Denton Creek as this section was
identified as part of the sediment supply reach for Denton Creek. Eroded material through this reach is
transported further downstream where it is deposited within the flood control channel of the DCLID-1.
Figure 4.1: 2-year Existing Velocity Map (River Station 36500 to 34000)
Denton Creek Drainage Study
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Figure 4.2: 2-year Existing Velocity Map (River Station 35000 to 31500)
Figure 4.3: 2-year Existing Velocity Map (River Station 31500 to 28500)
Denton Creek Drainage Study
City of Coppell, TX
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Figure 4.4 below shows the 2-year existing velocity results along an approximately 1,200 foot stretch of
Denton Creek located 1,900 feet downstream of the DCLID-1. Within this area, homeowners located along
the western bank have expressed concerns to the City of Coppell due to erosion claiming portions of their
backyard. There are also two City of Coppell storm sewer outfalls located in this area as shown in the
figure. Based on field reconnaissance the existing 36” diameter Reinforced Concrete Pipe (RCP) and
headwall are currently being undermine due to the erosion in this area. Velocities within this section of
the creek were found to be generally higher as flow meanders around the bend. A maximum 2-year
velocity of 6.2 feet per second (fps) occurs within the channel in this area. The 2D model reproduces
erosive velocities along the locations with documented erosion. These homes were also identified to be
within the EHZ as part of the geomorphology assessment.
Figure 4.4: 2-year Existing Velocity Map (River Station 16000 to 14800)
Denton Creek Drainage Study
City of Coppell, TX
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Figures 4.5 and 4.6 below shows the 2-year existing velocity results along an approximately 2,000 foot
stretch of Denton Creek located 3,750 feet downstream of the DCLID-1. Homeowners within this area
have also expressed concerns to the City of Coppell due to erosion and scouring along the creek banks.
During field reconnaissance several concrete riprap/gabion structures were found along the residential
side of the creek from river station 14137 to 13030. Although these structures appear to be functioning
as intended based upon visual inspection, the depth of the foundations and other design details are not
known and it is difficult to predict the long-term stability of the existing bank protection measures. There
are three City of Coppell storm sewer outfalls located in this area as shown in the figure. Although there
is no evidence of failure at the outfalls for these storm sewers, they are located within the EHZ and are
thus at greater risk of future failure. A maximum 2-year velocity of 6.4 fps occurs downstream of these
structures in an area where no bank protection is present. Referring back to Table 4.6, this shows that the
velocities in this area are erosive and, if not addressed, have the potential to cause similar problem
occurring upstream.
Figure 4.5: 2-year Existing Velocity Map (River Station 14000 to 12700)
Denton Creek Drainage Study
City of Coppell, TX
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Figure 4.6: 2-year Existing Velocity Map (River Station 13200 to 11950)
Denton Creek Drainage Study
City of Coppell, TX
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Figure 4.7 below shows the 2-year existing velocity results along an approximately 4,000 foot stretch of
Denton Creek located 9,300 feet upstream of its confluence with the Elm Fork Trinity River. The proposed
Blackberry Farms residential development is located within this section of the creek. Velocities within this
section range from approximately 3.0 to 5.5 fps showing a need for a carefully designed erosion control
measures during the developed of this proposed site.
Figure 4.7: 2-year Existing Velocity Map (River Station 9400 to 5400)
Denton Creek Drainage Study
City of Coppell, TX
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V. DEVELOPMENT OF ALTERNATIVES
The project scope of study calls for the development of two alternatives for the purpose of addressing the
erosion problem areas along Denton Creek in the City of Coppell. Several factors were considered during
the alternative selection process including stream characteristics, velocity reduction, and the presence of
existing city infrastructure. The two alternatives analyzed were 1) a bypass channel installed downstream
of DCLID-1 and 2) to install stream barbs at locations of channel bank erosion. A third alternative was also
developed which includes a buyout option for those 6 to 7 homes located on Parker Drive that are
significantly impacted by erosion. All three of these alternatives include the repair of the City’s existing
headwall approximately 2,400 feet downstream of DCLID-1 and the construction of a grade control
structure at Denton Tap Road. The replacement of the existing headwall has been itemized in the cost
estimate in Appendix C. The grade control structure is discussed later in this section. It should be noted
that these alternatives were modeled as stand-alone projects and that any DCLID-1 alternatives were not
modeled as part of these proposed alternatives provided to the City of Coppell.
A. ALTERNATIVES ANALYSIS
Alternative 1- Bypass Channel
This alternative includes the evaluation of a proposed bypass channel along the lower reach of Denton
Creek. The goal of this alternative is to reduce velocities within the main channel, thereby reducing the
risk of erosion between river stations 15983 and 12551, as shown in Figure 5.1. The proposed bypass
channel would begin approximately 1,900 feet downstream of DCLID-1 and extends approximately 3,000
feet downstream. The proposed alignment and 2D velocity results are shown in Appendix A, Exhibit 8.
The bypass channel would be located to the east of the existing creek within the property belonging to
the Dallas Gun Club within the city limits of the Cities of Coppell and Carrollton. The objective of this
alternative is to convey the low flows in the bypass channel instead of the main channel thereby reducing
the frequency erosive flows in the existing natural channel. The existing channel would then serve as
emergency conveyance for the higher flows and storage for backwater. The location of the bypass channel
is within the Elm Fork Trinity River floodplain but was not evaluated in the Elm Fork Trinity River CDC
model.
Conceptual Design
Per the recommendation of the geomorphological evaluation, the bypass channel will follow the
recommend stable channel design outlined in the Fluvial-Geomorphic Assessment of the Denton Creek:
DCLID No. 1 Downstream to the Elm Fork provided in Appendix B.
The design factors used for this alternative are provided in the list below:
1) A berm approximately 6.5 feet high must be constructed at the junction of the main and bypass
channel to force the flows into the bypass channel.
2) The proposed bypass channel geometry would consist of a 40-foot bottom width, 3:1 slide slopes,
at a 0.0004 ft/ft slope with a total length of 3,000 feet.
3) The bypass channel length and meander radius would mimic the existing channel per the
geomorphology recommendation.
4) Four grade control structures will be placed along the new channel at the following locations: the
most upstream and downstream points, approximately 800 feet downstream of the beginning of
the proposed bypass channel, and approximately 1,500 feet downstream the beginning of the
proposed bypass channel. These grade control structures serve primarily as “hard points” to
prevent future downcutting and widening of the channel.
Denton Creek Drainage Study
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5) The banks must be vegetated or protected to reduce erosion and minimize lateral stream
movement.
Model Results
This alternative was evaluated using the 1D/2D unsteady flow and 2D unsteady flow hydraulic HEC-RAS
v5.03 models to determine the potential impacts to water surface elevations (WSEL) and velocities. Figure
5.1 shows the 2-year velocity results for Alternative 1. In general, velocities in the main channel were
reduced from 5+ fps to 1.5-2 fps. Velocities in the proposed bypass channel vary from 2.3-3.2 fps. As
previously mentioned the bypass channel banks shall be vegetated or protected and can therefore
withstand higher velocities. Table 5.1 shows the 100-year water surface elevation comparison for the
proposed bypass channel. The proposed bypass channel causes no negative impacts upstream along
Denton Creek. The water surface elevation increases downstream of the proposed bypass channel are
due to shifts in hydrograph peaks and changes in the flow interaction between Denton Creek and the Elm
Fork. The max water surface elevation rise is 0.19 feet at river station 12551.
Figure 5.1: Alternative 1 2-year Velocity Map (River Station 17500 to 11500)
Denton Creek Drainage Study
City of Coppell, TX
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Table 5.1: Alternative 1 Water Surface Elevation Comparison
Cross
Section
100-Year WSEL (ft) Difference
(ft) Existing Proposed
15983 451.24 449.77 -1.47
15671 450.82 449.35 -1.47
15359 450.45 449.14 -1.31
15238 450.26 449.05 -1.21
15050 449.81 448.91 -0.9
14973 449.75 448.88 -0.87
14819 449.46 448.77 -0.69
14706 449.26 448.69 -0.57
14425 448.97 448.56 -0.41
14137 448.74 448.46 -0.28
13942 448.61 448.4 -0.21
13768 448.48 448.35 -0.13
13646 448.33 448.29 -0.04
13307 448.12 448.23 0.11
13144 448.08 448.2 0.12
12970 448.04 448.18 0.14
12654 447.95 448.13 0.18
12551 447.93 448.12 0.19
Advantages
i. Eliminates erosive velocities through problem residential areas
ii. Excess excavated earth may be provided to homeowners to restore areas of erosion
within their property
iii. Provides increased flood storage
Disadvantages
i. Expensive option to address erosion concerns
ii. Will require environmental permitting and negation with the Dallas Gun Club and the City
of Carrollton to obtain necessary R.O.W.
iii. High Operating and maintenance (O&M) cost
iv. May result in stagnant water along the existing Denton Creek due to diversion of flow
along bypass channel
At the request of the City, the above alternative was modified to consider the hydraulic impacts of placing
the excavated material from the proposed bypass channel into the current Denton Creek Channel
between the upstream and downstream confluences with the bypass channel. This evaluation was
accomplished using the 1D unsteady-state HEC-RAS model by adding blocked obstructions within the
existing channel from cross sections 12970 to 15671. When compared to revised existing conditions, a
Denton Creek Drainage Study
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maximum rise of 0.25 feet in the 100-year water surface elevation downstream occurs at cross section
12551 and a maximum reduction of 1.05 feet at cross section 15671. Minor decreases in water surface
elevation were also observed upstream of the proposed bypass channel. When compared with keeping
the existing Denton Creek Channel in its current condition, there was a decrease of 0.02 feet in water
surface elevation downstream, a maximum rise of 0.45 feet at cross section 15983, and a maximum rise
of 0.24 feet occurs upstream of the proposed channel at cross section 16294. Based on this analysis,
realigning the creek yields slightly higher water surface elevations than maintaining the existing channel
in conjunction with the bypass. However, the realigned channel would result in approximately 19% and
8% gain in valley storage from cross section 12046 – 16294 in Alternative 1 and the stand alone channel
when compared to revised existing conditions, respectively. The 2-year velocities through the stand alone
channel are not erosive, with an average of approximately 1.5 ft/s. There are erosive velocities at the
upstream confluence; however, due to the recommended grade control structures, downcutting would
not be expected.
Table 5.2: Stand Alone Channel Water Surface Elevation Comparison
Cross
Section
100-YR WSEL (ft) Difference
(ft) Existing Stand Alone
15983 451.11 450.22 -0.89
15671 450.7 449.65 -1.05
15359 450.33 449.34 -0.99
15238 450.14 449.25 -0.89
15050 449.69 449.08 -0.61
14973 449.63 449.04 -0.59
14819 449.35 448.88 -0.47
14706 449.15 448.79 -0.36
14425 448.87 448.64 -0.23
14137 448.64 448.5 -0.14
13942 448.52 448.42 -0.1
13768 448.39 448.37 -0.02
13646 448.24 448.28 0.04
13307 448.04 448.21 0.17
13144 447.99 448.18 0.19
12970 447.96 448.16 0.2
12654 447.87 448.11 0.24
12551 447.85 448.1 0.25
Denton Creek Drainage Study
City of Coppell, TX
42
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Alternative 2- Stream Barbs
The second alternative that was evaluated were stream barbs. Stream barbs, also called bendway weirs
or vanes, are weir-like structures made of rock. According to the United States Department of Agriculture
(USDA), stream barbs serve to provide stability to a stream bank by diverting the erosive flows away from
the bank and promoting deposition along the toe of the bank.
Conceptual Design
The effectiveness of this alternative is primarily contingent upon the alignment and placement of the
stream barbs. Half of the barb extends into the creek bed and half extends into the bank (referred to as
the bank key). Conceptual design calculations were based on USDA Technical Supplement 14H – Flow
Changing Techniques (TS14H). Figure 5.2 shown below illustrates the typical barb design layout based
directly from TS14H. The barbs are designed utilizing the recommended channel design based on the
bankfull discharge and to be fully submerged at bankfull elevation. The recommended dimensions of the
barb are approximately three feet above grade and 17.5 feet long. The bed key height is approximately
four (4) feet tall and 15.75 feet bank key length into the bank. The stream barbs are angled upstream at
no more than a 30 degree angle from the bank and are spaced approximately 43.75 feet apart. The barbs
must begin at the beginning and end of the erosion problem areas. The first barb is located approximately
2,400 feet downstream of DCLID-1 and ends about 273 feet at the end of the erosion problem area for a
total of seven (7) barbs. The proposed layout and configuration of the barbs can be seen in Appendix A,
Exhibit 9. For this alternative, stream barbs were evaluated and designed between river stations 15480
and 15200. An example of a successfully applied project along Aquilla Creek near Waco, Texas is shown
in Figure 5.3 which incorporated bendway weirs (which are similar in design and application as stream
barbs).
Figure 5.2: Stream Barb Design Layout
Denton Creek Drainage Study
City of Coppell, TX
43
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Figure 5.3: Aquilla Creek Bendway Weir, Waco, TX
Model Results
This alternative was evaluated using the 1D/2D unsteady and 2D hydraulic HEC-RAS v5.03 models to
determine the potential impacts to water surface elevations and velocities. In the 1D/2D unsteady
hydraulic model, the barbs were modeled as in-line weirs. In the 2D model, the barb geometry was spliced
into the existing terrain model in order to evaluate the hydraulics around the barbs. Based on the results
from the 1D/2D and 2D hydraulic models, there are minimal impacts to water surface elevations at
upstream or downstream of the proposed barbs. However, due to the size and scale of the hydraulic
models compared to the relatively small size of the barbs, the impacts to velocities are difficult to
evaluate. The recommended design of the barbs results in full submergence for the bankfull discharge.
Thus, the velocity impacts along the bank are not visible in the 1D/2D model. In the 1D/2D model, only
three cross sections (15671, 15359, and 15238) are located in the vicinity of the barbs and which can only
be modeled as in-line structures in 1D. The 1D model has three in-line weirs that represent the barbs.
Since 1D HEC-RAS only performs calculations by cross section, the full definition of each barb cannot be
accurately modeled to determine velocity impacts and can only be used to determine potential impacts
to water surface elevations. The 2D hydraulic model better addresses this issue as the geometry of each
barb is added to the terrain. The 2D bankfull velocity is shown in Figure 5.4. It can be seen at the upstream
barbs that the flow arrows have an elliptical shape to them. This represents the stream barbs forcing the
water back to the center of the creek and away from the banks. The 100-year water surface elevation
comparison are shown in Table 5.2. The barbs cause a decrease in water surface elevations along the
proposed stretch of the barbs and upstream. There are minor rises downstream of the proposed barbs
due to shifts in hydrograph peaks and changes in the flow interaction between Denton Creek and the Elm
Fork Trinity. The max rise is 0.13 feet at river station 15050.
Denton Creek Drainage Study
City of Coppell, TX
44
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Figure 5.4: Alternative 2 Bankfull Velocity
Table 5.3: Alternative 2 Water Surface Elevations Comparison
River
Station
100-Year WSEL (ft) Difference
(ft) Existing Proposed
16501 452.31 452.04 -0.27
16294 451.7 451.33 -0.37
15983 451.24 450.77 -0.47
15671 450.82 450.11 -0.71
15359 450.45 450.09 -0.36
15238 450.26 450.03 -0.23
15050 449.81 449.94 0.13
14973 449.75 449.87 0.12
14819 449.46 449.58 0.12
Denton Creek Drainage Study
City of Coppell, TX
45
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Advantages
i. Cost effective option in reducing erosive along problem residential areas
ii. Restores eroded channel banks along residential properties
iii. Protects bank from further erosion
Disadvantages
i. Required to be built on private property
ii. May required to apply at additional locations at downstream bend locations due to
change in velocity distribution within the creek
Denton Tap Grade Control Structure
Based on the findings from the geomorphological evaluation, the channel will continue to down cut
upstream of Denton Tap Road, if not addressed. This would then continue to supply sediment into the
DCLID-1 section of Denton Creek, resulting in deposition within the DCLID-1 flood control channel, which
in term, will result in increased flood risks. In order to address this issue, a grade control structure is
proposed just downstream of Denton Tap Road. Based on the Geomorphology Assessment
recommendations, the recommended structure would be a concrete drop structure. An example design
for the drop structure applicable for this area downstream of Denton Tap Road can be seen in Figure 5.6.
This figure is from the “Colorado Floodplain and Stormwater Criteria Manual: Chapter 13- Hydraulic
Analysis and Design, Section 6- Drop Structures” published September 30, 2008 which is shown as a
grouted rock boulder structure. For conceptual level design and cost estimate purposes, this drop
structure’s geometric layout was utilized. However, the proposed drop structure shall be composed of
concrete instead of the grouted boulder shown in Figure 5.5. The conceptual cost estimates can be found
in Appendix C.
Figure 5.5: Grouted Sloping Boulder Drop for Unstable Channels in Erosive Soils
Denton Creek Drainage Study
City of Coppell, TX
46
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Property Buyout Option
As part of the alternative analysis, a two-phase nonstructural option was investigated consisting of a
voluntary buyout of the affected properties along Denton Creek identified in the Fluvial-Geomorphic
Assessment of the Denton Creek: DCLID No. 1 Downstream to the Elm Fork in Appendix B. Based on the
assessment, Denton Creek will continue to erode its banks if not stabilized. The erosion hazard zone area
determined in this study estimates approximately 30 feet of lateral migration of the creek banks. An
estimated 41 structures fall within this zone. Of these 41 properties, seven (7) were selected for the first
phase of potential buyouts due to the extent of erosion, lack of bank protection and proximity to the
creek. The second phase would include a buyout of the remaining 34 properties that fall in the EHZ.
However, the buyout of these 34 homes would be dependent upon a condition assessment of any existing
toe and/or slope protection to determine its adequacy. A cost estimate for the two-phase buyout option
of homes currently and potentially impacted by the stream degradation was assessed. Once the
properties have been purchased, the land could then be converted for City purposes. A full discussion of
the erosion hazard zone can be found in section 5.5 of the Fluvial-Geomorphic Assessment of Denton
Creek: DCLID No. 1 Downstream to the Elm Fork provided in Appendix B. Limits of the EHZ along with the
affected properties can be found in Appendix A, Figure 10.
No Action Option
Per the findings of the geomorphology evaluation, not addressing the erosion issues can continue to cause
major problems to homeowners located along Denton Creek. Reduction in vegetation could cause an
increase in lateral migration up to 30 feet and degrade up to 9 feet depending on subsurface conditions.
Potentially, this lateral migration could be even greater considering the majority of these homes are
located on the cutbank side of Denton Creek. Based on the estimated EHZ the creek banks will continue
to erode slowly reclaiming more land and putting structures at risk. While several homes are protected
by existing bank protection, they should be checked for their susceptibility to failure due to stream
degradation.
B. COST ESTIMATES
In order to evaluate the alternatives on an economic basis, Halff performed conceptual level cost
estimates for the three alternatives. The two alternatives selected were itemized and given an estimated
unit price based on the Texas Department of Transportation (TxDOT) Average Unit Low Bid Prices for
Dallas County. All three alternatives and their cost estimates include the replacement of the existing
headwall approximately 2,400 feet downstream of DCLID-1 and a grade control structure just downstream
of Denton Tap Road. The grade control structure at Denton Tap Road is recommended to prevent further
down-cutting of the channel upstream. This would reduce sediment load transport downstream that
would be deposited within the DCLID-1 flood control channel. A construction contingency allowance (40%
of the estimated construction cost and a professional design and construction phase services fee (18% of
estimated construction cost) were added to the total estimated cost for the bypass channel and stream
barbs alternatives. The property buyout alternative cost includes the 2017 Dallas County Appraisal District
property values for each of the affect properties with an additional 30% to account for market cost. An
additional 30% contingency was included to account for any post-acquisition construction. All cost are
based on 2017 US dollars. Table 5.3 provides a summary of cost estimates of the selected alternatives
including a buyout. The itemized cost estimates for each alternative can be found in Appendix C.
Denton Creek Drainage Study
City of Coppell, TX
47
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Table 5.4: Summary of Cost Estimates
Alternative Alternative Description Cost1
1 Denton Creek Bypass Channel $ 7,400,000
2 Stream Barbs $ 836,000
3.1 Property Buyout- Phase 1 (Initial) $ 5,300,000
3.2 Property Buyout- Phase 2 (Future) $ 34,600,000
1. Includes 40% for Alternatives 1 and 2 and 30% for Alternative 3 for Construction Contingency, 18% Engineering Fee
VI. CONCLUSIONS
The Denton Creek Drainage Study was developed to reduce erosion along Denton Creek in the City of
Coppell. This study focused on evaluating the existing conditions of Denton Creek and propose conceptual
level alternatives to address erosion issues at problem locations. With the aid of Dr. Peter Allen and Dr.
John Dunbar of Baylor University along with Dr. Jeff Arnold of USDA, a geomorphology evaluation was
conducted to determine the source of sedimentation and provide stable channel design
recommendations. Two (2) conceptual level structural alternatives were developed and evaluated
including a proposed bypass channel and stream barbs. Both alternatives were found to be viable options
in reducing erosion. A nonstructural alternative including a two-phase property buyout option was also
provided as an option to mitigate for the erosion and flood risk. If no alternative is implemented the creek
shall continue to down cut and erode its banks, putting more structures at risk. Regardless of the selected
alternative, it is recommended that the grade control structure at Denton Tap Road be a part of any
decision made by the City of Coppell to address the erosion and flooding concerns. Allowing the creek to
continue to down cut will not reduce the risk of flooding within the DCLID-1 segment of Denton Creek due
to the continuing deposition of material within this reach or reduce the maintenance cost associated with
removing log jams within Denton Creek.
Denton Creek Drainage Study
City of Coppell, TX
48
`
VII. REFERENCES
1. US Army Corps of Engineers. HEC-RAS River Analysis System, 2D Modeling User’s Manual.
February, 2016.
2. City of Dallas, iSWM Criteria Manual for Site Development and Construction. 2010.
3. United States Department of Agriculture. Flow Changing Techniques- Technical Supplement 14H.
August, 2007.
4. United States Department of Agriculture. Engineering Technical Note No. 23, Design of Stream
Barbs. May, 2005.
5. Colorado Floodplain and Stormwater Criteria Manual. Chapter 13 Hydraulic Analysis and Design
Section 6 Drop Structures. September, 2008.
APPENDIX A: FIGURES
MAC ARTHUR BLVDFREEPORT PKWYBELT LINE RDDENTON TAP RDLAKES I DE P KW Y
NORTHWEST HIG HWAY
BELT LINE RD
"B 2499
"B1171
"B 3040
LUNA RDOLD DENTON RD"B 2281
Dallas CountyDenton County
Tarrant County
Tarrant CountyDallas CountyDenton County
Flower Mound
Southlake
Irving
Dallas
Farmers Branch
Carrollton
Lewisville
Coppell
Denton Creek
Elm Fork TrinityCottonwoodBranch
GrapevineLake
DFW AIRPORT
Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
County Boundary
Political Boundary
Grapevine Lake
Project Area
*Denton County Levee Improvement District No. 1
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ExhibitDenton Creek
´Exhibit 1Denton Creek Drainage StudyProject
Project Area MapTitle
Watershed
0 2,500 5,000
Scale in Feet1 inch = 5,000 feet
?d
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Aerial Imagery from 2015 Woolpert
MAC ARTHUR BLVDFREEPORT PKWYBELT LINE RDDENTON TAP RDLAKES I DE P KW Y
NORTHWEST HIG HWAY
BELT LINE RD
"B 2499
"B1171
"B 3040
LUNA RDOLD DENTON RD"B 2281
DCLID_0260
DCLID_0300
DCLID_0120
DCLID_0290
DCLID_0280
DCLID_0020
DCLID_0060
DCLID_0150
DCLID_0230
DCLID_0070
DCLID_0040
DCLID_0200
DCLID_0080
DCLID_0270
DCLID_0250
DCLID_0240
DCLID_0170
DCLID_0010
DCLID_0160
DCLID_0190
DCLID_0100
DCLID_0130
DCLID_0180
DCLID_0090
DCLID_0030
DCLID_0140
DCLID_0210
DCLID_0050
DCLID_0110
Dallas CountyDenton County
Tarrant County
Tarrant CountyDallas CountyDenton County
Flower Mound
Southlake
Irving
Dallas
Carrollton
Lewisville
Coppell
Denton Creek
Elm Fork TrinityCottonwoodBranch
GrapevineLake
DFW AIRPORT
Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
County Boundary
Political Boundary
Drainage Area
Grapevine Lake
Project Area
*Denton County Levee Improvement District No. 1
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ExhibitDenton Creek
´Exhibit 2Denton Creek Drainage StudyProject
Drainage Area MapTitle
Watershed
0 2,500 5,000
Scale in Feet1 inch = 5,000 feet
?d
%&c(
Aerial Imagery from 2015 Woolpert
DCLID_0110 0.01DCLID_0050 0.02DCLID_0210 0.04DCLID_0140 0.05DCLID_0030 0.08DCLID_0090 0.08DCLID_0180 0.1DCLID_0130 0.13DCLID_0100 0.16DCLID_0190 0.22DCLID_0160 0.25DCLID_0010 0.28DCLID_0170 0.34DCLID_0240 0.40DCLID_0250 0.42DCLID_0270 0.42DCLID_0080 0.5DCLID_0200 0.62DCLID_0230 0.76DCLID_0040 0.81DCLID_0150 0.93DCLID_0070 1.02DCLID_0060 1.22DCLID_0020 1.29DCLID_0280 1.34DCLID_0290 1.68DCLID_0120 3.02DCLID_0300 3.12DCLID_0260 6.11
Area (mi²)Drainage Area
FREEPORT PKWYBELT LINE RDDENTON TAP RDLAKES I DE P KW Y
NORTHWEST HIG HWAY
BELT LINE RD
"B 2499
"B1171
"B 3040
LUNA RDOLD DENTON RD"B 2281
DCLID_0260
DCLID_0300
DCLID_0120
DCLID_0290
DCLID_0280
DCLID_0020
DCLID_0060
DCLID_0150
DCLID_0230
DCLID_0070
DCLID_0040
DCLID_0200
DCLID_0080
DCLID_0270
DCLID_0250
DCLID_0240
DCLID_0170
DCLID_0010
DCLID_0160
DCLID_0190
DCLID_0100
DCLID_0130
DCLID_0180
DCLID_0090
DCLID_0030
DCLID_0140
DCLID_0210
DCLID_0050
DCLID_0110
DCLID_J0040
DCLID_J0060
DCLID_J0080
DCLID_J0090
DCLID_J0100
DCLID_J0120
DCLID_J0170
DCLID_J0290
DCLID_J0280
DCLID_J0270DCLID_J0260
DCLID_J0240
DCLID_J0230
DCLID_J0180
DCLID_J0130
DCLID_J0150 DCLID_J0120
Outfall
Denton Creek
Elm Fork Trinity
CottonwoodBranch
GrapevineLake
DFW AIRPORT
Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
Drainage Area
Grapevine Lake
Project Area
Flow Change Location
*Denton County Levee Improvement District No. 1
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ExhibitDenton Creek
´Exhibit 3Denton Creek Drainage StudyProject
Flow Change Locations MapTitle
Watershed
0 2,500 5,000
Scale in Feet1 inch = 5,000 feet
?d
%&c(
Aerial Imagery from 2015 Woolpert
** Discharge controlled by releases from Grapevine LakeDCLID_J0040 2.45 13,000**DCLID_J0060 3.7 13,000**DCLID_J0080 5.22 13,000**DCLID_J0090 5.3 13,000**DCLID_J0100 5.46 13,000**DCLID_J0120 8.49 13,000**DCLID_J0130 8.62 13,000**DCLID_J0150 9.59 13,000**DCLID_J0170 10.18 13,000**DCLID_J0180 10.28 13,000**DCLID_J0200 11.13 13,000**DCLID_J0230 11.93 13,100DCLID_J0240 12.33 13,100DCLID_J0260 18.86 13,200DCLID_J0270 19.28 20,800DCLID_J0280 20.62 20,900DCLID_J0290 22.3 21,200Outfall25.42 23,000
Cumulative Are a (mi²)HMS Node 100 -Year Discharge (cfs)
Denton Creek
Elm Fork TrinityCottonwoodBranch
GrapevineLake
DFW AIRPORT
Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
County Boundary
Political Boundary
Drainage Area
Grapevine Lake
Denton Creek Hydrologic Soils
Soil Group A
Soil Group B
Soil Group C
Soil Group D
*Denton County Levee Improvement District No. 1
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ExhibitDenton Creek
´Exhibit 4Denton Creek Drainage StudyProject
Hydrologic Soils MapTitle
Watershed
0 2,500 5,000
Scale in Feet1 inch = 5,000 feet
?d
%&c(
Aerial Imagery from 2015 Woolpert
Denton Creek
Elm Fork TrinityCottonwoodBranch
GrapevineLake
DFW AIRPORT
Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
County Boundary
Political Boundary
Drainage Area
Grapevine Lake
*Denton County Levee Improvement District No. 1
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ExhibitDenton Creek
´Exhibit 5Denton Creek Drainage StudyProject
Land Use MapTitle
Watershed
0 2,500 5,000
Scale in Feet1 inch = 5,000 feet
?d
%&c(
Denton Creek Land Use (Fully Developed)AirportCemeteriesCommercialCommunicationEducationFarmlandFlood controlGroup quartersHotel/motelIndustrialInstitutional/semi-publicMobile homeMulti-familyOffice
ParkingParks/recreationRailroadRanch landResidential acreageRetailRoadwayRunwaySingle familySmall water bodiesTimberlandTransportationUnder constructionUtilitiesVacantWaterAerial Imagery from 2015 Woolpert
Denton Creek
CottonwoodBranch
Coppell
Dallas
Irving
CarrolltonLewisville
Panel 01 of 07
FREEPORT PKWYDENTON TAP RDMAC ARTHUR BLVDBELT LINE RD
Panel 02 of 07
Panel 03 of 07
Panel 04 of 07
Panel 05 of 07
Panel 06 of 07
Panel 07 of 07
Denton County
Dallas County
SANDY LAKE RD
*Denton County Levee Improvement District No. 1
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KEY TO FEATURES
ExhibitDenton CreekExhibit 6Index MapDenton Creek Drainage StudyProject
Hydraulic Work MapTitle
Watershed
Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
Panel Extent
County Boundary
Political Boundary
Effective FEMA 100 Year Zone Type
A
AE
FLOODWAY
X
X With Reduced Risk Due to Levee
0 1,000 2,000
Scale in Feet
1 inch = 2,000 feet ´
Aerial Imagery from 2015 Woolpert
33696337663385236345321053223131949340643509034141346763421834892352783397035215344583458534638 334003332633580324793550433087 3310832586331643568135888357703618136036328973161131660A C E R D
CANYON DR
GIFFORD DRMADISON STLAYTON DR
COPPERSTONE TRL
AVALON LN
GRAYWOOD LN PEDMORE DRWESTMINSTER WAY
LOXLEY DR
AUBURN WAYWESTMINSTER CTFAIRLANDS CIRCANEMOUNT LNCOMPTON CTCLIFTON CT
MARTEL CTB L A C K F I E L D D R
GIFFORD CT
SH EF FIE LD C THAMPT
ON DRCROMWELL CTJOSHUA LN
BUTTONWOOD DRBANKERS COTTAGE LNHARDWICK CT
GRAYWOOD CTPA RKW A YDentonCreek
?m
470460
450480
440490460
4804
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470460470470470
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460
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4 6 0
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464
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446 444
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464464
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4 7 4472476 468468456474486478478
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4 7 2 476472468482472464
47247 8
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Study
Non-Study
Cross Section
Index Contour*
Intermediate Contour*
Major Road
Local Road
Political Boundary
100 Year Revised Existing (FullyDeveloped) Conditions
Effective FEMA 100 Year
*Contours generated from 2009 TNRIS LiDAR and 2016 Halff Survey Data.
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Hydraulic Work MapTitle
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 6Panel 1 of 7Aerial Imagery from 2015 Woolpert
27892295302724827041269702760326621271452729826828 2668827672281222745628217287912858628380285103210532231319493179729331292062905028891300633025730366 304243077930531311053121631376316113166029817DENTON TAPNATCHES TRCE
LY N D S IE D R
MARTEL LN
COWBOY DRMADISON STLEVEE PLWAVE
R
L
Y
L
NPLAZA BLVDCOPPERSTONE TRL
AVALON LN
C H E S T N U TLNAUBURN WAYM I L A N S T
N HEARTZ RDS
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ENCLAVES CTKAILEY WAYCANEMOUNT LNCROSS TIM BERS TRL
P
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FLIN TSH IR E W A YBANKERS COTTAGE LNRU STIC M EA D O W W AYPARKWAY
NATCHES TRCEDentonCreek
CottonwoodBranchatDenton
Andy Brown Park Pond
?m
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450
440
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490 470450460 470440 4404604604504 6 0
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46
8
436
472
474
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482
484
486
434
488 474436
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454
468
466452462 4 5 8
4 5 6
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452
438
468
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468
466
45847
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6
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466
44446647246 4
4 7 2
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488
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4524 5 8
4 6 8
4 6 8
442
454 4564 5 2
466452
462
472456
462466
466464
4524 5 2
434
464474 4544724
6
6 Study
Non-Study
DCLID-1*
Cross Section
Index Contour**
Intermediate Contour**
Major Road
Local Road
Political Boundary
100 Year Revised Existing (FullyDeveloped) Conditions
Effective FEMA 100 Year
**Contours generated from 2009 TNRIS LiDAR and 2016 Halff Survey Data.
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Hydraulic Work MapTitle
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 6Panel 2 of 7*Denton County Levee Improvement District No. 1Aerial Imagery from 2015 Woolpert
227952261622424232292341323506220802221121798
236282182225168253562724827041 2161125499269702760326621271452729826828 266882767223802255582745625760259272608726194249472474823868263832451924099
24058
242642155824198
2299723063
23198
MOORELODGE RDSAMUEL BLVDPHI
LL
I
PS DRW ATERVIEW DRHOOD D RLYNDSIE D R
PA R KV IE W P L
ALEX DR
DUNCAN DR
CRIBBS DR
KYLE DR PARKWOOD
L
NROCKCREST DRLAKE PARK DR
MEADOWOOD LN
JOHNSON DR
HARWELL STBELLA VI
S
T
A DR
PLUMLEE PL
THOM PSON DR
STI
LL
FOREST DRWILLINGHAM PLHARRISON DR
COATS ST
GLEN LAKES DR
MICHELLE PL
C
R
E
S
T
WOOD DR
CLAYTON CIRBENT TREE CTPRESTWICK CTS
P
R
I
N
G
H
IL
L
D
R
CLEAR HAVEN DRENCLAVES CTKAILEY WAYC
R
E
S
T
HAVE
N
R
DP A R K L N
P
A
R
K
H
I
G
H
L
A
N
D
S
D
R WI
L
L
OW RI
DGE
CT
BRANT DRMORNING MISTNORTHSHORECT
HOOD CT
QUIET VALLEY DRPARKWAY
O l dDen t o nCreek
Andy BrownPark Pond
Andy Brown Park Pond
Andy BrownPark PondDentonCree k4504404604 7 0
460
460450450
4704704 6 0
4604404704604
7
0
4 5 0470 4604604 6 047045045046 0
4604604404
5
0
4
6
0470 4
6
04504
6
0
4504 5 0 460460
460
4 6 0
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04504704544524484464444424564584384624644
6
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4684724744764684724 6 4
4 4 8454474
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5
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46 2 4524584524
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4
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458464
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4 6 4
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462456
4 5 8
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464
4 6 2
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468 454438446448448462452
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448458
4 5 8
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466466
444
4 4 2
458472
4 5 8
4 6 2
446454
4 6 2 4624484 5 8472 462
438448
464464
466452458466458
4564
5
8
456442
4544624644564 4 6 4664584524 6 4 4524 3 8
4 5 8
4 5 6 4544544584584
7
2
4
7
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4684684624584 5 8
448454
4 6 6 4624584524
5
6
464
462
462458458
458466
4 6 6
4624 5 2
458
4664664 6 2438454456 4 4 8
4564
5
4
464456
Study
Non-Study
DCLID-1*
Cross Section
Index Contour**
Intermediate Contour**
Major Road
Local Road
Political Boundary
100 Year Revised Existing (FullyDeveloped) Conditions
Effective FEMA 100 Year
**Contours generated from 2009 TNRIS LiDAR and 2016 Halff Survey Data.
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Hydraulic Work MapTitle
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 6Panel 3 of 7*Denton County Levee Improvement District No. 1Aerial Imagery from 2015 Woolpert
1799118114178921822318335227952261622997
23063
2242423198
23229184792341318592235062208022211176491864621798
2362821822216112380224748238682451924099
24058
242642155824198
2141620616205792039720314 20224 2001218826192231942119742
2135421169207282105920944190712087321275 1980719614DE FOREST RD
FO REST HILL D R
CRIBBS DR LAKEVIEW DRSTRATFORD LNLAKE PARK DR CASTLE CREEK DRINGLENOOK CTCAMBRIDGE MANOR LNCH ES HIR E DRRAINTREE CIR DEFOREST CTGLEN LAKES DR
E PENINSULA DR
BENT TREE CTPRESTWICK CTW PENINSULADR
K I N G S C A N Y O N C T
V
I
L
L
AGE
GR
E
E
N DR
NORTHSHORECTMAC ARTHUR BLVDLAKE VISTA DR
O l dDen t o nCreek
Old
DentonCreekDentonCreek?m
450
440
460470440
440
4 5 0
440450450450
4 6 0
450
450
460
460 460460 470450450
4 6 0
4
5
0 4 6 0
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450
460
450440450
4 5 0
4504
6
0
450
4504504 4 0
450
4404 6 0456454452 444 446442
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458
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442
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4 5 6
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452456
4524564
5
2
4 5 2
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438
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452
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452454438
4
5
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454446
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448
436
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448
4 5 6452456452452452452
4 4 4
448
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4 4 8
458458
452
4 4 6
4564544 4 8
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454
4 4 6
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444
458
452456
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452
446442
448446448
456456454
442
4464484 5 2
452438
456444448
4484584564524 5 8
4 3 8
452
452
4 5 4
Study
Non-Study
DCLID-1*
Cross Section
Index Contour**
Intermediate Contour**
Major Road
Local Road
Political Boundary
100 Year Revised Existing (FullyDeveloped) Conditions
Effective FEMA 100 Year
**Contours generated from 2009 TNRIS LiDAR and 2016 Halff Survey Data.
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Hydraulic Work MapTitle
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 6Panel 4 of 7*Denton County Levee Improvement District No. 1Aerial Imagery from 2015 Woolpert
179911811417892182231833518479
1364613307139421413713768185921442517649186461297014819147061497315050
1 5 2 3 8 17410126541255115359
15671
1598318826192231942119742
1 7 1 9 7
16956190711 6 5 0 1
1 6 7 0 2
1 6 2 9 41980719614
120461182113144
DE FOREST RD LAKE VISTA DRA
LLE
N R
D
LAKEVIEW DR
CASTLE CREEK DR
WOODLAKE DR
ASHFORD DR
A
N
D
O
V
E
R L
N
CH ES HIR E DR
WARREN CT
BEAU DRST JAMESCH ALF ON T P L DEFOREST CTPARKERDRN
O
T
TIN
G
H
A
M
D
R
DOVER CTOld
DentonCreek
D e ntonCreek Tim berCre ek
44045 0
460
430470
440
450
4
3
0
450
4 5 0
4 5 0
450
440
440
440
440
4404 3 0450 440450
440440450 4404504404
6
0
4 4 0 440440
450450
450450
440450
460
446
444
442
438
448
452454436456
434
4324584
6
24644
6
6
468
472
4
54 438444
446
442 444
4
5
6
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454
4 4 4
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444
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4384444
5
6
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444
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446
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442452
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456
4 4 8
442
4 4 8
456454
448
4
4
8
44244244 6
444454442442456
436
458442
448448 438
4564444464464
4
2
444
45444 6
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448 446446438456454444 436
452436
4
4
2
442
446438448438446444442436448
4 4 6
456
4 5 6
452
442438 4424 5 4
454446452
4 5 8
432
4 5 8
448438
446
454
4 5 6
444
452
4 5 2 444446452
4544444 4 6
442
454
4
4
6452452
4484544484
4
2
45
6
444448
4
5
4
4 3 8
456 4464 4 2
436
4484 5 6
438
456
462
438
44245 6 444442
44644
4
452442444442
438442446438
Study
Non-Study
Cross Section
Index Contour*
Intermediate Contour*
Major Road
Local Road
Political Boundary
100 Year Revised Existing (FullyDeveloped) Conditions
Effective FEMA 100 Year
*Contours generated from 2009 TNRIS LiDAR and 2016 Halff Survey Data.
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Hydraulic Work MapTitle
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 6Panel 5 of 7Aerial Imagery from 2015 Woolpert
1364613307139421413713768144251314412970148191470612654125513196
3097
33268 7 5 6
2849822580448898
3598257290558325941585889327
43787563
388441867 4 0 9
73159 5 7 9
45142389
2148
7 1 7 7
989612046
1880
914118211047910581
159511650
65791019410877
1309
6895
1 1 4 7 9
111751078
1194
643558405564SANDY LKCOVE DRCREEK XING
VI
L
L
AGE PKWYG I B B S X I N G
LAGUNA DRHOLLYWOOD DRB A S I LW O O D D RBEVERLY DRWARREN CT
KIMBLE KOURTP I N TA I L C T REDWOOD DRBAY CIRF O R E S T W O O D L NDRIFT
WOOD DRC H E R R Y W O O D T R L
R O U N D R O C K C I R
O A K W O O D L N BURNS XINGMAC ARTHUR BLVDDentonCreek440450430 460450 440430460450440430440
440
4
6
0
450450
440
4304
5
0
450 4504 5 0
4504304
4
04404
5
0
45044045045 0450450450 4404
3
0
4
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44 8
4
5
2 432454428456
4 5 8
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424
456
452 442428
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452
452
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4424564 4 2
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428
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4
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432
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6
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4
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452446448 4284424 5 2 432454
454
428
4 4 2
446
4544 5 4
4 5 2 4364264 4 8428 442446438452446442446448 4424 5 4
4524444 4 8
456452Study
Non-Study
Cross Section
Index Contour*
Intermediate Contour*
Major Road
Local Road
Political Boundary
100 Year Revised Existing (FullyDeveloped) Conditions
Effective FEMA 100 Year
*Contours generated from 2009 TNRIS LiDAR and 2016 Halff Survey Data.
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Hydraulic Work MapTitle
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 6Panel 6 of 7Aerial Imagery from 2015 Woolpert
3196
3097
33268 7 5 6
2849822580448898
359825729055 8383259 4 1 5
68385889 3 2 7
43787563
388441867 4 0 9
7315611
9 5 7 9
45142389
2148
3 5 3
7 1 7 7 1880
914
1595
65792 3 9
1309
6895
1078
1194
643558405564
478549995287RIVERCHASESTARLEAF STFALLS RDHOLLYWOOD DRGLADE POINT DR TRI
NI
TY CTL
O
N
G
M
E
A
D
O
W D
R
GRAPEVINE CREEK DR
B
RIT
T
A
N
Y D
RBREANNA W AYWILSHIRE DRRIVERVIEW DRSUNRISE DRCROWN POI
NT DRELM FORK DRFALLS CTFPREST CPVEJE N N IN G S C T
SANDY LK
DentonCreek
ElmForkofTrinityRiver
440
4
3
0
4 5 0
420410450440440
4 4 0
440
450450430440450440 4404 4 0420
4
5
0450 4404404504404
5
0
440
450450450
4 4 0440
440430
450440450
45 0
450430450430444
442
438
446436
4 3 4
432
4
2
8
448
4
2
6
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4
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426
448444442
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428
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4264484
3
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4 4 6 444438 4244384464 4 4428 444
448448442448436432
448
4 4 2
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448
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446438426442442
444436442448
444 442428446
442442
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444
442444
4 4 8
422
438
424
428
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444 436442448 438444436
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4
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436
446
446 448438448442
446
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4464
4
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438
4 3 6442
42 8
446424 442446442
444 442448448 442446 4444
4
4
446
444
Study
Non-Study
Cross Section
Index Contour*
Intermediate Contour*
Major Road
Local Road
Political Boundary
100 Year Revised Existing (FullyDeveloped) Conditions
Effective FEMA 100 Year
*Contours generated from 2009 TNRIS LiDAR and 2016 Halff Survey Data.
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Hydraulic Work MapTitle
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 6Panel 7 of 7Aerial Imagery from 2015 Woolpert
Denton Creek
CottonwoodBranch
Coppell
Dallas
Irving
CarrolltonLewisville
Panel 01 of 07
FREEPORT PKWYDENTON TAP RDMAC ARTHUR BLVDBELT LINE RD
Panel 02 of 07
Panel 03 of 07
Panel 04 of 07
Panel 05 of 07
Panel 06 of 07
Panel 07 of 07
Denton County
Dallas County
SANDY LAKE RD
*Denton County Levee Improvement District No. 1
%&c(
?m
?m
KEY TO FEATURES
ExhibitDenton CreekExhibit 7Index MapDenton Creek Drainage StudyProject
Revised Existing 2-Year Velocity Distribution Map
Title
Watershed
0 1,000 2,000
Scale in Feet
1 inch = 2,000 feet ´
Aerial Imagery from 2015 Woolpert
Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
Panel Extent
County Boundary
Political BoundaryRevised Existing 2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
A C E R D
CANYON DR
GIFFORD DRMADISON STLAYTON DR
COPPERSTONE TRL
AVALON LN
GRAYWOOD LN PEDMORE DRWESTMINSTER WAY
LOXLEY DR
AUBURN WAYWESTMINSTER CTFAIRLANDS CIRCANEMOUNT LNCOMPTON CTCLIFTON CT
MARTEL CTB L A C K F I E L D D R
GIFFORD CT
SH EF FIE LD C THAMPT
ON DRCROMWELL CTJOSHUA LN
BUTTONWOOD DRBANKERS COTTAGE LNHARDWICK CT
GRAYWOOD CTPA RKW A Y37000
36500
36000
35500
35000 3450034000
3350033000
32500
32000
DentonCreek
?m KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Revised Existing 2-YearVelocity Distribution Map
Title
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 7Panel 1 of 7Study Stream
Non-Study Stream
Major Road
Local Road
River Station1000
Aerial Imagery from 2015 Woolpert
Revised Existing 2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
DENTON TAPNATCHES TRCE
LY N D S IE D R
MARTEL LN
COWBOY DRMADISON STLEVEE PLWAVE
R
L
Y
L
NPLAZA BLVDCOPPERSTONE TRL
AVALON LN
C H E S T N U TLNAUBURN WAYM I L A N S T
N HEARTZ RDS
P
R
I
N
G
H
IL
L
D
R
ENCLAVES CTKAILEY WAYCANEMOUNT LNCROSS TIM BERS TRL
P
A
R
K
H
I
G
H
L
A
N
D
S
D
R
MARTEL CTBRUSHY CREEK TRLS
TONEMEADE WAYC
R
O
O
K
E
D
T
R
E
E C
T
FLIN TSH IR E W A YBANKERS COTTAGE LNRU STIC M EA D O W W AYPARKWAY
NATCHES TRCE
31500 3100030500
30000
29500 290002850028 0 0 0
2 7 5 0 0
2 7 0 0 0
2 6 5 0 032000DentonCreek
CottonwoodBranchatDenton
Andy Brown Park Pond
?m
*Denton County Levee Improvement District No. 1
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Revised Existing 2-YearVelocity Distribution Map
Title
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 7Panel 2 of 7Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
River Station1000
Aerial Imagery from 2015 Woolpert
Revised Existing 2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
MOORELODGE RDSAMUEL BLVDPHI
LL
I
PS DRW ATERVIEW DRHOOD D RLYNDSIE D R
PA R KV IE W P L
ALEX DR
DUNCAN DR
CRIBBS DR
KYLE DR PARKWOOD
L
NROCKCREST DRLAKE PARK DR
MEADOWOOD LN
JOHNSON DR
HARWELL STBELLA VI
S
T
A DR
PLUMLEE PL
THOM PSON DR
STI
LL
FOREST DRWILLINGHAM PLHARRISON DR
COATS ST
GLEN LAKES DR
MICHELLE PL
C
R
E
S
T
WOOD DR
CLAYTON CIRBENT TREE CTPRESTWICK CTS
P
R
I
N
G
H
IL
L
D
R
CLEAR HAVEN DRENCLAVES CTKAILEY WAYC
R
E
S
T
HAVE
N
R
DP A R K L N
P
A
R
K
H
I
G
H
L
A
N
D
S
D
R WI
L
L
OW RI
DGE
CT
BRANT DRMORNING MISTNORTHSHORECT
HOOD CT
QUIET VALLEY DRPARKWAY
2 6 0 0 0 25500250002450024000235002 7 0 0 0
2 6 5 0 0
O l dDen t o nCreek
Andy BrownPark Pond
Andy Brown Park Pond
Andy BrownPark PondDentonCre ek*Denton County Levee Improvement District No. 1
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Revised Existing 2-YearVelocity Distribution Map
Title
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 7Panel 3 of 7Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
River Station1000
Aerial Imagery from 2015 Woolpert
Revised Existing 2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
DE FOREST RD
FO REST HILL D R
CRIBBS DR LAKEVIEW DRSTRATFORD LNLAKE PARK DR CASTLE CREEK DRINGLENOOK CTCAMBRIDGE MANOR LNCH ES HIR E DRRAINTREE CIR DEFOREST CTGLEN LAKES DR
E PENINSULA DR
BENT TREE CTPRESTWICK CTW PENINSULADR
K I N G S C A N Y O N C T
V
I
L
L
AGE
GR
E
E
N DR
NORTHSHORECTMAC ARTHUR BLVDLAKE VISTA DR
230002 2 5 0 0
22000 2 1 5 0 0 2 1 0 0 0 2 0 5 0 0 20000
19500
19000
235002450024000O l dDen t o nCreek
Old
DentonCreekDentonCreek?m
*Denton County Levee Improvement District No. 1
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Revised Existing 2-YearVelocity Distribution Map
Title
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 7Panel 4 of 7Study Stream
Non-Study Stream
DCLID-1* Levee
Major Road
Local Road
River Station1000
Aerial Imagery from 2015 Woolpert
Revised Existing 2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
DE FOREST RD LAKE VISTA DRA
LLE
N R
D
LAKEVIEW DR
CASTLE CREEK DR
WOODLAKE DR
ASHFORD DR
A
N
D
O
V
E
R L
N
CH ES HIR E DR
WARREN CT
BEAU DRST JAMESCH ALF ON T P L DEFOREST CTPARKERDRN
O
T
TIN
G
H
A
M
D
R
DOVER CT18500
18000
1750
0
170001650016000
1 5 5 0 0
15000
14500
19500
19000
14000
Old
DentonCreek
D e ntonCreek Tim berCre ek
BRENTWOOD DR
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Revised Existing 2-YearVelocity Distribution Map
Title
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 7Panel 5 of 7Study Stream
Non-Study Stream
Major Road
Local Road
River Station1000
Aerial Imagery from 2015 Woolpert
Revised Existing 2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
SANDY LKCOVE DRCREEK XING
VI
L
L
AGE PKWYG I B B S X I N G
LAGUNA DRHOLLYWOOD DRB A S I LW O O D D RBEVERLY DRWARREN CT
KIMBLE KOURTP I N TA I L C T REDWOOD DRBAY CIRF O R E S T W O O D L NDRIFT
WOOD DRC H E R R Y W O O D T R L
R O U N D R O C K C I R
O A K W O O D L N BURNS XINGMAC ARTHUR BLVD1400013500
1 3 0 0 0
12500
12 0 0 0
115001 1 0 0 0
1050010000950090008500
8 0 0 0 750070006000
2500 2000150014500
DentonCreek
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Revised Existing 2-YearVelocity Distribution Map
Title
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 7Panel 6 of 7Study Stream
Non-Study Stream
Major Road
Local Road
River Station1000
Aerial Imagery from 2015 Woolpert
Revised Existing 2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
RIVERCHASESTARLEAF STFALLS RDHOLLYWOOD DRGLADE POINT DR TRI
NI
TY CTL
O
N
G
M
E
A
D
O
W D
R
GRAPEVINE CREEK DR
B
RIT
T
A
N
Y D
RBREANNA W AYWILSHIRE DRRIVERVIEW DRSUNRISE DRCROWN POI
NT DRELM FORK DRFALLS CTFPREST CPVEJE N N IN G S C T
SANDY LK65005500500045004000
3500 30001 0 0 0
5
0
0
0950090008500
8 0 0 0
7
5
0
0
70006000
2500 20001500DentonCreek
ElmForkofTrinityRiver
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Revised Existing 2-YearVelocity Distribution Map
Title
Watershed
0 200 400
Scale in Feet
1 inch = 400 feet
Exhibit 7Panel 7 of 7Study Stream
Non-Study Stream
Major Road
Local Road
River Station1000
Aerial Imagery from 2015 Woolpert
Revised Existing 2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
A
LLE
N R
D
CREEK XING
G I B B S X I N GBEVERLY DRWARREN CT
BEAU DRST JAMESPARKERDRN
O
T
TIN
G
H
A
M
D
R
RO U N D R O C K C I RBURNS XINGHARRISON HILL CT
D e ntonCreek
18500
18000
17500
170001650016000
1 5 5 0 0
15000
14500
1400013500
1 3 0 0 0
12500
12 0 0 0
115001 1 0 0 0
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Alternative 1Proposed Bypass Channel
Title
Watershed
0 250 500
Scale in Feet
1 inch = 500 feet
Exhibit 8Index MapA
LLE
N R
D
CREEK XING
G I B B S X I N GBEVERLY DRWARREN CT
BEAU DRST JAMESPARKERDRN
O
T
TIN
G
H
A
M
D
R
RO U N D R O C K C I RBURNS XINGHARRISON HILL CT
D e ntonCreek
18500
18000
17500
170001650016000
1 5 5 0 0
15000
14500
1400013500
1 3 0 0 0
12500
12 0 0 0
115001 1 0 0 0
EXISTING CONDITIONS PROPOSED CONDITONS
BRENTWOOD DRBRENTWOOD DR Panel 01 of 03
Panel 02 of 03
Coppell
Carrollton
Coppell
Carrollton
Panel 03 of 03
Panel 01 of 03
Panel 02 of 03
Panel 03 of 03
A
A
Aerial Imagery from 2015 Woolpert
River Station1000
Study Stream
Non-Study Stream
Local Road
Proposed Bypass Channel
Political Boundary
2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
16000
1 5 5 0 0
15000
Coppell
Carrollton
D e n t o n C r e e k
BEAU DR
A
LLE
N R
D
BRENTWOOD D R
N
O
T
TIN
G
H
A
M
D
R
PARKE
R DRKEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Alternative 1Proposed Bypass Channel
Title
Watershed
0 100 200
Scale in Feet
1 inch = 200 feet
Exhibit 8Panel 1 of 316000
1 5 5 0 0
15000
Coppell
Carrollton
D e n t o n C r e e k
BEAU DR
A
LLE
N R
D
BRENTWOOD D R
N
O
T
TIN
G
H
A
M
D
R
PARKE
R DRPROPOSED CONDITIONSEXISTING CONDITIONSAerial Imagery from 2015 Woolpert
Panel 3
Panel 1
Panel 2
River Station1000
Study Stream
Non-Study Stream
Local Road
Proposed Bypass Channel
Political Boundary
2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
15000
14500
140001 2 0 0 0
Coppell
Carrollton
Denton Creek
W
ARREN CT
A
LL
E
N
R
D
PARKER DRBEVERLY DRM
ILL TRL
HARRISON HILL CT
KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Alternative 1Proposed Bypass Channel
Title
Watershed
0 100 200
Scale in Feet
1 inch = 200 feet
Exhibit 8Panel 2 of 315000
14500
140001 2 0 0 0
Coppell
Carrollton
Denton Creek
W
ARREN CT
A
LL
E
N
R
D
PARKER DRBEVERLY DRM
ILL TRL
HARRISON HILL CTPROPOSED CONDITIONSEXISTING CONDITIONSAerial Imagery from 2015 Woolpert
Panel 3
Panel 1
Panel 2
River Station1000
Study Stream
Non-Study Stream
Local Road
Proposed Bypass Channel
Political Boundary
2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
1400013500
1 3 0 0 0
12500
1 2 0 0 0
115001 1 0 0 0
Coppell
Carrollton
Denton Creek
C R E E K X IN GBEVERLY DRVILLAGE PKWY
GIBBS XINGBURNS XINGKEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Alternative 1Proposed Bypass Channel
Title
Watershed
0 100 200
Scale in Feet
1 inch = 200 feet
Exhibit 8Panel 3 of 31400013500
1 3 0 0 0
12500
1 2 0 0 0
115001 1 0 0 0
Coppell
Carrollton
Denton Creek
C R E E K X IN GBEVERLY DRVILLAGE PKWY
GIBBS XINGBURNS XINGPROPOSED CONDITIONSEXISTING CONDITIONSAerial Imagery from 2015 Woolpert
Panel 3
Panel 1
Panel 2
River Station1000
Study Stream
Non-Study Stream
Local Road
Proposed Bypass Channel
Political Boundary
2-Year Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
PARKER DRBRENTWOOD DR4504404 3 0
440440450440448446444 4 4 2
4 3 8
43643 4
452432454438
454
4424444 4 8
442
438KEY TO FEATURES
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Alternative 2Proposed Stream Barbs
Title
Watershed
0 25 50
Scale in Feet
1 inch = 50 feet
Exhibit 9D e n t o n C r e e kCoppellCarrollto n1 5 5 0 0
15000
Aerial Imagery from 2015 Woolpert*Contours generated from 2009 TNRIS LiDAR and 2016 Halff Survey Data.
15000
Bankfull Velocity (ft/s)
5.5 - 6.0
6.0 +
0.0 - 1.0
1.0 - 2.0
2.0 - 3.0
3.0 - 3.5
3.5- 4.0
4.0 - 4.5
4.5 - 5.0
5.0 - 5.5
1000 River Station
Political Boundary
Study Stream
Proposed Bank Key
Proposed Stream Barb
Storm Sewer Line
Index Contour*
Intermediate Contour*
Local Road
Affected Property
4404504304
6
0
450
440430440
4504 3 0
450450450
450430
450450
450
4
4
0450430436 438
442434444
4
4
6 4484524
5
4 432456
4 5 8
4284
4
8456456454
448452
454
454
432446
452
438442444456
4 5 2
448
454
456448454 438452
4564
5
6
456
4
5
4
4
4
2
45 6
452456
4 4 8
4 4 6
444
44644244244844
2
454 4564524 4 8
4
5
4
452
4 5 6
454
452454432
446446
452452 44845445
6
4464544
5
4
448
448432
442
456454456 438438
454456
454
442
4 5 8
454
456
452436
4
4
6
4
4
8
456
446454 4564
5
6
454
4564484 5 4
454
4324 4 8
456456456
456
446
452
4 5 4
442
452
ExhibitDenton Creek
´
Denton Creek Drainage StudyProject
Alternative 3Proposed Property Buyout& Erosion Hazard Zone
Title
Watershed
0 150 300
Scale in Feet
1 inch = 300 feet
Exhibit 10Denton Creek
Coppell Carrollton
Study Stream
Erosion Hazard Setback
Index Contour*
Intermediate Contour*
Affected Property
Buyout Property
Political Boundary
*Contours generated from 2009 TNRIS LiDAR and 2016 Halff Survey Data.
Aerial Imagery from 2015 Woolpert
APPENDIX B: FLUVIAL-GEOMORPHIC ASSESSMENT OF THE DE NTON CREEK: DCLID NO. 1-
DOWNSTREAM TO THE ELM FORK
Fluvial-Geomorphic Assessment
of Denton Creek: DCLID No. 1-
Downstream to the Elm Fork
Report to Halff Associates August 2017
Peter M. Allen, PhD., PG
John Dunbar, PhD., PG
2
Fluvial-Geomorphic Assessment of
Denton Creek: DCLID No. 1-Downstream
to the Elm Fork
3
SECTION 1-INTRODUCTION
1.1 STUDY LOCATION
1.2 STUDY OBJECTIVES
1.3 STABILITY CONCEPTS
1.4 STUDY APPLICATIONS
1.5 DATA SOURCES
1.6 LIMITATIONS AND ASSUMPTIONS
SECTION 2-STUDY AREA DESCRIPTION
2.1 GEOLOGY
2.2 SOILS
2.3 CLIMATE
2.4 HISTORICAL PERSPECTIVE
SECTION 3-HYDROLOGIC DATA
3.1 FLOW DURATION ANALYSIS
3.2 FLOOD FREQUENCY
SECTION 4-FIELD DATA
4.1 FIELD DATA COLLECTION OBSERVATIONS
4
4.2 GRAIN SIZE ANALYSIS BED MATERIAL (POINT BARS)
4.3 CHANNEL ERODIBILITY
SECTION 5-FLUVIAL GEOMORPHIC ASSESSMENT OF REACH
5.1 EFFECTIVE DISCHARGE ASSUMPTIONS AND CALCULATIONS: CAPACITY SUPPLY ANALYSIS
5.2 CHANNEL MEANDER ASSESSMENT
5.3 CHANNEL MEANDER AND ASSOCIATED SHEAR
5.4 CHANNEL MIGRATION POTENTIAL
5.5 HOMES AND RIVER DYNAMICS
SECTION 6-CONCLUSIONS
BIBLIOGRAPHY
LIST FIGURES
Figure 1. Location of Study Area (Denton Creek in Yellow). USGS Gage 08055500
Elm Fork green dot.
Figure 2. Slope of survey reach. Pool, Riffle designation based on mean channel
slope and can vary based on backwater effects.
Figure 3. Methods of River Stability Analysis (Stroth, 2017)
Figure 4. Geologic Map of the Study Area (Bureau of Economic Geology, Dallas
Sheet, Texas)
Figure 5. General Strength Parameters (Hsu and Nelson,2002)
5
Figure 6. Mapped Soils in the Study Area by the USDA (Web Soil Survey). The red
highlights the mapped Frio Silty Clay .
Figure 7. Daily average ranges in temperature.
Figure 8. Chance of precipitation
Figure 9. Average Monthly Rainfall in North Central Texas
Figure 10. Flow duration curve of the gage above the Levee District (51 years)
Figure 11. Flow duration curves derived for USGS 08055000 using two time
periods to assess the changes in land use on flow.
Figure 12. Flood Frequency of the Study Area based on USGS 08055000.
Figure 13. Meander Arc 1. Survey Site.
Figure 14. Meander Arc 1.
Figure 15. Meander Arc 1.
Figure 16. Meander Arc 1.
Figure 17. Meander Arc 1.
Figure 18. Meander Arc 1.
Figure 19. Meander Arc 1.
Figure 20. Area between Meander Arcs.
Figure 21. Meander Arc 2 Location Map.
Figure 22. Meander Arc 2.
Figure 23. Meander Arc 2.
Figure 24. Meander Arc 2.
Figure 25. Meander Arc 2.
Figure 26. Meander Arc 2.
Figure 27. Meander Arc 2
Figure 28. Meander Arc 2.
Figure 29. Meander Arc 2.
Figure 30. Meander Arc 2.
Figure 31. Meander Arc 2.
Figure 32. Meander Arc 2.
Figure 32. Meander Arc 2.
Figure 33. Meander Arc 2.
Figure 34. Meander Arc 2.
Figure 35. Meander Arc 2.
Figure 36. Meander Arc 2.
Figure 37. Area Between Meander Arc 2 and 3.
6
Figure 38. Area downstream Meander Arc 2.
Figure 39. Area downstream Meander Arc 2.
Figure 40. Area downstream Meander Arc 2.
Figure 41. Area downstream Meander Arc 2.
Figure 42. Area downstream Meander Arc 2, pedestrian bridge.
Figure 43. Area downstream Meander Arc 2; pedestrian bridge.
Figure 44. Area downstream Meander Arc 2; location of entrance of abandoned
channel to left (blue arrow)
Figure 44. Location of study area along Meander Arc 3.
Figure 45. Area downstream Meander Arc 3.
Figure 46. Meander Arc 3.
Figure 47. Meander Arc 3.
Figure 48. Meander Arc 3.
Figure 49. Meander Arc 3.
Figure 50. Meander Arc 3
Figures 51,52. Meander Arc 3.
Figures 53,54. Meander Arc 3.
Figures 55,56. Meander Arc 3.
Figures 57,58. Meander Arc 3.
Figures 59,60. Meander Arc 3.
Figures 61,62. Meander Arc 3.
Figures 63,64. Meander Arc 3.
Figures 65,66. Meander Arc 3.
Figures 67,68. Meander Arc 3.
Figures 69,67. Meander Arc 3.
Figures 71,72. Meander Arc 3.
Figure 73. Meander Arc 3.
Figure 74. Results of Field Survey: relationship of Homesite Stability to Channel
Width Depth Ratio
Figure 75. Grainsize of bed material (Point Bars) The sizes are shown in percent
finer than categories, for example, (d(9)=90%finer than) and the sizes are given in
micrometers where 1 micrometer=.001mm
Figure 76. Plot of Shields Curve. The large red dot indicates the material is highly
mobile at low flows.
Figure 77. Critical Tractive Force USACE. The bed material in the channel
corresponds to fine sand which moves at very low tractive force or about .003-
0.004psf.
7
Figure 78. Illustrates the computation of the critical tractive force and erosion
rate constant using the Submerged Jet Test.
Figure 79. Results, and plot of Tc versus Kd for alluvium in the Denton Creek. Soils
within the levee area plot as very erodible. The test results are shown in color on
the figure. Prior testing by the USBR (US Bureau of Reclamation) is shown for
comparison.
Figure 80. Bulk density of sediment reach in association with the Jet Test. (Multiply
gm/cm3 X 62.4 to get pcf)
Figure 81. The CSR Method illustrating the balance between incoming sediment
and the capacity of the design reach to convey this sediment without aggradation
or degradation (Stroth, 2017).
Figure 82. Field indicators of the bankfull flow around 9-10 feet.
Figure 83. Predicted meander dimensions in the study reach based on comparison
with measured meanders and regime theory modeled above
Figure 84. Plot of modeled shear with HEC-RAS with adjustment applied (3) for
meander Rc/w.
Figure 85. Plot of adjusted shear along the channel at cross sections (Halff
Associates, Inc).
Figure 86. Plot of adjusted shear along the channel at cross sections (Halff
Associates).
Figure 87. Illustrates permissible shear for sand channels shown in red for study
area; approximately .02-.05 lbs/sq.ft. From USDA NEH Part 654 Chapter 8.
Figure 88. Permissible shear for various bank materials from Fischenich, 2001.
Figure 89. Plot of Stream Sediment Load,Stream Type and Discharge and relative
stability Schumm
Figure 90. Relationship of Drainage Area to Migration Rate in meanders after
Briaud et al. (2007)
Figure 90. Relationship between migration rate and channel width after Briaud, et
al. (2007).
Figure 91. Relationship of Radius of Curvature to Channel Width and migration
Rate Nanson and Hickin (1983).
Figure 92. Relationship of Radius of Curvature to Channel Width and migration
Rate Nanson and Hickin (1983).
Figure 93. Erosion rate and bank and bed materials after Briaud and Montalvo-
Bartolomei (2014). The study area would be in Erosion Category I.
Figure 94. Erosion rate and rate exponent based on Briaud and Montalvo-
Bartolomei (2014). The study area would be in the Very High Erodibility Category I.
8
Figure 95. Comparison of River patterns for two time periods, 1968 and 2015.
Figure 96. City of Austin Erosion Hazard Zone Delineation
Figure 97. Example of the Austin Method
Figure 98. Method 2 for Erosion Hazard Zone Calculation
Figure 99. Calculation of equilibrium slope.
Figure 100. Approximate limits of Erosion Hazard Zone. Again, increases in lateral
migration rate would move the zone toward the structures.
Figure 101. Approximate limits of Erosion Hazard Zone
LIST OF TABLES
Table 1. Soil Properties from USDA Web Soil Survey.
Table 2. Design values for reach
Table 3. Field Data Collected
Table 4. Computed Erosion Hazard Zone Setback Distance from toe of the slope
using the Austin method and Cruden Method.
Table 5. Approximate setback encroachment for structures considering 100 foot
EHZ. (Location of structure (Lat-Long) is in center of roof area)
9
Fluvial-Geomorphic Assessment of
Denton Creek: DCLID No. 1 Downstream
to the Elm Fork
10
SECTION 1 -INTRODUCTION
This report identifies and evaluates fluvial geomorphic processes in the
project area which can affect long term design and stability calculations
for the channel from river station 17649 to station 12046; Figures 1,2.
1.1 STUDY LOCATION
Figure 1. Location of Study Area (Denton Creek in Yellow). USGS Gage
08055500 Elm Fork green dot.
11
Figure 2. Slope of survey reach. Pool, Riffle designation based on mean
channel slope and can vary based on backwater effects.
1.2 STUDY OBJECTIVES
Rivers are dynamic with the major drivers of change being discharge
and sediment supply. Adjustments to these inputs are vertical changes
( river slope/ or cutting and or filling of the channel ) and lateral
changes (planform-sinuosity changes or changes in width and/or
meander pattern). The changes are modulated through the rivers
physical and biological (riparian vegetation) attributes. Rivers can be
12
classified on a simple basis as either “Alluvial” or, “Threshold” channels.
Alluvial channels are able to adjust rapidly both vertically and
horizontally to changes in discharge and sediment inputs. Threshold
channels (bedrock controlled) are typically slower to respond to
changes in inputs. Biological controls of riparian vegetation can exert
large control on lateral changes in rivers. Denton Creek is classified as
an alluvial channel.
There are many methods to assess the potential impacts on rivers but
they essentially fall into three categories Figure 3.
Figure 3. Methods of River Stability Analysis (Stroth, 2017)
The most common methods are the analog and empirical methods. The
analog method places reliance on emulation of a reference reach to
formulate a design. While there are studies of river effects below main
stem dams, there are no viable stable reference areas to which one can
compare the study area. Therefore, this method was not considered.
Literature review of effects of mainstem dams on rivers was evaluated.
The empirical approach is limited to the data sets upon which the
equations were derived. These methods were used in the study to
13
establish upper and lower boundary conditions for comparison of
model outputs.
The alternative approach, used here is the analytical approach or
process based approach. One application of this approach is the SAM
method developed by Copeland (1994) and incorporated in the HEC
(USACE) models. This method relies on calculating the sediment
balance using a single dominant discharge and sediment size gradation
to assess channel dimensions and equilibrium slope. Since it just uses
one flow or the “dominant discharge,” the problem with this method is
that the solution can result in unstable channel designs since other
influential flows can affect sediment transport. Therefore, this method
was not chosen for the study.
Stroth (2017) improved this approach based on work by Soar and
Thorne (2001) where he balances the total sediment delivered from
and upstream “Supply Reach” through a “Design Reach” across the
entire flow duration curve rather than one single discharge. In addition,
the method incorporates overbank flow into the analysis.
Therefore, Stroth's improved method is used in this study. The
objectives of this study are:
1. Analyze the current condition of the channel through visual survey of
channel.
2. Assess what a stable channel configuration would be for the channel.
This is based on conducting a stability analysis using empirical and
analytical methods including Capacity Supply Analysis (CSA) which
includes:
a. Assess sediment contribution and source of sediment in
supply reach.
b. Physically measure erodibility of banks through submerged
jet testing.
14
c. Measure the grain size in the supply reach upstream and
assess incipient motion of bed material
3. Coordinate findings with Halff Associates, Inc. in terms of potential
solutions given the flow requirements and status of the homes
within the river reach.
4. Coordinate the findings of this report with concurrent studies on
Denton Creek as available.
5. This study’s purpose is to assess the trends and relative stability of
the study reach over a projected design life (assumed 30 years). It is
meant to show the relative trends in erosion and stability of the
channel based on visual survey with respect to homes along the
channel. Owing to the level of precision of GPS used in the channel
and wooded riparian zone, it is advised that while individual home-
sites will be cited with reference to observed problems, they should
not be used to assign specific risk to individual structures. This would
require access to the home-sites above the channel as well has
survey grade GPS to determine exact limits of structural protection
in the channel below, more specific information on construction
plans of individual bank protection in terms of depth of footings,
tiebacks etc.
1.3 STABILITY CONCEPTS
The concept of stream channel stability needs to be defined in terms of
the time frame involved. In the case of natural rivers, stability must
include allowances for the river’s tendency to erode its banks,
15
meander, and adjusts its geometry in response to changes in watershed
land use and climate over long periods of time. When a river is in
equilibrium with upstream inputs of sediment load, discharge and bank
vegetation, it develops a channel planform, slope and width that tend
to fluctuate around some observable mean. Rivers change in response
to alterations in driving variables as discharge and sediment supply.
For urban settings, the time frame of change is accelerated due to rapid
changes in land use and up and downstream channel modifications
(roads, bridges, pipelines, dams, channelization, storm sewers).
Therefore, the concepts of stability must be restated in terms of
potential changes in decadal timeframes.
Lateral Stability:
This defines the limits of expected lateral movements of the river for
the project. It will address the factors which control lateral stability and
assess potential rates of meander migration and channel widening.
Vertical Stability:
Vertical stability is defined by the point at which the slope of the
stream, given the input of sediment load and discharge will tend to
remain stable or will not degrade or fill. Assessment of vertical stability
typically compares existing channel slope to the projected “equilibrium
slope” or “stable” slope. This is dependent upon the dominant or
effective discharge and the size and quantity of sediment to the study
reach.
16
Composite Stability Evaluation
The channel assessment procedure used in this report consisted of the
following steps:
• Literature review and conversations with engineers (Halff
Associates, Inc.) concerning site attributes and cited
problems based on their conversations with the City of
Coppell.
• Survey of bank and bed (where visible) and adjacent homes
in the reach for potential problems using kayaks and local
access where permitted.
• Analysis of flow conditions in the reach utilizing data from
the flow duration curve (FDC) from upstream USGS gage
08055000 and hydrology and hydraulics data provided by
the engineers.
• Evaluation of driving variables of sediment load and
discharge on the dependent variables of channel with,
depth, and planform (slope) while taking into account bed
material, bank material, and bank vegetation.
• Synthesis of data by comparing observed site conditions to
erosion hazards computed for the reach and summarizing
findings for Halff Associates, Inc.
1.4 Study Applications
This study is a supplement to the Denton Creek Drainage Study being
performed by Halff Associates, Inc. This study will give the conditions
under which stable channels, which carry sediment through the reach,
can be designed. The study will aid Halff Associates, Inc. in evaluating if
17
the stable channel and slope configurations allow for the reach to
convey the design floods mandated by FEMA and the USACE, and not
cause erosion of the existing properties along the stream.
1.5 DATA SOURCES
The data for the flow analysis comes from the gage operated by the
USGS (08055000) and field data obtained by the authors. There was no
sediment data for the project area (below Grapevine Dam). Hence, the
sediment load was modeled using empirical methods, and the
Copeland(1994) and CSA methods. Slope and elevation data used in
flow analysis came from Halff Associates, Inc., as well as HEC-RAS
output used in evaluation. Other data sources utilized were: soils data
came from the USDA Web Soil Survey, geologic data from literature and
the Geologic Map of Texas, and historical air photography from the US
Geological Survey Earthexplorer.
1.6 LIMITATIONS AND ASSUMPTIONS
Ideally sediment data would be based on historical gaged sediment
transport measurements which could then be used to assess the actual
input to the reach which, along with the gaged flow data, are the inputs
for assessing the stable design of the channel. Since there was no
sediment data and the upstream reach has been “cut off’ from the
larger watershed by the dam on Grapevine Lake, assumptions of
sediment supply had to be made based on limited field observations
and measurements. Sand sized sediment enters the reach from the
upstream DCLID No. 1. based on concurrent studies of this area. Most
18
of this sediment is derived from bank and bed erosion and
transportation from upstream of the DCLID No. 1 and transported
through DCLID No.1 to the study reach. The current assumption is that
the sand supply furnished to the project site will continue until the
upstream channel is in equilibrium with the complex flow regime
derived from the dam, and rapid urbanization of the area below the
dam, and channel degradation and widening above DCLID No. 1.
Furthermore, it is assumed that no changes will be made to the study
area channel in terms of changes in channel configuration,
channelization, and or modification of floodplain conditions.
Since flow calculations for the CSA analysis are based on the Flow
Duration Curve (FDC), and this is subject to reservoir management
practices by the USACE, any change in reservoir management will have
to be taken into consideration and the output of the models used in
this report recalibrated. The CSA analysis, summarized in NCHRP
Research Report 853 by Bledsoe, et al., 2017, utilizes the FDC as one of
the inputs for calculating equilibrium channel dimensions and channel
slope.
The Erosion Setback Hazard Zone assumptions are based on a
preliminary field visit which incorporated handheld laser and
photographs to document approximate locations of problems with
erosion along the study reach. This study is not meant for design or
evaluation of individual sites but as a general appraisal of reach
conditions and the overall erosion hazard of the area. Areas with
existing bank protection were assumed to be stable and not part of the
structures with problems. This assumption is subject to detailed site
verification.
The degradation limits (channel downcutting) are controlled to a large
extent by stream bottom lithology. This study did not have access to
19
any boring information and the bottom was assumed to be mobile.
Depth to the Eagle Ford Shale bedrock was not obtained.
SECTION 2 -STUDY AREA DESCRIPTION
2.1 GEOLOGY
The bedrock of the area is mapped as the Woodbine Formation and
overlying Eagle Ford Shale Figure 4. Within north Texas, these
formations dip to the southeast at approximately 100 feet per mile
(Marr, 1986). It appears as if most of the study area is underlain by the
lower portion of the Cretaceous Eagle Ford formation. The alluvium
deposited by the river and in past flood events consists of
predominantly fine sands. Historically, before the dam, floodplain
sedimentation resulted in 1-12 feet of sediment being deposited along
the channel banks with a decrease in thickness away from the channel
(USDA, SCS, 1956). The velocity of the overbank flows was less than
needed to scour the deposited fine sands. It is postulated that much of
the sediment close to the channel was derived from pre-dam
sedimentation from Denton Creek Watershed. Owing to the lack of
boring control in the area, it is unclear where the contact with the
overlying the Eagle Ford Shale occurs. However, Eagle Ford shale was
seen in the channel bank at water level near station 14600.
20
Figure 4. Geologic Map of the Study Area (Bureau of Economic
Geology, Dallas Sheet, Texas)
The lower section of Eagle Ford shale which outcrops in the study area
is a smectitic (mineralogy) clay shale, which is subject to shrinking and
swelling with changes in moisture content; liquid limits average 87 and
Plasticity indices 58 (Hsu and Nelson, 2002), Figure 5. The cited uniaxial
compressive strength ranges from 0.44 to 5.82 MPa (1MPa=145psi).
21
Figure 5. General Strength Parameters (Hsu and Nelson,2002)
The properties given should not be used for design but are meant to
show general engineering behavior of the material. Borings and in situ
testing is highly recommended. For more information on the properties
of the shale with respect to retaining structures see Wright (2005) CTR
Technical Report 5-1874-01-1 which details research regarding shales
and embankment strength.
2.2 SOILS
The soils mapped by the USDA for the study area are shown in Figure
6.
22
Figure 6. Mapped Soils in the Study Area by the USDA (Web Soil
Survey). The red highlights the mapped Frio Silty Clay .
Table 1. Soil Properties from USDA Web Soil Survey.
The major soil series mapped in the floodplain area is the Frio silty
clay(red). The general properties of the soil are given in Table 1. and
show the alluvial material has about 7-14 % sand and 93-86% silt and
clay with a Unified classification of CH-CL. In the field, along the channel
the banks appeared to have a lot of fine sand deposited. This has been
transported from up Denton Creek and is thought to be an overlay of
varying thickness adjacent to the channel and overlies the Frio silty clay.
2.3 CLIMATE
Geomorphic processes are controlled by seasonal variations in
precipitation and temperature Figures 7-9. The discussion of the
23
climate indicates the range and seasonal variability of temperature,
rainfall which have an effect on subaerial weathering of the bank and as
such will affect erosivity and potential changes in shear strength of the
material. The following figures indicate the bimodal distribution of
rainfall (peaks in the spring and fall) which leads to soil saturation, and
the extremes in summer temperatures which promote drying and
dessication of bank materials. Together, these effects tend to weaken
the soil material in the banks and make the soil more erodible. Peak
erodibility is typically during the late summer following long dry spells
and soil dessication and during the springfloods, after winter freeze-
thaw events (Wynn and Mostaghimi, 2006).
The summers are hot and muggy and the winters are cold and windy.
The temperature varies from 35 to 96 F. The warm season ranged from
June 3 to September 17 with an average high above 88 F. The cool
season lasts for 3 months from November 25th to February 24th with an
average daily temperature below 63 F.
https://weatherspark.com/y/8159/Average-Weather-in-Denton-Texas-United-States
24
Figure 7. Daily average ranges in temperature.
A chance of wet days (defined as having at least .04 inches of
precipitation), varies throughout the year. The wet season lasts 6.2
months from April 16th to October 21st with a greater than a 26%
chance of a given day being a wet day. The chance of having a wet day
peaks on May 31st with a 38% chance. The drier season lasts from
October 21st to April 16th or 5.8 months.
https://weatherspark.com/y/8159/Average-Weather-in-Denton-Texas-United-States
Figure 8. Chance of precipitation
25
https://weatherspark.com/y/8159/Average-Weather-in-Denton-Texas-United-States
Figure 9. Average Monthly Rainfall in North Central Texas
Rain falls throughout the year in the study area. Most rain falls
centered around the 31 days centered on May 24 with an average
rainfall of 4.4 inches; the least rain falls around the first of August with
an average accumulation of 1.6 inches. The annual precipitation in the
study area averages about 31.76 inches, ranging from a low of 17.91 to
a high of 51.03 inches per year. The average length of the growing
season is about 250 days. The average humidity is about 53%.
2.4 HISTORICAL PERSPECTIVE
Based on directives from Halff Associates, Inc. a study was undertaken
along Denton Creek within the City of Coppell based on erosion and
flood concerns of homeowners.
26
SECTION 3 – HYDROLOGIC DATA
3.1 FLOW DURATION ANALYSIS
Flow duration data may be obtained directly from stream monitoring
gages or they can be estimated using a hydrologic simulation model.
The former may be obtained for USGS gage sites at
waterwatch.usgs.gov (toolkit/streamgage statistics) or
streamstats.usgs.gov., (Ries III, K.G., 2007). Since sediment transport
calculations used in this analysis are based on the FDC, the curve
produced for the upstream gage, USGS 08055000 was derived from the
USGS Stream Stats site, Figure 10.
27
Figure 10. Flow duration curve of the gage above the Levee District (51
years)
The FDC represents the integration of daily flows for the period of
record and as such gives the probability of average daily flows for the
period under a variety of land use changes and may not reflect the
current and future conditions of the area. The flow duration curve was
dissected to see how historical land use changes which may have
affected the flow duration curve. The results of analyzing subsets of
flow at USGS 08055000 for periods of 1957-1991 and 2004-2015 were
undertaken to assess the effects of the rapid land use changes in the
area above and below the dam on the flow. The figure illustrates that
the changes in land use appear to affect the lower flows but, only
28
slightly. This is interpreted to be a result of (1) most of the flow at the
gage is derived from the dam and therefore subject to reservoir
operations, and (2) the flows generated by the areas below the
reservoir being a much smaller area contribute to increases in the more
frequent smaller flows.
Figure 11. Flow duration curves derived for USGS 08055000 using two
time periods to assess the changes in land use on flow.
29
3.2 FLOOD FREQUENCY
Figure 12. Flood Frequency of the Study Area based on USGS
08055000.
Stream channel width /depth worldwide seem to be related to flows
which average around the 1.5 to 2 year frequency. This will vary
somewhat by climate regime but is used as a first order estimate of
channel dimensions when used in conjunction with Mannings equation
and appropriate roughness estimates. Recent work in the United States
relating channel dimensions based on site assessment at stream gages
reinforces this assumption (Bieger, et. al., 2016). The flow corresponding
to this frequency at the gage ranges from 1076 to 1742 cfs. at the gage
or slightly less than the 1 year event.
30
Downstream from the gage, at river station 17046, owing to increasing
drainage contributions, Halff Associates, Inc., have calculated the
following discharges for the reach, Table 2.
Discharge
(cfs)
Velocity
(fps)
Depth
(ft.)
Q active channel= 1522 2.9 14.6
Q 1 yr.= 3282 4.3 17.8
Table 2. Design values for reach
SECTION 4 -FIELD DATA
4.1 FIELD DATA COLLECTION OBSERVATIONS
The following dimensions of the reach were measured using a True
Logic Laser to ascertain approximate active channel widths and stadia
rod to obtain channel depths in the reach during low flow (59cfs).
Field Survey Dimensions at low flow:
Average Bottom Width = 49 ft. std. dev.= 7.5
Average Bottom Depth = 3.83 ft. std. dev. 1.75 (@57 cfs flow)
Average Width Depth Ratio = 16
31
Column 1. Column 2. Column 3. Column 4. Column 5. Column 6.
1 36 3.5 10.29 BP
2 40 4 10 BP
3 40 4 10 BP
4 40 3 13.33 BP
1 55 2.7 20.37 bare slump
2 54 2.7 20 bare slump
3 41 4 10.25 bag outlet slump
4 37 3 12.33 bare slump
5 45 6 7.5 bare slump
6 35 7.2 4.86 bare slump
7 43 6.2 6.94 bare slump
8 51 3.8 13.42 1/2 BP slump?
9 46 2.4 19.17 BP
10 53 2.7 19.63 Point Bar
11 55 5.4 10.19 bare slump
12 46 4.9 9.39 End Point Bar
13 61.5 4.3 14.3 BP
1 54 2.8 19.29 BP
2 54 2.8 19.29 BP
3 50 4.5 11.11 .5BP scour
4 52 2.8 18.57 scour scour
5 50 2.4 20.83 BP
6 51 2.1 24.29 BP
7 50 1.5 33.33 BP
8 52 1.5 34.67 BP
9 41 1.5 27.33 BP
10 45 1.1 40.91 BP
11 45 1.1 40.91 BP
12 42 1.2 35 .5BP
32
13 46 2.6 17.69 BP
14 53 5.7 9.3 BP
15 45 7.1 6.34 BP
16 53 6.6 8.03 scour scour
17 55 5.1 10.78 wall no toe protection
18 57 3.7 15.41 BP slump
19 52 3.7 14.05 BP--- rotating out slump
20 53 6 8.83 bare scour
21 65 5.9 11.02 bare scour
22 57 5 11.4 BP
23 60 5.9 10.17 point bar
24 66 6.6 10 point bar
Table 3. Field Data Collected (BP=bank protection)
The field survey was done in Kayaks and the position of the homes from
the channel bottom was at times hard to see but in general, the homes
are numbered beginning at the upstream of the three major meander
arcs, Table 3.
Columns refer to the following:
Column 1. House Number (beginning upstream see photographic data)
Column 2. Channel bottom width (ft.)
Column 3. Channel depth (ft.) Flow at USGS 08055000 was 57cfs.
Column 4. Width Depth Ratio
Column 5. Structural control observed in channel in front of structure
BP= bank protection which can vary from stacked gabions to riprap and
rail road timber.
Column 6. Processes observed in front of structure
33
In the following figures, areas with red arrows indicate homes where
there is observed scour/slope instability and no structural protection.
Figure 13. Meander Arc 1. Survey Site.
34
Figure 14. Meander Arc 1.
Figure 15. Meander Arc 1.
35
Figure 16. Meander Arc 1.
Figure 17. Meander Arc 1.
36
Figure 18. Meander Arc 1.
Figure 19. Meander Arc 1.
37
Figure 20. Area between Meander Arcs.
38
Figure 21. Meander Arc 2 Location Map.
Figure 22. Meander Arc 2.
39
Figure 23. Meander Arc 2.
Figure 24. Meander Arc 2.
40
Figure 25. Meander Arc 2.
Figure 26. Meander Arc 2.
41
Figure 27. Meander Arc 2.
Figure 28. Meander Arc 2.
42
Figure 29. Meander Arc 2.
Figure 30. Meander Arc 2.
43
Figure 31. Meander Arc 2.
Figure 32. Meander Arc 2.
44
Figure 33. Meander Arc 2.
Figure 34. Meander Arc 2.
45
Figure 35. Meander Arc 2.
Figure 36. Meander Arc 2.
46
Figure 37. Area Between Meander Arc 2 and 3.
Figure 38. Area downstream Meander Arc 2.
47
Figure 39. Area downstream Meander Arc 2.
Figure 40. Area downstream Meander Arc 2.
48
Figure 41. Area downstream Meander Arc 2.
Figure 42. Area downstream Meander Arc 2, pedestrian bridge.
49
Figure 43. Area downstream Meander Arc 2; pedestrian bridge.
Figure 44. Area downstream Meander Arc 2; location of entrance of
abandoned channel to left (blue arrow)
50
Figure 45. Location of study area along Meander Arc 3.
51
Figure 46. Area downstream Meander Arc 3.
Figure 47. Meander Arc 3.
52
Figure 48. Meander Arc 3.
53
Figure 49. Meander Arc 3.
Figure 50. Meander Arc 3.
54
Figures 51,52. Meander Arc 3.
55
Figures 53,54. Meander Arc 3.
56
Figures 55,56. Meander Arc 3.
57
Figures 57,58. Meander Arc 3.
58
Figures 59,60. Meander Arc 3.
59
Figures 61,62. Meander Arc 3.
60
Figures 63,64. Meander Arc 3.
61
Figures 65,66. Meander Arc 3.
62
Figures 67,68. Meander Arc 3.
63
Figures 69,70. Meander Arc 3.
64
Figures 71,72. Meander Arc 3.
65
Figure 73. Meander Arc 3.
66
Figure 74. Results of Field Survey: relationship of Homesite Stability to
Channel Width Depth Ratio
The result of the field survey indicated that the narrower and deeper
the channel, the more the problems associated with the structures,
Figure 74. The plot shows the channel width depth ratio (red) and mean
(16) in black and the processes observed in the field in blue, divided
into stable, scour or slumping areas. Low width depth ratios correspond
to problem sites. This is the width and depth of the low flow or active
channel taken in this case as flow at 57 cfs.
67
4.2 GRAIN SIZE ANALYSIS BED MATERIAL (POINT BARS)
Lane’s equation indicates there is a relationship between a stream’s
discharge (Q)-slope (S) product and the size (D50) and amount (Qs) of
bed material in the channel:
QS~D50Qs
This implies that the river will adjust its slope to able to move the bed
material through the reach, given the range of flows it receives over
time. Therefore, knowledge of the size of the bed material is a
fundamental property in river equilibrium calculations. Bedload
entering the reach from upstream has been analyzed (owing to its small
size) with a Malvern laser grain size system. Results indicate that the
bed material is a fine sand, Figure 75.
68
Figure 75. Grainsize of bed material (Point Bars) The sizes are shown
in percent finer than categories, for example, (d(9)=90%finer than) and
the sizes are given in micrometers where 1 micrometer=.001mm
Scour and incipient movement of bed material is often calculated using
Shields equation (1) shown below:
(1)
69
Figure 76. Plot of Shields Curve. The large red dot indicates the material
is highly mobile at low flows.
Using a slope of 0.0006-0.0008 and a water depth of 3 feet, the fine
sand would be mobile according to Shields relationship, Figure 76. This
infers that the sand is highly mobile and subject to suspension in
Denton Creek at very small frequency flows.
Another way to assess sand mobility is to compare the critical tractive
force to thresholds given in the literature, Figure 77. Assuming the
same water depth and slope from above, the critical tractive force
would be based on slope X depth X unit weight water:
(0.0006 x 3 ft. x 62.4 lbs. /ft3) = 0.1123lbs./ft2
70
Comparison of this tractive force with the results in the Figure 77, again
indicates the sand in the channel is highly mobile at low flow depths.
From Fischenich, C., 2001: USCE EMRRP Stability Thresholds for Stream Restoration Materials.
Figure 77. Critical Tractive Force USACE. The bed material in the
channel corresponds to fine sand which moves at very low tractive
force or about 0.003-0.004psf.
4.3 CHANNEL ERODIBILITY
Sediment in the reach is very erodible with a critical tractive force
averaging 3.0 Pa or 0.09 lbs./ft2 and an erosion rate constant of 9.2
cm/hr/Pa or 14 ft/hr/psf, and bulk densities varying from 84-112 pcf.
71
This is based on the average of three submerged jet tests on channel
material, Figures 78-80.
The submerged jet test procedure (Hanson and Cook, 2004) allows
either in situ or lab analysis of cohesive soil erodibility parameters for
the excess stress equation (2) where:
Er=Kd x (Te-Tc) x Time (hrs.) (2)
Er=erosion in cm
Kd=cm/hr/Pa (detachment coefficient)
Te= applied shear (unit weight water x R x S) in Pa
Tc= critical shear in Pa (Pascal)
The NRCS procedure computes Te as the product of (1-Cf) x (ns/n)2
where Cf is a cover factor based on type of cover and cover density and
(ns/n)2 is the grain roughness where ns = .0156 for cohesive fine
grained material and n is Mannings roughness for the channel. Both Kd
and Tc are given from the test results of the submerged jet. It is always
advisable to compare the Tc with literature. The NRCS gives a value of
3.5 Pa for clays with a slight adjustment possible for void ratio or
compaction. Tc for sand has been given, Figure 77.
72
Figure 78. Illustrates the computation of the critical tractive force and
erosion rate constant using the Submerged Jet Test.
73
Figure 79. Results, and plot of Tc versus Kd for alluvium in the Denton
Creek. Soils within the levee area plot as very erodible. The test results
are shown in color on the figure. Prior testing by the USBR (US Bureau
of Reclamation) is shown for comparison.
Figure 80. Bulk density of sediment reach in association with the Jet
Test. (Multiply gm/cm3 X 62.4 to get pcf)
It should be noted that the jet was run under bare soil conditions. If
grass is established it can increase the critical tractive force appreciably.
74
Past work has shown a well grassed channel can be equivalent to a 2in.
cobble in terms of tractive force at the inception of flow. However, the
grass tends to lose its strength over time so flow duration should be
taken into account. A second point should be made in that the jet
testing was done on the sand alluvial fill material. Soils and geology
maps indicate a more clayey material may underlie this material.
Typical erodibility values for the silty clay from previous jet testing has
had a Tc of 2-4 Pa (.04-.08psf) and Kd in cm/hr/Pa of 0.4 (.63 ft/hr/psf)
or plot in the erodible to moderately resistant material (Briaud, et al.,
2017).
SECTION -5 FLUVIAL GEOMORPHIC ASSESSMENT OF
REACH
5.1 EFFECTIVE DISCHARGE ASSUMPTIONS AND CALCULATIONS:
CAPACITY /SUPPLY ANALYSIS
The Capacity/Supply Ratio approach is an extension of the SAM method
of analytical channel design for sand channels. SAM is an integrated
system of programs developed through the Flood Reduction and
Stream Restoration Research Program of the USACE and Copeland
75
(1994) to aid engineers in analysis associated with designing, operating,
and maintaining flood control channels and stream restoration
projects. It is a n analytical channel design approach developed solely to
design sand-bed channels by estimating sediment continuity in a design
reach using the Brownlie (1981) total load sediment transport and
depth prediction equations. For a given discharge, SAM solves for
stable depth and slope for a range of bottom widths in trapezoidal
channels.This method relies on calculating the sediment balance using
a single dominant discharge and sediment size gradation to assess
channel dimensions and equilibrium slope. The problem with this
method, since it just uses one flow or the dominant discharge, is that
the methodology can result in unstable channel designs since other
influential flows can affect sediment transport. The CSR method
balances the sediment transport capacity of a design reach with the
sediment supply of an upstream reach over the entire flow duration
curve rather than a single discharge (Stroth, Bledsoe and Nelson, 2017).
The CSR Tool was employed to efficiently utilize design techniques that
can promote sediment balance in the system thereby ensuring better
long- term channel stability in restoration reaches. The method has
been tested in over 18 sand bed channels from across the United States
with positive results (Stroth, Beldsoe, Nelson, 2017).
Basically, as shown in the Figure 81, the CSR is defined as the bed
material load transported through the river reach by a sequence of
flows over an extended period of time divided by the bed material load
transported into the reach by the same sequence of flows over the
same time period (Stroth, Bledsoe, and Nelson, 2017). A CSR greater
than one means degradation and a CSR less than one aggradation. A
stream would be in equilibrium when the CSR=1 (within 10% of 1) or
the channel width and depth and slope are in equilibrium with the
discharge and sediment supply.
76
Three scenarios were run using the CSR Model: (1) Low urbanization
period , 1957-1991, (2) rapidly urbanizing period, 2004-2015, (3) future
urbanized modeled.
Figure 81. The CSR Method illustrating the balance between incoming
sediment and the capacity of the design reach to convey this sediment
without aggradation or degradation (Stroth, 2017).
The results of the analysis for the CSR indicate that as the basin
urbanizes, the equilibrium shifts to the left (less width), and upward,
(slightly greater slope). The slope for the less urbanized basin is
0.000438 and for the more urbanized basin 0.000455. The channel
bottom widths are 53 feet for the less urbanized basin and 47 feet for
the more urbanized basin. The effective or design discharge is
77
approximately 1655-1700 cfs. The design slope is less than the exisiting
slope of approximately 0.0006. Therefore, the channel is subject to
degradation over time.
The bottom widths noted in the field survey are similar to those
predicted with the CSR method. The effective discharge is based on
analysis of the upstream gage over time. The Halff Associates, Inc.
hydrology assessment, Table 1, indicates that the 1 year flow is
substantially larger than this discharge.
Figure 82. Field indicators of the bankfull flow around 9-10 feet.
78
The effective discharge is lower than the new Halff Associates, Inc.,1
year flow modeled in the channel. However, present field indicators of
the height of the lower bank and point bars suggests that the effective
discharge calculated from the Capacity Supply Analysis is the flow that
is moving most of the sediment. This flow also aligns best in terms of
channel morphology (widths and depths) seen in the field (Figure 82).
One possibility is that the channel has yet to adjust to the newer flows,
the other is that the persistent low flow regime due to dam releases is
more dominant in dictating channel behavior in this reach. The channel
did not appear to be widening on both banks, nor was it eroding
laterally more than would be projected by air photo analysis and
watersheds of a similar size (section 5.2). While channel erosion should
be monitored, it appears that the dam release policy is still the
dominant control on downstream channel morphology and will be the
ultimate control in downstream channel stability calculations.
5.2 CHANNEL MEANDER ASSESSMENT
The average radius of curvature of 14 measured meanders in the reach
was 239ft. with a standard deviation of 57ft. The minimum measured
was 189ft. and the maximum was 367ft. The reach sinuosity was 1.3.
This corresponds to the general meander properties illustrated in
79
Figure,83. The channel top width of 90ft. is approximately the width in
the field at the top of the point bars or lower bank. This idealized
meander pattern is representative of average field meander
measurements indicating the systems seems to be in equilibrium with
current channel flow conditions.
Figure 83. Predicted meander dimensions in the study reach based on
comparison with measured meanders and regime theory modeled above.
5.3 CHANNEL MEANDER AND ASSOCIATED SHEAR
80
Based on HEC-RAS analysis by Halff Associates, Inc., the adjusted shear
at the cross sections is shown. HEC-RAS generally tends to underpredict
measured boundary shear stress in bends (Sclafani, et al., 2012). Using
the upper envelop equation shown below, the following shear was
developed (3) for the meanders and shown in Figure 84.
KBEND = 1.11(RC/TW).098 (3)
RC= meander radius of curvature
TW= channel top width
81
Figure 84. Plot of modeled shear with HEC-RAS with adjustment
applied (3) for meander Rc/w.
Of note is the fact that the shear is more than the strength of the
material under bare conditions but when vegetated, the meanders are
the only areas where it exceeds the shear strength of the banks
resulting in potential erosion.
82
Figure 85. Plot of adjusted shear along the channel at cross sections
(Halff Associates, Inc).
83
Figure 86. Plot of adjusted shear along the channel at cross sections
(Halff Associates).
The figures (85,86) indicate that the shear increases on the outside of
meanders accounting for more erosion in these areas.
Figure 87 the critical tractive force for entrainment of sand as found in
the channel banks. This then infers that most banks should be eroding
as the channel shear exceeds the permissible shear. The channel shear
and hence erosion of the banks is highly regulated by bank vegetation
for channels, Figure 88. Homeowners and municipalities should be
aware of the potential for changes in vegetation to cause more erosion
and bank instability.
84
Figure 87. Illustrates permissible shear for sand channels shown in red
for study area; approximately .02-.05 lbs/sq.ft. From USDA NEH Part
654 Chapter 8.
85
Figure 88. Permissible shear for various bank materials from Fischenich,
2001.
86
5.4 CHANNEL MIGRATION POTENTIAL
The relative stability of a stream has been shown to be based on the
sediment load and gradient Figure 89. In general, a sand bed stream is
predicted to meander for S0Q.25 less than or equal to 0.0017 and
braided for S0Q.25 greater than or equal to 0.010 with a transition
occurring between these two zones. (S0 is channel slope in ft/ft. and Q
is mean annual discharge in cfs), Richardson, et al., 2001. Rates of
meander migration are highly variable and meandering takes place
through complex interactions between flow and morphology
depending on a number of factors as:
• Bank erodibiilty
• Bank slope stability
• Bank vegetation
• Bank Toe erosion rates
• Human structural changes in bank and in flow regulation (dams)
87
Figure 89. Plot of Stream Sediment Load,Stream Type and Discharge
and relative stability Schumm
Prediction of meander migration is difficult. Lagasse et al. (2004) of the
Transportation Research Board states:
88
So, to simplify the prediction of rates of erosion in the study area, three
methods were used: (1) correlation with the study site with other rivers
from national and state surveys, (2) using flow records and previous
studies of migration rates based on work by Briaud and Montalvo-
Bartolomei (2014), and finally (3) overlays of the historic channel (1968)
and the present channel (2015) to note any major changes in channel
pattern.
The first method is shown in Figures 90 through 92. Assuming a
drainage area of approximately 800 sq. miles (including Lake Grapevine
drainage), a channel top width of 120 feet, and an average meander
R/W ratio of 3.4, the predicted meander migration rate is 1.0,0.2, and
0.59 or an average rate of 0.6 m/year (1.97 ft/yr.). As can be seen in
the plots, the data is quite scattered and this rate is considered a first
order guide to potential rates of movement.
The second method uses the flow from the upstream stream gage for a
10yr. period, 2004-2014. The method is based on past erosion testing
by Briaud and others at Texas A&M University on the Erosion Function
Apparatus (EFA) and abundant work in Texas on meandering channels.
89
Figure 90. Relationship of Drainage Area to Migration Rate in
meanders after Briaud et al. (2007)
Figure 91. Relationship between migration rate and channel width after
Briaud, et al. (2007).
90
Figure 92. Relationship of Radius of Curvature to Channel Width and
migration Rate Nanson and Hickin (1983).
Based on Briaud and Montalvo-Bartolomei (2014), the observational
method utilizes known rates of meander migration from aerial
photographs, and then, based on flow records a velocity rating curve is
compiled. Channel bank material is chosen from Figures 93 and 94
and the appropriate exponent is assigned equation (1). Work with
historic aerial photographs (Figure, 95) indicated that very little
migration of Denton Creek has taken place downstream of the Levee
District. Therefore, migration analysis using equation (1) based on time
series movement was problematic. To solve the equation, the following
steps were taken: (1) the channel material was chosen from Figures 93-
94, and the exponent of 8.58 based on field estimates of bank material
was used in the equation, (2) channel critical velocity was taken from
Figure 83. Flow from USGS gage 08055000 was used from 2004-2014 in
the equation and the equation was solved so that the average annual
rate approached a maximum of 2 m/year as was shown in from the
previous analysis. The equation represents the approximate
relationship of flow to meander migration in the reach and can be
cautiously used to approximate future rates of retreat given flood
events and or changes in vegetation (change the critical velocity vc).
91
Figure 93. Erosion rate and bank and bed materials after Briaud and
Montalvo-Bartolomei (2014). The study area would be in Erosion
Category I.
Figure 94. Erosion rate and rate exponent based on Briaud and
Montalvo-Bartolomei (2014). The study area would be in the Very High
Erodibility Category I.
92
(1)
Based on the slow migration potential of the channel, the following
equation appears to be reasonable based on research on migration
rates on the Brazos and Trinity Rivers by Briaud and Montalvo-
Bartolomei (2014) where:
ἀ=1.39 x 10-8
ß= 8.58
Vc=2.7 fps
The equation was solved assuming some channel vegetation, thus the
2.7 fps critical velocity. If the channel is bare, with no root
reinforcement, then the critical velocity would drop to 2 fps (Figure 88)
and the predicted annual erosion rate could increase to 10 feet a year
based on equation (1). The results indicate that the channel erosion
rates can realistically vary between 1-10 feet a year based on similar
future flow conditions and the degree of vegetative cover protecting
the banks.
93
Figure 95. Comparison of River patterns for two time periods, 1968 and
2015.
There is no apparent shift in the rivers path over the observation
period. Given the scale of the photographs, the predicted meander
migration is within the limits of accuracy of the historical approach
shown. The photograph was overlain on the Google base map and
rectified. The absence of major deviations from the 2015 Google
channel and the channel on the 1968 base infers a slow meander
migration rate.
94
5.5 HOMES AND RIVER DYNAMICS
In order to assess the potential problem areas both at present and in
the future, it is necessary to assess the Erodible Corridor of the river.
This should take into account vertical and lateral stability: the rivers
potential to degrade as well as move laterally. Two methods are used
here with slightly different approaches to estimate the Erosion Hazard
Zone (EHZ). The City of Austin Method (Figures 96,97) requires
knowledge of the potential for degradation (a default shown in the
figure is 3 x Bankfull depth), as well as a geotechnical setback (here
shown as a 4:1) and lateral migration potential of the meander.
Figure 96. City of Austin Erosion Hazard Zone Delineation
95
Figure 97. Example of the Austin Method
96
The second method after Cruden et al. (1989) is a little more involved
and uses more information on the slopes geotechnical properties as
well as adds a maintenance component along with the meander lateral
migration and degradation rates, Figure, 98.
Figure 98. Method 2 for Erosion Hazard Zone Calculation
97
Assumptions Austin Method:
• Slope angle for setback is 4:1
• Degradation limit is (equilibrium slope-reach slope) * distance Elm
Fork
• Lateral migration is 30 feet
Assumptions Method 2:
• Average slope angle is 60 degrees
• Average shear angle is 20 degrees
• Erosion is 30 feet
• Maintenance is 10 feet
• Degradation limit (equilibrium slope-reach slope) * distance Elm
Fork
The equilibrium slope calculations are based on assessment of bed
material and the use of bed material equations, Figure 99. Given the
bed material at the site, the equilibrium slope would be 0.0000558. This
assumes that the depth of rock is well below the degradation depth
(conservative). The change in setback distance is dominantly due to the
decrease in channel degradation computed downstream as well as
channel migration distance.
98
Figure 99. Calculation of equilibrium slope.
The results of setbacks from the stream bottom are given in the Table,
3. There is not much difference in the results of the two methods which
reinforces the approach. The Austin method is shown in Figures 100-
101. Superimposing the setbacks on the homes along the reach results
in most of the homes falling within the setback distance. The
implications are that if these structures do not have some sort of bank-
slope and toe protection, degradation and lateral erosion, over time
can result in erosion and slope stability problems to the structures. The
lateral migration distance was based on 1 foot a year for 30 years which
seems reasonable given the previous calculations. Rates could increase
based on land use changes, changes in reservoir operation/climate, and
changes in protective vegetation along the banks. Increasing the lateral
migration rate would put more homes in the Erosion Hazard Zone.
99
Table 4. Computed Erosion Hazard Zone Setback Distance from toe of
the slope using the Austin method and Cruden Method.
Station Austin Method Cruden Method
17649 98.5783432 98.84130554
17410 98.418088 98.46706853
17197 97.1944296 97.53915266
16956 96.6698208 96.96215037
16702 94.4769136 95.4521288
16501 92.4393768 94.09099728
16294 89.7087792 92.34154424
15983 87.3917944 90.69505325
15671 85.2326328 89.13415778
15359 83.4334712 87.7712392
15238 82.5700784 87.15157949
15050 80.60084 85.84357001
14973 80.3532264 85.61522171
14819 79.1779992 84.78456881
14706 78.3720208 84.20606013
14425 77.00034 83.11533863
14137 75.6934216 82.05185259
13942 74.9089456 81.38700664
13768 74.2901824 80.83843119
13646 73.7046128 80.37035929
13307 72.6066776 79.36074848
13144 72.2918592 78.99249125
12970 71.993096 78.61989525
12654 71.3452272 77.88532536
12551 71.1610168 77.66072015
12046 69.1817328 75.96770547
11821 67.7719528 74.92306947
11650 66.91972 74.24969204
11479 66.1074872 73.59831203
11175 65.28574 72.78248539
10877 63.9570536 71.69505735
10581 63.2327208 70.94237917
10479 63.0506872 70.72016816
10194 62.4702992 70.05981848
9896 61.6616128 69.25835705
9579 61.0115672 68.52139295
9415 60.614572 68.10674666
9327 60.3830136 67.8740596
9055 59.910924 67.28882938
8898 59.6091664 66.93493735
8756 59.3000608 66.5949609
100
98
98
89 87
83
83
80
79
74
Figure 100. Approximate limits of Erosion Hazard Zone. Again, increases
in lateral migration rate would move the zone toward the structures.
Numbers are the erosion setback distances for the computed EHZ from
the toe of the slope given in Table 4.
101
73
72 72
Figure 101. Approximate limits of Erosion Hazard Zone.
Numbers refer to the computed distance from the toe of the slope for
the EHZ given in Table 4.
102
Table 5. Approximate setback encroachment for structures considering
100 foot EHZ. (Location of structure (Lat-Long) is in center of roof area).
Houses Latitude N Longitude W Distance Toe-House (ft.)House Seback-EHZ(ft.)
1 32°59'0.35"N 96°57'37.16"W 79 -21
2 32°58'59.81"N 96°57'36.86"W 69 -31
3 32°58'59.31"N 96°57'36.89"W 79 -21
4 32°58'58.81"N 96°57'36.66"W 64 -36
1 32°58'57.41"N 96°57'37.41"W 68 -32
2 32°58'57.02"N 96°57'37.87"W 64 -36
3 32°58'56.72"N 96°57'38.40"W 52 -48
4 32°58'56.47"N 96°57'38.97"W 62 -38
5 32°58'56.11"N 96°57'39.40"W 68 -32
6 32°58'55.60"N 96°57'39.71"W 57 -43
7 32°58'55.16"N 96°57'40.02"W 45 -55
8 32°58'54.62"N 96°57'39.97"W 42 -58
9 32°58'54.06"N 96°57'39.92"W 33 -67
10 32°58'53.51"N 96°57'39.74"W 34 -66
11 32°58'53.03"N 96°57'39.70"W 58 -42
12 32°58'52.49"N 96°57'39.52"W 58 -42
13 32°58'51.93"N 96°57'39.54"W 68 -32
1 32°58'46.31"N 96°57'34.80"W 26 -74
2 32°58'45.42"N 96°57'35.33"W 26 -74
3 32°58'44.64"N 96°57'35.48"W 52 -48
4 32°58'43.93"N 96°57'35.47"W 55 -45
5 32°58'43.24"N 96°57'35.66"W 84 -16
6 32°58'42.61"N 96°57'35.64"W 100 0
7 32°58'41.96"N 96°57'35.19"W 54 -46
8 32°58'41.17"N 96°57'34.60"W 49 -51
9 32°58'40.54"N 96°57'34.21"W 61 -39
10 32°58'39.94"N 96°57'33.69"W 70 -30
11 32°58'39.55"N 96°57'32.89"W 67 -33
12 32°58'39.55"N 96°57'32.89"W 75 -25
13 32°58'38.79"N 96°57'31.40"W 78 -22
14 32°58'38.74"N 96°57'30.54"W 70 -30
15 32°58'38.72"N 96°57'29.57"W 65 -35
16 32°58'38.80"N 96°57'28.83"W 64 -36
17 32°58'38.94"N 96°57'27.98"W 45 -55
18 32°58'39.06"N 96°57'27.21"W 46 -54
19 32°58'39.24"N 96°57'26.41"W 64 -36
20 32°58'39.33"N 96°57'25.54"W 73 -27
21 32°58'39.43"N 96°57'24.61"W 73 -27
22 32°58'39.39"N 96°57'23.77"W 74 -26
23 32°58'39.24"N 96°57'22.89"W 84 -16
24 32°58'39.13"N 96°57'22.06"W 81 -19
103
While figures 100-101 show the homes in relationship to the EHZ, it
was thought that it would be beneficial to see how close homes are to
the stream using a simpler 100 feet EHZ for the whole reach. The
distances are taken from the projected toe of the slope at low flow (37
cfs.) to the roofline of the structures using Google Earth Pro. The
measurements and setback are meant to illustrate that the majority of
homes would be inside the EHZ (denoted by a negative number). This
implies that over time, without some form of bank protection, these
homes may have erosion and slope stability problems.
In summary, based on field estimates and calculations, of the 46 homes
bordering the river in the study reach, about 21.5 of the homes appear
to have some form of bank protection, 15 homes are having serious
erosion and or bank issues that will require more immediate attention,
and 41 of the homes are within the EHZ as computed using the Austin
Method.
SECTION 6-CONCLUSIONS
1. The Denton Creek channel in the study area is a sinuous, low
gradient, single thread, meandering, alluvial sand channel.
2. The banks of the stream are cut into alluvial material that appears
to be composed of fine sand to silty clay material.
3. The Eagle Ford Shale bedrock underlies the channel; the depth of
the Eagle ford Shale with regard to the channel bottom is not
known but is important in prediction of future channel
104
degradation because it is more resistant to degradation than the
sand (inferred in this assessment).
4. The channel’s bed material load is principally fine sand with a D50
of .18mm.
5. Incipient motion analysis (Shields) indicates this material is very
mobile at low flows and is easily moved.
6. The channel is highly erodible with the magnitude of erodibility
being tied to bank cover vegetation.
7. CSR analysis indicates that the channel appears to have the
predicted width to carry the bed material over time and widening
should not be a major design factor.
8. Channel slope is currently greater than equilibrium slope and the
channel is prone to degradation.
10. Using maximum rates of degradation, the channel could degrade
at the upper project station up to 9 feet. This degradation depth
would decrease to 4.8 feet downstream at station 12046.
11. Based on analysis of historical photographs, the channel
meander migration rate is low (lateral stability appears high);
rates of migration appear similar to channels with similar sized
drainage basins and channel widths or from 1.5-10 feet a year.
12. Rates of meander migration were calculated based on flow
conditions (FDC) and an equation was calculated to assess the
changes in lateral erosion with flow and velocity based on
methods by Briaud and others. Rates up to 10 feet a year are
possible with reduced bank vegetation.
13. While rates are relatively low, the close proximity of homes to
the meander cutbanks requires assessment of erosion hazard
along the reach.
14. Erosion Hazard Zones (EHZ) were formulated using two
methods. Both methods gave similar setbacks for structures in
105
the channel assuming about 30 feet of lateral migration (1 foot
year for 30 years) and from 9 to 5 feet of degradation. Note:
Increased lateral migration is possible.
15. While some homes appear well protected by existing walls, etc.,
walls should be checked for their susceptibility to failure with
steam degradation, eg. footings, tiebacks.
16. Maintenance of bank vegetation is important to channel bank
stability.
17. Changes in flow regime due to changes in reservoir release
strategies by the USACE will affect the study reach and should be
evaluated in conversations with the USACE.
18. The implications shown in the setbacks are that if structures do
not have some sort of bank-slope and toe protection,
degradation and lateral erosion, over time will likely result in the
erosion and slope stability problems with most homes along the
reach.
19. In summary, based on field estimates and calculations, about
21.5 of the homes appear to have some form of bank protection,
11 homes are having serious erosion and or bank issues that will
require more immediate attention, and 41 of the homes are
within the EHZ as computed using the Austin Method.
20. The worst problems appear to be associated with meander bend
2. This is consistent with predicted degradation within this zone,
low width depth ratios, as well as the high bank shear from the
Halff Associates, Inc., models. The second area of problems is in
meander bend 3 where problems are similarly associated with a
lower width depth ratio and higher shear (0.66psf) from the Halff
Associates model, resulting in toe erosion and related slumping
of the banks.
106
21. This study’s purpose is to assess the trends and relative stability
of the study reach over a projected period of time. While
individual points were listed in tables to show relative numbers
of structures in relationship to channel erosion and stability,
owing to the level of precision of GPS used in the channel and
wooded riparian zone, it is advised that they should not be used
to assign specific risk to individual structures. This would require
access to the home sites above the channel, survey grade GPS to
determine exact limits of structural protection in the channel
below, lot lines, and more specific information regarding the
construction plans of individual bank protection in terms of
depth of footings, tiebacks etc.
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Addendum to Coppell Study for Halff Associates, Inc.
Geomorphologically, the study reach extends from the end of the Denton Creek Levee District,
downstream to the confluence with the Elm Fork. The study reach is herein classified according
to the Channel Evolution Model (Bledsoe, et. al, 2002). Channel instability is caused by an
imbalance between the transport capacity and sediment supply that alters channel morphology
(width, depth, slope) through bed and bank erosion. Consistent sequential changes have been
noted throughout the world in incised channel morphology which may be quantified and used
to predict changes in a channel over time.
In many channels within the metroplex, increased discharge due to urbanization has led to
subsequent changes in channel slope and degradation of the channel. The streams then follow
the Channel Evolution Model (CEM) where the slope progressively is lowered through
headward propagation of a knickpoint or Knickzone which results in a lower slope and the
progression of channel changes described by Bledsoe, et. al. 2002.
In the study area, the simple model is complicated by structural changes up and downstream of
the area.
• Upstream Lake Grapevine controlling discharge and altering the flow duration curve in
the study reach
• Excavation and lowering the slope near Denton Tap during Levee Construction
• Increased infilling of the watershed and increased urbanization upstream of the Levee
District
• Sediment capture (deposition of sand) in the Levee District
• Downstream Construction of a dam on the Elm Fork causing backwater up Denton Creek
So, while there is an observed knickpoint which appears to be propagating headward from
Denton Tap to Highway 121, (Halff Associates, Inc. 2018) which follows the CEM, the other
changes make strict adherence to this model somewhat suspect. This is a very complicated
system that is reacting over time to the cited man-induced changes. The CEM would suggest
that the upper reaches of Denton Creek in the study area would be subject to degradation. This
results from both less sediment making it downstream but also to the longitudinal adjustment
of the stream below the knickzone. Based on calculations, the stream is trying to reach a quasi-
equilibrium between discharge, slope, and sediment load and is projected to degrade. The
fulcrum of such degradation will be the backwater caused by the downstream dam on the Elm
Fork. Therefore, degradation will be greatest in the upper reaches of Denton Creek in Coppell.
The projections in the report and figures are made based on assumptions from other
watersheds and rivers, many of which do not contain the complexity of this reach. The lateral
migration of the channel is also tied to channel slope. A river can also adjust (lower) its slope
through increased sinuosity which would result in greater meander arcs and lateral erosion.
From field observations, the channel appears to be more prone to degradation under current
conditions of bank vegetation than lateral migration. This fact was noted in the original text.
The authors have used conservative estimates of degradation and subsequent changes based
on literature, engineering studies and past experience.
Description of CEM Stages
Bledsoe, et al. 2002.
APPENDIX C: COST ESTIMATES
Item Unit Quantity Unit Price Rounded Cost
Proposed Channel
Mobilization LS 1 $394,000 $394,000
Care of Water LS 1 $50,000 $50,000
Storm Water Pollution Prevention Plan LS 1 $106,549 $106,550
Implement Erosion Control Plan LS 1 $106,549 $106,550
Performance Bonds LS 1 $178,000 $178,000
Property Acquisition AC 50 $7,300 $365,000
Clearing and Grubbing AC 15 $7,500 $112,500
Seeding for Erosion Control SY 121,000 $0.60 $72,600
Excavation (Channel)CY 175,000 $15 $2,625,000
Erosion Control Mats SY 1,500 $15 $22,500
Rockchute Hard Points - 4 (channel)CY 340 $110 $37,400
Bank Vegetation (willows)EA 6,000 $5 $30,000
Estimated Cost $4,101,000
Denton Tap Road Grade Control Stucture
Storm Water Pollution Prevention Plan LS 1 $8,348 $8,348
Care of Water LS 1 $50,000 $50,000
Excavation (Channel)CY 3,300 $15 $49,500
Concrete Class "B"CY 650 $275 $178,750
Estimated Cost $287,000
Repair of Existing Headwall
Storm Water Pollution Prevention Plan LS 1 $1,751 $1,751
Care of Water LS 1 $50,000 $50,000
Remove exisiting headwall EA 1 $1,070 $1,070
Replace existing headwall EA 1 $5,000 $5,000
Remove 36" Class III RCP LF 10 $16 $155
Replace 36" Class III RCP LF 10 $106 $1,064
24" Rock Rprap CY 5 $115 $575
Geotextile (8 oz. minumum)SY 3 $1 $3
Fill (95% compaction)CY 50 $10 $500
Estimated Cost $61,000
SUBTOTAL $4,449,000
40% Construction Contingency $1,779,600
TOTAL ESTIMATED CONSTRUCTION COST $6,228,600
18% Engineering Services1 $1,121,148
Total $7,400,000
Assumptions:
1. Cost of the Engineering Services is based on 18% of the estimates construction cost, including contingency.
2. All cost are in 2017 US Dollars as of Spetember 19, 2017.
These estimates were prepared utilizing standard cost estimating practices. These statements exclude "soft" costs including, but not limited to, administrative costs, financing costs, USACE
permitting, geotechnical investigations, and construction materials testing. It is understood and agreed that this is an estimate only, and that Engineer shall not be liable to Owner or to a third
party for any failure to accurately estimate the cost of the project, or any part thereof.
Denton Creek Drainage Study
ALTERNATIVE 1
Engineer's Opinion of Probable Cost
BY
HALFF ASSOCIATES, INC
Denton Creek Bypass Channel
Item Unit Quantity Unit Price Rounded Cost
Stream Barbs
Mobilization LS 1 $41,000 $41,000
Care of Water LS 1 $50,000 $50,000
Storm Water Pollution Prevention Plan LS 1 $11,000 $11,000
Implement Erosion Control Plan LS 1 $11,000 $11,000
Performance Bonds LS 1 $18,000 $18,000
Clearing and Grubbing AC 2 $7,500 $15,000
Seeding for Erosion Control SY 400 $0.60 $240
Excavation (banks)CY 229 $15 $3,430
Barb Rocks (24")CY 470 $115 $54,050
Erosion Control Mats SY 400 $15 $6,000
Estimated Cost $210,000
Denton Tap Road Grade Control Stucture
Storm Water Pollution Prevention Plan LS 1 $8,348 $8,348
Care of Water LS 1 $50,000 $50,000
Excavation (Channel)CY 3,300 $15 $49,500
Concrete Class "B"CY 650 $275 $178,750
Estimated Cost $287,000
Repair of Existing Headwall
Remove exisiting headwall EA 1 $1,070 $1,070
Replace existing headwall EA 1 $5,000 $5,000
Remove 36" Class III RCP LF 10 $16 $155
Replace 36" Class III RCP LF 10 $106 $1,064
24" Rock Rprap CY 5 $115 $575
Geotextile (8 oz. minumum)SY 3 $1 $3
Fill (95% compaction)CY 50 $10 $500
Estimated Cost $9,000
SUBTOTAL $506,000
40% Construction Contingency $202,400
TOTAL ESTIMATED CONSTRUCTION COST $708,400
18% Engineering Services1 $127,512
Total $836,000
Assumptions:
1. Cost of the Engineering Services is based on 18% of the estimates construction cost, including contingency.
2. All cost are in 2017 US Dollars as of September 19, 2017.
These estimates were prepared utilizing standard cost estimating practices. These statements exclude "soft" costs including, but not limited to, administrative costs, financing costs, USACE
permitting, geotechnical investigations, and construction materials testing. It is understood and agreed that this is an estimate only, and that Engineer shall not be liable to Owner or to a third
party for any failure to accurately estimate the cost of the project, or any part thereof.
Denton Creek Drainage Study
ALTERNATIVE 2
Engineer's Opinion of Probable Cost
BY
HALFF ASSOCIATES, INC
Denton Creek Stream Barbs
Item Unit Quantity Unit Cost Buyout Cost1
Buyout
Mobilization LS 1 $326,000.00 $326,000
Storm Water Pollution Prevention Plan LS 1 $98,000.00 $98,000
Implement Erosion Control Plan LS 1 $98,000.00 $98,000
Performance Bonds LS 1 $163,000.00 $163,000
Affected Properties in Meander #2 LS 1 $2,216,140.00 $2,882,100
Demolition EA 7 $15,000.00 $105,000
Seed empty lots SF 56,000 $0.60 $34,000
Estimated Cost $3,707,000
Denton Tap Road Grade Control Stucture
Storm Water Pollution Prevention Plan LS 1 $8,348.00 $8,348
Care of Water LS 1 $50,000.00 $50,000
Excavation (Channel)CY 3,300 $15.00 $49,500
Concrete Class "B"CY 650 $275.00 $178,750
Estimated Cost $287,000
Repair of Existing Headwall
Storm Water Pollution Prevention Plan LS 1 $1,751 $1,751
Care of Water LS 1 $50,000 $50,000
Remove exisiting headwall EA 1 $1,070 $1,070
Replace existing headwall EA 1 $5,000 $5,000
Remove 36" Class III RCP LF 10 $16 $155
Replace 36" Class III RCP LF 10 $106 $1,064
24" Rock Rprap CY 5 $115 $575
Geotextile (8 oz. minumum)SY 3 $1 $3
Fill (95% compaction)CY 50 $10 $500
Estimated Cost $61,000
SUBTOTAL $4,055,000
30% Construction Contingency $1,216,500
TOTAL $5,300,000
Assumptions:
1. Buyout Cost includes additional 30% based on DCAD 2017 Apprasial to account for market value
2. All cost are in 2017 US Dollars as of September 19, 2017.
These estimates were prepared utilizing standard cost estimating practices. These statements exclude "soft" costs including, but not limited to, administrative costs, financing costs, USACE
permitting, geotechnical investigations, and construction materials testing. It is understood and agreed that this is an estimate only, and that Engineer shall not be liable to Owner or to a
third party for any failure to accurately estimate the cost of the project, or any part thereof.
Denton Creek Drainage Study
No Alternative
Engineer's Opinion of Probable Cost
BY
HALFF ASSOCIATES, INC
Buyout of Affected Properties Phase 1- Initial Buyout
Item Unit Quantity Unit Cost Buyout Cost1
Buyout
Mobilization LS 1 $2,146,000.00 $2,146,000
Storm Water Pollution Prevention Plan LS 1 $785,000.00 $785,000
Implement Erosion Control Plan LS 1 $785,000.00 $785,000
Performance Bonds LS 1 $1,264,000.00 $1,300,000
Affected Properties in EHZ LS 1 $15,876,690.00 $20,639,700
Demolition EA 34 $15,000.00 $510,000
Seed empty lots SF 122,100 $0.60 $73,000
Estimated Cost $26,239,000
Denton Tap Road Grade Control Stucture
Storm Water Pollution Prevention Plan LS 1 $8,348.00 $8,348
Care of Water LS 1 $50,000.00 $50,000
Excavation (Channel)CY 3,300 $15.00 $49,500
Concrete Class "B"CY 650 $275.00 $178,750
Estimated Cost $287,000
Repair of Existing Headwall
Storm Water Pollution Prevention Plan LS 1 $1,751 $1,751
Care of Water LS 1 $50,000 $50,000
Remove exisiting headwall EA 1 $1,070 $1,070
Replace existing headwall EA 1 $5,000 $5,000
Remove 36" Class III RCP LF 10 $16 $155
Replace 36" Class III RCP LF 10 $106 $1,064
24" Rock Rprap CY 5 $115 $575
Geotextile (8 oz. minumum)SY 3 $1 $3
Fill (95% compaction)CY 50 $10 $500
Estimated Cost $61,000
SUBTOTAL $26,587,000
30% Construction Contingency $7,976,100
TOTAL $34,600,000
Assumptions:
1. Buyout Cost includes additional 30% based on DCAD 2017 Apprasial to account for market value
2. All cost are in 2017 US Dollars as of September 19, 2017.
These estimates were prepared utilizing standard cost estimating practices. These statements exclude "soft" costs including, but not limited to, administrative costs, financing costs, USACE
permitting, geotechnical investigations, and construction materials testing. It is understood and agreed that this is an estimate only, and that Engineer shall not be liable to Owner or to a
third party for any failure to accurately estimate the cost of the project, or any part thereof.
3. Future Buyout is based on homes located within the EHZ only. If homes have adequate toe protection, no buyout may be needed.
Denton Creek Drainage Study
No Alternative
Engineer's Opinion of Probable Cost
BY
HALFF ASSOCIATES, INC
Buyout of Affected Properties Phase 2- Future Buyout³
APPENDIX D: HEC-HMS OUTPUT
Project: Denton2012Future Analysis: DCLID_001yr_1min Run: DCLID_001yr_1min
Start of Run: 01Jan2012, 00:00 Basin Model: DCLID_001yr_1min
End of Run: 02Jan2012, 00:00 Meteorologic Model: 1−Year
Compute Time: 13Oct2017, 12:40:22 Control Specifications: Control 1_1min
Analysis
Point
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
DCLID_J0020 1.57 1599.56 01Jan2012, 12:24
DCLID_J0030 1.64 1597.97 01Jan2012, 12:32
DCLID_J0040 2.45 2188.41 01Jan2012, 12:32
DCLID_J0050 2.48 2175.46 01Jan2012, 12:36
DCLID_J0060 3.70 3247.26 01Jan2012, 12:36
DCLID_J0070 4.72 3498.26 01Jan2012, 12:59
DCLID_J0080 5.22 3620.71 01Jan2012, 12:59
DCLID_J0090 5.30 3607.08 01Jan2012, 13:03
DCLID_J0100 5.46 3553.60 01Jan2012, 13:14
DCLID_J0110 5.47 3496.52 01Jan2012, 13:27
DCLID_J0120 8.49 4425.47 01Jan2012, 13:24
DCLID_J0130 8.62 4431.39 01Jan2012, 13:25
DCLID_J0140 8.67 4410.19 01Jan2012, 13:35
DCLID_J0150 9.59 4476.14 01Jan2012, 13:34
DCLID_J0160 9.84 4407.80 01Jan2012, 14:02
DCLID_J0170 10.18 4425.44 01Jan2012, 14:02
DCLID_J0180 10.28 4425.20 01Jan2012, 14:03
DCLID_J0190 10.50 4418.08 01Jan2012, 14:11
DCLID_J0200 11.13 4445.64 01Jan2012, 14:11
DCLID_J0210 11.17 4440.01 01Jan2012, 14:16
DCLID_J0230 11.93 4474.43 01Jan2012, 14:16
DCLID_J0240 12.33 4432.82 01Jan2012, 14:34
DCLID_J0250 12.75 4431.52 01Jan2012, 14:42
DCLID_J0260 18.86 5804.94 01Jan2012, 14:10
DCLID_J0270 19.28 5784.14 01Jan2012, 14:32
DCLID_J0280 20.62 5772.67 01Jan2012, 15:00
DCLID_J0290 22.30 5719.43 01Jan2012, 15:37
DCLID_JOutlet 25.42 5824.38 01Jan2012, 16:35
Project: Denton2012Future Analysis: DCLID_002yr_1min Run: DCLID_002yr_1min
Start of Run: 01Jan2012, 00:00 Basin Model: DCLID_002yr_1min
End of Run: 02Jan2012, 00:00 Meteorologic Model: 2−year
Compute Time: 13Oct2017, 12:41:44 Control Specifications: Control 1_1min
Analysis
Point
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
DCLID_J0020 1.57 2282.62 01Jan2012, 12:23
DCLID_J0030 1.64 2285.04 01Jan2012, 12:30
DCLID_J0040 2.45 3178.93 01Jan2012, 12:31
DCLID_J0050 2.48 3163.00 01Jan2012, 12:35
DCLID_J0060 3.70 4605.27 01Jan2012, 12:34
DCLID_J0070 4.72 4978.79 01Jan2012, 12:57
DCLID_J0080 5.22 5151.17 01Jan2012, 12:56
DCLID_J0090 5.30 5097.31 01Jan2012, 13:03
DCLID_J0100 5.46 5029.85 01Jan2012, 13:14
DCLID_J0110 5.47 4965.85 01Jan2012, 13:26
DCLID_J0120 8.49 6383.23 01Jan2012, 13:22
DCLID_J0130 8.62 6376.28 01Jan2012, 13:25
DCLID_J0140 8.67 6323.75 01Jan2012, 13:35
DCLID_J0150 9.59 6415.29 01Jan2012, 13:35
DCLID_J0160 9.84 6294.90 01Jan2012, 14:00
DCLID_J0170 10.18 6322.38 01Jan2012, 14:00
DCLID_J0180 10.28 6321.21 01Jan2012, 14:02
DCLID_J0190 10.50 6281.30 01Jan2012, 14:13
DCLID_J0200 11.13 6323.02 01Jan2012, 14:13
DCLID_J0210 11.17 6286.78 01Jan2012, 14:23
DCLID_J0230 11.93 6334.13 01Jan2012, 14:22
DCLID_J0240 12.33 6300.77 01Jan2012, 14:36
DCLID_J0250 12.75 6294.87 01Jan2012, 14:44
DCLID_J0260 18.86 8139.96 01Jan2012, 14:05
DCLID_J0270 19.28 8128.60 01Jan2012, 14:26
DCLID_J0280 20.62 8131.86 01Jan2012, 14:50
DCLID_J0290 22.30 8441.97 01Jan2012, 15:25
DCLID_JOutlet 25.42 8655.69 01Jan2012, 16:23
Project: Denton2012Future Analysis: DCLID_005yr_1min Run: DCLID_005yr_1min
Start of Run: 01Jan2012, 00:00 Basin Model: DCLID_005yr_1min
End of Run: 02Jan2012, 00:00 Meteorologic Model: 5−Year
Compute Time: 13Oct2017, 12:43:07 Control Specifications: Control 1_1min
Analysis
Point
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
DCLID_J0020 1.57 3021.00 01Jan2012, 12:22
DCLID_J0030 1.64 3045.79 01Jan2012, 12:28
DCLID_J0040 2.45 4298.35 01Jan2012, 12:29
DCLID_J0050 2.48 4284.88 01Jan2012, 12:33
DCLID_J0060 3.70 6183.07 01Jan2012, 12:33
DCLID_J0070 4.72 5957.56 01Jan2012, 13:17
DCLID_J0080 5.22 6311.43 01Jan2012, 12:48
DCLID_J0090 5.30 6246.84 01Jan2012, 12:57
DCLID_J0100 5.46 6160.26 01Jan2012, 13:18
DCLID_J0110 5.47 6031.56 01Jan2012, 13:55
DCLID_J0120 8.49 8175.45 01Jan2012, 12:59
DCLID_J0130 8.62 8190.25 01Jan2012, 13:02
DCLID_J0140 8.67 8158.06 01Jan2012, 13:13
DCLID_J0150 9.59 8481.75 01Jan2012, 13:12
DCLID_J0160 9.84 8449.57 01Jan2012, 13:34
DCLID_J0170 10.18 8513.14 01Jan2012, 13:34
DCLID_J0180 10.28 8520.14 01Jan2012, 13:36
DCLID_J0190 10.50 8502.30 01Jan2012, 13:49
DCLID_J0200 11.13 8598.86 01Jan2012, 13:48
DCLID_J0210 11.17 8574.08 01Jan2012, 13:58
DCLID_J0230 11.93 8709.75 01Jan2012, 13:57
DCLID_J0240 12.33 8714.96 01Jan2012, 14:08
DCLID_J0250 12.75 8724.03 01Jan2012, 14:19
DCLID_J0260 18.86 11949.63 01Jan2012, 14:11
DCLID_J0270 19.28 11916.61 01Jan2012, 14:33
DCLID_J0280 20.62 11914.20 01Jan2012, 14:59
DCLID_J0290 22.30 12527.93 01Jan2012, 15:21
DCLID_JOutlet 25.42 12917.05 01Jan2012, 16:20
Project: Denton2012Future Analysis: DCLID_010yr_1min Run: DCLID_010yr_1min
Start of Run: 01Jan2012, 00:00 Basin Model: DCLID_010yr_1min
End of Run: 02Jan2012, 00:00 Meteorologic Model: 10−Year
Compute Time: 13Oct2017, 12:44:34 Control Specifications: Control 1_1min
Analysis
Point
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
DCLID_J0020 1.57 3437.69 01Jan2012, 12:22
DCLID_J0030 1.64 3470.85 01Jan2012, 12:28
DCLID_J0040 2.45 4915.01 01Jan2012, 12:29
DCLID_J0050 2.48 4902.30 01Jan2012, 12:33
DCLID_J0060 3.70 7075.27 01Jan2012, 12:33
DCLID_J0070 4.72 6846.35 01Jan2012, 13:21
DCLID_J0080 5.22 7010.62 01Jan2012, 13:21
DCLID_J0090 5.30 6955.99 01Jan2012, 13:28
DCLID_J0100 5.46 6811.52 01Jan2012, 13:42
DCLID_J0110 5.47 6611.84 01Jan2012, 14:05
DCLID_J0120 8.49 9166.88 01Jan2012, 12:50
DCLID_J0130 8.62 9191.88 01Jan2012, 12:54
DCLID_J0140 8.67 9153.56 01Jan2012, 13:05
DCLID_J0150 9.59 9678.00 01Jan2012, 13:04
DCLID_J0160 9.84 9637.23 01Jan2012, 13:27
DCLID_J0170 10.18 9735.85 01Jan2012, 13:27
DCLID_J0180 10.28 9750.26 01Jan2012, 13:29
DCLID_J0190 10.50 9733.40 01Jan2012, 13:42
DCLID_J0200 11.13 9884.04 01Jan2012, 13:41
DCLID_J0210 11.17 9852.80 01Jan2012, 13:51
DCLID_J0230 11.93 10068.55 01Jan2012, 13:50
DCLID_J0240 12.33 10072.25 01Jan2012, 14:04
DCLID_J0250 12.75 10096.35 01Jan2012, 14:14
DCLID_J0260 18.86 14355.23 01Jan2012, 14:04
DCLID_J0270 19.28 14389.85 01Jan2012, 14:13
DCLID_J0280 20.62 14514.93 01Jan2012, 14:24
DCLID_J0290 22.30 15343.06 01Jan2012, 14:59
DCLID_JOutlet 25.42 16074.56 01Jan2012, 15:56
Project: Denton2012Future Analysis: 10yr_May31 Run: 10yr_May31
Start of Run: 01Jan2012, 00:00 Basin Model: 10−year_May31_Event
End of Run: 02Jan2012, 00:00 Meteorologic Model: 10−Year
Compute Time: 16Oct2017, 10:33:35 Control Specifications: Control 1_1min
Analysis
Point
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
DCLID_J0020 1.57 3477.69 01Jan2012, 12:22
DCLID_J0030 1.64 3510.85 01Jan2012, 12:28
DCLID_J0040 2.45 4955.01 01Jan2012, 12:29
DCLID_J0050 2.48 4942.31 01Jan2012, 12:33
DCLID_J0060 3.70 7115.28 01Jan2012, 12:33
DCLID_J0070 4.72 6884.70 01Jan2012, 13:22
DCLID_J0080 5.22 7048.22 01Jan2012, 13:21
DCLID_J0090 5.30 6994.28 01Jan2012, 13:28
DCLID_J0100 5.46 6847.93 01Jan2012, 13:42
DCLID_J0110 5.47 6636.11 01Jan2012, 14:06
DCLID_J0120 8.49 9170.79 01Jan2012, 12:50
DCLID_J0130 8.62 9196.75 01Jan2012, 12:54
DCLID_J0140 8.67 9160.39 01Jan2012, 13:05
DCLID_J0150 9.59 9686.74 01Jan2012, 13:04
DCLID_J0160 9.84 9647.81 01Jan2012, 13:27
DCLID_J0170 10.18 9746.57 01Jan2012, 13:27
DCLID_J0180 10.28 9761.62 01Jan2012, 13:28
DCLID_J0190 10.50 9745.08 01Jan2012, 13:42
DCLID_J0200 11.13 9897.06 01Jan2012, 13:41
DCLID_J0210 11.17 9865.91 01Jan2012, 13:50
DCLID_J0230 11.93 10082.39 01Jan2012, 13:50
DCLID_J0240 12.33 10082.17 01Jan2012, 14:04
DCLID_J0250 12.75 10107.04 01Jan2012, 14:15
DCLID_J0260 18.86 14381.81 01Jan2012, 14:03
DCLID_J0280 20.62 14542.98 01Jan2012, 14:23
DCLID_J0290 22.30 15372.50 01Jan2012, 14:59
DCLID_JOutlet 25.42 16107.50 01Jan2012, 15:56
DCLID_R0270 18.86 14370.30 01Jan2012, 14:13
Project: Denton2012Future Analysis: DCLID_025yr_1min Run: DCLID_025yr_1min
Start of Run: 01Jan2012, 00:00 Basin Model: DCLID_025yr_1min
End of Run: 02Jan2012, 00:00 Meteorologic Model: 25−Year
Compute Time: 13Oct2017, 12:48:23 Control Specifications: Control 1_1min
Analysis
Point
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
DCLID_J0020 1.57 4030.85 01Jan2012, 12:22
DCLID_J0030 1.64 4083.89 01Jan2012, 12:28
DCLID_J0040 2.45 5780.81 01Jan2012, 12:29
DCLID_J0050 2.48 5626.08 01Jan2012, 12:38
DCLID_J0060 3.70 8118.46 01Jan2012, 12:36
DCLID_J0070 4.72 7913.70 01Jan2012, 13:26
DCLID_J0080 5.22 8100.46 01Jan2012, 13:25
DCLID_J0090 5.30 8034.12 01Jan2012, 13:33
DCLID_J0100 5.46 7925.91 01Jan2012, 13:48
DCLID_J0110 5.47 7557.07 01Jan2012, 14:16
DCLID_J0120 8.49 9983.74 01Jan2012, 12:49
DCLID_J0130 8.62 10039.28 01Jan2012, 12:52
DCLID_J0140 8.67 10023.33 01Jan2012, 13:05
DCLID_J0150 9.59 10692.62 01Jan2012, 13:01
DCLID_J0160 9.84 10644.72 01Jan2012, 13:30
DCLID_J0170 10.18 10755.75 01Jan2012, 13:30
DCLID_J0180 10.28 10776.10 01Jan2012, 13:32
DCLID_J0190 10.50 10786.16 01Jan2012, 13:45
DCLID_J0200 11.13 10958.11 01Jan2012, 13:44
DCLID_J0210 11.17 10935.52 01Jan2012, 13:55
DCLID_J0230 11.93 11178.58 01Jan2012, 13:53
DCLID_J0240 12.33 11200.15 01Jan2012, 14:10
DCLID_J0250 12.75 11236.64 01Jan2012, 14:24
DCLID_J0260 18.86 16490.24 01Jan2012, 13:42
DCLID_J0270 19.28 16559.40 01Jan2012, 13:50
DCLID_J0280 20.62 16794.57 01Jan2012, 14:02
DCLID_J0290 22.30 17542.76 01Jan2012, 14:54
DCLID_JOutlet 25.42 18542.97 01Jan2012, 15:51
Project: Denton2012Future Analysis: DCLID_050yr_1min Run: DCLID_050yr_1min
Start of Run: 01Jan2012, 00:00 Basin Model: DCLID_050yr_1min
End of Run: 02Jan2012, 00:00 Meteorologic Model: 50−Year
Compute Time: 13Oct2017, 12:46:40 Control Specifications: Control 1_1min
Analysis
Point
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
DCLID_J0020 1.57 4496.61 01Jan2012, 12:22
DCLID_J0030 1.64 4559.11 01Jan2012, 12:28
DCLID_J0040 2.45 6461.81 01Jan2012, 12:29
DCLID_J0050 2.48 6276.35 01Jan2012, 12:39
DCLID_J0060 3.70 9051.69 01Jan2012, 12:37
DCLID_J0070 4.72 8320.99 01Jan2012, 13:38
DCLID_J0080 5.22 8496.67 01Jan2012, 13:37
DCLID_J0090 5.30 8471.01 01Jan2012, 13:43
DCLID_J0100 5.46 8442.23 01Jan2012, 13:55
DCLID_J0110 5.47 8188.97 01Jan2012, 14:22
DCLID_J0120 8.49 10798.16 01Jan2012, 13:25
DCLID_J0130 8.62 10830.40 01Jan2012, 13:28
DCLID_J0140 8.67 10811.03 01Jan2012, 13:42
DCLID_J0150 9.59 11395.64 01Jan2012, 13:05
DCLID_J0160 9.84 11416.16 01Jan2012, 13:34
DCLID_J0170 10.18 11538.26 01Jan2012, 13:33
DCLID_J0180 10.28 11563.39 01Jan2012, 13:35
DCLID_J0190 10.50 11598.40 01Jan2012, 13:48
DCLID_J0200 11.13 11790.59 01Jan2012, 13:46
DCLID_J0210 11.17 11780.13 01Jan2012, 13:57
DCLID_J0230 11.93 12052.18 01Jan2012, 13:55
DCLID_J0240 12.33 12099.39 01Jan2012, 14:12
DCLID_J0250 12.75 12174.60 01Jan2012, 14:19
DCLID_J0260 18.86 18135.20 01Jan2012, 13:45
DCLID_J0270 19.28 18229.17 01Jan2012, 13:53
DCLID_J0280 20.62 18522.75 01Jan2012, 14:02
DCLID_J0290 22.30 19358.01 01Jan2012, 14:51
DCLID_JOutlet 25.42 20595.30 01Jan2012, 15:45
Project: Denton2012Future Analysis: DCLID_100yr_1min Run: DCLID_100yr_1min
Start of Run: 01Jan2012, 00:00 Basin Model: DCLID_100yr_1min
End of Run: 02Jan2012, 00:00 Meteorologic Model: 100−Year
Compute Time: 13Oct2017, 12:49:48 Control Specifications: Control 1_1min
Analysis
Point
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
DCLID_J0020 1.57 4965.81 01Jan2012, 12:22
DCLID_J0030 1.64 5038.04 01Jan2012, 12:28
DCLID_J0040 2.45 7148.63 01Jan2012, 12:29
DCLID_J0050 2.48 6943.16 01Jan2012, 12:39
DCLID_J0060 3.70 10008.21 01Jan2012, 12:37
DCLID_J0070 4.72 9046.85 01Jan2012, 13:44
DCLID_J0080 5.22 9224.63 01Jan2012, 13:44
DCLID_J0090 5.30 9142.29 01Jan2012, 13:51
DCLID_J0100 5.46 9026.51 01Jan2012, 14:03
DCLID_J0110 5.47 8746.10 01Jan2012, 14:29
DCLID_J0120 8.49 11899.42 01Jan2012, 13:22
DCLID_J0130 8.62 11938.16 01Jan2012, 13:26
DCLID_J0140 8.67 11914.80 01Jan2012, 13:40
DCLID_J0150 9.59 12291.43 01Jan2012, 13:38
DCLID_J0160 9.84 12301.05 01Jan2012, 14:08
DCLID_J0170 10.18 12389.63 01Jan2012, 13:45
DCLID_J0180 10.28 12415.89 01Jan2012, 13:46
DCLID_J0190 10.50 12476.31 01Jan2012, 13:54
DCLID_J0200 11.13 12683.34 01Jan2012, 13:49
DCLID_J0210 11.17 12690.03 01Jan2012, 13:58
DCLID_J0230 11.93 13027.76 01Jan2012, 13:49
DCLID_J0240 12.33 13106.63 01Jan2012, 14:08
DCLID_J0250 12.75 13206.32 01Jan2012, 14:15
DCLID_J0260 18.86 20236.58 01Jan2012, 13:46
DCLID_J0270 19.28 20285.19 01Jan2012, 13:57
DCLID_J0280 20.62 20572.12 01Jan2012, 14:10
DCLID_J0290 22.30 21378.91 01Jan2012, 14:59
DCLID_JOutlet 25.42 22723.30 01Jan2012, 15:51
Project: Denton2012Future Analysis: DCLID_500yr_1min Run: DCLID_500yr_1min
Start of Run: 01Jan2012, 00:00 Basin Model: DCLID_500yr_1min
End of Run: 02Jan2012, 00:00 Meteorologic Model: 500−Year
Compute Time: 13Oct2017, 12:51:09 Control Specifications: Control 1_1min
Analysis
Point
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
DCLID_J0020 1.57 6314.15 01Jan2012, 12:22
DCLID_J0030 1.64 6234.94 01Jan2012, 12:33
DCLID_J0040 2.45 8923.80 01Jan2012, 12:33
DCLID_J0050 2.48 8692.04 01Jan2012, 12:42
DCLID_J0060 3.70 12358.64 01Jan2012, 12:39
DCLID_J0070 4.72 10925.02 01Jan2012, 13:54
DCLID_J0080 5.22 11124.42 01Jan2012, 13:54
DCLID_J0090 5.30 11028.63 01Jan2012, 14:02
DCLID_J0100 5.46 10895.40 01Jan2012, 14:15
DCLID_J0110 5.47 10415.46 01Jan2012, 14:42
DCLID_J0120 8.49 14351.12 01Jan2012, 13:20
DCLID_J0130 8.62 14393.12 01Jan2012, 13:23
DCLID_J0140 8.67 14323.82 01Jan2012, 13:40
DCLID_J0150 9.59 14796.85 01Jan2012, 13:39
DCLID_J0160 9.84 14776.39 01Jan2012, 14:11
DCLID_J0170 10.18 14888.50 01Jan2012, 14:11
DCLID_J0180 10.28 14916.00 01Jan2012, 14:12
DCLID_J0190 10.50 14972.53 01Jan2012, 14:20
DCLID_J0200 11.13 15172.06 01Jan2012, 14:20
DCLID_J0210 11.17 15178.15 01Jan2012, 14:25
DCLID_J0230 11.93 15446.40 01Jan2012, 14:24
DCLID_J0240 12.33 15524.68 01Jan2012, 14:40
DCLID_J0250 12.75 15627.71 01Jan2012, 14:46
DCLID_J0260 18.86 24818.60 01Jan2012, 13:37
DCLID_J0270 19.28 24961.96 01Jan2012, 13:47
DCLID_J0280 20.62 25412.67 01Jan2012, 14:01
DCLID_J0290 22.30 26074.72 01Jan2012, 14:57
DCLID_JOutlet 25.42 27869.12 01Jan2012, 15:50
APPENDIX E: HEC-RAS OUTPUT
APPENDIX F: HYDROLOGIC PARAMETER CALCULATIONS
SUB_NAME PCT_IMP PCT_URB
DCLID_0010 6.7 11.6
DCLID_0020 60.3 67.4
DCLID_0030 39.9 55.1
DCLID_0040 38.7 50.7
DCLID_0050 67.3 91.4
DCLID_0060 70.1 77.9
DCLID_0070 71.6 83.1
DCLID_0080 81.2 88.5
DCLID_0090 87.6 94.4
DCLID_0100 75.2 80.7
DCLID_0110 7.9 8.3
DCLID_0120 43 69.9
DCLID_0130 80.9 85.4
DCLID_0140 26.2 33.3
DCLID_0150 68.5 82.4
DCLID_0160 55.3 64.6
DCLID_0170 85 92.3
DCLID_0180 45.5 81.8
DCLID_0190 60.2 71
DCLID_0200 77.5 91.5
DCLID_0210 23 44
DCLID_0230 68.5 87.1
DCLID_0240 37.2 63.4
DCLID_0250 59.5 80.6
DCLID_0260 67.9 82.6
DCLID_0270 47.4 71
DCLID_0280 45.3 75.4
DCLID_0290 64.8 82.3
DCLID_0300 31 49.8
Percent Impervious and Urban
Halff USACE Halff %Sand %Clay Area
SUB_NAME Subbasin DA_Area
DCLID_0010 1 7844677.533 47 53 0.28139
DCLID_0020 2 35857485.37 46 54 1.28621
DCLID_0030 3 2113021.486 39 61 0.07579
DCLID_0040 4 22618927.22 52 48 0.81134
DCLID_0050 5 648813.1202 39 61 0.02327
DCLID_0060 6 33932875.49 47 53 1.21717
DCLID_0070 7 28502728.77 48 52 1.02239
DCLID_0080 8 14051240.15 55 45 0.50402
DCLID_0100 9 4386581.908 55 45 0.15735
DCLID_0090 10 2141222.759 42 58 0.07681
DCLID_0110 11 331404.7442 31 69 0.01189
DCLID_0120 12 84315281.86 52 48 3.02439
DCLID_0130 13 3569636.8 50 50 0.12804
DCLID_0140 14 1265220.088 34 66 0.04538
DCLID_0150 15 25907222.75 51 49 0.92929
DCLID_0160 16 6939173.69 52 48 0.24891
DCLID_0170 17 9341457.252 68 32 0.33508
DCLID_0180 18 2773169.772 58 42 0.09947
DCLID_0190 19 6223986.727 64 36 0.22325
DCLID_0200 20 17416182.06 58 42 0.62472
DCLID_0210 21 1182178.361 32 68 0.0424
DCLID_0230 23 21259594.01 59 41 0.76258
DCLID_0240 24 11200563.01 46 54 0.40176
DCLID_0250 25 11590139.87 49 51 0.41574
DCLID_0260 26 170323756.7 40 60 6.10952
DCLID_0280 27 37247410.57 50 50 1.33607
DCLID_0270 28 11782610.06 45 55 0.42264
DCLID_0290 29 46835080.46 44 56 1.67998
DCLID_0300 30 87112435.41 39 61 3.12473
DA Size Curve L LCAL LCAStsLCAL/(Sst)0.5%CLAY %SAND PCT_Urb tp (clay) tp (sand) tptpDA Name HMS Basin(mi2)Number (ft) (ft) (miles) (miles) (ft/mile) (%) (%) (hours) (hours) (hours) (minutes)DCLID_0010 Lower Denton Creek 0.00000 6142.47 2280.851.16 0.43 101.40 0.0499 53.00 47.00 11.60 0.27 0.52 0.39 23.47DCLID_0020Lower Denton Creek0.0000012798.096019.782.42 1.14 71.36 0.3271 54.00 46.00 67.40 0.40 0.76 0.57 34.06DCLID_0030Lower Denton Creek0.000002223.131053.040.42 0.20 290.07 0.0049 61.00 39.00 55.10 0.09 0.16 0.12 7.03DCLID_0040Lower Denton Creek0.0000015371.457609.372.91 1.44 59.39 0.5444 48.00 52.00 50.70 0.54 1.03 0.79 47.62DCLID_0050Lower Denton Creek0.000002296.46944.100.43 0.18 254.08 0.0049 61.00 39.00 91.40 0.07 0.13 0.10 6.00DCLID_0060Lower Denton Creek0.0000017424.7910385.103.30 1.97 54.92 0.8759 53.00 47.00 77.90 0.55 1.04 0.78 46.88DCLID_0070Lower Denton Creek0.0000014328.486018.582.71 1.14 53.85 0.4215 52.00 48.00 83.10 0.40 0.76 0.58 34.53DCLID_0080Lower Denton Creek0.000008398.663878.741.59 0.73 55.28 0.1572 45.00 55.00 88.50 0.27 0.51 0.40 23.90DCLID_0090Lower Denton Creek0.000003321.64751.120.63 0.14 16.85 0.0218 58.00 42.00 94.40 0.12 0.23 0.17 9.96DCLID_0100Lower Denton Creek0.000003299.08580.120.62 0.11 82.01 0.0076 45.00 55.00 80.70 0.09 0.17 0.13 7.84DCLID_0110Lower Denton Creek0.000001756.27737.690.33 0.14 0.80 0.0519 69.00 31.00 8.30 0.28 0.54 0.36 21.84DCLID_0120Lower Denton Creek0.0000027552.8613121.905.22 2.49 35.46 2.1777 48.00 52.00 69.90 0.82 1.55 1.20 72.02DCLID_0130Lower Denton Creek0.000005331.051490.931.01 0.28 102.15 0.0282 50.00 50.00 85.40 0.14 0.27 0.20 12.23DCLID_0140Lower Denton Creek0.000002193.131005.410.42 0.19 138.10 0.0067 66.00 34.00 33.30 0.11 0.21 0.15 8.75DCLID_0150Lower Denton Creek0.000009695.154912.551.84 0.93 69.54 0.2049 49.00 51.00 82.40 0.31 0.58 0.45 26.80DCLID_0160Lower Denton Creek0.000005359.532215.501.02 0.42 55.89 0.0570 48.00 52.00 64.60 0.21 0.40 0.31 18.41DCLID_0170Lower Denton Creek0.000006657.172884.091.26 0.55 25.12 0.1374 32.00 68.00 92.30 0.25 0.47 0.40 23.92DCLID_0180Lower Denton Creek0.000002036.30409.600.39 0.08 102.16 0.0030 42.00 58.00 81.80 0.06 0.12 0.10 6.00DCLID_0190Lower Denton Creek0.000005937.242519.911.12 0.48 58.37 0.0702 36.00 64.00 71.00 0.22 0.41 0.34 20.60DCLID_0200Lower Denton Creek0.000009271.095066.751.76 0.96 68.69 0.2033 42.00 58.00 91.50 0.29 0.55 0.44 26.36LAG TIME
APPENDIX G: DIGITAL DATA