Parks Coppell FS-CS 881010 FILE COPY
! (~/ // L_~ // ~,'~ ~,,/ ,~/ ~ .' ,' .' PO. Box 478
~/ /~~ ~ ~/~/~ Coppe!l. Texas 75019
2~4-462-0022
The City With A Beautiful Future
October l0, 1988
Mr. Chris Ulsh HAND CARRIED
Dewberry & Davis TO: FEMA, DENTON, TX.
8401 Arlington Boulevard
Fairfax, Virginia 22031
RE:Request for Conditional Letter of Map Revision
Parks of Coppell - Coppell, Texas
Dear Mr. Ulsh:
The City of Coppell has received the enclosed technical report on
existing and proposed floodplain reclamation studies to the west of
Denton Tap Road within the confluence of the Cottonwood Branch and
Denton Creek. This report, as indicated, by Jerry Parche Consulting
Engineers, includes a detailed hydraulic analysis of the existing
channel and overbank conditions as well as proposed improvements.
Please process this request for a Conditional Letter of Map Revision.
Please no%e that this reclamation will allow extension of Parkway
Boulevard to the west of Denton Tap Road, thereby providing access
roadways to our new Hiah School in the spring of 1989.
If you have any technical questions on this request, please contact
Mr. Jerry Parche at (817) 572-3458, and keep us informed. Any
administrative questions shouid be indicated to Shohre Daneshmand,
Civil Engineer, or myself at (214)462-0022.
We appreciate your expeditous review and consideration of this
request. Thank you.
Sincerely ~
RRD/SD/lsg
xc: Alan Ratliff, City Manager
Shohre Daneshmand, Civil Engineer
Jerry Parche, Parche fngineers
Cheryl Holke, F.E.M.A.
FLOOD PLAIN -REC4.AMATION STUDY
COTTOI~ BRANCH AND DE~ON C~K
FOR
CONS~TI~ OF PARKWAY BOULEVARD
ABO DEVELOPMENT CO.OPTION
,q,BUi:;~IEI::K31J~ N.M. 87125
OCT~ 1988
COPPELL, DALLAS COUNTY, TEXAS
Prepared By:
6~01 ~r' Ir~erst~e 2.0 * Su~e 209. IR 32 ,, Arl~gto~, rexa~ 76016
Me~ro ~817J S72-3458 · (8! 71 561-210B
Jerry Parch% Consulting Engineerr
Mr. Russell Doyle. P.E. .I OCT ?
City Engineer
City of Coppell, Texas 1~
HAND DELIVERED
RE: JP No. 88009; Request for Conditional
Letter of Map Revision; Parks of Coppell;
Coppell, Texas
Dear Russell:
In order to comply with the Coppe11 Independent School District
timetable for the opening of the new High School, ABQ Development
Corporation, has directed our firm to prepare this study of flood
plain impacts resulting from the reclamation necessary to
construct access roadways to the new school.
In this regard, we are pleased to submit two copies of the
following information to support our request to the City of
Coppell and the Federal Emergency Management Agency to reclaim a
portion of the flood plain of Denton Creek and Cottonwood Branch
west of Denton Tap Road to permit construction of Parkway
Boulevard and the High School Access Road.
1. A written report, with computer models and exhibits.
2. Drawings of Denton Creek and Cottonwood Branch cross
sections utilized in the hydraulic study (6 sheets).
This information is submitted to support a request to FEMA for a
Conditional Letter of Map Revision for this project. The primary
purpose of this request is to secure approval to reclaim flood
plain land necessary to construct Parkway Bouelvard from Denton
Tap Road west to the High School Access Road and to construct the
High School Access Road from Parkway Boulevard to the High School
site.
Since time is of the essence, we will be happy to assist you in
your review and to provide delivery services to expedite this
submittal to FEMA. Approval of this request by the City of
Coppell and FEMA is necessary before construction of the
aformentioned roadways can proceed.
Please call if you have any questions. Thank you.
S~ncerely~
err~ Parche', P.E.
cc: Mr Jay Chester/ABQ Development Corporation
6001 V~/. Interstate 20, Suite 209, LB 32 · Arlington, Texas 76016 · Metro 1817) 572-3458 · 1817J 561-2108
FLOOD PLAIN RECLAMATION STUDY
COTTONWOOD BRANCH
AND DENTON CREEK
COPPELL, TEXAS
I. PURPOSE AND SCOPE
This report presents the results of an analysis of proposed
flood plain reclamation lying within the common flood plain
of Cottonwood Branch and Denton Creek in Coppell, Texas.
The project is located just west of Denton Tap Road on the
south side of Cottonwood Branch. The proposed reclamation
area lies within the boundaries of the Parks of Coppell
Development.
The relatively limited amount of reclamation proposed at
this time is specifically intended to permit construction of
approximately 800 feet of Parkway Boulevard and a collector
street connecting Parkway Boulevard to Coppell High School,
which is currently under construction. The proposed streets
will provide the sole access to the High School site. The
purpose of this study is to develop technical information to
support a request by the property owners, ABQ Development
Corporation, to the Federal Emergency Management Agency for
a Conditional Letter of Map Revision for this project.
The project lies within an area of Coppell that has been the
subject of several flood plain studies in the last several
years. The scope of this study is as follows.
A. Obtain and review hydraulic models prepared for
projects located adjacent to or near the subject
property that impact flooding conditions on the
proposed reclamation site or may be impacted by the
proposed reclamation.
B. Develop an accurate model of existing flood plain
conditions on the site and adjacent sites to establish
criteria for evaluation of the proposed reclamation.
C. Prepare hydraulic models to analyze the response of the
flood plain to the proposed reclamation and provide
documentation that the proposed project complies with
requirements of the City of Coppell and FEMA.
II. LOCATION AND DRSCRIPTION
The project site is shown on Figure 1 and flood plain
features and location of surrounding developments are shown
on Exhibit A, located in the map pocket in the back of this
report. The flood plains of Denton Creek and Cottonwood
Branch join together within the portion of the Parks of
Coppell development that is west of Denton Tap Road. This
area is bounded on the west by the Villages of Cottonwood
Creek project and on the north by the Century Park Addition,
formerly known as Lincoln/Coppell. Andrew Brown Community
Park, a city park, lies between the Parks of Coppell and
Denton Tap Road and is north of the proposed reclamation
area. Downstream or east of Denton Tap Road, the Vista
Ridge project is located north of Denton Creek and
additional City Park property and additional area in the
Parks of Coppell are located south of Denton Creek. Grading
and flood plain reclamation in surrounding projects is
complete.
As shown on Exhibit A, the Cottonwood Branch channel is
located just north of the proposed reclamation area.
Parkway Boulevard intersects Denton Tap Road approximately
600 feet south of the Cottonwood Branch bridge and currently
extends only east from this intersection. Parkway Boulevard
is constructed west of the Parks of Coppell in the Villages
of Cottonwood Creek.
III. EXISTING 100-YEAR FhOOD PLAIN
A. Flood Plain Studies - Adjacent Projects
Hydraulic models were obtained for the Vista Ridge
project, formerly known as Campbell Ranch, the
hincoln/Coppell project and the Villages of Cottonwood
Creek project to help establish existing flood plain
conditions in this area. The currently effective model
of the Denton Creek flood plain downstream of Denton
Tap Road, which includes Cottonwood Branch, is the
Campbell Ranch model. Completed grading in both
Campbell Ranch and the Parks of Coppell Projects
downstream (east) of Denton Tap Road is included in the
Campbell Ranch model.
Hydraulic models prepared for the hincoln/Coppell
project were obtained from engineers for that
development. This project included extensive
reclamation and regrading of flood plain and floodway
areas on the north side of Denton Creek west of Denton
LA)~E
LIW I ~J ViLLg
STUDY SITE
CC) COPPEL~
~
FIGURE 1
LOCATION MAP
PARKS OF COPPELL
-3-
Tap Road. Lincoln/Coppell hydraui~c models we received
commenced just downstream of Denton Tap Road with water
surface elevations determined in the Campbell Ranch
models. Since the project is located on the north side
of Denton Creek, the hydraulic models prepared for that
project analyze the common Denton Creek/Cottonwood
Branch flood plain west of Denton Tap Road and then
continue upstream in the Denton Creek flood plain only.
Cross sections of the proposed Lincoln/Coppell project
extend south of Denton Creek through the City Park and
into the Parks of Coppell as shown on Exhibit A.
Discharges are in accordance with discharges used in
previous Flood Insurance Studies. Cross sections of
the Denton Creek flood plain upstream of the
Lincoln/Coppell project used in previous flood
insurance studies have been incorporated into the
Lincoln/Coppell Study. Hydraulic models prepared for
the Lincoln/Coppell project generally represent
existing conditions in the Denton Creek flood plain
west of Denton Tap Road.
A hydraulic model of Cottonwood Branch was obtained
from Dewberry & Davis, engineering consultants to FEMA,
that had been prepared for the Villages of Cottonwood
Creek Project upstream of the Parks of Coppell. Flood
plain reclamation for this project included areas north
of the Cottonwood Branch floodway. Cross sections from
this model were incorporated into the Cottonwood Branch
models prepared for our study.
B. Hydraulic Models - This Study
The computer program HEC-2 was used to determine
hydraulic conditions in the existing flood plain. Two
computer models were prepared for determining the
existing lO0-year flood plain and floodway in Denton
Creek and Cottonwood Branch.
1. Model DEEXPK - This computer model determines 100-
year flood plain and floodway
conditions in the Denton Creek
flood plain upstream of Denton Tap
Road based on existing topography.
-4-
2. Model COEXPK - This computer model determines 100-
year flood plain and floodway
conditions in the Denton Creek
flood plain between the Cottonwood
Branch confluence and Denton Tap
Road and in the Cottonwood Branch
flood plain upstream of the Denton
Creek flood plain, based on
existing topography.
Both of the computer models described above are
initiated at Cross Section 32150 in Denton Creek just
downstream of Denton Tap Road. 100-year flood
discharge at this point is 21,300 c.f.s. The computer
models are extended upstream of the Lincoln/Coppell
Project on Denton Creek and into the Villages of
Cottonwood Creek project on Cottonwood Branch so that
water surface profiles determined with proposed
conditions can tie into existing condition water
surface profiles upstream of the reclamation area.
Cross sections utilized in the Denton Creek analysis
were taken from the Lincoln/Coppell model. These
sections were modified where appropriate for recent
grading that was performed in the City Park and for
compliance with detailed topography available in the
Parks of Coppell property. The cross sections utilized
in the computer models of Denton Creek are submitted
separately with this report.
A detailed topographic map of the Parks of Coppell
Project west of Denton Tap Road was used to develop
cross sections prepared for our analysis of existing
100-year flood conditions in Cottonwood Branch. These
cross sections are shown on Exhibit A. This detailed
information permitted us to use additional
topographic
cross sections in the Cottonwood Branch model than were
utilized in previous studies.
This topographic map also permitted a more detailed
study of the interface of the Cottonwood Branch and
Denton Creek flood plains. The Lincoln/Coppell model
developed for Denton Creek assumed that Cottonwood
Branch discharges contributed to Denton Creek flooding
at Denton Creek cross section 32725. This appears to
be a reasonable judgement based on existing topography
and 100-year flood elevations. Cross section 32816, as
shown on Exhibit A, was selected as the downstream
cross section on Cottonwood Branch and is just upstream
of Denton Creek cross section 32725.
--5--
Existing topography in the Parks of Coppell was used to
prepare cross sections 32816 through cross section
34075 in model COEXPK of Cottonwood Branch. Cross
section 35170 was taken from the Villages of Cottonwood
Creek model where it is labelled cross section 5275.
Two cross sections at the upstream end of model COEXPK,
numbers 6710 and 8000, were also taken from the
Villages of Cottonwood Creek model. Cross section
locations are shown on Exhibit A. Cross sections
utilized in the computer models of Cottonwood Branch
are submitted separately with this report.
The 100-year flood discharge in the studied reach of
Cottonwood Branch is 7300 c.f.s, as used in previous
flood insurance studies. Computer outputs of existing
condition models DEEXPK and COEXPK of Denton Creek and
Cottonwood Branch respectively are given in Appendix A.
Limits of the 100-year flood plain and floodway
determined in these models are shown on Exhibit A.
IV. PROPOSED REC~.ANATION
The 'proposed area to be reclaimed is shown on Exhibit B
located in the map pocket in the back of this report. The
following computer models were prepared to analyze the
proposed flood plain conditions.
3. Model DEPRPK - This computer model determines 100-year
flood plain and floodway conditions in
the Denton Creek flood plain with
proposed reclamation as shown on
Exhibit B.
4. Model COPRPK - This computer model determines 100-year
flood plain and floodway conditions in
the Cottonwood Branch flood plain with
proposed reclamation as shown on
Exhibit B.
The proposed area to be reclaimed is shown on Exhibit B.
This area is outside the floodway. Floodway stations at
each cross section developed for proposed and existing
conditions are similar. Denton Creek cross sections 32250,
32305 and 32725 and Cottonwood Branch cross sections 32816,
32916 and 33016 are modified for proposed fills in the right
overbank areas.
-6-
One hundred year flood discharges used in the proposed
condition models are similar to the discharges used in the
existing condition models. Computer outputs of proposed
condition models DEPRPK and COPRPK of Denton Creek and
Cottonwood Branch respectively are given in Appendix B.
Table 1 presents 100-year flood water surface elevations for
existing and proposed conditions as well as 100-year
floodway elevations determined in the Denton Creek flood
plain models. A comparision of the 100-year flood
elevations for existing and proposed conditions shows that
the proposed fill area generates only very slight increases
in water surface elevation for this event. Also, the 100-
year flood elevation with proposed fill is below the 100-
year floodway elevations determined in the Denton Creek
model at each cross section studied, as shown in Column 5 of
Table 1.
Table 2 presents 100-year flood water surface elevations in
Cottonwood Branch for existing and proposed conditions and
100-year floodway elevations. Proposed fills are limited to
areas outside of the completed floodway and therefore, as
shown in Table 2, 100-year flood elevations with proposed
conditions are lower that floodway elevations at every cross
section studied. In addition 100-year flood plain and
floodway elevations in upstream cross sections are
essentially unchanged from elevations computed in the
Villages of Cottonwood Creek hydraulic models.
V. SUMMARY
Detailed HEC-2 computer models were developed and presented
herein that model existing 100-year flood conditions in
Denton Creek and Cottonwood Branch upstream of Denton Tap
Road. The analysis of existing conditions is prepared in
order to present a computer model representative of
topographical conditions now existing in the flood plain
resulting from numerous projects in the area in the last few
years.
Hydraulic models are also prepared for proposed reclamation
of the Denton Creek and Cottonwood Branch flood plains on
the south side of Cottonwood Branch west of Denton Tap Road.
The proposed reclamation is outside of the existing
floodway. Water surface elevations determined in the
proposed condition models are lower than 100-year floodway
elevations at each cross section studied.
-7-
TABLE 1: EXISTING AND PROPOSED 100-YEAR FLOOD WATER SURFACE
ELEVATIONS - DENTON CREEK
CROSS SECTION EXISTING FLOODWAY PROPOSED DIFFERENCE
CONDITIONS CONDITIONS COLUMN 3 & 4
1 2 3 4 5
32150 458.81 459.81 458.81 -1.00
32200 459.28 460.04 459.28 -0.76
32230 459.29 460.05 459.29 -0.76
32250 459.29 460.14 459,26 -0,88
32305 458.57 459.56 458.58 -0.98
32725 461.89 462,29 461.91 -0.38
33145 462.16 462.58 462.19 -0.39
33470 462.41 462.80 462.44 -0.36
34260 463.17 463.53 463.20 -0,33
34850 463.23 463.56 463.25 -0.31
34950 464.26 464.35 464.28 -0.07
35170 464.52 464.80 464.54 -0.26
36970 465.48 466.30 465.49 -0.81
39440 467.82 468.75 467.82 -0.93
-8-
TABLE 2: EXISTING AND PROPOSED iO0-YEAR FLOOD WATER SURFACE
ELEVATIONS - COTTONWOOD BRANCH
CROSS SECTION EXISTING FLOODWAY PROPOSED DIFFERENCE
CONDITIONS CONDITIONS COLUMN 3 & 4
i 2 3 4 5
32816 461.88 462.52 462.50 -0.02
32916 463.26 464.26 464.19 -0.07
33016 463.65 464.52 464.44 -0.08
33116 463.86 464.86 464.57 -0.29
33560 465.31 466.16 465.45 -0.71
34075 467.31 467.96 467.32 -0.64
35170 468.22 469.18 468.23 -0.95
6710 470.63 471.61 470.63 -0.98
8000 473.05 473.71 473.04 -0.67
-9-
Hydraulic response of the flood plain to the proposed
reclamation is in compliance with regulations of the Federal
Emergency Management Agency. In order that we may proceed
with construction of Parkway Boulevard and the High School
Access Road, we request on behalf of our client, ABQ
Development Corporation, that the City of Coppell review the
information presented herein and forward this information to
FEMA with an endorsement of our request for a Conditional
Letter of Map Revision for this project.
-10-
APPENDIX A
DENTON CREEK AND COTTONWOOO BRANCH
IO0--YEAR FLOOO PLAIN AND FLOODWAY
GINN, INC. CONSULTING ENGINEERS
June 21, 1988 RECEIVED
Jerry arc e', P.E. JUN 2 J88
Jerry Parche' Consulting Engineers
6001 W. Interstate 20, Suite 209, LB 32 ~pg~,l~E,I-.
Arlington, Texas 76016
Re: Denton Tap Road Improvements and the Parks of Coppell
Dear Mr. Parche':
This letter is in response to your letters of June 7 and 8, 1988
and questions raised in the meeting with ABQ Development on June
13, 1988. We will address the items in the June 7, 1988 letter
first.
The easements requested from Univest Development, some time ago,
were for the purpose of establishing a temporary working area in
which to complete the construction of the road improvements
within the existing R.O.W.. The only exception to this is
the slight encroachment of the property lines at the locations
where the recessed storm water inlets occur. The storm water
inlets will encroach the property line about a foot and a half,
and therefore we feel it is better to secure an easement around
the inlets now than waiting for future R.O.W~ or utility easement
dedications.
In the matter of the requested water line extensions, we agree
that water mains or services must be extended to the west side of
the road. However, the size of, location of, and developer
participation in these extensions must be determined prior to
adding them to the Denton Tap Road construction contract. We
have enclosed blue line copies of sheets 13 through 17 of the
paving plans for your use in laying out your proposed water mains
or service extensions to serve the ABQ property. According to
the subdivision ordinance, ABQ will be responsible for the entire
cost of these extensions, but under the prorata provisions of
the ordinance some reimbursement may be available if these
extensions are mains which will serve adjacent properties.
In our discussions with Mike Allen regarding the median openings
and left turn lanes, we agreed to show these as "future" with the
exception of the proposed opening at Mills Lane. We stated that
we had no objection to the locations of the left turn lanes and
median openings shown on the attached "Median-Left Turn Sketch"
dated 5-88, by Roberts & Dowdey Civil Engineers, as long .as
property owners on both sides of the road agreed on the
locations. We cannot include the construction of these
facilities in the Denton Tap Road Improvements unless the
17103 Prcsto, RnRd · S,ite 100 · IBIIR · Dall~.~.TexRs 75248 · Phone 214/24R-4900
property owners escrow the cost of them with the City in advance
of construction. Also discussed was the improvement of Hills
Lane by the adjacent property owners. The Mills Lane
intersection can be revised to conform to the future layout of
Mills Lane to the west if the property owners will coordinate
their efforts with us and give us the surveyed location and
design layout of proposed Mills Lane. The same applies to the
west side of the Parkway Blvd. intersection. It is our
understanding that you are currently preparing the Parkway Blvd.
layout on the west side of the intersection as we discussed so
that we may include the entire intersection in the project.
In response to the requests in your letter of June 8, 1988
concerning the floodplain issues associated with the properties
recently acquired by ABQ we understand by our telephone
conversation of yesterday that you have already begun addressing
the concerns you had regarding the appropriate hydrologic and
hydraulic modeling in paragraph A of your letter. In that
regard, we will stipulate that you use the modeling which has
been accepted by FEMA, but that you must also use your best
professional Judgment in considering other data which is more
recent and/or more conservative than that currently in use.
Regarding the hydraulic design requirements for the bridge
structure on Parkway Blvd. at Cottonwood Branch, the discharges
analyzed shall be those that are customarily analyzed for
projects of this type. The freeboard requirements shall be such
that a two (2) foot clearance be maintained between the proposed
base flood elevation and the low chord of the bridge structure.
The determination of allowable flow velocities will be based on
your best professional judgment considering the flow conditions
and soil conditions, and any concerns expressed by FEMA in their
review of your proposed floodplain reclamation models.
Items C and D of your letter shall be addressed by Ordinance No.
219, a copy of which is attached. For the interim period until
the new City Engineer comes on board and assumes the duties of
Floodplain Administrator, the acting City Engineer/Floodplain
Administrator, H. Wayne Glnn, P.E., shall receive your submittals
and coordinate the reviews mentioned in item E of your June 8,
1988 letter.
In response to your request of June 13, 1988 we are also
enclosing a blue line copy of the Bid Tabulation and the R.O.W.
Map for the project..
I trust that the above information satisfactorily addresses your
questions.
JCK/HWG/dsp
cc: Alan D. Ratliff
John C. Karlsruher, P.E.
File J-379, 241-044