Villages C LOMR-SY 900216 Villages of Coppell
Phase III
Coppell, Texas
Existing FloOdplain Study
~ FEBRUARY, 1990
I,
CONSULTING ENGINEER$, INC.
il Dallas, Texas
! (214) 739-4741
NATHAN D. MAIER
CONSULTING ENGINEERS, INC.
February 16, 1990
Mr. Russell Doyle
City of Coppell
P.O. Box 478
Coppell, Texas 75019
Re: Villages of Coppell, Phase III
NDM Job No.: 84-10-054
Dear Mr. Doyle:
Per your letter of January 29, 1989, Nathan D. Maier Consulting Engineers, Inc. (NDMCE), has prepared
-- this study which shows the existing flood conditions for the referenced project.
This study represents our understanding of the best available data for the Elm Fork Trinity River and
Denton Creek. We respectfully request that the City of Coppell, as floodplain administrator, review the
-- submitted data to insure its compliance with the FIS, FIRM, and Coppell's Floodplain Management
Ordinance.
-- If you have any questions, please feel free to call me.
Sincerely,
NATHAN D. MAIER
CONSULTING ENGINEERS, INC.
~illiam I. ~allace, P.E.
WL~/rdp
Three NorthPark/8800 N. Central Expwy./Suite 300/Dallas, Texas 75231/(214) 739-4741
VILLAGES OF COPPELL
- Phase III
EXISTING FLOOD CONDITIONS
Project Description
The Villlages of Coppell, Phase III, is a combined 23.8± and 17.1±acre tract in the City of Coppell. The
project area is located north of Sandy Lake Road and south and west of Denton Creek. The existing
property was partially filled as a portion of the Lakes of Coppell project. The property is impacted by
both the Elm Fork Trinity River and Denton Creek. The intent of this report is to define the current
floodplain conditions for the property.
'- Existing Floodplain C0nditi0n~
Elm Fork Trinity River -- The Elm Fork Trinity River impacts the referenced property along the eastern
property boundary. The hydraulic model, provided in Appendix A, was developed to reflect the ultimate
100-year flood conditions as required by the City of Coppell's Floodplain Management Ordinance. The
HEC-2 model was developed by the Corps of Engineers for the Reconnaissance Study on the Trinity
Rivers and reflects existing hydraulic conditions. Hydrologic computations were perfromed using
NUDALLAS to determine 100-year discharges for ultimate development of the contributing drainage
basins. The resulting ultimate condition discharges were inserted into the hydraulic model to provided
flood profiles for the ultimate floodplain elevations for this 100-year event. Table I provides a summary
of these ultimate elevations for the 100-year event.
TABLE 1
Elm F{)rk Trinity River
ULTIMATE
CROSS ULTIMATE 100-YEAR
SECTION Q (CFS) ELEVATION
1000+40 58,400 447.59
1030+60 61,900 448.97
1060+80 61,900 451.95
First floors of residences will be based on one foot above the ultimate flood elevations provided in Table
1.
Denton Creek - The Denton Creek flood profiles are controlled by the Elm Fork Trinity River to cross
section 184+40. Water surface elevations are based on the most recent hydraulic models available for
Denton Creek. These recent models show that the existing 100-year flood profile will control on Denton
Creek. Table 2 provides the existing 100-year water surface elevations from file "DCEXIST."
TABLE 2
Denton ~reek
100-YEAR
_ CROSS DISCHARGE EXISTING
SECTION ELEVATION
18440 20,600 452. i0
19330 20,600 452.23
19930 20,600 452.23
21560 20,600 452.38
22370 20,600 452.56
23800 20,600 452.96
24700 20,600 433.44
25530 20,600 453.65
First floor elevations will be established at 2 feet above the existing 100-year elevations provided in
Table 2.
- FIo0dplain Limit~
Plate I shows the 100-year floodplain limits as previously pro.vided in Tables I and 2 or the Elm Fork
Trinity River and Denton Creek, respectively. To the best of our knowledge, these data represent the
best available data for these flooding sources for the 100-year events.
APPENDIX A
Elm Fork Trinity River
ULTIMATE 100-YEAR MODEL
D2ELMFU
- APPENDIX B
Denton Creek
EXISTING 100-YEAR MODEL
- D2EXIST
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Three NorthPbTk / 8800 N.Central Expwy. / Suite 300
Dallas, Texas 75231 / (214) 739-4741
design
drawn
sca
date
notes
C'
/Z - 48-89
job no.