Northlake WE P10C-SY 920601DO N A. TIPTON1 INC.
CONSULTING ENGINEERS
FLOODPLAIN HYDRAULICS STUDY
GRAPEVINE CREEK
Coppell, Texas
Prepared For:
NORTHLAKE WOODLANDS EAST NO. 12
Coppell, Texas
FLOODPLAIN RECLAMATION
JUDY TROTH - PARSONS 3.77 ACRE TRACT
Prepared By:
DON A. TIPTON, INC.
6330 Belt Line Road, Suite C
Garland, Texas 75043
214-226-2967
Project No. 3246.hyd/40
PURPOSE
This submittal is for the purpose of seeking a revision to the
designated floodplain for a portion of Grapevine Creek in the
City of Coppell, Texas. One project is documented herein: a
proposed reclamation just upstream of the St. Louis and
Southwestern Railway right-of-way. An 3.77 acre tract of land
owned by Judy Troth-Parsons is the subject tract, with Don A.
Tipton, Inc. acting as design engineers. Fill is to be placed in
the left overbank area, from stream station 156+30, at the up-
stream side of the St. Louis and Southwestern Railway bridge, to
stream station 160+70, the north property line of the Northlake
Woodlands East No. 12. The proposed fill will result in a
reclaimed area of approximately 013 acres.
HYDROLOGY
Discharges used for the current analyses are those of the
effective Flood Insurance Study (FIS) for Grapevine Creek in the
City of Coppell, Texas. The 100-yr mean recurrence interval
discharges have been used to evaluate the effects of the proposed
project. More-specifically, the 100-yr discharge is 11,000 cfs
through the project areas.
HYDRAULICS
Hydraulic investigations of this study were conducted with the
use of the backwater computer program HEC-2 Water Surface
Profiles, developed by the US Army Corps of Engineers (Hydrologic
Engineering Center, Davis, California, May 1984 update).
Evaluation of the proposed project has resulted in the generation
of four HEC-2 computer models and other support materials, which
are included as the following appendices:
Appendix 1 - the effective HEC-2 computer model, with ultimate
discharges as per Kimley Horn Co. (existing
conditions);
Appendix 2- the effective HEC-2 computer model with added
sections to produce an extended FIS model of
existing conditions;
Appendix 3 - a proposed conditions HEC-2 computer model for the
proposed floodplain reclamation;
Appendix 4 - a proposed conditions H5C-2 computer model to show
equal conveyance;
Appendix 5 - a comparison chart of Appendix ~2 and Appendix ~3,
for storage loss data;
Appendix 6 - platted cross sections for both existing and
proposed conditions;
Appendix 7 - comparison profiles of the 100-yr water surfaces
for the existing and proposed conditions;
Appendix 8 - Floodplain work maps.
The original effective FIS model was obtained from the Fort
Worth, Texas office of the US Army Corps of Engineers. This
model was then modified by Kimley Horn to produce the extende~
FIS model contained in Appendix 1.
The existing conditions of Grapevine Creek is modeled usin~
Manning's "n" values for the overbanks ranging from 0.06 to 0.07.
Through the project in this study, an "n" value of 0.05 is used
for the channel.
Channel velocities occuring downstream of the project area in the
existing condition scenario range from 6.05 to 9.24 fps. The
minimum channel velocity occurs at stream station 155+20, and the
maximum at stream station 153+50. In the region where the recla-
mation action is proposed, existing condition channel velocities
vary from a minimum of 4.19 fps at stream station 164+80 to a
r. aximum of 7.13 fps at stream station 156+60.
RESULTS
Comparisons of the output tables of Appendices 2 and 3 indicate
that both scenarios of proposed conditions result in water
surface elevations in general agreement with the existing
conditions represented by the extended FIS model. The
comparisons show no increase in water surface elevations and
r. inor differences in the velocities.
CONCLUSIONS AND RECOMMENDATIONS
The proposed floodplain reclamation are documented and
technically supported hereon. Additionally, construction plans
for each project are provided for review and clarification.
2
It is recommended that the proposed project be approved for
modification of the designated floodplain and regulatory floodway
for Grapevine Creek within the City of Coppell, Texas. It is
also recommended that any buildings constructed along the stream
be constructed such that the finish floor elevations (including
basements) be placed a minimum of 2 ft above the 100-yr water
surface elevation as shown in the extended FIS model of this
study or the Master Drainage Plan for the City of Coppell,
whichever is greater. The provisions of the proposed City of
Coppell Floodplain Management Ordinance also are applicable to
the projects addressed in this study.
3
APPENDIX 1
GRAPEVINE CREEK - COPPELL, TEXAS
EXISTING CONDITION HEC-2 COMPUTER MODEL
WITH ULTIMATE DISCHARGES AS PER
KIMLEY HORN CO. (DAT 1)