Big Cedar-CS 910909FILE COP11'
P.O. Box 478
Coppell, Texas 75019
214-462-0022
Mr. Matthew Miller, P.E.
Risk Studies Division
Federal Insurance Administration
Federal Emergency Management Agency
500 C Street, SW
Washington, D.C. 20472
Re:
city of Coppell Conditional Flood Insurance Study
Revision for Tributary G-1 to Grapevine Creek as
a Result of a Proposed Floodway Fringe Development
Dear Mr. Miller:
This letter will present information for your review relative to a
proposed fill project in the Tributary G-1 flood plain. This
project involves the establishment of a detailed flood plain and
floodway and proposes fill outside of the established existing
floodway.
This report has been reviewed by Morrison Hydrology/Engineering,
Inc., for the City and is recommended for approval, assuming that
the requirements are met for a Corps of Engineers 404 Permit which
is presently being reviewed by the Corps. (See attached letter
dated 9/4/91).
We request that FEMAconsiderthis conditional request and provide
a response as soon as possible. If you have any technical
questions concerning this submittal, please direct them to Goodwin
& Marshall, Inc., at (817) 429--4373. For administrative questions,
please call me at (214) 393-1016.
Thank you for your attention to this matter.
Sincerely,
cc:
D. Matthew Goodwin, P.E.
Ron Morrison, P.E.
msd/gch/bhj
~OBRISON HYDROLOGY
520 AVBN~E H BAST, SUITE 102
ARLI~ON, TEXAS 76011
September 4, 1991
Ms. Shohre Daneshmand
Acting City Engineer
City of Coppell
P. O. Box 478
Coppell, Texas 75019
Re: Review of:
Floodplain Analysis for a portion of Tributary G-1 of
Grapevine Creek City of Coppell, Dallas County, Texas
by Goodwin and Marshall, Inc. of Fort Worth, Texas
Dear Ms. Daneshmand:
This is a follow-up letter to our previous review letters of
July 27 and August 5 1991, same subject. We have received a
copy of the FEMA submittal for this project. This report
addressed most of our concerns with the previous submittals.
It is our understanding that Goodwin and Marshall, Inc. have
contacted the Fort Worth District Corps of Eugineers and
requested a Section 404 Permit as required by Section 4.C.g
of the Coppell City Floodplain Management Ordinance.
When a plat is provided it should be reviewed regardin~
information to be contained on the plat related to the flood
plain. These are fully explained in the Ordinance. One of
the most important items is to show the lowest finished floor
of all construction elevated to a minimum of two (2) feet
above the FIS base flood elevation or to one (1) foot above
the design base flood elevation whichever is higher.
Conditional upon a favorable response from the Corps of
Engineers 404 Permit we recommend approval of this report
and suggest that you send it to FEMA for a Conditional Letter
of Map Revision as per the City Floodplain Management
Ordinance.
Coppell Review
September 4, 1991
Page -2-
We have attached a sample letter that might be used as a
guide in submitting the report to FEMA. We will be glad to
provide additional information if needed.
Sincerely,
Senior Hydrologist
Attachment
FLOODP~ ANALYSIS
for a Portkm of
TRIBUTARY G-I at GRAPEVINE CR~Z~uc
City of Coppelk DMlm Comity, Tm
Fred Joyce - Mary Myers Entmpds~, Inc.
and
August, 1991
0ODW] l
6001 Blidge Strcct, Suitc 100
Fort Worth, Tggm '76112
'?.-~' ~. r :' :". %¥:"
FLOODPLAIN ANALYSIS
for
TRIBUTARY G-1 of GRAPEVINE CREEK
City of Coppell, Dallas County, Texas
TABLE OF CONTENTS
Parc Number
INTRODUCTION .......................................................... 1
Project Location ........................................................ 1
ENGINEERING METHODOLOGY ............................................ 2
General ............................................................... 2
H~h'olo~c Anal~is ...................................................... 2
Methodology ...................................................... 3
Existing Conditions Model ............................................ 4
Hydraulic Analysis ....................................................... ~
Existing Conditions ................................................. ~
Proposed Improved Conditions ........................................ 6
Floodway ......................................................... 8
DISCUSSION .............................................................. 8
SUMMARY ............................................................... 9
CONCLUSION ............................................................ 10
TABI.FS
TABI.F. ONE - Peak Discharges at the Confluence of
Tn'buta.ry G-1 and Grapevine Creek .......................................... 4
TABLE TWO - Existing & Proposed Improved Conditions 100-Year Water
Surface Elevations and Velocity Calculations ................................... 7
TAB!~ OF CO~ (Continued)
FIGURES
Figure 1 ...................................................... Location Map
Figures 2 through 11 .................................... Tn'butary G-1 Crms-Sectiom
Figure 12 ...................... 100-Year Water Surface Profiles for Existing Watershed
Plate 1
Plate 2
Plate 3
PLATES
.................................. Watershed Area Map for Tn'butary G-1
........................ Exis~g Conditions 100-Year Floodplain Delineations
............... Proposed Improved Conditions 100-Year Floodplain Delineations
APPENDIX A ............................. Hydrologic Analysis for Existing Conditions
Watershed; 10-, 50-, 10(L, & 500-Year Frequency Events
APPENDIX B ......................... Existing Conditions Hydraulic Model & Results
APPENDIX C ................. Proposed Improved Conditions Hydraulic Model & Results
APPENDIX D ................................ Floodway Hydraulic Model and Results
APPENDIX E ...................... Floodway Model with Proposed Improved Conditions