FS9901-CS 991101h= Halff Associates
ENGINEERS ° ARCHITECTS · SCIENTISTS
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8616 NORTHWEST PLAZA DRIVE
DALLAS, TEXAS 75225
(214) 346-6200
FAX (214) 739-0095
November 1, 1999
AVO 17669
Mr. Kenneth M. Griffin, P.E.
Director of Engineering and Public Works
City of Coppell
P.O. Box 478
Coppell, Texas 75019-4409
RE: Comments by Kimley-Horn and Associates, Inc. on CLOMR for Windsor Estates
and DeForest Court
Dear Mr. Griffin:
Halff Associates, Inc. has reviewed the comments made by Kimley-Hom and Associates, Inc. for
the Conditional Letter of Map Revision for Windsor Estates and DeForest Court, and would like
to offer the following response to those comments:
In the Corrected Effective model of the CLOMR, the Split Flow Routine of the HEC~2
program was used to analyze the conditions in which flow crosses the Dallas Gun Club Road
(weir) from the Denton Creek flood plain into the Elm Fork of the Trinity River flood plain.
Weir coefficients, location, length, and elevation, are described on the WS (Weir Parameter
Data) and WC (Weir Coordinate Data) cards of the Split Flow Routine. The reduced
discharges downstream calculated by the HEC-2 Split Flow model were also used for the
Revised (Proposed) Conditions model in the CLOMR. The discharges that splits into the Elm
Fork flood plain is the difference between tlte total peak and resultant peak discharge after the
split flow calculation (see attached table).
We have looked at our exhibits and agree that we show our floodways outside the 100-year
and 500-year floodplains. Changes to these exhibits to show the correct location of the
floodway will be made before final submittal to you and FEMA.
Evaluation of ultimate conditions for Windsor Estates in the form of a Corridor Development
Certificate Application was submitted to the City in July 1999. Approval from the Corps of
Engineers is still pending. It is our understanding that if the Corps cannot complete the
review in 30 days, the District will send an letter explaining the delay. Has the City received
such a letter? For DeForest Court, the application will be submitted upon owners approval to
proceed with the CDC application.
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'll
h, Halff Associates
ENGINEERS · ARCHITECTS · SCIENTISTS
PLANNERS ° SURVEYORS
Mr. Kenneth M. Griffin, P.E.
Director of Engineering and Public Works
City of Coppell
November 2, 1999
Page 2
If you have any questions or comments, please feel free to contact me at (214) 346-6220 or
Russell Erskine at (214) 346-6225.
Sincerely,
HALFF ASSOCIATES, INC.
Walter/~E. Si~pwith; E
Vice-President
cc: Kelly Jordan
Split Flow Comparison
100-Year Discharges
.... Denton Creek Split FloWLost
· S~ . :T0tel. Flow DIscharge to Elm FOrk'
0 20600 10277.1 10322.9
1 20600 10277.1 10322.9
1.1 20600 10277.1 10322.9
2 20600 10277.1 10322.9
3 20600 10277.1 10322.9
4 20600 10277,1 10322.9
5 20600 10277.1 10322.9
6 20600 10277.1 10322.9
7 20600 10277.6 10322.4
9 20600 10622.9 9977.1
10 20600 11630.4 8969.6
11 20600 12776 7824
12 20600 15466.9 5133.1
13 20600 20600 0