FS9906-CS 990922 c Kimley -Horn
and Associates, Inc.
•
September 22, 1999 •
Suite 1100
Via Mail & Facsimile: (972) 370 -3570 801 Cherry Street
Fort Worth, Texas
76102 -6803
Mr. Ken Griffin, P.E.
Director of Engineering and Public Works
City of Coppell
P.O. Box 478
Coppell, TX 75019 -4409
Re: Review of Coppell High School
CLOMR for Cottonwood Branch
KHA No. 06312402
Dear Mr. Griffin:
Kimley -Horn and Associates, Inc. has completed the initial review of the Flood
Study in Support ofa Conditional Letter of Map Revision for Cottonwood Creek
at the Coppell High School in Coppell, Texas prepared by Morrison Hydrology
Engineering, Inc. dated August 1999. Our review comments are summarized
below.
1. An analysis of the valley storage for Cottonwood Branch should be included
in the report. The City Floodplain Management Ordinance specifies that no
reductions in valley storage for the 100 -year ultimate event are allowed in
Cottonwood Branch.
2. The ultimate condition model is based on cross - sections from the FEMA
effective model and flows and starting water surface elevations obtained
from the "City -Wide Storm Water Management Study ". The engineer
should verify that the flows and water surface elevations taken from the city
study is the most current information available.
3. The ultimate condition model ends at Section 34822, which is at the
upstream limits of the proposed development. The model should include
cross - sections upstream of the proposed development in order to determine
upstream impacts. Cross - sections included in the model for upstream
analysis should be from the most recently approved City model. Upstream
cross - sections should be added to both the existing and proposed condition
models.
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TEL 817 335 6511
MET 817 654 4266
FAX 817 335 5070
ppi■=.11 Kimley -Horn Mr. Ken Griffin, P.E., September 22, 1999, Page 2
and Associates, Inc.
4. The Manning's n -value in the right overbank has been lowered from 0.055 to
0.035 at Sections 33560 and 34075. The report states that this area is to be
maintained and will be mowed twice each year. Tree and brush removal is
also recommended in the report. A maintenance agreement should be
submitted to the City and included with the CLOMR request.
Kimley -Horn recommends that information described above be included with the
CLOMR submittal. An additional review will be required once this information
has been provided.
We appreciate the opportunity to be of continued service to the City of Coppell.
If you have any questions, do not hesitate to call.
Very truly yours,
KIMLEY -HORN AND ASSOCIATES, INC.
-eA
Paul D. Berg, P.E. Michelle Evans
Project Manager
PDB:pts
P:\ 06312402\INITIAL.DOC
Kimley -Horn 12700 Park Central Dr.
Suite 1800
and Associates, Inc Dallas, TX 75251
TEL 972 770 1300
FAX 972 239 3820
Transmittal
Date: September 22, 1999 Job. No: 063124002
To: Ken Griffin, P.E.
Director of Engineering and Public Works
City of Coppell
P.O. Box 478
Coppell, TX 75019
Re:
We are sending you
® Attached ® Sending the following via Mail
Shop Drawings 0 Prints /Plans 0 Samples Specifications 1=1 Change Orders
El Other:
Copies Date No Description
1 1 Floodplain Review for Coppell High School
1 More seen 1-hdd rci14 Fri I f\ €f;r C LOYY1P,
These are transmitted as checked below:
® For your use ❑ Approved as submitted ❑ Resubmit Copies for approval
El As requested ❑ Approved as noted ❑ Submit El Copies for distribution
For review and comment 0 Returned for corrections El Return 0 Corrected prints
Remarks:
Please call if you have any questions.
cc: Signed: Michelle Evans