FS9905-CS 99052605/26/99, WED 15:56 FAX 9722393820
Kimley-Horn and Associates, Inc.
9722393~20
DALLAS
001
VIA FACSIMILE
Fax no. 972°30434570 Su,, ~a~
127D0 ~lrk Csnlr81 Drive
No. of pages,J_ Dallas, Texas
75251
May 26, 1999
Ken Griffin, P.E.
Director of Engineering and Public Works
City of Coppell
P.O. Box 478
Coppell, TX 75019-4409
Coppell, TX
Re:
Final Review of CLOM'R for River Chase Elementary School
(Elm Fork of the Trinity River)
Dear Mr. Griffin:
We have completed our review of the Flood Study in Support of a Conditional
Letter of Map Revision for River Chase Elementary School in the City of Coppell,
Texas for the Elm Fork of the Trinity River prepared by Morrison Hydrology
Engineering Inc. dated May 1999.
Following are the initial review comments sent via facsimile to the City and Ron
Morrison on May 21, 1999:
1. Is the proposed condition HEC-2 model identical to the effective and existing
condition models? Please confirm.
2. Please explain the following items in the storage table (Table 2).
E:\HYDRO\projccts\06312402~'¢vicws\River~tl nal doc
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TEL 972 T/0 1300
FAX 972 239 3820
05/26/99 WED 15:56 FAX 9722393820 DALLAS ~ 002
and Associates, lnc,
a. What is the 48-acre tract and 1 O-acre tract? The report mentions the 10-
acre tract only. PIece provide either a drawing or an explanation,
The HEC-2 storage models reflect 7 cross-sections. The storage table
for the 48-acre tract reflects 8 sections while the table for the 10-acre
tract reflects 4 sections. Please explain.
3. Please provide cross-sections from both the existing and proposed storage
models so the proposed cut and fill areas can be easily identified.
These items were discussed with Ron Morrlson during a phone conversation on
May 24, 1999. His was response was the following:
The proposed condition HEC-2 models are identical to the effective and
existing condition models and were included to remain consistent with
standard CLOMR submittals. The project lies within an ineffective flow area
and no cross-sections in the effective FIEC-2 model cross the project site;
therefore, the proposed condition HEC-2 model does not reflect any changes.
The table included in the submittal is incorrect. The correct storage summary
table was faxed (see attached), This table should be included in the final
version of the report,
The storage calculations show 0% loss in storage for the 100-year design
flood and 4.77% loss in storage for the Standard Project Flood (SPF). The
calculations are based on the following;
a. Cross-sections were cut through existing and proposed site topography.
These cross-sections were incorporated into a new HEC-2 model
(outside of the FEMA HEC-2 regulatory model) and X5 cards were used
to set water surface elevations,
The following water surface elevations were used:
100-yr design = 444.82
SPF ~ 450.09
Based on the above comments and our final review, we request that ~e following
information be incorporated into the report:
l, Include tile correct table summarizing the storage analysis.
2. Provide cross-section printouts from the HEC-2 storage models for
existing and proposed conditions.
3. Add a paragraph explaining why this is a CLOMR request and not a
CLOMR-F-
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Kirnley-Hom
and Assoeiales, Inc.
4. Add a statement explaining that this study lies outside of the CDC regulatory
zolle.
5, Clarify within the report that the effective HEC-2 models were not revised as
part of this project.
6. Specify within the report text the proposed finished floor elevation and the
water surface elevation it is based on.
7. Add the site location to the existing and proposed floodplain maps in
Appendices 5 & 6.
8. Add a note explaining the hatched area shown on the proposed storage
computation drawing in Appendix 8.
Morrison Hydrology should submit two copies of the revised report to the City,
one of which will be returned to Kimley-Horn for a final review of the comments
described above.
Based on this review, the information provided in the report, and the information
received via phone, the proposed project meets City of Coppell requirements
reSarding floodplain encroachment. We recommend submittal to FEMA for a
CLOMR once these review comments are incorporated into the final report.
In addition, the grading proposed in this submittal should be referred to during
the plan review process by the Cily. The requested cross-sections should provide
useful information during this process.
If you have any questions, do not hesitate to call us at 972/770-1300.
Very truly yours,
KIMLEY-I. IORN AND ASSOCIATES, INC.
Michel le Evans
Reviewer
Proj~;t Manager
MRE/f~s
Ran Morrison, Morrison Hydrology Engineering. Inc. via t~csirnilc
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