FIRM-890910I.
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Kimley -Horn and Associates, Inc. 12660 Coit Road, suite 200, Dallas, Texas 75251 . (214) 386 -7007
Raleigh, Charlotte, Nashville, Virginia Beach, Washingbn, Dallas, Phoenix,
Septemt�e r 10, 1989 West Palm Beach, Tampa, Orlando, Ft Lauderdale, Vero Beach, Ft Myers, Stuart
Mr. Russel Doyle, P.E.
City Engineer
City of Coppell
P. O. Box 478
Coppell, Texas 75019
Re: Response to the FEMA Comments Regarding the FIS Review Study Completed
for the City of Coppell
Dear Mr. Doyle:
The purpose of this letter is to address concerns regarding the subject
study completed by our office. The attached letters from the Federal
Emergency Management Agency (FEMA) that were provided to us as information
copies outline a number concerns regarding the city response to the FEMA
Flood Insurance Study (FIS) revision. We have reanalyzed the study in
response to these FEMA concerns. The following are comments from FEMA and
our study changes:
1. FEMA pointed out that the FIS Review Study did not include the 10-
and SO- year floods for any of the streams analyzed. This will
result in the deletion of these profiles from the FIS. FEMA wants a
verification that this is the city intention.
The 10 and 50 year floodplain was not determined in the FIS Review
Study because FEMA did not include a detailed zone determination in
the FEMA study. However, after conversations with Mr. Matt Miller of
FEMA it was concluded that the city should have access to these
additional frequencies. As part of the ongoing city watershed
masterplan these additional frequencies will be determined and
provided to FEMA. They are not included with this submittal.
Building client relationships since 1967
Coppell
Sept. 10, 1989
Page -TWO-
2. F EMA
concluded that the
FIS Review Study
did not include all of the
Moore
Road Bridge cross
sections developed in the study for the Moore
Road Bridge revision. This was apparently
an oversight on our part,
and is
corrected in this
submittal. All cross sections used in the
Moore
Road Bridge study
are included in the
submittal.
3. According to FEMA the starting water - surface elevations for Grapevine
Creek and Denton Creek were determined using the HEC -2 tributary
option. This option assumes coincidential peak flooding of the two
streams. This approach is correct only when the two streams have
equal watershed characteristics. This approach is usually
conservative in determining flood levels. However, FEMA suggests
that another approach would be more appropriate. They suggest the
use of the slope area method to determine starting conditions. While
the slope area method is generally more appropriate in these cases it
can often produce results that are unconservative. In this particular
case we reviewed each stream to determine the most appropriate method
in the interest of city floodplain management. Since FEMA NFIP
Regulations encourage more stringent applications of floodplain
management they should have no problem with a more conservative
approach. Therefore, we completed a new analysis using the slope area
method for all streams in the city except for Grapevine Creek.
Grapevine Creek in the area affected by starting condition is
contained in an improved channel. So it would not affect the
floodplain or floodway. However, it would require higher structure
elevations adjacent to the channel.
4. FEMA requires that the city resolve the study differences between the
FIS Review Study and that prepared by Jerry Parche' for Parkway Blvd.
We have had a number of meetings with Mr. Parche, to discuss the
technical coorelation of his model and the FEMA resubmittal. At our
Coppell
Sept. 10, 1989
Page - THREE-
last meeting we agreed on a model that covered the area of Mr.
Parche's project. We have now corrdinated all the changes in the
Parche' model.
We have contacted Mr. Matt Miller of the FEMA Headquarters Office regarding
the time frame for submittal of these response items. He said that FEMA
had recieved a request from the city for an extension of the time allowed
to respond to the FEMA concerns and that the extra time requested was
agreeable to FEMA.
If we can provide further information please call me.
Sincerely,
KIMLEY -HORN AND ASSOCIATES, INC.
Ronald W. Morrison, P.E.
Senior Hydrologist
Attachments