Villages C P3&4-CS 920114MORRISON HYDROLGY/ENGINEERING, INC.
FILE COPY
~20 ~V~IO~ H ~ SU.Z*2~ .102
~ (8~7) 640-4554
·
January 14, 1992
Mr. Ken Griffin, P. E.
City Engineer
City of Coppell
255 Parkway Blvd
P. O. Box 478
Coppell, Texas 75019
Re: Review of Elm Fork of Trinity River and Denton Creek, City
of Coppell, Dallas County, Texas Floodplain Reclamation
Study, Village of Coppell Phases 3 & 4 by Don A. Tipton, Inc.
of Garland, Texas
Dear Mr. Griffin:
This letter constitutes a review of the subject report for
compliance with City of Coppell Ordinance 87390, often referred
to as the "Floodplain Management" Ordinance.
The following comments we offer regarding this review:
1. According to article 4 paragraph e the report must
demonstrate that at any point in the city, the cumulative
effects of the proposed development when combined with all
other existing and approved development "Will not increase
the water surface of-~the design base flood". This means
that the 100-year water surface of the ultimate discharge
used in the existing condition watershed must be less than
the 100-year water surface of the ultimate discharge
applied to the proposed development.
In the case of this project the requirement has not been
met. There is a 0.01 foot increase in the Trinity River
elevation and a 0.02 foot increase in Denton Creek
according to the report. It is our understanding that the
city considers these small increases as unacceptable.
2. A review of Map 19 and the preliminary FEMA FIS attached
shows that the project area is very close to a floodway.
We recommend that the location of this floodway be shown in
the report to verify that no floodway encroachment exists.
Mr. Ken Griffin
January 14, 1992
Page -2-
3. The subject report refers to a floodplain delineation
developed as part of an earlier study by Nathan Meir and
Associates. This floodplain does not match the latest
floodplain delineation or elevation shown in the latest
FEMA FIS Revision. We commend that the true floodplain
line be shown.
4. Article 4 e-2g requires that all necessary permits must be
obtained prior to granting project approvals. A request
has been sent to the Corps of Engineers requesting a 404
determination for this project. As yet, a reply has not
been received.
5. Article 4e-2f requires that any floodplain revisions must
be submitted to FEMA for approvals. The attached FEMA
checklist is provided which shows additional items needed
for this project to comply with FEMA requirements.
6. We noticed that at least one of the cross sections shows
the toe of fill extending past the property line. We
recommend that this be coordinated with the property owner
of the adjacent property.
7. It is our understanding that there is some erosion
protection work being completed in this area by the place-
ment of rock. We recommend that the effects of this work
be considered in the report.
We will be glad to explain this review further is needed.
Sincerely,
MORRISON HYDROLOGY/ENGINEERINg, INC.
Ronald W. Morrison, P. E.
Senior Hydrologist
Attachments 3
MATCH SHEET~O
insurance asem or call the Nationat Flood tn,L:r3nce Prosram at t8001 638-b620.
APPROXIMATE SCALE
1000 0 1000 FEET
NATIONAL FLOOD INSURANCE PROGRAM
FIR8
FLOOD INSURANCE RATE MAP
oncI " --
STREET ,INDEX
CITY OF
COPPELL,
· DALLAS~ AND DENTON COUNTIES
· " ONLY pANEL PRINTED
"- PRELIMINARY
DEC 1 8 1991
COMMUNITY-PANEL NUMBER
480170 0010 E
MAP REVISED:
Federal Emergency Management Agency
DEWBERRY & DAVIS
TRIM
I.... '~ CORPORATE, LIMITS
THIS AREA PROTECTL~,'ROM THE 100-YEAR FLOOD
BY LEVEE, DIKE, OR OTHER STRUCTURES SUBJECT TO
FAILURE OR OVERTOPPING DURING LARGER FLOODS,
'.ONE X ...... -.
)ZONE X
· - --.~OUNTY BOUNDARY '- ' DENTON COUNTY
DALLAS COUNTY
ELNa.
'h REFERENCE ELEVATION
:: ., !l MARK IN FT. (NGV[:
!~ · RM 196.. 467.22
' ~[~ RM 198 460.91
~ ZONE
, -' .... BRACEBRIDGE
-- , DRIVE ~ ','t CIRCLE ] ~ RM 200 .. - 510.71
Z ~ ~ ' -~ ~ ' / ' ' t~-~CHESHIRE
'~.80,,F i( '~'<.C ~Nati(~nal Geodetic Vertical Daturr
~. =:l PARKWAY BOULEVARD
'ZONE
WILLOW LANE ~ ~-; 3 ~
~KE ~! !~ , I SANDY ~KE ROAD
, ZONE X ~ -
'
(~'
ZONE X
Federal Emergency Management Agency.
Washington, D.C. 20472
Communl~7: ........ -
FOR REVI$ION$ TO FLOOD INSURANCE STUDIES AND
NATIONAL FLOOD INSURANCE PROGRAHHAP$
.. Date:
Requestor: _
The items'checked below in Column I are required to process the request for a
revision to the National Flood Insurance Program (NFIP) maps. Items checked
~n Column'2 have been received and should not be resubmicted unless specifi-
cally,requested. '
(1) '(2) ·
Required Received
1. A description of =he nature and extent of =he revision
request. "
~// 2. Community approval of the revision request.
~'/ 3. Abrief statement describing the methodology used to
determine the hydrologic and/or hydraulic parameters.
v/ ~. New/r.v~s.d hydrologic anal~,es C computer models- input'
and ~utput and back-up calculations for input parameters).
5. Hydraulic backwater models of the 10-, 50-, 100-, and 500-
year floods for =he following:
~/ a. Duplicate of the effective Flood Insurance Study
(FIS) model .
b. Corrected effectiv~ Fig model
----~ c. Existing conditions
6.' Floodway hydraulic backwater models of the following:
a. Duplicate effective
b. Corrected effective
~ c. Existing conditions
7. Map of the community's current corporate limits
8. Topographic mapping of the entire area covered by the
existing conditions model, indicating ~he locations of all
cross sections used in the.hydraulic model and delineating
the following:
Required Received
~/~ ~; ,, a. The revised 100- and 500-year floodplain boundaries
~/ b. The revised floodway boundary
9//. 9. Annotated NFIP.maps delinea=in$ =he revised 100- and 500-
year floodplain boundaries, 100-year floodway boundary,
base (100oyear) flood.elevations, cross sections., stream
alignment, roads and'roadnames, and corporate limits.
v'/ -- 10. AnnoTated FIS Flood Profiles depid~ing the revised 10-, .....
50-, 100-, and 500-year flood elevations. ..
%/ 11. Annotated FIS Floodway Data table(s) with revised floodway
data.
12. "As-built" plans
, certified by a registered professional engineer.
13. Certification by a registered professional engineer or
" soils engineer that fill placed meets the requirements for
95% compaction.
la. Certification from a Federal agency or registered
professional engineer indicating, structural flood
protection measures are adequately desi~ne~ and will be
maintained to withstand a 1001year flood event.
15' An operation and maintenance plan for any structural flood
protectio~ measures.
16. Written statement from the community indicating =ha= they
will accept ultimate responsibility for maintenance of a
structural flood protection system.
17. Study that addresses interior drainage for any area
protected by a levee or dike system.
18. Other: