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July 26, 1991
Ms. Shobre Daneshmand
Actin~ City Engineer
City of Coppell
P. O. Box 478
Coppell, Texas 75019
Engineering
Re: Review of:
Floodplain Analysis for a Floodplain Development Permit
for a portion of Tributary G-1 of Grapevine Creek City
of Coppell, Dallas County, Texas by Goodwin and
Marshall, Inc. of Fort Worth, Texas
Dear Ms. Daneshmand:
The subject study is a request for a Floodplain Development
Permit for property which lies in an area currently shown as
Zone ~ on the present FEMA FILM. The update of the current
FEMA FIRM is presently under review by FEHA. This update
shows the subject area in a Zone A flood plain.
According to the City Floodplain Ordinance No. 87390, Section
4B (11) The Floodplain Administrator must "Require Floodplain
Development Permits for all .... developmenC in floodplain
managemenc areas of ~he CitT". Flood management areas are
defined by the ordinance as "Ail floodplain lands wichin ~he
jurisdiccion of ~he city whether or no~ =he land is
iden£ified special flood hazard area (FEMA floodplain)".
Section 4B (ll)(a) states that the floodplain administrator
must "assure tha~ conditional approvals are received from
F£HA before a Floodplain Development Permi= is issued."
The ordinance is very clear that all flood plain projects
whether in a FEMA floodplain or an undesignated floodplain
must obtain FEMA conditional approvals before the city can
issue a Floodplain Development Permit.
Review /
July 2~, 1991
Page -2-
If the applicant wishes to request a variance from this
procedure Section D of the ordinance addresses the procedure
for obtaining a variance. The city council serves as the
appeal board in hearing such variances. The council may
grant a variance if the applicant provides the following:
1) Showing a good and sufficient cause
2) A determination that failure to grant the variance would
result in exceptional hardship to the aPPlicant; and
3) A determination that the granting of a variance will not
result in increased flood heights, additional threats to
public or conflict with existin~ local laws or
ordinances.
Our understanding is that the project would not proceed if a
FEMA Conditional Approval must be obtained before a
Floodplain Development Permit is issued. For this reason we
contacted you before continuing with our review. In your
absence Mr. Gary Seib authorized us to continue the review.
The following is a detailed review of the request with
appropriate comments for additional information.
1. Section 4.C.g requires the applicant to obtain all
necessary permits from other agencies. This includes the
Corps of Engineers 404 Permit. This was not addressed in
the subject study. The applicant should either obtain a
wetland determination from the Corps or state that he has
completed this determination and found no jurisdictional
wetlands impacted by the project.
2. The applicant has chosen to use a Peak-on-Peak method to
start the hydraulic model. That is the model ass,,mes that
Grapevine Creek and the subject Grapevine Creek Tributary
both have a lO0-year flood peak at the same time. While
this is conservative in establishing flood levels for
construction in the area it is not usually conservative in
evaluating velocity increases. Also, FEMA does not accept
this approach when the watersheds are vastly different in
size such as the case here.
We recommend that the applicant review the model using the
Slope Area Method for the 100 year flood to determine if
it has an adverse impact. We do not believe that this is
asking too much since FEMAwill require this when it is
submitted to them.
Review ~ ~
July,~l~, 1991
Page -3-
Since a plat was not provided with the report we could not
comment on this. However, the applicant should be aware that
there are a number of requirements regarding information to
be contained on the plat related to the flood plain. These
are fully explained in the Ordinance. One of the most
important is to show the lowest finished floor of all
construction elevated to a minimum of two (2) feet above the
FIS base flood elevation or to one (1) foot above the design
base flood elevation whichever is higher.
We will be glad to provide additional information if needed.
Sincerely,
MORRISOMIIFDRDLO6T/A~Ii~INEERIMG, INC.
Ronald W. Morrison, P.E.
Senior Hydrologist