ST8402-CS 890519 HANDWRITTEN MEMORANDUM
THE CITY WITH A
GINN, INC.
May 17, 1989
Mr. Russell Doyle, P.E.
City Engineer
City of Coppell
P.O. Box 478
Coppell, Texas 75019
CONSULTING
Re:
Denton Tap Road Improvements from Belt Line Road to Sandy
Lake Road, and from Sandy Lake Road to Denton Creek - FEMA
Approvals.
Dear Mr. Doyle:
This letter is in response to your Handwritten Memorandum of May
10, 1989, copy attached. Attached you will find additional
documentation including the Conditional Letter of Map Revision
for the Denton Tap Road bridge structures over Grapevine Creek,
which should complete your files regarding to the floodplain
aspects of the subject projects. Please note that the
Conditional Letter for the Grapevine Creek bridge structures
requires that as-built drawings, HEC-2 hydraulic models and
supporting data must be prepared and submitted to FEMA for
verification of compliance with the Conditional Letter as soon as
construction is completed. It is our intention to furnish these
services under special servi~ for ~h~ Droject, however you may
contract directI~--~i-~imT~-Horn and Ass~o6ia~s, Inc. for this
if you wish. Please let us know your intentions regarding the
foregoing as soon as possible.
On the advice of our Floodplain Hydraulics/Hydrology Consultant,
Kimley-Horn and Associates, Inc., there was no submittal prepared
or made for the widening of the Cottonwood Branch bridge
structure. Their opinion of the plans to widen the existing
bridge structure was that since the hydraulic cross section of
the bridge was not being changed, the affects on the floodplain
and base flood elevations would be negligible.
Please call me if you have any questions.
Sincerely,
John C. Karlsruher,
Project Engineer
PoEo
attachment
H. Wayne Ginn, P.E.
Ron Morrison, P.E. - Kimley-Horn and Associates,
File J-378, 379 (a:denfema)
Inc.
17103 Preston Road · Suite 100 · LB 118 · Dallas, Texas 75248 · Phone 214/248-4900
Federal Emergency Management Agency
Washington, D.C. 20472
coppoll, Texas - 81988
Dear Nayor Dugqan:
~is is ~n reference to a letter ],,~ o~p~ ~5, ;~. 7, s~mitt~
Hr. H. ~a~ne G~nn, P.E., C~t~ En~neer [or ~e C~ty off Cop~l, ~ch ~as
Eo~arded ~ us b~ our Req~on VI offff~ce, in ~h~ch ~e r~uest~ ~at ~e
F~era~ ~e~ency ~naqement A~ency (F~) rev~e~ a [~pla~n st~ ffo~ ~e
pr~s~ br~d~e ~ep~acement projec~ at ~nton Tap Road over Gra~v~ne Cre~
a~ ~e propos~ E~o~pla~n rec~at~on project on Grapevine Cre~ just
ups~eam of ~nton Tap Road. ~s letter addresses ~e pro~s~ bridge
replacement project ~le ~e upstre~ reclamation project is ~dress~
a serrate ~etter, ~[~ h~s.[etter, ~r. G~nn s~m~tt~ a fflo~p[a~n stud~
ent~t~ .F~la~n H~drau[[cs Stud~, Crater[ne Creek, Cop~ll, T~,~r~ dat~
Sept~er 22, 1987, prepar~ b~ PAHA-~e~mann & ~soc~ates, Incor~rat~
(no~ ~m~ey-Horn and ~soc[ates, ~ncor~rated), ~[ch ~ncl~ ~e ffo~[n~
~t~s~ a description o~ ~e ~odol~es us~ H~-2 h~draul~c ~els
· apsl p~ott~ cross sections7 a cr~s-sect[on location ~p~ a~ p~ott~ ~ater-
s~face prorates, We also rece~v~ a ~etter dat~ Janua~ 12, 1988, a~
~ley~Horn a~ ~soc~ates, ~nco~orat~. ~s ~o~at~on ~dress~ ou~
concer~ as ~scuss~ ~n our Janua~ 8, 1988 phone conversa~on
H~. ~derson.
After reviewing the submitted data, we have determined that the proposed
bridge replaceeent project mee~s the minimum floodplain management criteria of
the National Flood Insurance Program (NFIP). If the project is completed as
proposed, a revision to the Flood Insurance Study {FIS), Flood Insurance Rate
Map (FIRM), and Flood Boundary and Floodway Map (FBFM) for the City of Coppell
would be warranted. This revision would show a decrease in the Base (100-
year) Flood Elevations (BFEs), the regulatory floodway width, and the 100-year
floodplain of Grapevine Creek in the vicinity of Denton Tap Road. Future
revisions ~o the FIe, FIRM, and FBFM for the City of Coppell or future restudies
of the flood hazards in these areas could modify this deteL~uina~ion.
This determination is based on the 100-year flood discharges computed in the
effective FIe for your coomunity, and does not consider subsequent changes in
watershed characteristics that would tend to increase flood discharges. The
development of this project and other projects upstream could result in
increased flood discharges, which, in turn, could result in increased 100-year
flood elevations. Future rest~adies of your coumunity,s flood hazards, w~ich
would take into acco~ult the cumulative effects of development on flood discharges,
could establish higher 100-year flood elevations in this area.
Please note the requireuents for floodway revisions as outlined in Parc 65
of the NFIP regulations, Sect~Lon 65.7 (copy enclosed). The prol~sed floodway
represents a decrease in w~dth at several cross sections with respoct to the
current regulatory floodway in the City of Coppoll. When a floodway change is
proposed, a copy of a public notice distributed by the community stating the
community's intent to revise ~he floodway or a statement by the community that
it has notified all affected property owners and affected adjacent jurisdictions
must be submitted to FEMA. This requirement will have to be addressed when
requesting a map revision to reflect the effects of the completed project.
This coD~itional Letter of Map Revision is based on ~inimum floodplain ~an-
agement criteria established under ~he NFIP. Your community is resEonsible
for approving all proposed floodplain developments, including this request,
and for assuring that necessary ~e~nits required by Federal or State law have
been received. State and community officials, based on knowledge of local
conditions and in the interest of safety, may set higher standards for con-
struction or may limit development in floodplain areas. If the State of Texas
or the City of Coppell has adopted more restrictive or comprehensive floodplain
management criteria, these criteria take precedence over the minimum NFIP
requirements.
NFIP regulation 44 CFR 60.3(b)(7) requires co~munities ~artici~ating in the
Program to 'assure that the flood carrying capacity within the altered or
relocated ~ortion of any watercourse is maintained.= Without proper mainte-
nance, such as the regular clearing of a channelized stream, channel madifi-
cation projects will, in time, fail to function as designed, thereby recreating
the flood hazard that they were intended to mitigate. Therefore, u~on com-
pletion of the project, your community must uphold its responsibility for
assuring that the modified channel i~ maintained in order to preserve its
design function.
Upen completion of the proposed bridge replacement project, your community may
request a revision to the effective F~S, FII~M, and FBFN. The revision request
must include supporting da~a as outlined in the enclosed documents, Conditions
and Criteria for Ma~> Revisions and Conditions and Criteria for Floodway Revi-
sions and must address the requirements of NFIP regulation 65.7 as outlined
earlier. Compliance with the criteria outlined in these documents will
expedite FEMA~s review process, thus allowing the FIS, FI~M, and FBFM for your
community ~o be revised as appropriate, in a timely manner.
Should you have any questions regarding this matter, please do not hesitate to
contact the Chief, Natural and Technological Hazards Division of the Federal
Emergency Management Agency in Denton, Texas, at (817) 898-9127 or members of
our Headquarters staff in Washington, D.C., at (202) 646-2754.
Sincerely,
Chef, Risk Studies Division
Federal Insurance Administration
Enclosu~e~
cc~ ~. Carl V. AndeFson, P.E. Mr. H. Wayne ~inn, P.E.
Hro John Co ~arls=uher, p.E., Giun, Incorporated