Stratford Manor-CS 970605O'B ienl ll i fi
r~ ~, Tex~ 75234
Ph.: ~,~ 24,-0336
Fox: g7 241-0370
H~r~gcs/Hyd~y
C~ EnglM~fing
C~
June 5, 1997
Hrs. Jeanette Auerbach
Cambridge Hanor Homeowners Association
625 Ca~bridge Hanor Lane
Coppell, TX 75019
RE: Floodplain Evaluation of Denton Creek with Respect to
Proposed Stratford Manor Addition
Dear Jeanette:
At your request I have reviewed the following:
I mapping and information which you provided with regard to the subject
project,
I Coppell Floodplain Ordinance, and
I North Central Texas Council of Governments (NCTCOG) Corridor Development
Certificate (CDC) Manual.
I have the following preliminary observations:
.~-~,~ ~-1)~ The proposed project may he (at least partially) within the CDC
'._5,T,~v-~ 'o'~ regulatory zone. Any project within the regulatory zone requires
'~'~_'~ 2'~..J~ on/_processing a permit through NCTCOG.
~ i~ s~'~ 2) The Coppell Floodplain Ordinance states that valley storage may not be
·. ""t-~reduced for drainage areas in excess of 100 square miles. ~/ith headwaters
~':~*kt~,~,~': near Bowie, Texas, Denton Creek drains an area well in excess of 100
r.~ ~< ' ..~:-. c square miles. The preliminary plat indicates reclamation of nearly all of
~ ...... · ,,~..~ ~.,:, ~ ~he floodplain on the property with no apparent co~pensation proposed for
- ~ . .,~x3~ The Ordinance also states that a proposed development may not increase, the
;,¢ '~,~ ~' :; water surface elevation of the design base flood (based on a fully
~. ,~.a .-~. ~"~ urbanized watershed) l/ith the loss of as much conveyance as appears to
'~ ......~%'-~.~be proposed, it is 'doubtful that the project would not result in an
(~' :., ..~ ~;~ '- ~-~ increase In the water surface.
_ ~ ,~ ,~.i¢.~ .... 4) The Ordinance also states that the floodplain adsintstrator =ay restrict
~'~ ~ .~.~,.~. or prohibit uses of the floodplain ~Ltch result in damaging increoses in
~..~-~ ~ erosion or in flood heights or velocities. The reclamation of floodplain
>~ without compensation of conveyance virtually always results in increased
~'~-'~'~ ;"~ ~' channel velocities. The hydraulic ~odel should be reviewed to verify that
' ~'~-~ '~ velocities will not be increased to erosive levels.
~trs. Jeauette Auerbach
June 5, 1997
Page 2
r ---- .~ ~.~,~_._5.) Recently, the Corps of Engineers significantly modified "section 404"
nationwide pemit number 26 and other permits which may affect this
~!~? ~ property. The effect of the modification was to apply much more control
i>~t to the potential loss of wetlands and waters of the United States. I have
,, attached a copy of the final rule as well as a copy of an interpretive
--. ~r~ letter from the Corps Fort Worth office. Due to the profound impact of
;~. the new regulations, it would be most prudent for a developer to start the
404 permitting process at the beginning of the project, to assure that the
proposed development meets the necessary requirements.
6) Since the project appears to be at the prelimfnary platting and zoning
stage, specific plans likely have not been prepared. However, with the
~*~' ~-~ submittal of a final plat, the City requires the developer to provide
,..~.~ plans and specifications for the proposed project. Per the Ordinance, the
developer will also need to request a conditional letter of map revision
..~.~.~ (CLOHR) from 1~ for any proposed modification of the floodplain. It is
advisable to obtain copies of these documents when they become available,
~ 'c"~- to review the proposed project in terms of what impact it may have on
'.~u~-~'~- Cambridge Manor Estates. At your request, I will gladly review and
comment on these documents on behalf of the Homeowner's Association.
If you have any questions or require further information, please do not hesitate
to call.
Sincerely,
O'BRIEN ENGINI~ING
m O'Brien, P.E.
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