ST8601-CS 900827GINN IN('
CONSULTING ENGINEERS
August 27, 1990
Ms. Shohre Daneshmand, P.E.
City of Coppell
P.O. Box 478
Coppell, TX 75019
Re: MacArthur Boulevard Extension/Denton Creek Split Flow
Analysis at the MacArthur Boulevard Bridge
Dear Ms. Daneshmand:
We have reviewed the second set of city comments on the
engineering plans for the MacArthur Boulevard project and the
draft of the Kimley-Horn letter transmitting the Denton Creek
Split Flow Analysis to FEMA. We have no objections to the plans
if corrected as marked. A discussion of the matters pertaining
to the improvements in the floodplain and floodway of Denton
Creek follows.
The floodplain/floodway matters relating to the extension of
MacArthur Boulevard northward across the natural floodplain and
channel of Denton Creek have been studied and discussed at length
between Carter and Burgess, Kimley-Horn and Ginn, Inc. (acting as
the City of Coppell's representative). The result of these
studies and discussions is a plan of action which should yield a
safe, economical and satisfactory solution to the problem of how
to get the MacArthur Boulevard project moving as soon as
possible.
The basis of the proposed plan is rooted in the fact that over
th~ period of time tkis project has be~n developing, several key
factors pertaining to the floodplain and floodway of Denton Creek
have changed, making it difficult to evaluate all of the
restrictions and regulations governing the design and
construction of the proposed improvements. However, as proposed,
it is our belief, based on assurances from both Carter and
Burgess and Kimley-Horn, that the project will not have any
significant negative impact on the 100 year flood elevations in
Denton Creek. All of the elements of the project were studied by
Dannenbaum Engineers (now Carter and Burgess) in their original
study for the vista Ridge project flood control channel which was
approved by FEMA and the Texas Water Commission. Their study,
which was considered to be in Lewisville, showed the post
construction floodway to be confined within the proposed new
channel, thereby removing all land and the natural Denton Creek
17103 Preston Road · Suite 100 · LB 118 · Dallas, Texas 75248 · Phone 214/248-4900
Channel south of the south bank of the new channel from the
designated floodway. At the time this was done, it would have
been feasible under the then existing regulations to construct
the proposed improvements without the necessity of further
reviews by FEMA had all of the proposed project been located in
Lewisville. In the ensuing time period local floodplain
regulations have changed and FEMA has never integrated the Vista
Ridge floodplain/floodway information of the Lewisville study
into the Coppell floodplain/floodway. FEMA has looked at each
side of Denton Creek separately and therefore the two sides have
been regulated separately. Also, the floodplain/floodway
development criteria for the City of Coppell has changed
dramatically.
It is essential that Kimley-Horn's Denton Creek Split Flow
Analysis be forwarded to FEMA i~ediately to get the ball roiiin9
for integrating data from both sides of Denton Creek and removing
the floodway designation from the project area as currently shown
on the Coppell Flood Insurance Rate Map. The proposed plan is to
allow construction of the MacArthur Boulevard Bridge over the
natural channel of Denton Creek to begin at once based on the
approvals received by Vista Ridge under the Lewisville study.
The roadway construction may follow under the same conditions.
Upon completion of the construction of the project, it would be
appropriate for Vista Ridge to submit the "As-Built" data and
hydraulics to FEMA to secure the final Letter of Map Revisions
for the City of Coppell.
In preliminary discussions with FEMA regarding this plan, they
have told Kimley-Horn that it is essential that the bridge be
addressed in a separate submittal from the roadway. This is
necessary because the bridge is an improvement to the floodway
and the roadway is a floodplain reclamation project.
The end result of this unavoidably complex process will be the
successful completion of this long awaited project, the addition
of tax base to the City of Coppell and the "cleaning-up" of the
Flood Insurance Rate Maps for this area of Denton Creek.
Please call me if you have any questions.
Sincerely,
ohn C. Karlsruher,
P.E.
JCK/dsp
Steve Goram
Ron Morrison, P.E. - Kimley-Horn
Phil Deaton, P.E. - Carter and Burgess
H. Wayne Ginn, P.E.
File 89409