N.D. Maier ltr. re variance-NDM
NATHAN D. MAIER
CONSULTING ENGINEERS, INC.
December 18, 1987
FILE COPY
Mr. Kevin Pieffer
Ginn, Incorporated
17103 Preston Road
Suite 100, LB 118
Dallas, TX 75248
Re: Creekview Variance
NDM No.: 87-6-062
Dear Mr. Peiffer:
Pursuant to our meeting of December 14, 1987, we provide you, the City
of Coppell and Mr. Carl Anderson, with this request for a v~gF.~to the new
floodplain ordinance for the Creek'view project. We would like to be included
on the agenda for the Jgnuar~ 12, 1988 co%mcilmeeti~
Additional changes have been made to t. he plans and we have again changed
the hydraulic models to reflect additional compromise from those plans
previously submitted. Prom our December 7, 1987 letter, while not our
preference, we have incorporated chamnelization of the overbank along the west
end of the ~roJect and actually reduced the 100-year ultimate water surface
upstream from the site. Basic changes that were made to the December 7, 1987
hydraulic model, include widening the floodplain at sections 1.0, 22600, 3.0,
and 4.0, a distance of 20', 10', 10', and 10', respectively by moving the fill
limit line back farther from the Creek, changed the fill boundary to a 3:1
sloped encroachment rather than a vertical encroachment, and lowering the
right overbank 'nm value to account for underbrush clearing on the backside of
several of the lots. Tabulations of water surface elevations amd velocities
are enclosed for your review.
At this point, we have taken all reasonable measures to comply with the
present ordinance. The fill limit boundary on most of the lots fronting the
Creek has been reduced to a "bare minimum", and will certainly limit the
building alternatives on these lots. While we must ask eflr a varianae due to
,am. slt technical deviations to o dinan .,
alternati.~e of choate lzatio, throug~h the reside~nclal area is n~ thou&hr
Three NorthPark/8800 N. Central Expwy./Suite 300/Dallas, Texas 75231/(214) 739-4741
Mr. Kevin Pieffer
December 18, 1987
Page 2
Working with you, John Kahrlsruher, Carl Anderson and Shohre Daneshmand,
we have together provided for some very significant improvements to the
previous models. These include:
1. Lowering water levels and velocities in certain parts of the study
reach up to 0.21 feet. Water levels increase up to 0.27 feet with
this project in certain areas, however, no existing structures will
be flooded. The maximum water surface increase with the enclosed
hydraulic model has been reduced from 0.42 (12/7/87 model) to 0.27
feet. Similarily, the maximum channel velocity increase has been
reduced from 0.82 to 0.56 feet per second. The velocity increases
generally occur at straight sections of the Creek (e.g. sections
1.0, 22600 and 4.0). The north overbank velocities along the toe of
slope of the existing homes, is generally 2.05 to 4.31 feet per
second, which is not erosive and should not threaten existing
structures.
Actually reducing ultimate lO0-year flood waters upstream from
Denton Top Road by up to 0.20 feet.
The project will have no impact on the 2-year flood for ultimate
watershed build-out conditions.
Being in compliance with all FEMA regulations, and in compliance
with the City of Coppell ordinance in effect at the time the project
was conceived and largely designed.
Lots along the north side of Bethel Road will be filled by each home
builder and architect, only to the extent necessary to design a home. To this
end, maximum fill will ~9~ occur on most of the 26 lots along Grapevine Creek,
especially since each owners motivation will be the preservation of the large
trees that presently occupy most. of this area. As you are aware, the models,
however detailed, cannot account for these situations, and conditions will
surely be benefited by these accommodations. The fill limit boundary on each
of these lots has been revised to the absolute minimum without requiring
si~nificant channelization of the Creek, loss of trees and vegetation, and
without requiring a major redesign of the already approved final plat.