Deforest Court-CS010501ii · 8616 NORTHWEST PLAZA DRIVE
Halff A ss oc ates
ENGINEERS · ~CH~S · SChiSTS
PL~RS · S~VEYORS
May 1,2001
AVO 17898
Jim O'Brien, PE
Suite 108
4011 West Plano Parkway
Plano, Texas 75093
Coppell, TX 75019
RE: Deforest Court Development/Drainage Issues
Dear Jim:
For some time now, we have been analyzing drainage issues related to the proposed Deforest Court
development and the Cooper property located to the west. Our analysis is, in part, in response to
comments made and questions raised in your review on behalf of the Coopers. Based on the analysis, the
following is a summary of our findings.
Historical Site Drainage Patterns. The attached exhibit shows topography and spot elevations prior to the
development of DeForest Court. Based on the topography, it does appear that portions of the Cooper
property did drain toward and across the DeForest Court site. However, the drainage path is obscure at
best and it appears that water would have had to pond to elevation 449.6 before it would drain from the
Cooper site across what is now DeForest Court, again based on the topography. Because the drainage
path is obscure, it would appear to me that the developer of the Cooper site should have secured a
drainage easement across the DeForest Court site if the developer of the Cooper site desired to retain
fight to drain in that direction.
Proposed Site Drainage. The original DeForest Court site development plan provided for site drainage of
the Cooper site. You had expressed an opinion that this drainage needed to be upgraded and taken south
to DeForest Road, rather than north as originally planned. This has been done as can be seen on the
attached storm sewer plans. As shown, 5-year storm events are expected to reach an elevation of 449.35
before draining out from the Cooper site. In Halff Associates opinion, this proposed system would
provide superior drainage to the situation that existed on the Cooper site prior to the development of
DeForest Court.
Denton Creek Flooding. The floodplain status of the Cooper site is unaffected by the DeForest Court
development, as far as the City of Coppell and Federal Emergency Management Agency rules and
regulations are concerned. However, portions of the Cooper site may have some minor protection fi.om
smaller Denton Creek flooding events (less than the 10-year flood; see flood levels noted on exhibit)
based on the existence of higher ground located adjacent to Denton Creek. This protection is also
unaffected by the reclamation of the DeForest site. If the DeForest Road storm sewer system is extended
into the Cooper site, this protection from smaller Denton Creek floods may be diminished unless a flap
gate is provided at the outlet of the DeForest Road storm sewer system to prevent Denton Creek
floodwaters from backing up the system to the Cooper Property. However, the City of Coppell does not
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Jim O'Brien, PE
April 30, 2001
Page 2
allow flap gates. As a result, the preservation of protection from smaller Denton Creek floods and the
provision of improved site drainage for the Cooper site cannot both be achieved. If you want continued
protection from the small Denton Creek floods, the storm drainage system should not be extended into
the Cooper property. If you want improved site drainage for the Cooper site, it must be accepted that
some site flooding from minor floods on Denton Creek may occur. Halff Associates developed the
current plan based on the direction that improved site drainage for the Cooper site was the goal.
At this point, we feel that we have exhausted all logical engineering alternatives for resolving the Cooper
property/Deforest Court drainage issues, as we perceive them. If you have any other engineering
alternatives, which would equitably accomplish the drainage needs of the Cooper site in conjunction with
the proposed development of DeForest Court, please advise us immediately. Otherwise, we are available
at your convenience to answer any questions or, meet together with the City to achieve a final resolution
to this problem.
Sincerely,
HALFF ASSOCIATES, INC.
Walter E. Skipwith, P.E.
Vice President
cc: Kelly Jordan, Castellan Development
Mike Martin, PE- City of Coppell