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GARRETT - McCLURE ENGINE.ERING
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Post Office Box 4063 / 1520A Cavitt Avenue
Mike
Res. 713/846-1117
Bryan, Texas 77801
Bus. 822-5487
Don
Res. 713/846.sSH7
November 24, 1980
Mr. Elrey Ash, P.E.
City Engineer
City of College station
College Station, Texas 77840
RE: 0.889 Acre Tract @ N.E. corner of Hwy 30 and East Bypass
College Station, Texas
Owner: Edward Hancock
Cameron Highway
Hearne, Texas 77859
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Dear Mr. Ash:
~~ehave studied the watershed of the Carters Creel{ tributary that
Ineanders along the north side of the above described tract__ According
to the recent drainage study prepared by Turner, Collie and Braden of
the Ci ty of College Station and in talking wi th l\~r. Joe Barrow wi th
said company, it can be shown that an error in the size of the drainage
area has been made .' Actually the watershed drainage area at this project
site is 241 acres and not the 467 acres as used in the report. This
results in a reduction in the amount of storm runoff" and more importantly,
will reduce the 100 year Flood Hazard Profile at this site.
Spencer J. Buchanan and Associa-tes, lne. prepared a 100, year Flood plain
study for this area in July, 1978. According to this study the 100 year
flood elevation at t~e 0.889 acre tract is 256.0. The proposed building
is completely out of the flood plain as defined by this study.
The Turner, Collie and Braden report predicts that the existing 3 barrel
7' x 4' concrete box culvert under the East Bypass is too small to handle
the proposed flow and the water will overflow its channel banks on the
West side of the Bypass and flow through the state High\"1ay 30 grade
separation structure. From this point, the storm drainage flows overland
to i~s natural channel, th~n on to its confluence with Carter Creek.
In applying the findings of the Turner, Collie and Braden report to this
proposed development, even though it is grossly conservative, it can be
s.een that the development is largely si tuated in the channel overflow area
and will not raise the floow profile, nor have an adverse affect on
downstrearn property. It can only affect upstream property. In this case
page 2
the East Bypass acts as a dam and pre\rents any .damage to upstream
property.
The developer on this site has proposed a 6000 square foot building
placed on the highest ground in the tract (approximately 2500 square
feet is above the flood hazard profile). Since the proposed- building
is elevated above the flood hazard area and will obstruct flow (if the
Turner, Collie and Braden report were considered accuratel,the developer
is proposing to offset' the obstruction by improving the flow characteristics
of the remainder of the tract. This is done by constructing a 3 barrel
7' x 4' concrete box culvert widening and stabilizing the existing
channel \vi th concrete riprap and eliminating all underbrush on thetraci:;.
We feel that this development will not affect the 100 year flood plain
as described above.
Sincerely, <M ... .... ~
JIJz.t Lt,u.Jtk1dT
Donald D. Garrett, P.E.
Garrett McClure Engineering
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