ST9905-CS061027Keith Marvin -Bethel Road Storm Drainage Design
From: "Chovan, Dennis" <dchovan@halff.com>
To: "Dayton Conklin" <DConklin@trammellcrow.com>
Date: 10/27/2006 9:05:52 AM
Subject: Bethel Road Storm Drainage Design
Dayton
I performed a quick review of the drainage plans for the Bethel Road
Improvements and have some concerns about the drainage. The plans seem
to indicate that the triple 5x10 box culvert is designed for the 100
year rainfall event. But after my review and analysis of the system it
appears that the velocity and hydraulic slope of the pipe is
significantly higher than shown on the plans. With a 100 year flow of
approximately 2,164 cfs in a 3-5x10 RBC I estimate a velocity of 14.3
fps and a hydraulic slope of 0.005 ft/ft. The plans indicate a velocity
of under 9.0 fps and a hydraulic slope of 0.0027ft/ft. I believe the
system is designed for something less than a 100 year rainfall event,
and we will be hard pressed to add any additional flow into the system.
Dennis J. Chovan P.E.
Vice President
HALFF ASSOCIATES, INC.
3801 Parkwood Blvd Suite 500
Frisco, Texas 75034
Phone 214-346-6224
Fax 214-217-6431
www. halff. com
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CC: <kmanrin@ci.coppell.tx.us>