Riverchase(5)-CS 881209 December 9, 1988
Mr. Russell Doyle, P.E. ~?,~ ,~
City of~oppell
255 P/a'rkway Blvd. I~ '
P.O. Box 478
Coppell, Texas 75019
Re: Riverchase Sanitary Sewer Ouffall
NDM No. 87-12-151
Dear Russell:
Enclosed is a depiction of the hydraulic grade line in the above referenced line. I used the top of the
TRA line as a beginning water surface elevation and a Manning's "n" value for the P.V.C. pipe of 0.011.
As we have discussed, this line was designed such that under peak flow, the line would be less than
full. The result is a gravity line which has a hydraulic grade line flatter than the grade of the pipe's flow
line. This means the greatest difference in height between the hydraulic grade line and the flow line of
the pipe occurs at the TRA line.
As I tried to articulate in my letter of November 14, the significance of all this is that our system won't
flood because, before that could happen, the TRA line would have to flood. This creates a ceiling on the
beginning water surface elevation for our line equal to the top of the manhole on the TRA line. This
ceiling occurs because, once the water elevation in the TRA manhole hits the lid, water spills on the
ground, preventing it from developing more head.
Please let me know if I can be of additional help.
Sincerely,
NATHAN D. MAIER
CONSULTI. J~I~NG IN EERS, INC.
MD/rdp
Enclosure
Three NorthPark/8800 N. Central £xpwy./Suite 300/Dallas, Texas 75231/(214) 739-4741
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