Your Hydraulics Thinking Cap On? 1

Assume an existing rectangular concrete flume,
slope varying from 0.020 to 0.040, width from
12' to 24', vertical wall height from 3' to 12',
overall length 2500'. ACE-style "channelization".

Plan to construct and install precast weirs at
average 25' oc, bevel-face, vertical back, with
a low-flow notch. Top of notch is +2', top of
weir is +2'-6", weir length is full flume width.
TOC weir elevations stair-step -0.7', weir:weir.

?How to model stormflow hydraulics? One approach
was used by applying Chezny-Manning formula, with
n=0.050 to simulate the "roughness" of the weirs,
Q=(1.49/n)(A^2/P)^0.67(S)^0.5. Fairly simplistic.

Another approach used the Sharp-Crested Weir
formula, Q=CL(d^1.5), modified for velocity
head with relative velocities from Chezny.
Gave much, much lower throughput capacity.

Another approach used a "hacked" HEC-RAS, but
no way to QED independently verify the results.

Design storm flow is estimated at 1200cfs. <---

Depending on method used (above), either flow
mostly passes through, or jumps out of bank.

Anyone out there an expert flume-weir modeler?

EXISTING Floor Wall
Station Width Elev. Height
290 17.0 107.4 4.7
354 17.8 108.6 5.3
390 12.2 109.3 2.8
520 13.3 112.6 6.2
570 14.1 114.1 9.4
660 12.0 116.8 6.3
700 13.0 118.0 8.0
759 12.9 119.8 6.4
913 13.0 123.9 6.0
1013 15.4 126.4 5.6
1113 13.8 130.4 5.7
1170 13.5 131.8 9.9
1313 19.3 136.6 6.4
1423 27.5 139.8 7.3
1553 22.9 143.2 8.5
1670 21.5 146.7 11.2
1913 13.3 153.6 6.7
2141 12.8 160.5 8.4
2293 19.4 165.1 7.5
2473 24.9 170.4 9.1
2571 23.5 173.3 8.8