TM 5-820-3/AFM 88-5, Chap. 3
d. The following design rules are based on hy-
upstream from the structure, the length of the weir
draulic considerations only. They are minimum
should be adjusted to maintain a head on the weir
standards subject to increase on the basis of other
equivalent to the depth of flow in the channel. A
considerations such as structural requirements and
trial-and-error procedure should be used to balance
special frost condition design.
the crest height and width with the channel cross
(1) Discharge over the weir should be
section.
computed from the equation Q = CWH 3/2 using a
(2) The relation between the height of drop,
C value of 3.0. To minimize erosion and obtain
h, critical depth at the drop, dc, and the required
maximum use of the available channel cross section
stilling basin length, LB, is defined by the equation
6-5
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