TM 5-820-3/AFM 88-5, Chap. 3
a. The berm at the edge of the fill will have suf-
eration should be given to effects of frost action in
ficient freeboard to prevent overtopping from dis-
the design. Experience has shown that a level apron
charges in excess of design runoff. A minimum
minimizes erosion of adjacent soil and is self-
height of wall of one and one-half times the com-
cleaning as a result of increased velocities ap-
puted depth of flow is suggested. Turfed berm
proaching the critical section.
slopes will not be steeper than 1V to 3H because
they cannot be properly mowed with gang mowers.
7-2. Design.
b. A paved approach apron is desirable to elimi-
a. The entrance to the chute can be level or a
nate erosion at the entrance to the chute. A cutoff
drop can be provided as shown in figure 7-2. The
wall should be provided around the upstream edge
advantage of providing the drop is to reduce the
of the apron to prevent undercutting, and consid-
depth of headwater upstream. The dimensions of
7-2
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