MIL-HDBK-1005/7A
c) The basin should be concrete, with sidewalls to
prevent the erosion of soils behind them.
4.6.4.3
Emergency Spillway.
This unit should:
a) Provide a capacity, combined with the main
spillway, to pass the maximum probable flood flow.
b)
Be located away from the intakes and the dam.
c) Have its crest set at an elevation such that the
design flood level of the main spillway will not be exceeded.
d) Have a low head discharge with a wide cross
section to keep the maximum crest velocity low; except where no
erosion from discharge will occur, when a fuse plug or washout
type may be used.
e) Have its slope reduced, so as to cause velocities
within the maximum allowable for the channel materials.
f)
Have a smooth approach section.
g) Be constructed on firm material and, if an earth
channel is used, always be well covered with grass and clear of
trees, bushes, structures, and any other obstructions to flow.
h) Use flash boards to provide any additional storage
or depth above the spillway crest. Special investigation of
resultant hazards and associated problems will be required.
Flash boards should be of the washout type. Use criteria in
American Civil Engineering Practice, Volume 2, by R. W. Abbett.
4.6.5
Rainwater Catchment Areas . The site should be
selected for the following desirable factors:
a) Topography presenting a large surface area where
rainwater can be easily collected. Slopes greater than 0.01
(1.0 percent) are desirable, as is space for a ponding basin to
store peak flows.
b)
Absence of heavily wooded areas.
c)
Absence of large swampy areas.
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