MIL-HDBK-1005/7A
d) The freeboard should suffice to prevent
overtopping during extreme high flood flow and wave action.
4.6.4
Spillways . Provide adequate main and emergency
spillways to protect dams against overtopping by floods. They
may be side channel, chute, or ogee type.
4.6.4.1
Main Spillway.
This appurtenance should:
a)
Provide a capacity to pass a 100-year flood.
b) Be located, wherever possible, away from the
intake and the dam.
c) Be built of concrete or stone, with sidewalls to
protect the dam structures from damage by sprays and the high
velocity in the spillway channel.
d) Be provided with an energy dissipater at its
downstream end to reduce the velocity to a rate that is harmless
to any downstream river channel on which the safety of the dam
depends, or to any downstream structures.
e) Provide a smooth approach section such that the
full design capacity of the spillway will be utilized.
f)
Be provided with gated spillway openings only
when:
(1)
Positive gate operation is assured,
(2)
Full-time staff attends the dam, and
(3) Good communications and flood routing
information are available.
4.6.4.2
Stilling Basin . This basin should be used as the
energy dissipater for the main spillway. Its design should
fulfill the following requirements:
a) The floor should be set so that the conjugate
water depth in the basin matches the tailwater elevation.
b) The length should embrace the hydraulic jump
within the basin at maximum flow.
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