Another factor that must be considered in the design of a dam is overtopping caused by
wave action. Such wave action can be initiated by slumping of the dam but it is more likely
to be caused by slides from unstable natural areas in the reservoir. Slides of this sort caused
failure of the Vaiont Reservoir in Italy ; the dam itself did not fail structurally.
Faulting or sudden settlement may also cause wave action. Such a settlement that took
place very rapidly at the dam itself caused the large waves at Hegben Lake (Anon, 1964).
Damage and serious danger may occur if an earth dam is in the neighbourhood of the fault
where the fault may intersect the dam and cause a break or fissure through it. When an
earth dam is founded on rock or a firm soil stratum, and is made of well compacted material,
the danger in an earthquake may be minimal. However, if the dam is located above a stratum
which can liquefy or lose its shearing strength an earthquake may cause a failure by spreading
of the dam even though the dam itself may have an ample factor of safety with respect to
failure in the material of the dam itself. In general, sites underlain by strata which may suffer
a major reduction in shearing resistance should be considered unsuitable unless the sensitive
strata can be removed.