Living with Dams: Extreme Rainfall Events | 2015
Could a dam fail as a result
of extreme rainfall events?
Failure of a dam from an
extreme rainfall event is similar
to the failure of a bridge or an
elevator whose weight/capacity is
The extreme rainfall event will
cause increased stream flows
resulting in the water level in the
reservoir to rise to heights that the
dam may have never previously
experienced. And, if the dam and
spillway system are not equipped
to safely pass an extreme rainfall
event, the reservoir level will rise
and water will go over the dam
itself. This is called “overtopping.”
Most dams are not designed to
Extreme rainfall events
can cause overtopping.
Overtopping of earthen
dams can often cause them
to fail catastrophically and
completely unless they are
designed to overtop.
Failure by overtopping is
one of the most common
forms of dam failure.
rainfall events, therefore, have the
potential to cause a dam to fail
from erosive forces of overtopping
In addition, as reservoir pool levels
rise from the increased stream
flows of an extreme rainfall event,
the structural and hydraulic
stresses that the weight of the
additional water in the reservoir
creates will likely exceed any levels
previously experienced in the
history of the dam. These stresses
may cause potential instability of
the dam leading to its failure.
Overtopping can fail an earthen dam.