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12 |

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

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.