16 / 24
14 |
Living with Dams: Extreme Rainfall Events | 2015
Slope Failure
Slope instability can be caused by
extreme rainfall events.
During the
time of elevated reservoir pool levels
caused by runoff from extreme
rainfall events, this phreatic surface
will become elevated, possibly to
levels never before experienced
by the dam. If this phreatic surface
begins to approach the surface of
the downstream slope, the dam
may experience a structural slope
failure, which could, under the right
conditions cause a total catastrophic
failure of the dam and release of the
entire reservoir of stored water.
General Seepage
All dams leak to some extent.
This leakage, commonly referred
to as seepage in the engineering
community, may or may not be
evident to the casual observer on
a day to day basis. Seepage may
develop through the soil particles
of an earthfill dam, may travel along
the outside perimeter of outlet
pipes passing through earthfill
dams, or may travel through the
naturally occurring materials of the
foundation under any dam.
Seepage can be evident on the
downstream slope or near the
downstream toe of earthfill dams.
In some dams that were possibly
built from less than ideal soils, not
compacted sufficiently, built with
overly steep downstream slopes or
any combination of these factors,
the phreatic surface may, intercept
the downstream slope of the dam.
When this happens, seepage will be
evident on the downstream slope or
near the toe of the dam and this can
become so concentrated at certain
locations that an uncontrolled
seepage path is created directly from
the reservoir to the downstream toe.
Piping Failure
Piping failures can be caused by
extreme rainfall events.
Again,
during the time of elevated reservoir
pool levels caused by runoff from
extreme rainfall events, the phreatic
surface will become elevated
within the embankment, possibly
to levels never before experienced
by a dam. The added pressure that
the elevated reservoir level creates
on an existing seepage path may
become so strong that soil particles
begin to be displaced out of the
Could a dam fail as a result
of extreme rainfall events?