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Living with Dams: Know Your Risk | April 2012
through vertical or sloping buttresses.
Gravity and buttress dams are constructed
of vertical blocks of concrete with flexible
seals in the joints between the blocks.
Concrete arch dams are typically thinner
in cross-section. The reservoir water forces
acting on an arch dam are carried laterally
into the abutments. The shape of the arch
may resemble a segment of a circle or
an ellipse, and the arch may be curved in
the vertical plane as well. Such dams are
usually constructed of a series of vertical
blocks that are keyed together; barriers
to stop water from flowing are provided
between blocks. Variations of arch dams
include multi-arch dams in which more
than one curved section is used and
arch-gravity dams which combine some
features of the two types of dams.
Other Types of Dams
Tailings dams are industrial waste dams
that impound waste materials from
mining operations or mineral processing.
Ash impoundments, or ponds, are used
to store or dispose of ash primarily
from the combustion of coal. These
impoundments are a type of waste
management facility consisting of an
excavated, dammed or diked reservoir
in which coal ashes are stored for future
removal or disposed of as a slurry or
sludge. The coal ash solids settle out
and leave water at the surface that is
discharged through a designed and
managed outlet structure to a nearby
stream, surface water or plant process
water system.
Spillway Discharge and
Seepage
Because the purpose of a dam is to retain
water effectively and safely, the water
retention ability of a dam is of prime
importance. Water may pass from the
reservoir to the downstream side of a dam
by:
Passing through the main spillway or
outlet works
Passing over an auxiliary spillway
Overtopping the dam
Seepage through dams, through
abutments or under dams.
Overtopping of an embankment
dam is very undesirable because the
embankment materials may be eroded
away. A number of concrete dams have
been designed to be overtopped.
DAMS BY PRIMARY
PURPOSE
Recreation – 34%
Flood Control – 16%
Fire Protection, Stock or Small Fish - 15%
Irrigation – 9%
Water Supply – 8%
Other – 6%
Unknown – 4%
Hydroelectric – 3%
Fish andWildlife Pond – 2%
Tailings - 1%
Debris Control – >1%
Navigation – >1%