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Although dams look solid, they do move
under the forces of nature, and water seeps through tiny pores
(or spaces) in their structure. The weight of an embankment
dam actually causes its own height to reduce over
a number years. This is called settlement. A reservoir
pushes a dam over a little and tries to make it slide on its
foundation.
Dams contract and expand as their temperature changes throughout
the year. Civil
engineers ensure the stability of dams by designing
them to minimise water seepage
and the effects of natural forces.
  Changes
in the behaviour of a dam occur slowly, so dams are monitored
regularly using scientific instruments that can measure very
small changes. This way any undesirable behaviour can be detected
well before it causes a major problem. Some instruments are
permanently installed in dams, while others are taken to the
site to make measurements.
These are some the things that are monitored.
Leakage
or increased seepage can indicate that there is a crack in a
dam. In embankment dams, it could indicate that internal erosion
of the fill material is taking place.
Levels on the crest
of an embankment dam are measured, using optical instruments,
to check whether there has been a reduction in the dam's height.
Settlement of the crest can be a warning of problem occurring
within the body of the dam. The crest level is designed to be
a certain height above the normal full reservoir level. This
ensures that the dam is not overtopped
by excess floodwater or by waves on windy days.
Pendulums
are installed in vertical shafts in concrete dams to measure
how much the dam is tilting over.
A dam can move horizontally, in either
the downstream
or upstream
direction. This movement can be measured on the crest using
optical or computer-based equipment. Excessive movements can
indicate that the dam is sliding and becoming unstable. |
