| Development of Artificial
Aquifers
Subsurface Dams
To prevent fast decrease of underground flow of seasonal
streams, subsurface dams are
built across sand river beds.
There are three types of underground dams designed to
prevent seepage: the clay-plug
dam, the masonry dam and the concrete subsurface dam
(fig. 1), ref. n.6.
For the three types of dams, a trench is dug down to the
impermeable rock below the
river bed and filled in either by compacted clay soil, or
by a masonry or concrete wall.
The dam acts as a barrier to the underground flow.
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Fig.
1 - Concrete or clay underground dam
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The selected alternative will
depend from economical consideration and the availability
of
local material. The first alternative is cheaper; the
clay plug, however, should be wetted
and compacted by mechanical or other means.
Sand Storage Dams
These dams are built across ephemeral stream beds to stop
the flow of coarse sand and
other materials transported by the water course during
the rainy season. The sediments
stored upstream from the dam will constitute an
artificial water reservoir.
If the water level is kept 1 meter below the sand
surface, the reservoir is practically not
affected by evaporation and it is more protected against
pollution. Sand storage dams are
built in stages, increasing progressively in height
according to the geomorphologic
conditions of the selected site and the amount of sand
deposited during yearly rainy
seasons. Sand storage dams are generally built right on
top of hard rock outcrops. Water
courses with their catchments covered by hard rocks and
transporting high sand load, can
deposit upstream the dam a considerable amount of
sediments in a relative short time.
Fig. 2 and fig. 3 show the two types of dams that
have been successfully constructed in
South Africa , ref. n. 7.
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Fig.
2 - Sand storage concrete dam
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Fig.
3 - Sand storage masonary dam
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