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74:
How to build a reservoir
A reservoir
is a man-made or artificial lake which is created behind a dam.
Look
at the texts in the boxes. They explain how a reservoir is created,
but they are all mixed
up. Cut out the boxes and put them in the right order.
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The
engineers begin to build the dam using concrete upstream from
the reservoir site.
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First
the engineers need to find a suitable site. The best site is where
the river travels through a valley. The valley sides make natural
walls.
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Facilities
at the reservoir, such as a boating club and visitors' centre,
are built last.
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The
engineers finish building the dam.
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If
the river valley is inhabited, people have to be moved out of
their homes and farms before the valley can be cleared.
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Two
towers are built on the upstream side of the dam to control the
flow of water.
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The
river valley is cleared. Trees, farms, houses, fences and roads
are all demolished.
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The
engineers clear the top soil and grass from the valley sides and
bottom.
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The
holes in the dam are closed. The flow of the river is stopped
so that the reservoir can fill up with water.
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The
valley is lined with sand. Clay is put on top of the sand to prevent
water from leaking through the ground.
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f
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f
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Now
draw a picture to go with each stage.
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