Construction of a Dam - Step 2
Work on diverting the river starts in summer when river levels are low. Earth-moving equipment is used to build a small dam (called a cofferdam ) upstream of the main construction area. This acts as a barrier to the river and causes it to flow through the diversion tunnel.
Another cofferdam is built downstream of the main dam site to prevent water flowing back into the construction area.
Pumps are used to remove any water that seeps through the cofferdams.
Diversion tunnels are not always necessary when concrete dams are being built. The river can sometimes be channelled through a large pipe and the dam constructed around it.
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