Our Environment — Dams and Levees Sample Pages

Document Sample
Our Environment — Dams and Levees Sample Pages Powered By Docstoc
					                       Why Build Dams and Levees?
                                                            21




How a hydroelectric dam works.

   Once the dam is completed, water is allowed to
return to the original riverbed. A reservoir is then
created as water builds up behind the dam.
Precautions are taken so that the dam operates
properly. For example, because debris—silt, rocks,
branches, and such—flows down a river, screens
are used to filter out this material. If it were not fil-
tered out, the debris could clog the turbines and
cause them to fail. Fish screens are also put in place
to keep fish from being sucked into the turbines.
   Finally, spillways are built to control water
overflow. Spillways are like the channels or tun-
nels used during the building of a dam. Instead of
The Grand Coulee Dam in Washington State is a
functioning hydroelectric dam.

diverting water all of the time, though, spillways
are used to let excess water go around the dam in
times when there is too much water in the reser-
voir. If there were no spillways, then the excess
water could flow over the dam and cause a great
deal of structural damage.
   In a world where much of the energy used cre-
ates pollution, dams are seen by many people as a
clean and renewable energy source. Burning coal
or oil pollutes the air, and generating nuclear
power creates dangerous nuclear waste. A hydro-
electric dam, however, uses only water and creates
no harmful waste.