Environmental Engineering Reference
In-Depth Information
Dams can be shut down immediately if needed.
Water evaporation increases due to an increase in
water surface area of the reservoir behind the dam.
Dams create lakes for recreation (fishing and boating).
The mating cycle of fish, such as salmon and steel-
head trout, can be altered.
Dams control downstream flooding and provide a uni-
form source of water year round.
Sediment is altered downstream, impacting water flow
and silt deposition.
There are no CO2 emissions during operations.
Provides electricity for a large number of people.
Case Study: The Colorado River
The Colorado River starts in the Rocky Mountains and passes through seven states and two Mexican states,
covering approximately 1,450 miles before emptying into the Gulf of California. There are six dams along the
river and much of the water is taken out for agricultural and domestic uses along the way. Some of the water is
moved hundreds of miles from the original river to distant cities. At the end of the river, the once large volume
is often a trickle, and the water return is frequently contaminated with pesticides, fertilizers, drugs, and other
contaminants.
Case Study: Salmon
Salmon are migrating fish, returning from the ocean to spawn in the stream where they were hatched. When
they hatch, salmon slowly make their way downstream toward the ocean. Later, they return to the river, swim
upstream to find the place they hatched, spawn, and die. Salmon usually return three years after they hatch to
spawn and die. Steelhead trout usually return in two or three years and may head back out to the oceans and
make several trips over their lifetime. Damming a river makes this migration difficult or impossible.
Almost every river system in the West has been blocked by a dam, often with more than one dam along the
length of a single river. These dams have destroyed important habitat for fish spawning, along with areas im-
portant for salmon's growth. For example, the Columbia River has less than 110 km (70 miles) of remaining
free-flowing water, which is not enough to sustain wild salmon. Of the estimated 130 West Coast salmon runs,
81 percent are extinct, and the remaining 19 percent are endangered. California has severely limited fishing on
several of its salmon runs and has even eliminated fishing altogether in some years.
To help mitigate this loss, fish passage facilities and fish ladders have been built to bypass dams. While juven-
ile fish are moving downstream toward the ocean, dams may allow water to pass over the spillway to encour-
age the fish to swim over the tops of dams instead of through the turbines. Juvenile fish also may be collected
and transported downstream.
Some salmon is farm raised. Fish farms often consist of holding pens in the ocean where the fish are kept and
fed for upwards of three years. There is concern that these farm-raised fish may escape and mate with the wild
salmon and contaminate the gene pool. Another issue with farm-raised salmon is the amount of waste pro-
duced by the fish, which is concentrated below the pens in the ocean. There is concern that this waste may be
harming the environment in the area.
In 2010, scientists announced that eggs of Atlantic salmon had been genetically modified by the insertion of
the gene from an ocean pout and a growth gene from the Pacific Chinook salmon, allowing the fish to grow
year-round. Commonly, native salmon do not grow in the winter months. With gene insertion, the fish can
grow to market size in approximately two years instead of three. There are claims that the modified eggs are
