Geoscience Reference
In-Depth Information
f igu r e 31. Map of the southwestern
United States showing the Colorado
River and its drainage basin (shaded
region). (Map redrawn by B. Lynn
Ingram.)
hydropower for the largest cities in the West: Phoenix, Las Vegas, Denver,
Los Angeles, and San Diego.
Every California river has at least one dam, and many have more than one,
with 1,500 dams in this state alone. h e reservoirs behind these dams hold
almost 42 million acre-feet of water, which is about 60 percent of the state's
total yearly river runof . h roughout the twentieth century, enormous water
projects were built by federal and state governments in California, including
the Central Valley Project, the State Water Project, San Francisco's Hetch
Hetchy Project, the Sacramento-San Joaquin Flood Control Project, the
Colorado River Aqueduct, and Los Angeles's Owens Valley Project. Water
is captured and stored in reservoirs, then transported from the snow-capped
Sierra Nevada range to the drier Central Valley farmlands and Southern
Californian cities, where about 60 percent of the population lives. h is
“water on demand,” in addition to extremely fertile soils, has transformed
California's Central Valley into the “bread basket of the world”—growing
55 percent of America's produce.
h e twentieth-century era of dam construction eventually came to an
end in the 1970s as the environmental impacts of water development could
no longer be ignored. h e extensive system of dams and aqueducts in the
American West had been built when the interconnections between water-
ways and the ecosystems they support were poorly understood and not yet
in the popular press. Since then, research and restoration has begun in an
attempt to save aquatic ecosystems that are on the verge of collapse. Today,
the l ows let in rivers to restore aquatic ecosystems—dubbed “environmental
