Page 421 - Environment: The Science Behind the Stories

cities and for farmland as the water proceeds downriver. When
it reaches Parker Dam on the California–Arizona state line,
large amounts are diverted into the Colorado River Aqueduct,
which brings water to millions of people in the Los Angeles
and San Diego areas via a long, open-air canal. From Parker
Dam, Arizona also draws water, transporting it in canals of the
Central Arizona Project. Further south, water is diverted into
the Coachella and All-American Canals, destined for agricul-
ture, mostly in California’s Imperial Valley.
The world’s largest diversion project is underway in
China. There, government leaders are pushing through
an ambitious plan to pipe water from the Yangtze River

Figure 15.14 Unusually high water levels in the Mississippi
River in May 2011 caused this levee in East Carroll Parish,
Louisiana, to collapse, flooding adjacent farmland. Levees
upstream in some less-populated areas were intentionally
destroyed and the floodplain inundated in order to lower river vol-
umes and protect more-populated areas downriver.

chance of a 100-year flood. Like spinning a roulette wheel,
one occasionally gets the same unlikely result twice in a row.
Scientists calculate the likelihood of major floods based on
natural historical conditions, but if conditions change (through
increased development, habitat loss, engineering and chan-
nelization, or global climate change), then the frequency of
flooding can change. Many of the levees that currently line
the Mississippi River were constructed after one such cata-
strophic flood struck the lower Mississippi River in 1927,
leading to public demand for greater protection from flooding.

We divert surface water to suit our needs

People have long diverted water from rivers and lakes to farm
fields, homes, and cities. Water in the Colorado River in the
western United States is heavily diverted and utilized as the
river flows toward the Pacific Ocean (Figure 15.15). Early in its
course, some Colorado River water is piped through a moun-
tain tunnel and down the Rockies’ eastern slope to supply
the city of Denver. More is removed for Las Vegas and other

WeIgHINg tHe ISSUeS

ReaCHINg FoR WateR Los Angeles is not the only con-
troversial diversion of fresh water in the United States. The
rapidly growing Las Vegas metropolitan area is exceeding its
allotment of water from the Colorado River and has proposed
a $3.5 billion project that would divert groundwater from
450 km (280 mi) away to meet the growing demand in
Nevada’s largest city. Do you think such diversions are ethi- Figure 15.15 The degree to which we have engineered
cally justified? If rural communities and wetland ecosystems the once-wild Colorado River led cartoonist Lester Dore
at the diversion site in eastern Nevada are destroyed by to portray the Colorado and its tributaries as an immense
this project, is this an acceptable cost given the economic plumbing system. Thirteen major dams pool water in enormous
activity generated in Las Vegas? How else might cities like reservoirs along the lengths of the Colorado River and its tributar-
ies. Several major canals divert water from the river, mostly to irri-
420 Las Vegas meet their future water needs? gate crops in desert regions. From High Country News, 10 November 1997.

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