Geoscience Reference
In-Depth Information
conservation and (2) producing hydroelectricity for southwest-
ern states. During the course of construction, the population
of Clark County swelled to about 25,000. It was at this time
that the first of the now-famous casinos were established in Las
Vegas to entertain the construction workers. After the dam was
completed in 1935, the structure and Lake Mead became tourist
attractions that further propelled the growth of Las Vegas, along
with an influx of organized crime. By 1950 the population of
Clark County was nearly 50,000.
Since the advent of air conditioning in the 1950s, the popu-
lation in the Las Vegas metropolitan area has grown at a rapid
rate to about 2 million (Figure 20.8a) and was expected to reach
3 million by 2020 prior to the current economic downturn. It
may still reach that figure, but such projections are a bit uncer-
tain as of early 2013. Regardless, the city is visited by about
40 million
tourists every year who are attracted to the casinos,
entertainment, and area's natural beauty. This rapid population
increase mirrors the rate of change in other hot southwestern
cities such as Phoenix, Tucson, and Albuquerque, and is part
of a general migration of Americans during the past 50 years
to the southern part of the country or
Sun Belt
. Over 6 million
people have moved into the region in that time, with urban areas
sprawling rapidly into the surrounding deserts. A comparison
of satellite images between 1973 and 2006 (Figure 20.8b) illus-
trates the impact that rapid population growth in Las Vegas has
had on the size of the city. Las Vegas is now a major American
city with wide boulevards lined with luxury hotels, waterfalls,
and fountains that spray millions of gallons of water into the
dry desert air.
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Project Canal
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Mexico
Figure 20.7 Regulation of water in the Colorado River
basin.
The Colorado River Compact divided the watershed into
an upper and lower basin. Water in each of these basins is strictly
regulated, with a set amount allowed for each region. The Central
Arizona Project and Colorado River Aqueduct divert water from
the Colorado River to southern Arizona and Southern California,
respectively, for human purposes. Note the locations of Los
Angeles, Las Vegas, Phoenix, and Tucson.
Will Water Supplies Disappear?
As the growth of Las Vegas accelerated in the latter part of the
20th century, many people began to become concerned about
the supply of water in the arid desert. Was there enough water
available for sustainable growth? Was it possible that water sup-
plies would disappear? These concerns resulted in the establish-
ment of the
Southern Nevada Water Authority (SNWA)
in 1991.
The purpose of this organization has been to develop and man-
age local water resources, theoretically in a sustainable way. At
the present time 90% of water used in Las Vegas comes from
Lake Mead on the Colorado, whereas the remaining 10% is de-
rived from groundwater. In an effort to manage these water sup-
plies, the SNWA established a four-phase hierarchy of drought
status, including (1) no drought, (2) drought watch, (3) drought
alert, and (4) drought critical, to keep people informed of cur-
rent environmental conditions and the various kinds of water
use that are permitted at each level.
The concerns about water have magnified since the late
1990s, when the southwestern United States entered into a ma-
jor drought that has only recently eased somewhat. Average an-
nual precipitation in the region has been about 70% to 75% of
normal, with a significant decrease in the amount of snowfall
each winter in the Rocky Mountains. The amount of snow is
important because it provides spring runoff to the Colorado
River and its tributaries, which is the major source of water for
New Mexico, and Utah) and a lower basin (including Nevada,
Arizona, and California; see Figure 20.7). The key stipulation of
the compact is that both the upper basin and lower basin are al-
lowed 7.5 million acre-feet of water per year, in other words, the
amount of water required to cover 7.5 million acres in 1 foot of
water. Given that the Colorado River flows for a short distance
in Mexico before it reaches the Gulf of California, 1.5 million
acre-feet of water is allocated to Mexico per year. This stipula-
tion means that the upper basin states cannot use all the water
they desire; instead, they must allow a sufficient amount of wa-
ter to flow downstream so that both the lower basin and Mexico
receive their share. The lower basin, in turn, must assure that
Mexico receives the amount of water required by the agreement.
The Colorado River Compact set the stage for construction
of the Boulder Dam (later renamed the Hoover Dam), which
began near Las Vegas in 1931. In association with the Colorado
River Compact, Hoover Dam was designed for two purposes:
(1) impounding water (in Lake Mead) for irrigation and water
