Geoscience Reference
In-Depth Information
the Central Valley into an inland sea. Floods have been a natural feature of
the Central Valley for millennia, which is why the soils are so rich and fertile.
However, l ooding on this scale does not mix well with the interests of a
modern agricultural system that depends on regularity and controlled water
supplies, or with the inland cities that are now replacing them.
Over the past century or so, Californians have prevented these catastrophic
l oods through massive hydro-engineering projects. Water managers have
essentially taken nearly full control of the timing and amount of water that
reaches the fertile lands within the Central Valley. h e consequence of this
transformation of the natural hydrolog y, combined with groundwater pump-
ing, soil compaction, and the draining of wetlands, has been that much of this
vast region has sunk by several feet and, in some areas, by as much as 28 feet.
Today, this sunken region may be more susceptible to l ooding than it was
in 1861-62. Moreover, the population of California has grown from 300,000
in 1861 to over 37 million in 2012, a number that is expected to double by the
year 2050. Room has to be made for this swelling population in the future,
and people have been i nding that space in the Central Valley. Increasingly,
the region has been providing more af ordable housing, with former agri-
cultural lands in the Central Valley l oodplains being converted to housing
developments. Should l oodwaters i ll the Central Valley, they will submerge
not just small towns, marshes, and farmlands but also major population cen-
ters in ten to thirty feet of water. In 2009, over six million people lived in
the Central Valley, many in densely populated cities like Modesto, Fresno,
Stockton, and Sacramento, all of which face potential catastrophe should
storms and l oods like the ones in 1861-62 strike again. h e recent trend in
urban sprawl seems to dance on the edge of disaster: l ooded i elds are one
thing, but l ooded homes are quite another.
h e long history of megal oods in the Central Valley is virtually unknown
to most residents today. Many new cities and housing developments are pro-
tected by a relatively primitive network of levees—some 6,000 miles of levees
in all—that line the rivers. h ese levees are fragile and they are the last—and
in some cases only—line of defense against the potential l oods spilling out
from the Sacramento and San Joaquin rivers. h e fragility of California's
levees has repeatedly been exposed in recent years. During the winter of 1986,
l oodwaters overwhelmed Folsom Dam on the American River and almost
l ooded Sacramento; in 1997, levees broke throughout the Central Valley,
causing the largest evacuation in California's history; and in 2006, multiple
levee breaks and massive l ooding in the Central Valley made national news.
