Geoscience Reference
In-Depth Information
h e wetlands between these lakes were initially i lled in (“reclaimed”)
following the winter of 1861-62, at er the series of severe atmospheric-river
storms that generated l oods submerging the entire Central Valley (see
chapter 2). More serious impacts on the lakes began in the early twentieth
century, when the rivers that fed them (the Kern, Tule, Kings, and Kaweah)
were diverted to irrigate crops in the Central Valley. What had been the
source of water for these great lakes for over a million years was cut of , and
the lakes dried up completely. h e wildlife that made this region home was
lost along with the water. h e remaining dry lakebeds were then ploughed
and planted with crops, primarily cotton. As a i nal irony, these crops had
to be irrigated with the very river waters that had been diverted from the
lakes in the i rst place. Today, it is dii cult to i nd even the remnants of these
ancient lakes within the expanse of crops in the southern San Joaquin Valley.
h
e Colorado River and Delta
Elsewhere in the West, water development similarly took place without any
consideration for the ecological consequences for rivers and their water-
sheds, l oodplains, or deltas. On the Colorado River and its major tribu-
taries, for instance, aquatic ecosystems began declining in the decades at er
Hoover Dam and i t y-seven other major dams were built on the river and
its tributaries starting in the 1930s. Important features of the Colorado River
were altered at er the construction of these dams, which hold back warm,
sediment-laden water, and these sediments then settle out of the still water
behind them. At the same time, the deeper parts of the reservoirs become
cooler without direct heat from the sun. h us, the water that is released from
the dams to the river downstream is clearer and much cooler than the natural
Colorado River water (warm and muddy) to which the native i sh species had
been accustomed for millennia. All of the 35 species of i sh that evolved in the
Colorado River—including minnows, chubs, and suckers—suf ered from
the changing environmental conditions at er dams were built.
h e Colorado River delta has also been decimated from dam construc-
tion and water diversion. h e Colorado reaches its delta just south of the
Mexican border, where it then empties into the Gulf of California. h ere, the
impacts of damming and water diversions are perhaps the most severe—but
least apparent. Before entering the gulf today, only a trickle of the Colorado
River remains, and, at times, especially during the dry years, the river no lon-
ger reaches its natural delta. Historically, this extensive delta covered about
