Forty percent of the land area of California drains through the delta, where the Sacramento and San Joaquin rivers join and meet salt water from the bay. The Bay-Delta ecosystem is the largest estuary on the west coast of the Americas and a natural resource of hemispheric importance.
Like all estuaries, the Bay-Delta depends on freshwater flows. The flows provide nutrients, create circulation patterns vital to aquatic life, and carry young salmon and other fish down rivers as they migrate to the bay and the ocean. They also prevent salt from building up in Suisun Marsh, the largest brackish estuarine marsh on the West Coast.
Demands on Bay-Delta Water
Two-thirds of California's precipitation falls north of the delta, while two-thirds of the state's demand for water comes from the south. As a result, the delta is the "switching yard" for much of California's water supply. In average years, California diverts more than half of the water that naturally flows through this ecosystem.
The vast majority of the diverted water is removed by two projects: the State Water Project and the federal Central Valley Project, which together form the world's most complex plumbing system. These massive projects started pumping water from the delta in large quantities 30 years ago. Since then, demand for water has increased steadily.
Where It All Goes
What is the water used for? About 20 percent is diverted for urban uses, but the vast majority -- the remaining 80 percent -- is used for agriculture. Much of that water is wasted through inefficient irrigation practices. And a great deal is used for low-value crops. For instance, 20 percent of the water diverted by the state is used to grow alfalfa, a crop used primarily to feed livestock.
Not surprisingly, removing these huge volumes of water has had equally huge consequences. It has disrupted natural processes and wildlife in countless ways -- killing millions of fish every year, altering salinity levels, and drying up marshlands. By the mid-1980s, average annual diversions from the state and federal projects reached 5 million acre-feet. (One acre-foot is approximately 326,000 gallons, the amount that would cover an area about the size of a football field with a foot of water.) The 1980s also saw the beginning of a disastrous downward spiral for many bay fisheries, such as the winter and spring runs of chinook salmon, delta smelt, longfin smelt, and Sacramento splittail.
Highest Level in History; Time for a Change
In 2000, approximately 6.3 million acre-feet were diverted from the delta, the highest level in history. A major factor in this dramatic increase was the completion of the Diamond Valley Reservoir in Southern California, which was filled largely through diversions from the State Water Project. It is not yet clear whether the reservoir, once filled, will continue to drive such high levels of diversion.
Another factor in future diversion levels will be CALFED, a plan established by California and the federal government to restore the Bay-Delta ecosystem and develop an environmentally and economically sustainable water policy for the state. But proposals to develop more surface storage and relax pumping limits in the delta could further increase diversions and damage to the ecosystem.
There is a limit to the amount of water that can be safely pumped from the Bay-Delta ecosystem. All signs indicate that California has exceeded that limit. Unless diversion levels are reduced, this great estuary could be damaged irreparably.