Delta blues - a plaintive riff on how we've mistreated California's biggest source of water

We expect the Delta to do so much. Unfortunately, it's just not up to all the tasks. There's now widespread agreement that our current treatment of the Delta and our expectations for it are harmful and unsustainable. What isn't so widely agreed upon is what to do about it.

The Delta, at the confluence of the Sacramento and San Joaquin Rivers, is an approximately 1,150-square-mile area comprised of a maze of channels, wetlands, and developed islands. Historically it held tremendous natural abundance; its waters teemed with fish, its skies darkened periodically with migrating birds. Today, Delta fish populations are plummeting, water quality is poor, development is increasing, and Delta development and infrastructure are threatened by the combined threats of sea-level rise, flooding, and earthquakes.

The Delta serves many, often competing, uses. Its water supports fish and wildlife, and is used by humans for recreation, water supply, agricultural and urban drainage, and shipping. The Delta's islands have been drained and surrounded by dikes, and are used primarily for agriculture and increasingly for suburban development. As the peat soils have dried out, however, the islands have subsided by 20 feet or more.

The Delta now is the hub and bottleneck of the state's water transport system. Without any dams or diversions, an average of 30 million acre-feet of water would flow each year into the Delta from the Sacramento and San Joaquin Rivers, and then into San Francisco Bay, draining about 40% of the state (an acre-foot is about the amount of water used by two families of four in a year). Currently, about 11 million acre-feet of water are intercepted annually for other uses (primarily agriculture) before reaching the Delta. Then approximately six million acre-feet of the water that does reach the Delta is sucked out at the southern end by the giant pumping facilities operated by the State Water Project and by the federal Central Valley Project. The exports provide water for millions of people and irrigation for three million acres in the San Joaquin Valley and southern California. The pumps are so strong that at times of the year the northern San Joaquin River actually flows uphill to the pumps.

Many native fish species have either disappeared entirely from the Delta or are currently threatened with extinction, including most of the historic salmon runs and the Delta smelt, a finger-sized fish that used to be extremely abundant. In the summer of 2007, the population index for Delta smelt was the second lowest ever measured (tied with 2006), just slightly greater than the lowest level ever recorded in 2005. The survival of the species is so precarious that in 2007 a federal judge ordered a reduction in the amount of water pumped from the Delta during critical times of the year to protect the species until new safeguards are in place. While in effect, the judge's ruling could reduce the volume of water exported from the Delta by up to one third. The decline of the Delta aquatic ecosystem is generally attributed to a combination of factors including increased diversion of fresh water, loss and modification of habitats, introduction of exotic species, and impaired water quality due to pesticides and other pollutants.

The Delta is also threatened by flooding. Over 1,000 miles of levees protect subsided Delta islands and infrastructure from flooding, but most of those levees are poorly engineered and vulnerable to severe storms and seismic activity. Over the next 50 years, the Delta faces a two-thirds chance of catastrophic levee failure that would flood multiple islands and greatly increase the intrusion of saltwater from the Bay. Saltwater would affect water quality for local water users as well as those dependent on exports.

The threats are expected to get more severe with climate change. The Sierra snowpack has historically served as a natural reservoir, storing precipitation that falls as snow during the winter and releasing it slowly as it melts in the spring. With rising temperatures, more of the precipitation will fall as rain. Climate change will decrease snowpack storage and increase the risks of downstream flooding. Meanwhile, sea level is predicted to rise by 22 - 55 inches by 2100, or even more. Rising sea levels will erode Delta levees and increase saltwater intrusion.

The health of the Delta is also endangered by proposed water developments. The governor and southern California water managers have proposed construction of a peripheral canal, similar to the canal turned down by the state's voters in 1982. The canal, sometimes called an "isolated conveyance" would bypass the Delta and extract Sacramento River water from a location north of the Delta and deliver it via the existing extensive aqueduct system to agricultural and urban uses in the San Joaquin Valley and southern California. The canal could eliminate the reverse-flow conditions that currently occur near the export pumps, and it would also isolate southern California water users from the numerous risks in the Delta including court-mandated reductions in export pumping. It would be likely, however, to facilitate increased water withdrawal from the vulnerable Delta system, reduce the flushing of agricultural discharges, and relieve southern California water users from feeling responsibility for health of the Delta ecosystem. The governor's Delta Vision Blue Ribbon Panel recently recommended study and analysis of a dual conveyance system - using both through-Delta and around-the-Delta conveyance of water to southern California.

Another threat is increased diversion of flow into new reservoirs. Water managers would like to enlarge the Shasta Reservoir and build a new reservoir west of the Sacramento River at a crossroads called Sites in the Antelope Valley to capture and store more of the river's flow at taxpayers' expense. Although some of the proponents argue that the stored water could be used to help restore the Sacramento River or the Delta ecosystem, there would be no safeguards to ensure that that occurs, and given the expense of these projects, it is more likely that the stored water would be transported to the south, either through a peripheral canal or through a compromised Delta. San Francisco's plan to increase diversions from the Tuolumne River would also result in less water flowing through the Delta.

One way to reduce the threats to the Delta ecosystem would be to reduce the volume of water diverted and exported. A campaign is currently under way to retire drainage impaired agricultural land on the west side of the San Joaquin Valley and the associated water rights to permanently reduce the volume of exports from the Delta. Additional protective measures are described in the Delta Vision article below.

Jody Zaitlin