The Delta serves as a unique “hub” in California’s water system, receiving runoff from other watersheds that goes for many beneficial uses throughout the state. The Delta provides a portion of the drinking water for more than 27 million Californians—nearly two-thirds of the state’s population. As the West Coast’s largest estuary, the Delta relies on water flows to ensure a healthy ecosystem while also providing water to irrigate more than 3 million acres of agricultural land. California’s water hub cannot continue to meet these demands.
Water deliveries from the Delta have been reduced significantly in recent years due to years of drought and other systemic problems in the Delta. Left unaddressed, this will create tremendous impacts on California’s economy, environment, agricultural industry and millions of residents throughout the state.
Water is essential to human life and health, and human consumptive uses are the top priority for developed water supply in California under existing law. Water supply, regardless of source, also is an important part of the California economy. Thus, water is both an important natural resource and an important economic resource, to be managed appropriately for identifiable public benefit, and to be preserved for future generations. There is great competition for the limited amount of developed water supply.
Public trust principles, well established in the American legal system with roots back to England and parallel principles in other legal systems, provide a way to frame decisions about the use of water in the Delta and Delta watershed. In our legal system, water is not owned by any user, but the State of California and public retain ownership. Users gain the right for use of water in various ways (riparian, appropriative, etc.), but those rights are conditional as stated both in the term reasonable use and by the underlying public trust for protection of the resource.
The Delta’s watershed is 27 percent of the land area of California and receives 36 percent of the precipitation for the state. Large populations outside of the watershed are serviced by exported Delta water. California has changed little over 116 years, though climate change projections suggest more rainfall than snow, reduced snow pack, and more severe storms in the future. This telling fact is often lost in our discussion over state water policy.
Because of California’s Mediterranean climate, the key challenge for the statewide water system has been to shift water from wet years, wet seasons, and wet locations to drier times and places. California’s major supply of water is from rain and snow that falls north and east of the Delta (with a relatively modest amount imported from other states). But the major demand for water is west and south of the Delta.
The Delta is an important, but not dominant, part of the California’s water supply. A relatively small proportion of total state water from rain, snow or inflow from other states flows into the Delta—15 percent in a wet year, 13 percent in an average year, and 9 percent in a dry year. But the Delta is more important than its share of water because it is the hub of the two largest water systems in the state, the federal Central Valley Project and the State Water Project. These projects use the Delta as a hub of their water conveyance system. The Delta also plays that role in some local water systems such as Contra Costa Water District, while other users take water directly from the Delta’s waterways for use in the Delta. In total, taking water from the Delta has increased significantly over the past half century, mostly for export.
More water is commonly exported from the Delta in average or dry water years than is exported during wet years. In wet years, about 4.6 million acre-feet of water is exported from the Delta; in average and dry years, water exports are about 6.3 million and 5.1 million acre-feet, respectively. The current infrastructure for water conveyance and storage limits ability to capture and store water during high flows for use in dry years.