Abstract
Much of the water supplied in California for agriculture and cities is taken directly from the Sacramento–San Joaquin Delta (Delta) or indirectly from surface and groundwater diversions upstream. These water supplies have great economic and social value, and considerable ecosystem effects. Long thought of as the major source of water for economic growth in California, the reliability of water supplied from the Delta is threatened by drought, flood, climate change, earthquakes, growing water demands, and deteriorating conditions for endangered species and native ecosystems. Research in recent years has improved understanding of how management of the Delta ties together the quantity and quality of water available statewide. These ties run from the Sierra mountains and coastal streams, through the Central Valley, to the San Francisco Bay Area, and over the Tehachapi Mountains to southern California. For decades, Californians counted on reducing Delta outflows to supply water for growing water demands in its watershed and in water importing areas. With greater competition for water, concern for environmental effects, and a changing climate, the reliability of such supplies is now diminishing. This must lead to tighter accounting and modeling of water supplies in the Delta and throughout its watershed. This paper reviews issues about Delta water supplies, operations, regulations, and reliability; the economic value of supply; costs of unreliability in quantity and quality; and several directions for further scientific and technical work on water supply reliability.
Highlights
The Sacramento–San Joaquin Delta (Delta) was created beginning about 6,000 years ago, after the last ice age, by sea level rise progressively drowning the confluence of the Sacramento and San Joaquin rivers, just upstream of San Francisco Bay
I offer some fundamental observations about the Delta and water supply, along with some directions and limitations for the use of science to improve our understanding and management of water supplies both diverted from Delta outflow, and flows within the Delta
The physical reliability of water quantity and quality for diversion is threatened by increasing water demands for ecosystem management and growing numbers of endangered species, risks of levee failure from subsidence, floods, earthquakes and sea level rise, more stringent water quality and drinking water standards, increasing upstream water diversions, and climate warming (Lund et al 2010; Anderson et al 2008)
Summary
The Sacramento–San Joaquin Delta (Delta) was created beginning about 6,000 years ago, after the last ice age, by sea level rise progressively drowning the confluence of the Sacramento and San Joaquin rivers, just upstream of San Francisco Bay. Modeling of water supply reliability is important and offers insights to decision-makers, Figure 8 Total Delta water project deliveries (SWP, CVP, and CCWD) estimated over historical hydrologic conditions (water years) with 2015 level of development and regulations (black solid line with diamond markers) and with BDCP Alternative 4 H3 conditions.
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