California Department of Water Resources (DWR) | August 26th, 2020
Summary
The California Department of Water Resources (DWR) has authority under state law to construct, operate, and maintain the State Water Project (SWP) to manage, store and de
The California Department of Water Resources (DWR) has authority under state law to construct, operate, and maintain the State Water Project (SWP) to manage, store and deliver water for the benefit of the State. This report is intended to provide information about the key factors affecting the operation of the SWP in California, its long-term capability as a source of water for beneficial use, and an estimate of its current delivery capability. This report meets the requirements of Attachment B to the Monterey Plus Settlement Agreement of May 2003.
Water provided by the SWP is a major source of the water supplies available to many SWP contractors. SWP contractors consist of 29 public entities that include cities, counties, urban water agencies, and agricultural irrigation districts. SWP contractors’ local/regional water users have long-term contracts with the California Department of Water Resources (DWR) for all, or a portion of their water supply needs. Thus, the delivery capability of water from the SWP system is an important component in the water supply planning of its recipients, and ultimately affects the amount of water available for beneficial use in California.
The availability of these water supplies may be highly variable. A sequence of relatively wet water years1 may be followed by a varying sequence of dry or critically dry years. Having good and reliable estimates on how much water each water user under contract with DWR will receive in a given year—whether it be a wet water year, a critical year, or somewhere in between—gives Contractors a better sense of the degree to which they may need to implement increased conservation measures, or plan for new facilities or back up sources of water to meet their needs.
The geography of California and the infrastructure of water transfer from the source areas, located in the Sierra Mountain Range, to areas of demand for water, makes the Sacramento-San Joaquin Delta a key feature of the SWP’s ability to deliver water to its agricultural and urban Contractors in the North Bay, the South Bay, California Central Valley, and Southern California. All but five of the 29 SWP Contractors receive water deliveries by diversions from the Delta. These water diversions are pumped by either the Harvey O. Banks or Barker Slough pumping plants.
DWR, and the United States Bureau of Reclamation (USBR), the managing entities of the two statewide systems of water transfer in California, face numerous challenges in the operation of their diversion facilities in the Delta, and are regulated by several state and federal agencies to maintain, and enhance the Delta’s long-term sustainability.
Maintaining suitable quality of water flowing in the channels of the Delta for the numerous in-basin beneficial uses, and the protection of endangered and threatened fish species, are important factors of concern for the operators of the Delta export diversion facilities. Ongoing regulatory restrictions, such as those aimed at protecting the estuary’s resident and migratory fish species are major challenges to a reliable, and at the same time, sustainable water delivery capability of both, SWP and the Central Valley Project (CVP) systems.
Complications induced by climate change also pose the threat of increased variability in floods and droughts, and the projected sea level rise, caused by the increase in average temperature, complicate efforts to manage salinity levels in the channels affected by tides. Higher ocean levels could result in more frequent water quality degradation in the Delta channels requiring additional outflow from the Delta to maintain water quality objectives, and reduced delivery capability.
Among the other challenges are continued subsidence of Delta islands, many of which are already below sea level, maintained by relatively unstable levee system, and the related threat of a catastrophic levee failure as water pressure increases on fragile levees.
The analyses in this report factor in all the current regulations governing SWP and CVP operations in the Delta and upstream, and assumptions about water uses upstream in the Sacramento River and San Joaquin River watersheds.
Analyses were conducted that considered the amounts of water that SWP Contractors use, and the amounts of water they choose to hold for use in a subsequent year.