California Aqueduct Subsidence Program

Subsidence and the SWP Aqueduct

The California Aqueduct, built and maintained by DWR, delivers water to 27 million people throughout the state.

Subsidence, or the sinking of land, has been documented throughout California for almost a century. Prior to the construction of the aqueduct in the mid-1960s, portions of land near the aqueduct dropped between 20 and 30 feet. While rates of subsidence stabilized for a few decades after original construction, the aqueduct has sustained an alarming and unprecedented increase in subsidence rates. In the three years of the drought from 2013 to 2016, areas of the aqueduct sunk nearly three feet.

Causes of Subsidence

Deep groundwater pumping has been long understood as the primary cause of this alarming trend, and typically ramps up during extended drought periods. The effects of climate change are predicted to exacerbate this trend. In addition, the recent conversion of row crops (often fallowed in dry years) to orchards and vineyards (cannot be fallowed in dry years) has resulted in more subsidence when surface water is unavailable during dry periods.

Impacts of Subsidence

Increased water delivery costs: Subsidence has reduced the flow capacity of the aqueduct in areas. To maintain water deliveries, operators must move water more often during on-peak hours, which increases operating costs and limits the use of renewable energy sources. Since the SWP is the largest user of electricity in California, this impacts all Californians.

Decreased reliability: As the aqueduct sinks, there is increased risk that water will go over the aqueduct liner which could result in erosion or damage to other delivery structures, delivery losses, flooding, and require emergency outages of the aqueduct.

Increased operations and maintenance: To address subsidence, DWR must continue raising the aqueduct lining and embankments, as well as repairing and/or modifying appurtenant structures.

The California Aqueduct Subsidence Study: Supplemental Report presents new data compilation, analysis, and modeling to supplement the 2017 California Aqueduct Subsidence Study report.

This supplemental report addresses land use within a 10-mile-wide study corridor centered on the California Aqueduct in the San Luis Field Division and the San Joaquin Field Division south of San Luis Reservoir; subsidence in the Lost Hills oil filed west of the aqueduct; modeling of aqueduct performance using the U.S. Army Corps of Engineers’ Hydrologic Engineering Center’s River Analysis System hydraulic model; and predictions of future subsidence.

To receive a copy of the original report, or if you need additional information, refer to the listed Contact Information on this page.

Contact Information

Jim Lopes

California Aqueduct Subsidence Program and Oroville Emergency Recovery Program
Division of Engineering

California Department of Water Resources
1416 Ninth Street, Room 1641-2
Sacramento, CA 95814