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California DWR allocates 5% of supplies from State Water Project

California DWR allocates 5% of supplies from State Water Project
(An aerial overview of the recently completed Lake Oroville main spillway during Phase 2 of the recovery efforts. Work continues on the concrete cap below the Lake Oroville emergency spillway weir at the Butte County, California site. Photo taken January 24, 2019. Kelly M. Grow / California Department of Water Resources, FOR EDITORIAL USE ONLY)

The Department of Water Resources (DWR) in California has announced an initial State Water Project (SWP) allocation of 5% of requested supplies for 2023. The SWP provides water to 29 public water agencies that serve 27 million Californians and also uses the water for hydropower generation.

The state is preparing for a fourth dry year and continued extreme drought conditions, so DWR said it will also assess requests for additional water that may be necessary for health and safety, including minimum domestic, sanitation and fire suppression needs.

The SWP is a system of 32 storage facilities, 21 pumping plants, four pumping-generating plants, eight conventional hydroelectric plants and about 700 miles of canals and pipelines. Among these generating plants is the 762 MW Hyatt Powerplant at the foot of Oroville Dam.

“This early in California’s traditional wet season, water allocations are typically low due to uncertainty in hydrologic forecasting. But the degree to which hotter and drier conditions are reducing runoff into rivers, streams and reservoirs means we have to be prepared for all possible outcomes,” said DWR Director Karla Nemeth.

The state’s water year runs from Oct. 1 to Sept. 30 and is the official 12-month timeframe water managers use to compile and compare hydrologic records.

Lake Oroville, the SWP’s largest reservoir, ended Water Year 2022 about 400,000 acre-feet higher than the previous year, which was the lowest storage level on record.  However, Oroville remains at just 55% of average for this time of year and DWR is conserving existing storage in Lake Oroville in the event dry conditions continue. The initial 5% allocation would be met by flows from winter storms entering the delta as well as stored water in San Luis Reservoir. If Lake Oroville storage levels improve as the wet season progresses, DWR said it will consider increasing the allocation if warranted. DWR is also working closely with senior water rights holders on the Feather River downstream of Lake Oroville to monitor conditions and assess water supply availability should dry weather persist.

California traditionally receives half its rain and snow by the end of January. Water managers will reassess conditions monthly throughout the winter and spring. Starting in February, the assessments will incorporate snowpack data and runoff forecasts. For the second year in a row, DWR is broadening the deployment of technologies such as aerial snow surveys that can collect snow measurements farther upslope of the Sierra Nevada. This will improve forecasts of spring runoff into reservoirs, according to a release.

If dry conditions persist, DWR may pursue submission of a Temporary Urgency Change Petition and re-installation of the West False River Emergency Drought Salinity Barrier in the Sacramento-San Joaquin Delta.

Each year, DWR provides the initial SWP allocation by Dec. 1 based on available water storage, projected water supply and water demands. Allocations are updated monthly as snowpack and runoff information is assessed, with a final allocation typically determined in May or June. The lowest initial SWP allocation was 0% on Dec. 1, 2021, with limited water designated only for any unmet human health and safety needs. Last year’s final allocation was 5% plus unmet health and safety needs.

In October, Hydro Review reported that projections at the beginning of California’s water year forecasted warmer, drier conditions, causing “fresh concerns about the fourth year of extreme drought for the state.”