Storm allows boost in Delta water diversions

The U.S. Bureau of Reclamation was able to take advantage of increased runoff from the wet weekend storms to boost water diversions from the Sacramento-San Joaquin Delta.

Reclamation tripled its diversions from the Delta on Sunday and expects to increase that pumping a little more on Tuesday.

Diversions from its Delta pumping plant near Tracy increased from about 500 cubic feet per second on Saturday to 1,600 cfs on Sunday. Spokesman Louis Moore said pumping was expected to increase to 1,900-2,000 cfs Tuesday morning.

The Delta is the hub of the state’s water supply system, and supplies about half of all the state’s fresh water supply for cities and farms, primarily from Sierra Nevada runoff. Diverting that water requires officials to constantly juggle runoff volume, water-quality rules and protection of endangered species like Delta smelt and Chinook salmon.

“Those flows are just the benefit of this rain and runoff that we’ve had,” Moore said. “They’ll run until further notice, until the runoff starts to just diminish, then they’ll look at what changes need to be made.”

Due to the most severe winter drought in California history, the State Water Resources Control Board on Jan. 31 passed an emergency rule restricting Delta water diversions to no more than 1,500 cfs and waiving some water-quality rules in the estuary. Also, these limited diversions are intended only for “health and safety” purposes, meaning primarily urban water demand, not agriculture.

On Friday, the board amended that rule by stating that DWR and Reclamation could divert more than 1,500 cfs to take advantage of storm runoff, as long as they could meet normal water-quality rules.

The increased pumping will ease some of the strain on Reclamation’s Central Valley Project water customers. But without additional storms, the higher pumping rates are unlikely to continue or significantly dent the drought strain facing the state.

For example, Moore said the storm helped boost storage in Folsom Reservoir but did little to help the much larger Shasta Reservoir, the largest in the state and the primary supply for the Central Valley Project.

The California Department of Water Resources has not yet increased pumping from its own Delta diversion works near Byron, which serve the State Water Project. Those diversions were at about 500 cfs on Monday, putting combined diversions from the state and federal pumps at about 2,100 cfs.

DWR spokesman Ted Thomas said there may be a “short window of opportunity” to increase pumping as runoff from the storm reaches the Delta. State water officials are weighing a number of factors to decide whether to boost diversions, including water-quality rules and endangered species protections.

“They believe they will be able to increase pumping a little bit during that window,” Thomas said, although he could not say when that might occur.