By Tuesday, the combined pumping levels for both projects will fall from approximately 11,000 cubic feet per second to roughly 7,000 cfs, even as modest storms are expected to boost runoff. The curtailment is a proactive effort on the part of SWP and CVP operators to avoid drawing turbid storm runoff toward the south Delta pumps that the projects use to supply 25 million Californians and three million acres of irrigated farmland.
The turbidity generated by this first set of big storms is very high and presents a significant risk of creating a turbidity bridge in the central and south Delta. Creating an expansive turbidity plume into the central Delta may make future management of smelt distribution difficult. The turbidity generated as these first big storms of the season churn streambeds and sweep away debris may draw smelt closer to the water project pumps in the south Delta. By curbing pumping levels now, water project operators hope to avoid a situation that would lead to a marked increase in entrainment of either delta or longfin smelt at the pumping plants and force a longer, more drastic cutback of pumping.
Foregoing the capture of tens of thousands of acre-feet of water over the next several days may allow water project operators to avoid the loss of hundreds of thousands of acre-feet of water supply later in the winter.
The Department of Water Resources and the U.S. Bureau of Reclamation, which operate the SWP and the CVP respectively, are coordinating Delta operations closely with federal and state wildlife agencies.
In December 2012, a plume of turbidity that extended into the central Delta helped to create the situation in which water project operators severely curtailed pumping storm runoff in order to avoid harm to smelt. As a result, hundreds of thousands of acre-feet of water were not moved into reservoir storage. Conditions quickly turned severely dry. In 2013, urban and agricultural water districts that depend upon the SWP and CVP got a small fraction of the supplies for which they contract.
Federal and state water and wildlife agencies, working together on a real-time drought operations team, will continue to monitor turbidity levels in the Delta and the movement of delta and longfin smelt, and will adjust pumping levels accordingly.