Although it’s a bit of a surprise that precipitation in the Sacramento River watershed is running more than 200 percent of average, the fact that we have returned to wetter than average years after a run of drier than average years is not. This has been the pattern in California for over 150 years, and this pattern is unlikely to change in the next 150.
But the State Water Project and the federal Central Valley Project were not designed to accommodate this climate variability. Rather they were designed primarily to store water during the winter and the spring snowmelt, both to prevent flooding and to provide water for Central Valley farms and Southern California cities.
In a drought, urban consumption is limited by voluntary and mandatory conservation and agriculture survives by pumping more groundwater. The groundwater basins under the Central Valley recover to some extent during wet years, but the long-term trend is for the groundwater table to sink lower and lower.
The solution to this problem is pretty obvious – extract more water from the river system during periods of higher river flows and store it primarily as groundwater in the depleted aquifers under the San Joaquin Valley. The U.S. Geological Survey estimates that as much as 50 million acre-feet of water – the equivalent of 10 Lake Shastas – has been drawn out, space just sitting there waiting to be reused.
The question then is how to do this? The pumps in the south Delta are operating at less than half their full capacity because there is nowhere to put the water. One possible answer is provided by the Western Delta Intakes Concept, which in periods of high river flows would extract water both from the Old River using existing pumps and at Sherman Island using new pumps. During low flows, water would only be extracted at Sherman Island so that all available water would go through the Delta naturally, helping to restore the ecosystem.
Twin tunnels from the north Delta to the existing pumps in the south Delta do not solve this problem. Those tunnels only provide better water quality for exporters at the expense of water quality in the western Delta. It is time for a real solution to the real problem rather than politics as usual.
Robert Pyke is a Walnut Creek consultant on geotechnical and water resources engineering. He can be contacted at firstname.lastname@example.org.