Unusually Heavy Precipitation October-December 2010
Despite a strong La Niña condition, the western United States received huge amounts of precipitation from October through December 2010. Only the Pacific Northwest experienced less precipitation than usual. Apparently a feature called a negative Arctic oscillation caused the jet stream to dip to the south, bringing storms to areas that normally would have remained relatively dry under La Nina conditions.
Effects of Increased Precipitation on Reservoirs in California
- Because of water piling up behind Oroville Dam, the State Water Project has increased its allocations to 50%.
- On January 7, 2011, Lake Isabella was at 42% of its capacity (it can be filled to only 66% of its capacity because of a weak auxiliary dam). If Lake Isabella receives too much water from its watershed during January and February, reservoir operators will have to send excess water downstream – well before the big agricultural areas need it. Some of this released water will be stored in aquifers and used later for irrigation (but because it must be pumped out, it is more expensive than water flowing by gravity down from Lake Isabella). An aside: the Kern Water Bank Authority is recharging its aquifer with water from local rainfall, from Lake Isabella, and from the State Water Project. This effort looks admirable, but the nearby Rosedale-Rio Bravo Water Storage District points out that the recent recharge amounts to only 10% of what Kern WBA had pumped out over the last few years. Rosedale-Rio Bravo is accusing Kerm WBA of taking Rosedale-Rio Bravo’s underground water (Kern pumped out so much that Rosedale-Rio Bravo’s water “migrated” into Kern’s aquifer).
- The operators of several reservoirs east of Fresno have been releasing water into the San Joaquin River and letting it flow to the Delta, because they thought it wise to increase capacity in the reservoirs (in case of heavy precipitation in January and February 2011) and because the Friant-Kern Canal was being repaired (normally excess water would be diverted into the canal). Releasing the water is a gamble. If January and February are dry, a good deal of agricultural irrigation water will have been lost.
Proper Water Storage: Dams vs. Underground Storage
We have been getting huge amounts of precipitation but not capturing as much of it as we should. Peter Gleick of the Pacific Institute believes that we are not using all of the underground storage available to us in California. In fact, we abuse the underground storage potential because we withdraw more than we put back in (e.g., Kern WBA). He points out that dams have brought great benefits and also great disadvantages. If dams are weak (as with Lake Isabella), they cannot be filled to capacity. They lose a great deal of water to evaporation. They fill with sediment. Only a one or two good dam sites remain in California, and there is no money to build dams.
Mr. Gleick believes that we need intentional and coordinated groundwater recharges on every major watershed. He praises the efforts of the Alta Irrigation District on the east side of the San Joaquin Valley, which has been recharging for decades.
To have coordinated, statewide groundwater recharge, we will need to have comprehensive statewide groundwater laws. We must intentionally monitor, measure, and report on all groundwater usage.