Rain Leaves Behind Gift that Keeps Giving

Drought-buster, not quite.

But the long-awaited storms that drenched the Southland in recent days brought benefits that will remain long past the departing precipitation, water officials say.

The snowpack of the High Sierra, California's main water resource, now contains another 2 inches of water, according to the monitoring system of the state Department of Water Resources. It will be banked until the spring thaw.

However, it's still less than one-third of normal, and with major reservoirs such as Oroville at less than half of capacity, Governor Jerry Brown's drought proclamation remains in effect.

Where the rainfall was heaviest, in the San Gabriel Mountains, a decades-old flood control system steered runoff to so-called "spreading basins," where water percolated into underground aquifers where it can be tapped by wells.

"Week ago today, this was dry as a bone," said Sterling Klippel, senior civil engineer with Los Angeles County, referring to a nearby channel still delivering water to the network of basins below San Gabriel Canyon. "Every drop is precious."

It's the silver lining of the cloudburts that unleashed so much mud from the San Gabriel's wildfire-denuded hillsides.

Apart from the water now being diverted into the spreading basins, more is stored in mountain reservoirs to be released later in the year.

The storms brought a measured 10.71 inches of rain to Cogswell Reservoir. Its water level rose 36 feet, Klippel said.

In LA County, it's estimated the captured runoff amounts to 14,300 acre-feet, enough to supply the needs of some 140,000 persons for a full year. (An acre-foot is the amount of water to cover an acre to a depth of 1 foot.)

The Orange County Water District calculates it captured and put into storage 2,880 acre-feet from the Santa Ana River, plus another 9,600 acre-feet now in Prado Dam will be released gradually to settling basins, according to spokeswoman Gina Ayala.

In the southeast portion of LA County, an area with 43 cities and 4 million residents, groundwater supplies 40 percent of the demand.

The amount of groundwater allocated to be withdrawn each year amounts to about twice the natural replenishment rate, said Robb Whitaker, general manger of the Water Replenishment District.

The spreading basins are part of the strategy to enhance the replenishment rate. 

The district also purchases imported surface water.

To reduce dependence on that, the district is increasing its capacity to treat sewage water for replenishment.

A new plant is planned to treat the outflow from LA County's San Jose Creek facility.

"In two years we'll be able to say our groundwater source is 100 percent sustainable, and as drought-proof as possible," said Whitaker. 

At that point, reclaimed water would provide two-thirds of its needs, stormwater one-third.

Meantime, LA County has taken steps to increase the amount of stormwater that can be recovered from the mountains.

Equipment upgrades have enabled the storage capability of Morris Reservoir above Azusa to be increased 10 percent, Klippel said.

Two years ago, the rebuilding of Tujunga Dam enabled water to be impounded in that canyon once again, and held for release to spreading basins used by the city of Los Angeles.

Bigger gains remain to be tapped in urban storm sewer systems that still send rainwater into channels that go straight to the ocean.

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