DWP Activates Holding Ponds for Sierra Runoff

For a brief time, some weedy fields in Sun Valley will resemble a miniature chain of lakes, thanks to unusually high runoff from the Eastern Sierra.

The Los Angeles Department of Water and Power has activated its Tujunga Spreading Grounds, a series of shallow basins near the Hollywood Freeway that are used to replenish the San Fernando Valley ground-water supply. The DWP draws 15% of the city’s drinking water from that supply and can tap it for up to 30% of the city’s water in a dry year.

The normally inactive spreading grounds, which cover about 130 acres, are used when city reservoirs are full and high runoff would otherwise be left to evaporate in the Owens Valley, more than 200 miles away. The interconnected basins are underlain by sand and gravelly soils, which absorb as much as four feet of water a day.

Laurent McReynolds, a water system engineer, said runoff this year from the Owens Valley and Mono Basin will be the fourth- or fifth-highest since the turn of the century. About 80% of the city’s water is brought from those areas by way of the Los Angeles Owens River Aqueduct system.

Since 1978, about 200,000 acre-feet of water--enough to supply Los Angeles’ water needs for four months--has been put into underground storage by means of the spreading grounds, McReynolds said.

On Tuesday, water began cascading over the top of a large concrete vault in a dry basin flanked by the freeway and a line of electric transmission towers. By Wednesday, as that basin filled, water was running through a culvert beneath Arleta Avenue and into smaller ponds across the street, where a few ducks were making the most of a temporary situation. McReynolds said water spreading will end in about a week unless it rains.

But this season’s abundance of rain should not be taken by consumers as a signal to start hosing down their driveways, DWP officials warn.

“We’re asking all our customers to continue their conservation efforts,” DWP spokeswoman Sandra Tanaka said.