WATER LARGELY GOES TO WASTE IN BIG STORMS EFFORTS UNDER WAY TO HELP KEEP RUNOFF IN AREA AQUIFERS.

Byline: Kerry Cavanaugh Staff Writer

Drought-prone Los Angeles faces a terrible irony every time it rains: Eighty percent of the precious downpour ends up in the Pacific Ocean and the harder it rains, the more water we lose.

That's because the city's flood-control system is designed to catch and carry storm water away from residents as quickly and safely as possible. That system, together with an increasingly paved and developed urban environment, means there is little time or space for rainwater to percolate into soil and replenish underground water tables.

And the few spreading grounds that are designed to hold storm water are overwhelmed by heavy rains, soaking up only a fraction of the water that hits them.

``The heavier the storm, the more water wasted compared to lighter storms over a couple of weeks,'' said Ken Pellman, spokesman for Los Angeles County's Public Works Department, which operates the San Fernando Valley's four spreading basins.

Water watchers are trying to stop the waste with various plans to catch storm water and use it to replenish diminishing underground aquifers.

The county, the city and the nonprofit environmental group TreePeople have been trying to create more open spaces to catch storm water so it can percolate into aquifers or be reused right away.

They are now installing a giant water-capture system beneath Sun Valley Park as the first step in a $100 million project to catch storm water. They have built smaller systems at Broadus Elementary School in Pacoima. They hope to acquire more land, particularly in flood-prone Sun Valley, to retain rainwater and replenish the aquifer.

``Cumulatively, over time if we can build more of these it might have a beneficial impact (on groundwater),'' said Mark Mackowski, water master for the Upper Los Angeles River Area, which includes the San Fernando Basin.

``These storms don't happen very often but when they do, we need to take advantage of them.''

Groundwater makes up about 14 percent of Angelenos' water supply and the San Fernando Valley aquifer supplies about 12 percent of the total.

However, the San Fernando Basin storage has been on a steady decline since the early 1990s, due to heavy pumping, a drought and the lack of space to recharge water.

``We get spikes in wet years and temporary increases but then we see a decline again,'' Mackowski said.

Precipitation will pump up the city's groundwater but it could take weeks, even months, for rain to percolate down some 200 feet to the aquifer and be measured.

Kerry Cavanaugh, [phone]

kerry.cavanaugh(at)dailynews.com