L.A. looks for ways to save ‘free liquid gold’
LOS ANGELES — During one of this winter’s frequent storms, sheets of rainwater spilled from roofs, washed across sidewalks and down gutters into a sprawling network of underground storm drains that empty into the Los Angeles River channel.
Normally a thin flow of treated sewage, the river swelled with mocha-colored runoff. For a time it poured into the Pacific Ocean at a rate of nearly 29 million gallons a minute.
“It kills me when I see all the water running off,” said Deborah Weinstein Bloome, senior policy director at the environmental group TreePeople.
Bloome is not alone in lamenting the loss of what she calls “free liquid gold.”
As the Los Angeles region strives to cut its historic dependence on increasingly irregular imported water supplies, local officials have developed a new appreciation for stormwater.
Instead of flushing it to the sea — as the L.A. Basin has done with studied efficiency ever since the catastrophic floods of the 1930s — cities are trying to figure out how to capture and use runoff to replenish local groundwater supplies.
As matters now stand, hundreds of square miles of concrete and asphalt roads, freeways, parking lots and storm drains turn the basin into a massive funnel whenever it rains.
No single project can change that.
But a multitude of small efforts could add sieve-like qualities to parts of the hardscape.
“You can’t take out the streets,” said David Pettijohn, water resources director for the Los Angeles Department of Water and Power. “So what do you do? You build stormwater capture projects that get water back into the ground.”
A 2012 Los Angeles ordinance requires most new developments to collect the runoff from three-quarters of an inch of rainfall — and reuse it on site or let it percolate into the ground.
The Wilshire Grand skyscraper downtown will have a 50,000-gallon cistern to collect stormwater and condensate from the building’s cooling system.
The University of Southern California’s new residential and retail complex, USC Village, is installing dry wells that will catch and filter nearly 200,000 gallons of runoff in a big storm, allowing the rainfall to soak into the earth instead of draining to the L.A. River and out to sea.
At the Tujunga Spreading Grounds in the San Fernando Valley, a giant excavator is scooping up piles of sandy dirt this winter to enlarge shallow basins that hold runoff released from upstream dams in the San Gabriel Mountains. The stormwater seeps through the porous soil of the spreading grounds into the valley aquifer that provides about 12 percent of L.A.’s water supply.
Still, such projects amount to mere sips of the runoff that rushes into gutters during major winter storms.
The L.A. County Department of Public Works estimates that from Jan. 18-31, roughly 25 billion gallons of stormwater — or about 77,000 acre-feet — drained into the ocean from the Los Angeles River watershed. (The entire city of L.A. uses about 550,000 acre-feet of water a year).
During that same period, the L.A. Department of Water and Power estimates the city retained about 4 billion gallons of runoff — or roughly 12,000 acre-feet. The largest portion of that simply soaked into unpaved land, such as parks. Less than half was actively captured behind upstream dams, in spreading grounds or by small collection projects.
“We haven’t made the progress we should have,” said Mark Gold, associate vice chancellor for environment and sustainability at the University of California, Los Angeles. “The money is not there. That’s been the big issue.”
Capture projects are not cheap. It is costing $28 million to double — to 16,000 acre-feet — the typical recharge capacity of the Tujunga Spreading Grounds.
The price tag for a green street project on Laurel Canyon Boulevard in Pacoima is $3 million, two-thirds of which is funded through a state water bond. The project, now under construction, will collect stormwater from streets, sidewalks and a nearby public school campus and let it percolate into the San Fernando Valley aquifer. The expected recharge is 40 acrefeet a year.
Officials argue that such numbers don’t tell the whole story.
Capture programs don’t just boost groundwater supplies. They divert runoff from floodprone streets, filtering out contaminants as the stormwater seeps through the ground. That helps the region meet water quality mandates to clean up urban runoff that fouls coastal waters — requirements that are expected to cost L.A. County $24 billion over the next couple of decades.