Behind-the-scenes Battle to Divert L.A.'s Stormwater from Going to Waste

The storm had gathered power for days as it crossed the Northern Pacific, and now its outer band was uppercutting the coast.

By the time Eric Batman arrived at work at 7 Monday morning, a hard west wind was driving rain and hail sideways against windows. Thunder reverberated across the L.A. Basin.

Batman reveled in El Niño's long-overdue rumbling.

His job, as senior civil engineer for the county Department of Public Works, is to keep as much rain as possible from escaping to the ocean.

He wished this storm would slow down a bit. Let the mountains wring more of that water out. Make it more of a challenge.

On the second floor of the department's headquarters in Alhambra, he checked in with the "storm boss," the on-duty engineer in charge of monitoring flow rates throughout the 3,300-mile network of storm drains, channels, debris basins, dams, spreading grounds — everything humans have built over the last century to control the water racing from the high San Gabriels to the sea.

"Where are we open?" Batman asked. "How much are we taking in?"

The storm boss told Batman that he had inflated one of the seven rubber dams along the lower San Gabriel River.

This move would divert the flow into a spreading ground in Pico Rivera — 90 acres of porous soil that can suck up 75 cubic feet of water every second to be stored in the aquifer below.

But the water wasn't there yet. The San Gabriel takes its time.

With age, the county's two big rivers — sisters born of the same weather systems and topography — have grown distinct in appearance and temperament .

The L.A. River is a fast and moody Type A, and it's had a lot of work done.

The San Gabriel is more natural and leisurely paced.

Both rivers and their tributaries cascade from above 7,000 feet to the Pacific Ocean in less than 60 miles and are historically prone to major flooding during wet years.

After floods in 1938 killed 87 people, the Army Corps of Engineers and the L.A. County Flood Control District rapidly sped up the push to build dams and channelize the rivers. Because development had already hemmed in the L.A. River, it had to be encased in concrete to keep it in line, and it became rainwater's 51-mile drag strip to Long Beach.

The concrete made the river safer, but for many — especially during the rare storms that grace a long drought — the sight of the Los Angeles River at full throttle became a disheartening ritual of squandered opportunity.

The 58-mile San Gabriel River, on the other hand, had more open space around it, giving water engineers more room to divert its flow to adjacent spreading grounds. Only the last 10 miles of its bottom is paved. For most of its run to the Pacific, it flows over rock and sand.

So by 9:30 a.m. Monday, while the L.A. River's water was already roaring to the sea at more than 7,200 cubic feet every second, the San Gabriel's was meandering down the riverbed and into spreading grounds far upstream, percolating as nature intended.

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Taxonomy

• Stormwater
• Water Storage
• Storm Water Management