Water Could Los Angeles design its way to water independence? A pair of architects are reinvisioning the city's relationship with water, starting with storm runoff.

The San Fernando Valley is a sprawling concrete metropolis of stucco-encrusted- apartment buildings and chain stores — a sun-baked suburb with freeways “running through the yard,” as songwriter Tom Petty aptly put it. To Peter Arnold, an architect in Los Angeles, the maze of cul-de-sacs and identical houses represents a failure of vision: a city that relies on a water system that is invisible, and therefore undervalued. “You just turn on a tap,” he says, “and there it is.”

For the past 17 years, Arnold and his wife, Hadley, who is also an architect, have worked to change that attitude. Through a small nonprofit research and design firm called the Arid Lands Institute, the Arnolds are creating a massive hydrologic model of Greater Los Angeles, part of a broad urban design initiative they hope will fundamentally change the way Western cities deal with water.

Raised in the outskirts of Denver, Peter Arnold first became fascinated by water through the lens of his large-format camera. Flying over the sweep of deserts and mountains from the Pacific Coast to the High Plains, he saw how landscapes are shaped by the capture of water.

He married Hadley, a New Englander, and the two began visiting rural New Mexico to learn about the ancient acequia systems, introduced by early Spanish settlers and still in use today. These communally managed irrigation ditches not only distribute water democratically among farmers, they include plans for water scarcity. In the acequias, the Arnolds saw equality, visibility, and local participation — everything modern water systems are not.

Courtesy Arid Lands Institute

Today’s systems — massive, opaque, bureaucratic infrastructure projects — are under stress. Like many Western cities, L.A. relies on snowmelt and a vast system of reservoirs, canals and pipelines for much of its water. But climate change is disrupting the system, bringing earlier spring melts, or rain instead of snow, or no precipitation at all. This year, for the first time, the manual measurement of the Sierra Nevada snowpack was conducted on bare grass. Meanwhile, in any given rainstorm, millions of gallons of unused rainwater gush straight into the Pacific.

That’s a lot of water, even for Los Angeles, a city on the edge of a desert. In 2013, the driest year in L.A.’s recorded history, it rained 3.6 inches, more than 12 billion gallons of water, and enough to supply more than 250,000 people annually. A well-designed L.A. could provide 82 percent of the city’s water needs locally, keeping 350,000 acre-feet of water in the Colorado River, says Arnold, citing a study commissioned by the Metropolitan Water District of Southern California.

As California lawmakers scramble to deal with the drought, imposing mandatory water restrictions and pushing big new storage projects, the Arnolds envision an entirely different approach, something more local — and more sponge-like. The key to their plan is a digital mapping tool they dubbed Hazel, after the wood used in traditional divining rods. Using geospatial data, Hazel exposes the landscape’s hidden hydrology. Right now, it’s looking at the San Fernando Valley, showing precisely — street by street, lot by lot — where 92,000 acre-feet of stormwater could best be captured, stored and treated, to offset the city’s dependence on piped-in water.

Hazel tries to make water sense of the city, identifying contaminated areas where water might best be captured in rooftop cisterns, or where, just a few blocks away, underground storage via permeable pavement might be a better bet. This detailed mapping could change the way planners and architects work, transforming every surface into a mini watershed. A well-placed urban forest might help absorb rainwater, for example, funneling it beneath Ventura Boulevard, or cisterns could be placed over the buildings lining Mulholland Drive.

Right now, the Arnolds are fine-tuning Hazel’s software so that they can begin figuring out how, exactly, 10,000 pieces of stormwater capture infrastructure might work in the San Fernando Valley.

But really, the model works best as a teacher. “What we’re trying to do with Hazel is to give neighborhoods information they need to design the right system,” Hadley Arnold says. The right system would build the knowledge of water into the design, much as New Mexico’s acequia communities have done. The goal, she adds, is more than just wringing water from the sky. It’s to make water visible — and therefore valuable.

“Every day, the built environment should tell you how you’re doing with your water supply,” she says. In a water-savvy L.A., metering systems could be public art installations at the local bus stop, or a sculpture that swells and shimmers to show water supply. The idea is actually an old one, perfected by the Romans thousands of years ago in places like Hadrian’s Villa, outside Rome — where the Arnolds first met. “We like to think beautiful space and incredible water infrastructure are part of our DNA as a couple,” Hadley says. The same could be said of L.A. We just can’t see it yet.