California is watching water go out to sea in drought.

LOS ANGELES — A century ago, Los Angeles built what is still widely considered one of the most sophisticated urban flood control systems in the world, designed to hold back waters from massive Pacific storms like the ones that have recently slammed the state.

A series of downpours in the San Gabriel Mountains over the past week poured up to 9 inches of rainfall. Some 8.4 billion gallons were captured behind 14 large dams. They eased floods and built up valuable reserves of water for the dryer summer months.

But in a state that is weathering a crippling, multiyear drought, much larger streams of water — estimated at tens of billions of gallons — have been rushing in recent days straight into the Pacific Ocean, a devastating conundrum for a state whose future depends on holding on to any drop it can.

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California’s multiple fronted environmental wars mean that the golden age of dam building is long gone. However, the county has been slow adopting alternative strategies. The vast majority, or $1 billion, of the nearly $1 billion collected by Los Angeles County taxpayers in the past four year to store more drinking water has been largely wasted.

Now, the county is attempting to expand its water supply by launching a risky experiment. A $300 million-per year program would create hundreds of small water capture projects in the next 30 to 50 decades that could eventually hold as much water as the mountain-dammed mountains.

“It is audacious what we are proposing, and it’s gigantic,” said Mark Pestrella, executive director of Los Angeles County Public Works.

Since December, at least 18 people have been killed by atmospheric rivers. This shows how urgent the situation is. On Friday, California was ready for yet another round of thunderstorms. There would be rain in Northern California later that day, and then a statewide drought forecast for Saturday. Forecasters also predicted heavy snowfall and strong wind gusts in Sierra Nevada.

Some hydrological experts say the new green approach to capturing more of Southern California’s rainfall will be expensive and may deliver less than expected. For more mountain water capture, they suggested that there may be some infrastructure improvements needed in the area.

The state has run out of water supplies and is in desperate need of new sources. This program reflects the dire need for water resources.

Reservoirs across the state have been depleted by drought over the past few years. They are also being destroyed by fire, falling farm fields, brown urban lawns and barren ski slopes. Add to these worries is the crisis at the Colorado River.

Images of floodwaters rushing into oceans as people helplessly watch have been a cruel irony after years of severe drought. California has had abundant water since the 1849 Gold Rush, which brought easterners to the state. But continued population growth, the emergence of the nation’s largest agriculture industry, increasingly tough environmental regulations and now climate change are leaving less and less slack in the system.

Experts say that capturing water during extreme events such as those this year poses a huge engineering, financial, and environmental challenge. Even with all the improvements planned, water supplies will get more limited for three major users: the environment (public), and agriculture.

“Everybody is going to lose something,” said Jay Lund, director of the Center for Watershed Sciences at the University of California, Davis, and a member of the National Academy of Engineering. Lund estimates that 25% to 25% of all agricultural land could become unproductive.

It may be difficult to get more water from rivers, since most of it is intended to support wildlife habitat as required by court orders and regulations. The state’s uncaptured water lies in two principal areas: 65% of it is in the wild and scenic rivers of the northern coast, and another 30% flows from the Sacramento Delta.

The rest of the water, 40% to 70% of all the state’s reservoir and groundwater, depending on precipitation in any given year, is used mostly by agriculture and cities.

The fate of proposals to build a water diversion tunnel within the delta have been a subject of debate for over four decades. Gov. Gavin Newsom backed a scaled down plan.

Until last month, California’s major reservoirs in the Sierra Nevada were far below normal levels, but by Thursday, the gap had significantly closed. Some of them are now higher than average, although Shasta Dam (the largest) was still at 72% and Oroville Dam (the second largest) was at 90%.

Management of storms requires skillful intervention and labor. Consider, for instance, the Los Angeles River. It keeps crews moving around the clock in heavy rains.

Alhambra’s operations center, which is manned by storm bosses, monitors the dam levels and adjusts releases to avoid flooding. Dam keepers up the mountains are alert for any issues and can manually turn valves in heavy rain.

Legal control of the river is held by the Army Corps of Engineers. Federal and local officials communicate continuously via phone. Crews of ground personnel in their hundreds are deployed to monitor and physically measure flows.

Lund explained that it would be financially difficult to build dams to protect water from flooding during major storms in Southern California, such as the current one. She compared it with building freeways so large that there would never be traffic jams. Public works engineers estimated that 18 billion gallons of water poured into the ocean by the Los Angeles River in the storm of Jan. 9.

Voters approved $2.7Billion in 2014 to expand dams. This will add 2.8 million acres of storage capacity. It is one of the largest attempts to increase reservoirs for decades. Construction will begin this year, but critics claim that the state has been slow to implement the plan.

California’s water capture is a mixed bag. Some rivers flow wild into the Pacific while others capture every drop. Groundwater is also subject to a controversial law. In 2014, lawmakers passed landmark groundwater management legislation that prohibits unlimited drawdowns from aquifers.

The new water capture effort in Los Angeles County was prompted not just by water shortages but by a series of environmental lawsuits that sought to stop pollution of the coast with contaminated runoff — the aim of the new system would be not only capturing runoff but cleaning it.

The Safe Clean Water Program, also known as this effort, was slow to get off the ground. It was created under Measure W 2018, which imposed large taxes on impervious surfaces and homes.

The program was able to accumulate money, but there was limited construction during its early years. Pestrella said that activity has picked up over the past year and that $400 million of the $1 billion in taxes collected have been used to fund projects.

Pestrella stated that the program was the most advanced and technically sophisticated effort to capture small amounts of water in the world. It also involves the most challenging terrain.

The bureaucratic structure is complex as multiple committees made up of engineers, environmentalists, and other experts review proposals and give technical scores. Priorities are also set by them. Although outside experts are in agreement about the ambitious scope, they believe the goals are achievable.

“It would not be surprising if they get less water than they hope,” Lund said. “There are lots of ways for things to go wrong and when there are lots of ways to go wrong, some of them will.”

Pestrella acknowledged that there were challenges, saying, “The governance of water is always bumpy.” But he added, “The program looks good to me.”

Bruce Reznik, executive director of the environmental group Los Angeles Waterkeeper and chairman of the capture program’s scoring committee, said the goal of capturing 300,000 acre feet of water per year (the same amount currently captured by dams) has to work or Los Angeles will face more critical water shortages. The county’s 30- to 50-year timeline for completing the program is too slow, he added.

“It is an ambitious goal, but we want to think big,” he said.

Engineers are concerned about maintaining hundreds of cisterns, wells, and other features. Many of these features have filters and permeable bottoms which can become clogged over time.

Water infrastructure has high maintenance costs, and nearly all of Measure W’s tax revenue could be consumed by upkeep at some point in the future, some analysts say.

Tony Zampiello (the water master of San Gabriel River Basin) said that water captured in cisterns may have been taken elsewhere in the past. He is also the executive director of an organization that enforces decades-old court judgments, which allocate water to 192 rightsholders.

“It isn’t new water if it would have entered the system somewhere else,” he said. He also said that a question was raised about how much water from new wells will actually be filtered into the aquifer.

The answer depends on Los Angeles County’s complex geology, which varies greatly through its watersheds. The San Gabriel River flows out of the mountains to a gravel-sand riverbed. As a result, 98% of the flow is captured in settling grounds — designed areas to accelerate infiltration — and percolated into the groundwater basin for later use.

The Los Angeles River does the opposite. It begins in the San Fernando Valley, and descends 40 miles to the bottom. This is as much as the Mississippi River did over 2,500 miles. It travels over extremely impermeable ground, and there is little space in its urban path to spread. About 90% of the flow ends up in ocean.

Zampiello stated, “The upcoming small-scale projects are more important than ever in the Los Angeles River Watershed. There they can prevent runoff and theoretically recharge groundwater basins.”

A 9-mile tunnel measuring 40 feet in diameter and measuring 40 feet in length is another option that the county is considering but has yet to approve. This tunnel would run along the river and divert water from Glendale Narrows where there is significant flooding risk. The tunnel would capture up to 30,000 acres of land per year and cost $2.5B.

California’s other counties are better at conserving water. Orange County Water District, located south of Los Angeles uses 81% domestic water sources. It recycles 100 percent of its wastewater, and captures nearly all of the water that flows along its section of Santa Ana River. This waterway is the longest in Southern California.

John Kennedy, the director of engineering, stated that the district spent $920 million to improve sewage treatment and buy land for settling ground. “We have made huge investments to get to this point,” he said.

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