California is preparing for a potentially historic El Niño winter by proactively emptying reservoirs to create flood-control cushions and accelerating groundwater recharge projects to divert raging stormwaters into subterranean aquifers.

Because state reservoirs are already relatively full from previous wet cycles, the state’s strategy has shifted heavily toward defensive water management and capturing rapid runoff before it triggers severe urban flooding.

 Reservoir Management:

Maximize Capacity: Water agencies are shifting away from water conservation and focusing entirely on flood control.

Preemptive Drawdowns: Major flood control agencies, such as LA County Public Works, are actively emptying major dam reservoirs and debris basins to build a 75% capacity cushion. For example, crews are aggressively clearing tens of thousands of cubic yards of sediment and dirt from reservoirs like the Devil's Gate Dam to handle sudden mountain runoff.

Controlled Water Releases: Reservoir operators are preparing for early, managed water releases.

Warm El Niño storms often drop heavy rain at lower elevations rather than mountain snow, sending runoff rushing into rivers and lakes almost instantly. Operators must clear this space ahead of time to prevent emergency spillway overflows.

Aquifer Recharge: Diverting the Deluge. The state is leaning heavily into "Flood-Managed Aquifer Recharge" (Flood-MAR) to turn a flood risk into a future water resource.

Groundwater Basin Capture: Local water districts, such as the Zone 7 Water Agency in Northern California, are upgrading their network of pipes, pumps, and spreading grounds. The goal is to capture excess stormwater that would otherwise flood towns and channel it directly into underground groundwater basins.

Spreading Grounds Expansion: Flat, porous zones of land are being prepared to act as giant sponges. By intentionally flooding these designated agricultural fields and open plains, the state slows down the destructive velocity of storm runoff and gives the water time to naturally seep into depleted aquifers.

Additional Infrastructure Reinforcements

Beyond water storage, intensive structural stabilization is happening across critical water channels:

Levee Reinforcements: In vulnerable choke points like the Sacramento-San Joaquin River Delta, engineers are working with local reclamation districts to strengthen levees against seepage, erosion, and prolonged high-water pressure.

Coastal and Estuary Controls: Coastal agencies are setting up temporary beach berms and planning strategic breaches of closed estuaries to prevent ocean surges from backing up into inland storm systems.

• LA County Flood Protection -Infrastructure & Safety
• California Department of Water Resources
• American Red Cross - Flood Preparedness
• LA City Emergency Management Department

2015 Credit LAist - 

"A wet winter could test some LA flood control dams choking with sediment"

Southern California could be in for above-normal rains this winter if predictions of a large El Niño system in the Pacific pan out. Flood control workers across Southern California have been preparing for possible torrential storms by clearing out debris basins and flood channels.

Civil Engineer Alma Fuentes rides a 2,000-foot long aerial tram to climb the 500 feet to reach the top of Pacoima Dam, July 22, 2015. The dam captures rain in a 28-square-mile watershed above Sylmar and the San Fernando Valley,. She oversees a project to clear the reservoir and the dam outlet works of sediment from the 2009 Station Fire.

(Sharon McNary/KPCC)

 

Dam operator Joe Torres greets Alma Fuentes as she steps aboard the small gondola that will take them 500 feet up to the top of the Pacoima Dam above Sylmar July 22, 2015. Fuentes is the civil engineer overseeing a project to remove sediment from the dam.

(Sharon McNary/KPCC)

 

Civil Engineer Alma Fuentes at the Pacoima Dam, July 22, 2015.

(Sharon McNary/KPCC)

 

Ann Job, (previous) president of the Sylmar Neighborhood Council, points out the Pacoima Dam far in the background. A proposal to clear sediment from the dam would transport it on a conveyor belt down the Pacoima Wash near where she is standing.

(Sharon McNary/KPCC)

 

Rear view of Pacoima Dam under construction, January 20, 1928. When the dam opened the following year, it was, at 365 feet tall, the highest concrete dam ever built in the United States.

(USC Libraries, Special Collections. California Historical Society Collection, 1860-1960)

 

A view of the Big Tujunga Dam in Angeles National Forest.

(Akaporn Bhothisuwan via Flickr Creative Commons)

Big dams and the water and debris basins behind them are the first line of defense against flooding. There are scores of these dams stretching from Santa Barbara to Orange counties. Officials in those counties — along with counterparts in Riverside, San Bernardino and Ventura — all say their flood control systems are ready for whatever El Niño throws at them.

But Los Angeles County still has some work to do. Five of the county’s 14 flood control dams have been filling up with sediment washed down from mountainsides stripped of trees and vegetation by catastrophic wildfires, like the Station Fire in 2009. The sediment has limited the capacity of the dams to hold storm water.

Devil’s Gate Dam above Pasadena is in the worst shape. Its storage capacity is down by 60 percent. In a major storm, of the type that usually hits the region every 50 years or so, Devil’s Gate Dam would not be able contain all the water and debris coming in. Parts of the Arroyo Seco could overflow, flooding nearly 500 homes and businesses and closing the 110 Freeway.

This map shows the footprint of the 2009 Station Fire and the locations of the five dams that the Los Angeles County Flood Control District has identified as needing sediment removal. Residents near the dams know the work needs to be done, but many have challenged the flood control district over how.

Still, even if all opposition evaporated today, final planning, permitting and approvals for these projects are still needed. It’s not likely even a single grain of sediment will be removed before this winter.

THE ABOVE STORY IS FROM 2015

Credit - LAist