Ballona Wetlands: Stormageddon 2025!

The media warnings were widespread and serious. A major winter storm, fueled by a tropical atmospheric river, would bring up to 7 inches of rain to Southern California. Our east coast friends texted their concern. They were certain we would be washed into Santa Monica Bay.

To be sure, some high mountain, foothill and burn areas received a lot of rain and its associated damaging flooding and mudflows.

Here at the mouth of Ballona Creek, the result was barely dramatic. NOAA recorded the maximum elevation of Ballona Creek during the storm of December 24-26 at 8.16 feet (above the creek channel bottom) on Christmas Eve morning. Streamflow data measured the peak slightly higher, at 9.15 feet.

Above: Hydrograph for the Christmas 2025 storm flows in Ballona Creek

This is a little more than half of the “flood” level of 15 feet. The channel begins to overtop and flood into adjacent areas at the 15-foot elevation.

Perturbed by a weak La Nina event, the Christmas storm was of the warm, atmospheric river variety, more typical these days due to our rising global temperatures. Such storms bring much rain, but at medium intensity over several days. They don’t usually fill up our storm channels, but rather keep them flowing moderately for days.

In contrast to El Niño events, our “normal” cold storms that brew in the Gulf of Alaska slam quickly into the state, dropping all of their rain in heavy downpours in just a few hours. These are the big events our flood control channels are designed to hold, and our Marina-Playa area is at the “end of the pipe”, so to speak.

Above: The Ballona Creek storm channel can safely hold a once every 100 years, 46,000 cubic feet per second runoff event.

Ballona Creek held a much larger runoff event in February of 2024, when the peak flood level was 11.64 feet, still well below what is considered the "flood stage."

Above: Hydrograph of the February 4-5, 2024 runoff event in Ballona Creek

Ballona Creek’s largest recorded runoff event was on November 21, 1967. The peak flood flow in Ballona Creek was 32,500 cubic feet per second (cfs) that day. The present Ballona storm channel is designed to hold 46,000 cfs, plus a factor of safety.

Our government flood agencies maintain a gauging station - a post of measuring instruments - installed in Ballona Creek near Sawtelle Boulevard. That station and its predecessor have calculated flood water flows from recorded flood surface elevations since around 1928.

Above: Like a sentry on the bike path near Sawtelle Blvd., stream gauging station No. F38C-R records Ballona Creek water levels and meteorological data.

Water flow, in cubic feet per second (cfs) can be calculated when the water surface elevation (above the channel bottom), flow velocity (speed) and channel dimensions are known. Computers hold all this data and crank out flow and elevation values every few minutes.

The Ballona Creek channel is designed to hold a 46,000 cfs flood flow, the 100-year event. The largest of our Christmas 2025 storm flows, 12,257 cfs, didn’t come close to the historical peak or channel capacity.

Above: Streamflow data of Ballona Creek on 12/24/2025 from Gauging Station No. F38C-R at Sawtelle Blvd.

The people who sued to stop the Ballona Wetlands Restoration Project made much ado about flood risk in their court petition. That, too, will turn out to be a big nothing-burger.

A sympathetic judge threw them a bone and ordered the state to reanalyze flood impacts of the Restoration Project using a ginormous and highly unlikely flood peak of 68,000 cfs. The results of reanalysis, I expect, will be no change in either flood impacts or of the Project design.

A flood that large, a roughly once in 600-year event, would swamp neighborhoods far upstream of the Ballona Wetlands. In our local Marina/Playa area, impacts would be limited to minor overtopping of the Ballona Creek levee near the UCLA crew team's launch ramp. That overtopping would occur even without the Wetlands Restoration Project, according to the initial Project analysis.

Above: A once in 600-year catastrophic flood would overtop the creek levee at the UCLA boat facility. Boats would get wet.

The proposed Ballona Wetlands Restoration will greatly expand the creek’s flood plain area, allowing peak flows to spread out between Fiji way and the Westchester Bluffs. Increased by hundreds of acres, the restored wetlands will act as a flood shock absorber, in effect. Today, flood flows are confined to the obsolete concrete channel built a century ago. The Restoration Project will change that for the better and create acres and acres of wetland habitat in the process.

Above: Peak flood flows will have much more area to spread out in the restored Ballona Wetlands.

When the opponents of the Ballona Wetlands Restoration Project wave their arms and yell “flood”, know that they are all wet.

Enjoy your Ballona Wetlands!

References

(1) NOAA Advanced Hydrologic Prediction Service. https://water.noaa.gov/gauges/...

(2) L.A. County Department of Public Works. Channel flow data. https://dpw.lacounty.gov/wrd/rainfall/Home/Flow

(3) L.A. County DPW. Annual Hydrologic Reports. https://ladpw.org/wrd/report/index.cfm

(4) How freeing rivers can help California ease flood risks and revive ecosystems. L.A.Times, 02/20/2024. https://www.latimes.com/environment/story/2024-02-20/california-floodplain-restoration

Manning’s Equation: https://en.wikipedia.org/wiki/Manning_formula

Author’s disclosure of affiliations:

Dr. David W. Kay served on the Board of Directors of the non-profit Friends of Ballona Wetlands from 2007 until 2015, and served as Board President in 2012-13. He presently serves on the Boards of Ballona Discovery Park in Playa Vista and the Playa Vista Parks and Landscape homeowners association.

Dr. Kay is a staunch advocate for the state of California's plans to restore the Ballona Wetlands Ecological Reserve.

From 1984 until 2022, Dr. Kay was employed by Southern California Edison Company, exclusively in the company's environmental services organizations. His many responsibilities included restoration of the 440-acre San Dieguito Wetlands near Del Mar. He retired in 2022 as Senior Manager for Major Project Environmental Management at the company, after 38 years of service.

Dr. Kay earned bachelor and masters degrees in biology and a doctorate in environmental science.

See Dr. Kay’s Patch Community Contributor profile here.