Heavy rain this week turned the Los Angeles River’s flood control channel into a raging torrent, and with more storms expected Monday, emergency officials are keeping a close eye on the notorious stretch that has long been vulnerable to flooding.
Glendale Narrows it’s a gorgeous seven-mile stretch of turbulent drainage between Griffith Park and the city center that attracts many walkers and cyclists. But despite its Instagram appeal, narrowing is a nightmare for flood managers.
This is one of the few areas along the World War II channel that has a soft bottom due to the high water table. As a result, it is prone to erosion and the accumulation of sediment, vegetation, and debris that can support flows dumped by heavy storms.
It is also the only major segment of the 51-mile Los Angeles River flood control system that was not designed to contain a 100-year flood or a major flood that has a 1% chance in any given year.
To make matters worse, this section of the river is often overgrown with weeds and trees.
“The Glendale Narrows is a choke point that we’re watching closely,” said Mark Pestrella, director and chief engineer for Los Angeles County flood control. “The big problem is that it is under the control of the Army[Corps of Engineers]which does not have adequate funding to clean out the area on a regular basis”[інжынернагакорпуса}якінемаеналежнагафінансаваннядлярэгулярнайачысткітэрыторыі»[ofEngineers}whichisnotadequatelyfundedtocleanouttheareaonaregularbasis”
Although it is “armored” by flood barriers installed by the Army Corps to protect surrounding neighborhoods, industrial areas and freeways, heavy downpours still have county leaders worried about flooding.
County officials have offered to take ownership of 40 miles of flood control canals that are still owned by the federal government. By doing so, they hope to speed up maintenance and improvements as climate change increases the frequency of extreme weather events.
However, such delegation of authority requires the approval of Congress. – It could happen very quickly, – said Pestrella, – or not in years and years.
The Army Corps of Engineers has helped reduce the risk of flooding by removing about 45,000 cubic yards of sediment from the Glendale Narrows area over the past five years, federal officials say.
At the same time, Pestrella said, his agency regularly makes up for hydraulic deficits in the area by “holding back the flow” of stormwater that flows from the Greater Tujunga and Pacoima County dams on the southern slopes of the San Gabriel Mountains.
Frequent catastrophic flooding prompted civic leaders in the 1930s to transform the Los Angeles River into an elaborate flood control channel and levee system to protect the developing plains.
But new research shows the system’s canals and levees were based on 20th-century assumptions that didn’t take into account recent “whiplash shifts” in extreme weather caused by global warming.
In the past decade alone, California has been hit by cycles of historic drought followed by historic rain, snow and flooding.
“I’m personally concerned about this because our levee systems are very, very old and mostly made of soil,” said Amir AgaKuchak, a professor at the University of California, Irvine. AghaKouchak is a co-author of the 2020 study effects of climate change on levees that protect critical infrastructure—power lines, roads, railroads, gas and oil pipelines—in densely populated areas such as the coastal communities of Southern California.
“The impact of increasingly extreme drought ending in extreme rainfall is something that the engineers who designed Los Angeles County’s flood control systems 80 years ago never considered,” he said.
The Department of Public Works is finalizing a report requested by the Los Angeles County Board of Supervisors on the viability of existing flood control infrastructure and plans to reduce flood risk and increase the resilience of disadvantaged communities.
The report was prompted by a recent study led by researchers at the University of California, Irvine, which showed how extreme weather conditions due to climate change could affect a region whose development was driven by social and racial divisions that favored white residents.
Communities at highest risk include Carson, Compton, Bell Gardens, South Gate, North Long Beach and parts of downtown Long Beach, including the south end of Pine Street near the Long Beach Convention Center.
A victim of geography and rapid growth, the 20-mile-long Compton Creek has drained a 42-square-mile watershed for centuries. However, by the 1920s, residents were asking for protection from floods that submerged businesses.
Today, the headwaters of the creek is a concrete-lined flood control channel that cuts through Compton, carrying water to the Los Angeles River and the Pacific Ocean at Long Beach Harbor.
The dirt bed of the creek passes through some of the most densely populated and industrialized regions of Southern California.
Forecasts for future storms have focused attention on the condition of the earth levees that protect the Compton Creek segment near the 91 Freeway, as well as a stretch of the Los Angeles River further south in Long Beach.
In 2017, the Army Corps conducted an inspection that noted several “serious deficiencies” in each of these 75-year-old levee systems, which are controlled by Los Angeles County.
On the Compton segment, he found trees with trunks more than 2 inches in diameter, depressions in the crown of the levee up to 8 inches deep, an unpermitted 15-inch oil pipeline penetrating the upper part of the river slope and, he said, “vines completely covering most of flood wall, which obstructs the view.’
Problems on the Los Angeles River section included erosion gullies up to 30 inches deep, several 16-inch diameter pressurized gas lines penetrating the toe of the river slope, and an unpermitted 12-inch diameter steel pipe on top of the levee.
Army Corps of Engineers levee officials rated the systems as “minimally acceptable” after determining that the deficiencies would not prevent them from functioning properly during the next significant runoff.
However, the district still has not provided the documentation showing that the deficiencies have been corrected, which is necessary for it to receive federal funding to pay for the repairs, Army Corps officials said.
“We haven’t been provided with documentation that the deficiencies have been corrected,” said Dena O’Dell, a spokeswoman for the Army Corps, “but that doesn’t mean the county didn’t do the job.”
The next periodic inspection of the dams will be conducted next year, federal officials said.
Among the Army Corps’ top priorities in Southern California is spending about $600 million to upgrade the 64-year-old Whittier Narrows Dam, built in a natural gap in the hills about 11 miles east of Los Angeles to collect water from the San Gabriel River and the Rio Hondo.
The three-mile earthen dam was classified as the agency’s highest risk when several potential failure scenarios were determined to threaten more than 1 million people downstream, from Peak Rivera to Long Beach.
The upgrade work, designed to make the dam more resilient to future storms, is expected to begin in 2025 and take four years to complete, officials said.
Meanwhile, a coalition led by the Federal Emergency Management Agency and local flood risk management professionals is preparing to launch an unprecedented annual public service crusade to raise flood risk awareness across the The area of the Los Angeles River watershed is 824 square miles.
Soon, multimedia alerts and television ads will appear across the region, targeting audiences who previously had no idea about the threat.
“Pretty soon,” Pestrella said, “you’ll see people, myself included, on television recommending that we invest in community awareness programs, promote flood insurance and upgrade structures where needed.”
“But now the most important message of all is, rain or shine, don’t go into the river,” he said. “It’s dangerous.”
