The Valley's Flood Record: 1938, the El Niño Winters, and What They Built Under Your Street

Published November 3, 2026 · BBC Rooter & Plumbing, Northridge · CSLB #720343

The San Fernando Valley was farmland and orchards when it took its worst flood. On the morning of March 2, 1938, downtown Los Angeles recorded 5.88 inches of rain in a single day, still the wettest day on its books. Over the two storms that ran from February 27 to March 4, downtown got 17.75 inches and the Burbank fire station gauge got 12.77. Runoff off the San Gabriels and the Verdugos came down the Tujunga Wash and the Pacoima Wash into a Los Angeles River that was mostly still a dirt riverbed.

Part of the Lankershim Boulevard bridge at Universal City fell into the river where the Tujunga Wash came in. Cars and debris floated down Sherman Way. Telephone lines went dead and whole sections of the Valley were cut off. Across Los Angeles County more than 100 people died and about 5,600 homes were destroyed.

What the 1938 flood built

Almost every piece of flood control you drive past in the Valley today was a direct answer to that week. Hansen Dam on the Tujunga Wash and Sepulveda Dam on the river itself went up right after it. Sepulveda opened in 1941 at a cost of about $6.65 million. It is a dry dam: the land behind it is the Balboa Sports Center, the golf courses and the wildlife reserve, and in a big storm the Corps of Engineers closes the gates and lets that land fill. When it does, Burbank Boulevard through the basin goes under water. The city closes it in the worst storms.

Downstream, the Army Corps spent about 20 years lining the river in concrete. The Tujunga Wash confluence was moved upstream and the Lankershim stretch got the vertical walls you see today. Only a few soft-bottom pieces remain, and the Sepulveda Basin is one of them.

The postwar tracts that filled the Valley after 1946 were built on top of that system. Each block got curb and gutter, a catch basin at the corner, and a storm drain pipe under the street carrying water toward the nearest wash or channel. Under the same streets the city laid a separate sewer main, and every new house got a 4-inch clay or cast iron lateral running out to it. Two buried systems, built at the same time, by the same crews, meant never to touch.

The El Niño winters that tested it

The flood channels have held since 1938. The pipes on private lots are another story, and the El Niño winters are when the weak ones showed up.

Season totals from the Los Angeles Almanac, July 1 to June 30.

The 1982-83 and 1997-98 winters doubled the normal total and kept the ground wet for weeks. In those winters the sewer mains in older parts of the Valley carried far more water than sewage, because rain was getting into them through cracked laterals, open joints and cleanouts with no caps. When a main runs full, every house on it backs up at its lowest drain.

The 2015-16 winter is the reminder that a forecast is a set of odds. It was rated a strong El Niño and Los Angeles got under ten inches. The storm track stayed north.

The February 2024 storm showed what one long atmospheric river can do even outside a record season. Between February 4 and 6 the Los Angeles area got 6 to 12 inches, downtown had its third wettest two-day stretch since the 1870s, and the city logged hundreds of mudslides. On Lockridge Road and Fryman Road in Studio City, mud and rock came down the hillside onto houses and cars.

Where the system is weak now

The public side of the system, meaning the river, the dams, the catch basins and the street storm drains, is the city's and the county's job. What fails on a typical Valley property is the private piping that ties into it, and most of that is now 50 to 75 years old.

• Sewer laterals from the 1950s and 1960s. Clay with mortar or early compression joints, or cast iron under the slab. Roots open the joints, the 1994 Northridge earthquake cracked and offset a lot of them, and the flat ground in the middle of the Valley means many have sags that hold water.
• Yard and area drain lines. Often thin-wall pipe put in by a landscaper, packed with silt and decomposed granite after years of dry seasons. We wrote about these in our storm drain and area drain post.
• Cross-connections. Downspouts or patio drains that someone tied into the sewer instead of the street. They work fine for years and then fill the sewer in the first real storm.

Getting ready for 2026-27

NOAA's October outlook calls this year's El Niño very strong and favors a wet December through February in Southern California. If that holds, the Valley gets another test like 1983 or 1998, and the private pipes are where it will show.

The work that pays off is plain: a camera run on the sewer lateral, a cleaning on any line that is slow, and a look at where the roof and yard water actually go. Where a line is packed with silt or roots, hydrojetting scours it back to full size. Where it is broken, the fix is easiest while the ground is dry.

Read next: what a very strong El Niño does to a Valley sewer line, or see our FAQ.

Call BBC Rooter & Plumbing at 818-280-9135, Northridge, CA. CSLB #720343. Open 7 days, 6am to 6pm.

Frequently asked questions

Why is the Los Angeles River lined with concrete?

Because of the flood of March 1938. Two storms between February 27 and March 4 dropped 17.75 inches on downtown, the river jumped its banks, and more than 100 people died in Los Angeles County. Under the federal Flood Control Act, the Army Corps of Engineers spent about 20 years lining the river in concrete and building dams to hold storm water back.

What does Sepulveda Dam do?

It is a dry dam. Most of the year the Sepulveda Basin behind it is parks, a golf course and a wildlife area. In a big storm the Corps closes the gates and lets the basin fill so the river below does not overtop. It opened in 1941 and can hold back 17,300 acre-feet of water from the 141 square miles of hills and Valley floor upstream.

Were the El Niño winters of 1983 and 1998 really that wet?

Yes. Downtown Los Angeles got 31.25 inches in the 1982-83 season and 31.01 inches in 1997-98, more than double the 14.25 inch normal. The wettest season on that list was not a classic El Niño at all: 2004-05 brought 37.25 inches.

Does the storm drain system connect to my house?

Not to your sewer. Rain from your roof and yard is supposed to leave the property through a yard drain line or across the surface to the curb, then into the street gutter and a catch basin. Your sewer lateral is a separate pipe that runs to the sewer main. Problems start when the two get cross-connected or when the private drain lines on your lot clog or break.

What part of the drainage system is the homeowner responsible for?

Everything on your lot. That includes your sewer lateral all the way to the main, your yard and area drain lines, and any pipe that carries roof water to the curb. The city and county look after the street gutters, catch basins, storm drain mains and the river channel.