Water and Power Associates Informing the Public about Critical Water and Energy Issues facing Los Angeles and California

For centuries, the Los Angeles River has been both a giver and a taker of life. During heavy rains, it transformed into a violent torrent, sweeping away homes, bridges, and farmland. During dry months, it often dwindled to a trickle or spread into marshlands. Its unpredictable nature shaped the history, culture, and urban development of Los Angeles.

The Los Angeles River crosses a vast alluvial plain—soil deposited over thousands of years by shifting watercourses. Floods repeatedly forced the river to carve new channels, changing its path through what is now Los Angeles and Orange counties. On average, Los Angeles receives just 15 inches of rain per year, but the surrounding mountains often collect more than 40 inches. Water from elevations near 1,000 feet rushes downhill to sea level in only 50 miles. This steep drop created the perfect conditions for flash floods each winter.

From the DWP Historical Archives

The Los Angeles River has often been described as temperamental: “She has changed her name, often her course, and many times the topography of the land she flows through.”

The river’s first written record by Europeans comes from August 2, 1769, when Father Juan Crespí of the Portolá expedition described a “beautiful river” lined with cottonwoods and alders. Because the date coincided with the Feast of Our Lady of the Angels of Porciúncula, the expedition named it Río de Porciúncula. His journal noted fertile soil, wild grapes, and rose bushes—factors that later influenced the decision to establish El Pueblo de Nuestra Señora la Reina de Los Ángeles in 1781.

Spanish settlers quickly tapped the river with the Zanja Madre (“Mother Ditch”), an irrigation system that supplied water to crops and the pueblo. But as they soon learned, the river was prone to dramatic floods.

Historical Notes

Originally a free-flowing alluvial river, the Los Angeles River shifted courses frequently. The flood of 1815 rerouted its waters through what is now downtown, flooding the original Plaza and forcing its relocation. Another major flood in 1825 returned the river to its present course and altered its outlet from Ballona Creek to San Pedro Bay. These floods drained marshes, destroyed sycamore forests, and even caused the Los Angeles and San Gabriel Rivers to merge temporarily.

For decades after, the river alternated between quiet periods and destructive floods, shaping settlement patterns and forcing residents to adapt to its power.

Historical Notes

During drought years, the Los Angeles River often ran dry, exposing its sandy bottom. Early industries along the banks—including agriculture, tanneries, and later railroads—depended on its water but also dumped waste into it. By the early 20th century, the river’s unpredictability made it both an essential lifeline and a threat to the city’s expansion.

Historical Notes

In the late 1930s, much of the river near downtown remained unpaved, and the adjacent corridor was heavily industrial. The towering gas holders of the Southern California Gas Company dominated the skyline, reflecting a period when utility infrastructure was built on a monumental scale and often positioned near waterways for logistical convenience. Facilities like these underscored the importance of the river’s corridor as both a natural and industrial artery, even as the city moved toward encasing the river in concrete.

Historical Notes

There have been eight major floods in the San Fernando Valley since 1861, but the 1938 flood was one of the worst. Rain lasted for three days, breaking the Big Tujunga Wash levee and destroying 77 spreading basins. Warner Bros. studio buildings and the Olive Avenue Bridge were washed out. It took 30 days to clear storm debris, while utilities such as telephone and power were cut off.

Historical Notes

From February 27 to March 1, a Pacific storm dropped 4.4 inches of rain on the lowlands and more than 32 inches in the mountains. A second storm on March 1 intensified the flooding. By March 3, the disaster had taken 115 lives.

Historical Notes

The 1938 flood destroyed 5,601 homes and businesses and damaged another 1,500. Flooding was accompanied by debris flows of mud, trees, and boulders. Roads and railways were buried, power and communication lines severed, and dozens of bridges swept away. Some communities were buried under six feet of sediment.

Historical Notes

About 108,000 acres were flooded countywide. The San Fernando Valley was the worst-hit area, as many homes had been built on former floodplains during the 1920s boom.

Historical Notes

Many homes were located on old riverbeds that had not flooded in recent memory, leaving residents unprepared for the disaster.

Historical Notes

Swollen by tributaries, the Los Angeles River reached a flood stage of 99,000 cubic feet per second. The waters surged south, inundating Compton and Long Beach. A bridge at the river’s mouth collapsed, killing ten people.

Historical Notes

Although the 1938 flood caused the greatest destruction in Los Angeles history, its rainfall totals and river flows were still less than the Great Flood of 1862. By 1938, however, Los Angeles was far more populated, magnifying the disaster’s impact.

Historical Notes

Rail lines were severely disrupted, with bridges washed away and tracks buried under debris.

Historical Notes

The 1941 flood reinforced public demand for permanent river control, leading to the Army Corps of Engineers’ decades-long channelization project.

Historical Notes

After the great storm of 1938, due to public outcry, the Army Corps of Engineers began a 20 year project to create the permanent concrete channel which still contains most of the of riverbed today. They also installed a network of channels and flood basins to control the rampages of the waterways feeding the Los Angeles River.

Historical Notes

Since 1938, 278 miles of river and tributaries were retrofitted and more than 300 bridges were built. With the river encased in cement, the natural sharp turns were now straightened. Any evidence of vegetation was completely removed, allowing runoff from the San Gabriel Mountains to escape through the river and out of Long Beach at up to 45 miles-per-hour. Streets and sewers were connected to drains along the river, designed to quickly capture and move rainfall away from the surrounding streets.

Historical Notes

The Corps’ standardized trapezoidal design—with sloping sides and a wide bottom—allowed for rapid drainage of floodwaters while making maintenance easier.

Historical Notes

The 1937 view shows the Los Angeles River as a wide, meandering waterway shaded by trees and flanked by open land. By 2015, the same location in Studio City had been converted into a straightened flood-control channel, with concrete replacing earth and vegetation. This transformation, carried out by the U.S. Army Corps of Engineers, reduced the flood risk for surrounding communities but erased much of the river’s natural character. The stark contrast captures the tension between safety and ecology, a theme that continues to shape discussions about river revitalization today.

Historical Notes

Before channelization, the Los Angeles River was a natural, meandering waterway. In the dry season it often appeared as a trickle, but during winter storms it could swell into a wide, unpredictable torrent. The soft-bottom river supported riparian habitat, with willows, sycamores, and wetlands providing shelter for wildlife. Yet its shifting course and seasonal flooding repeatedly threatened surrounding communities, setting the stage for the massive flood-control projects of the late 1930s and beyond.

Historical Notes

This photograph captures the transition from a natural riverbed to an engineered flood-control channel. Taylor Yard, at right, was at the time a major Southern Pacific rail hub, linking Los Angeles to national markets. The prominent tower of Forest Lawn’s Great Mausoleum punctuates the horizon, while rows of modest houses line the river’s banks—evidence of how closely neighborhoods were built to the once-unpredictable waterway. The photo underscores the dual character of the river: an engineered solution to flooding, and at the same time a defining geographic feature around which communities, industry, and cultural landmarks developed.

Historical Notes

In 1940, the Los Angeles River still retained sections of its natural bed as it wound past Elysian Valley and the Southern Pacific’s sprawling Taylor Yard rail facility. The riverbed was wide and unpaved, often reduced to a shallow stream in dry months but capable of overflowing during storms. By 2023, the scene has changed dramatically. The river here remains channelized, but much of Taylor Yard has been repurposed into the Rio de Los Angeles State Park, part of ongoing efforts to reclaim industrial land and reintroduce green space along the river. This “then and now” pairing illustrates both the loss of the river’s natural form and the city’s more recent attempts to reconnect communities with the waterway through parks, bike paths, and revitalization projects.

Historical Notes

From the vantage of the Glendale-Hyperion Bridge, the 1937 view reveals a broad, natural channel filled with vegetation and capable of spreading widely during storms. The 2015 view shows the same stretch after decades of channelization—its floodplain replaced by concrete walls, roads, and development. While the channel has largely succeeded in containing floodwaters, it has also become emblematic of the city’s sacrifice of natural landscapes in favor of urban expansion.

Unlike most of the river, however, this reach was left with a natural bottom so that stormwater could percolate into the ground and help recharge the San Fernando Valley aquifer. The bridge itself remains a link between eras, symbolizing continuity even as the river beneath it has been radically altered.

Historical Notes

The good news is that the introduction of the new flood control channels and concrete lining has alleviated most, but not all, of the flooding problems of the past.

The system successfully protected Los Angeles from massive flooding in 1969.

Historical Notes

Los Angeles Times Article dated Jan. 26, 1969:

The worst floods in 31 years hit Southern California as a double-barreled storm continued for the 8th straight day, leaving at least 82 persons dead, 2 missing and property damage estimated at more than $15 million.

At least 34 persons have been killed since the storm went into its second phase on Thursday–9 of them buried alive when mudslides invaded their homes–and whole communities were cut off by flood control waters.

Authorities in the area estimated more than 6,000 persons evacuated from danger areas as severe flooding hit cities from Fresno in the north to San Juan Capistrano in the south. …

Historical Notes

The North Broadway Bridge underwent an 18 month, $20-million dollar renovation and seismic retrofitting that was completed in 2000.

Historical Notes

By 2013, the Los Angeles River had long been confined within its concrete channel, a system designed in the wake of the devastating 1938 flood to prevent future disasters. This view near downtown shows the river as most Angelenos know it today—an engineered flood-control corridor running beneath city bridges. Though effective in protecting neighborhoods and infrastructure, the stark channel has also become a symbol of the city’s uneasy relationship with its natural waterway. In recent years, this stretch has been central to discussions about revitalization, with proposals to restore habitat, improve water quality, and create public spaces while still maintaining flood protection.

Historical Notes

The Los Feliz Bridge has long been a vantage point for witnessing the Los Angeles River at its most powerful. In 1969, a series of winter storms brought over five inches of rain in a week, producing the worst floods since 1938 and causing widespread damage across Southern California. More than 80 lives were lost and thousands were displaced. Over half a century later, the 2023 photo shows a similar scene as torrential rains again swelled the river, with water rushing nearly to the top of the channel walls. While the concrete lining has largely protected the city from catastrophic flooding since the mid-20th century, these images highlight the river’s enduring volatility and the challenges of balancing flood control with urban development and climate change–driven extremes.

Historical Notes

Today, the Los Angeles River stretches for about 60 miles from its headwaters in Canoga Park to its outlet in Long Beach Harbor. Though often seen as little more than a concrete flood channel, the river still plays a vital role in the region’s hydrology and identity. Along its length, it passes through diverse communities, industrial corridors, and green spaces, connecting the San Fernando Valley, downtown Los Angeles, and Gateway Cities before reaching the Pacific Ocean. In recent decades, renewed attention has been given to restoring portions of the river, reimagining it not just as a flood-control channel but as a civic and ecological asset. The map underscores how the river binds together much of Los Angeles County, both historically and in its future planning.

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