Los Angeles flood of 1938
The Los Angeles River jumped its banks in many places and broke through levees, as shown here near Victory Boulevard
|Damages||About US$40 million ($627 million in 2011 dollars)
5,601 buildings destroyed
1,500 buildings damaged
several small towns completely destroyed
Large portions of Riverside and Orange counties completely inundated
|Areas affected||Los Angeles, Orange, Riverside, San Bernardino and Ventura counties, California|
|Part of a series on the|
|History of California|
The Los Angeles flood of 1938 was responsible for inundating much of Los Angeles, Orange, and Riverside counties, California during February and March 1938. The flood was caused by a pair of Pacific storms that swept inland across the Los Angeles Basin, causing abnormally high rainfall across much of coastal Southern California. Between 113 to 115 people were killed in what ultimately became one of the most catastrophic natural disasters in Southern California history. The flood caused the Santa Ana, Los Angeles, and San Gabriel Rivers to burst their banks, washing away roads, bridges, and buildings, and stranding hundreds of people. Damages in parts of Los Angeles County were moderated by dams in the San Gabriel Mountains, while Orange and Riverside Counties took more damage because of the lack of flood-control works in the Santa Ana River system.
The flooding event of 1938 is considered a 50-year flood. It resulted in $40 million of damages, and the Red Cross deemed it the "fifth largest flood in history". In response to the floods, the U.S. Army Corps of Engineers began channelizing local streams and building more flood control dams. Dams built in the aftermath of the flood include Sepulveda Dam, Hansen Dam, Prado Dam, and Whittier Narrows Dam, which hydrologically connects the San Gabriel River to the Rio Hondo. These works have been instrumental in protecting coastal Southern California from subsequent flooding events, although the storms of 1969 and 2005, which had larger volume than the 1938 flood, still caused major damage and forced the evacuation of low-lying areas.
Between February 27 and 28, 1938, a storm from the Pacific Ocean moved inland into the Los Angeles Basin, running eastward into the San Gabriel Mountains. The area received almost constant rain totaling 4.4 in (110 mm) from February 27-March 1. This caused minor flooding that affected only a few buildings in isolated canyons and some low-lying areas along rivers.
Fifteen hours later on March 1, at approximately 8:45 PM, a second storm hit the area, creating gale-force winds along the coast and pouring down even more rain. The storm brought rainfall totals to 10 in (250 mm) in the lowlands and upwards of 32 in (810 mm) in the mountains. When the storm ended on March 3, the resulting damage was huge.
Overall, the flood of 1938 destroyed 5,601 buildings, damaging a further 1,500, and stranded over 800 cars. The floods carried large amounts of debris and sediment down from the mountains, burying roads and stopping traffic for many days. The general hospital of Los Angeles County was threatened by rising floodwaters, which had inundated the backup power generator. More than 20 structures were destroyed in the Arroyo Seco canyon, but there were no fatalities there.
Damage was probably most severe along the Santa Ana River in San Bernardino, Riverside and Orange Counties further south. Without any flood control dams, the river swelled to over 317,000 cu ft/s (9,000 m3/s), almost half the flow of the Mississippi River. The flooding was so intense that it transformed most of low-lying northwestern Riverside County and northern Orange County into a large lake. The town of Agua Mansa in Riverside County, with a population of over 200, was completely swept away. The cities of Anaheim and Santa Ana, further downstream in Orange County, were covered with up to 6 feet (1.8 m) of water.
The Los Angeles River reached a maximum flood stage of 130,000 cu ft/s (3,700 m3/s). The Tujunga Wash reached its peak flow on March 3, with a water flow of an estimated 50,000 cu ft/s (1,400 m3/s), after the Big Tujunga Dam had begun emergency spillway releases. The floodwaters swept through incomplete Hansen Dam, escaped the normal channel of Tujunga Creek and flooded a large part of the San Fernando Valley between Van Nuys and Lankershim Boulevard.
The San Gabriel River reached a peak of 150,000 cu ft/s (4,200 m3/s) at the confluence of the East and West Forks. The water swept into the reservoir of the nearly completed San Gabriel Dam, filling it to capacity. Dam operators held releases to a maximum of 90,000 cu ft/s (2,500 m3/s), while further downstream Morris Dam was able to reduce the flood to 65,700 cu ft/s (1,860 m3/s). As a results, large areas of the San Gabriel Valley were spared from flooding, although damages still occurred locally on smaller streams that drain out of the mountains.
Although most of the damage occurred on the seaward (western) side of the San Gabriel Mountains, large amounts of rain also fell on the east side which drains to the Mojave Desert. The Littlerock Dam on Little Rock Creek overtopped during the flood due to a damaged spillway siphon that had been plugged by debris swept downstream, while another dam in Pickens Canyon produced such large flood releases that it inundated the Roosevelt district of Lancaster.
Many people were marooned in the San Gabriel Mountains following the storms, as severe mudslides and flooding prevented their escape. It was said that all roads leading into the mountains had been washed out in some way and notably, Big Tujunga Canyon was "all but swept clean of structures that were not up above the flood line".
Dams such as the San Gabriel River dams and one on Big Tujunga Creek greatly reduced the flooding in many areas. It was said that "Were it not for the Big Tujunga Dam, which finally filled to capacity and began spilling, the flood on the Los Angeles River would have been much worse than it already was." 
Los Angeles County was not the most affected by the floods; Riverside and Orange "took the brunt of the waters" like "gargantuan saucers". (Los Angeles Times, 1938.) At the time, Los Angeles county was the most populous of the three; Orange and Riverside were mostly farming and ranching regions. Therefore, many people were spared by the distribution of floodwaters.
Media and news attention
The Los Angeles Times chartered a United Air Lines Mainliner to provide them an aerial view of flooding damage. The reporter was said to comment that "Disaster, gutted farmlands, ruined roads, shattered communications, wrecked railroad lines—all leap into sharp-etched reality from that altitude." The Los Angeles River also was not the most affected watershed; the Santa Ana River, at twice its length, was famously commented on as being "swollen crazy-mad".
- "The History of the Los Angeles River". L.A. River Connection. Retrieved 2009-05-12.
- "Los Angeles Basin's 1938 Catastrophic Flood Event". Retrieved 2009-05-12.
- Cram, Justin (2012-02-28). "Los Angeles Flood of 1938: Cementing the River's Future". Departures. KCET. Retrieved 2013-07-22.
- "Los Angeles, CA Downpour and Flooding, March 1938". GenDisasters. Retrieved 2009-05-12.
- “Scores trapped in mountains: Pilots report canyon retreats destroyed or heavily damaged.” In Los Angeles Times, March 5, 1938, p. 7.
- “Small Losses prove value of dam system: Huge amounts of water stored and damage held to minimum” in Los Angeles Times, March 4, 1938, p. 7.
- “Plane trip shows scene of desolation.” In Los Angeles Times, March 4, 1938, pp. 1-2.