| The Los Angeles River jumped its banks in many places and broke through levees, as shown here near Victory Boulevard | |
| Duration: | February-March 1938 |
| Fatalities: | 113-115 |
| Damages: | About $40 million USD or $627 million in 2011 dollars (5,601 buildings destroyed; 1,500 damaged; several small towns swept away; much of Riverside and Orange counties completely inundated) |
| Areas affected: | Los Angeles, Orange, Riverside, San Bernardino and Ventura counties, California |
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The Los Angeles Flood of 1938 or 1938 Los Angeles flood was a major flooding event that was responsible for inundating much of Los Angeles, Orange, and Riverside counties, California, during early 1938. The flood was caused by a pair of oceanic storms that swept inland across the Los Angeles Basin in February and March 1938, causing abnormal rainfall across much of coastal Southern California. 113[1] to 115 people perished in the flood, which was one of the most catastrophic disasters in area history.[2] The flood caused the destruction of roads, bridges, and buildings, stranded hundreds of people, and resulted in the flooding of three area rivers and their tributaries; these were the Santa Ana, Los Angeles, and San Gabriel. Despite the extent of the disaster, however, its effects were moderated by existing placements of flood control features in the San Gabriel Mountains; it is said that the damage would have been far worse if there were no flood control measures in place at all.[2]
The flooding event of 1938 was, however, considered a 50-year flood, meaning that it has a 2 percent chance of occurring any given year. The flood resulted in $40 million of damages, and was said by the Red Cross to be the "fifth largest flood in history".[1] It heavily affected public opinion on the safety of area rivers, and as a result, the U.S. Army Corps of Engineers was prompted to begin channelization of the river, and construction of more flood control dams. Dams built in the aftermath of the flood include Sepulveda Dam, Hansen Dam, and Whittier Narrows Dam, which hydrologically connects the San Gabriel River to the Rio Hondo. The channelization, however, does not remove all dangers of floods; there were major floods in 1969, 1980, 1983, 1992, and 1994, with the last said to probably be a 100 year flood.[1]
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Between February 27 and 28, 1938, a storm from the Pacific Ocean moved inland into the Los Angeles Basin, where its contents were stopped from progressing eastward by the San Gabriel Mountains. As the storm could progress no further, the area received almost constant rain on February 27, February 28, and early March 1, 1938, when it finally abated and began to clear. A total of 4.4 inches (11 cm) of rain had fallen thus far, and the storm had formed comparatively minor flooding that had flooded only a few buildings in the low-lying areas of the Los Angeles Basin.[2]
Fifteen hours later on March 1, at approximately 8:45 PM, the second storm entered the basin, creating gale-force winds along the coast and pouring even more rain into the region. Resultantly, the rains added more than 5 inches (13 cm) to the total rainfall amount. The storm ended on March 3, but damages remained huge.[2]
Overall, the flood of 1938 was responsible for destroying 5,601 houses, damaging a further 1,500, killing upwards of 110 people, and stranding over 800 cars.[2] Heavy silt content in floods buried roads and streets in the area, stopping traffic for many days. The Little Rock Dam in the northern San Gabriel Mountains on Little Rock Creek nearly collapsed during the flood, while another dam in Pickens Canyon produced such large flood releases that it inundated the Roosevelt district of Lancaster. The general hospital of Los Angeles County was threatened by rising floodwaters, which had inundated the hospital power generator.[3] More than 20 structures were destroyed in the Arroyo Seco canyon, but there were no fatalities there.[4]
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 cubic feet per second (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, 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 cubic feet (3,700 m3) per second. The Tujunga Wash reached its peak on March 3, 1938, with a water flow of an estimated 50,000 cubic feet (1,400 m3) per second, only 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 flowed from Van Nuys to Lankershim Boulevard and directly into the Los Angeles River.[4]
The San Gabriel River, however, was very much moderated by the extensive series of flood control dams it harbored. Releases from the San Gabriel Dam Number Two (Cogswell Dam) and the East Fork San Gabriel River joined to produce a flow of 100,000 cubic feet (2,800 m3) per second, which all flowed into the reservoir of San Gabriel Dam Number One (San Gabriel Dam). As it filled to capacity, releases of up to 60,000 cubic feet (1,700 m3) per second occurred from No. 1 into the reservoir of Morris Dam, further down on the river.[2]
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".[4]
It was found that the Big Tujunga Dam had actually prevented Big Tujunga Wash water from flowing excessively into the Los Angeles River. 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." [5]
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.[2]
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".[6]