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All types of floods can occur in California, though 90% are caused by riverine flooding. Such flooding generally occurs as a result of excessive rainfall, excessive snowmelt, excessive runoff, levee failure or a combination of these sources. Below is a list of flood events that were of significant impact to California
In January 1850, a major flood devastated the new city of Sacramento; rain from heavy storms saturated the grounds upon which Sacramento was built, and the American and Sacramento rivers crested simultaneously.
Many floods occurred later in the city of Sacramento and other low lying cities along the Sierra born rivers due to hydraulic mining at locations in the foothills e.g. malakoff diggings in which sludge runoffs purportedly raised the river beds in the valley below, an additional 2 ft.
Hydraulic Gold mining became a hot topic for the time and was eventually stopped by Ca. Lawmakers. Malokoff diggings is now a State Park missing a whole mountain due to the massive water jets that can still be seen there. Well worth the visit. Camping allowed, the old city still stands.
Beginning on December 24, 1861, and lasting for 45 days, the largest flood in California's recorded history was created, reaching full flood stage in different areas between January 9–12, 1862. The entire Sacramento and San Joaquin valleys were inundated for an extent of 300 miles (480 km), averaging 20 miles (32 km) in breadth. State government was forced to relocate from the capital in Sacramento for 18 months in San Francisco. The rain created an inland sea in Orange County, lasting about three weeks with water standing 4 feet (1.2 m) deep up to 4 miles (6 km) from the river. The Los Angeles basin was flooded from the San Gabriel Mountains to the Palos Verdes Peninsula, at variable depths, excluding the higher lands which became islands until the waters receded. The Los Angeles basin lost 200,000 cattle by way of drowning, as well as homes, ranches, farm crops & vineyards being swept-away.
The storm extended from Fort Ross on the coast to the Feather River basin. La Porte, in the Feather River basin, had 57.41 inches (1,458 mm) of rain in 20 days, an event with a return period of 12,000 years. The flood episodes of 1907 and 1909 in California resulted in an overhaul of planned statewide flood control designs.
In the last week of December 1933, 12 inches (300 mm) of rain fell in the communities of La Crescenta, La Cañada and Montrose just north of Los Angeles. On New Year's Eve, more rain fell. The result was a flood of mud and water that began around midnight, destroying more than 400 homes in this area. This was commemorated in Woody Guthrie's song "Los Angeles New Year's Flood". As a result of this flood, the Army Corps of Engineers and the County of Los Angeles built a flood control system of catch basins and concrete storm drains to prevent a repeat of the disaster.
The storm of February 4–7, 1937 resulted in the highest four-day rainfall totals at several stations in the Santa Ana River basin. The Riverside North station had over 8 inches (200 mm) of rain in that four days, which equaled a 450-year event. Other stations also received high amounts of rain within those four days.
The storm of December 1937 was a high-elevation event in the northeast corner of the state.
Two significant cyclones moved through the region; one between February 27 and March 1 and the second between March 1 and March 3. Over 254 mm (10.0 in) of rain had fallen during the five-day period. Massive debris flows moved out from the San Gabriel Mountains into the Los Angeles Basin. Although Los Angeles County experienced damage, Riverside and Orange counties bore the brunt of the flooding. A total of 5601 homes were destroyed, and an additional 1500 homes were left uninhabitable. The three transcontinental railroads connecting Los Angeles to the outside world experienced washed out bridges and flooded lines, isolating the city. Mail service after the flood was conducted by the U.S. Coast Guard. The death toll was 115. It was the region's worst flood since New Year's Day of 1934. The result of this flood was the Flood Control Act of 1941, which authorized the U.S. Army Corps of Engineers to build a series of concrete sewers.
A statewide disaster was declared November 21 when floods caused 9 deaths and $32 million in damage.
The storm affected the central Sierra and South Bay areas. The Eel River on the North Coast saw the greatest flow of record to that time while Central Valley rivers saw near-record flows. A statewide disaster was declared, with the storm resulting in 74 deaths and $200 million in economic losses. The heaviest 24-hour rainfall was recorded on December 20, when 15.34 inches (390 mm) fell in Shasta County. The storm's toll on Sutter County was severe. At 12:04 a.m. on December 24, 1955, a levee on the west bank of the Feather River, at Shanghai Bend, collapsed and a wall of water 21 feet high entered the county, flooding 90 percent of the City of Yuba City and the farmlands in the southern Yuba City basin. Some 600 people were rescued by helicopter, but 37 people drowned.
The six days from December 19–24, 1964 were the wettest ever recorded at many stations on the North Coast. Every major stream in the North Coast produced new high values of extreme peak flows. 34 California counties were declared disaster areas.
Heavy rainfall in the San Francisco Bay region triggered on January 3–5 triggered thousands of debris flows from Santa Cruz Country to Contra Costa and Sonoma Counties, as well as flooding along the San Lorenzo River, Soquel Creek, and Aptos Creek in Santa Cruz County. Floods along creeks in Marin County plus added significant amounts of sediment to Tomales Bay. The landslides caused at least $66 million in damage. Landslides caused 25 of the 33 storm-caused deaths. Total estimated storm-related losses were $280 million.
On February 11, 1986 a vigorous low pressure system drifted east out of the Pacific, creating a Pineapple Express that lasted through February 24 unleashing unprecedented amounts of rain on northern California and western Nevada. The nine-day storm over California constituted half of the average annual rainfall for the year. Record flooding occurred in three streams that drain to the southern part of the San Francisco Bay area. Extensive flooding occurred in the Napa and Russian rivers. Napa, north of San Francisco, recorded their worst flood to this time while nearby Calistoga recorded 29 inches (740 mm) of rain in 10 days, creating a once-in-a-thousand-year rainfall event. Records for 24-hour rain events were reported in the Central Valley and in the Sierra. One thousand-year rainfalls were recorded in the Sierras. The heaviest 24-hour rainfall ever recorded in the Central Valley at 17.60 inches (447 mm) occurred on February 17 at Four Trees in the Feather River basin. In Sacramento, nearly 10 inches (250 mm) of rain fell in an 11-day period. System breaks in the Sacramento River basin included disastrous levee breaks in the Olivehurst and Linda area on the Feather River. Linda, about 40 miles (64 km) north of Sacramento, was devastated after the levee broke on the Yuba River's south fork, forcing thousands of residents to evacuate. In the San Joaquin River basin and the Delta, levee breaks along the Mokelumne River caused flooding in the community of Thornton and the inundation of four Delta islands. Lake Tahoe rose 6 inches (150 mm) as a result of high inflow. The California flood resulted in 13 deaths, 50,000 people evacuated and over $400 million in property damage. 3000 residents of Linda joined in a class action lawsuit Paterno v. State of California, which eventually reached the California Supreme Court in 2004. The California high court affirmed the District Court of Appeal's decision that said California was liable for millions of dollars in damages.
During the events of January and March 1995, over 100 stations recorded their greatest 1-day rainfalls in that station’s history. The major brunt of the January storms hit the Sacramento River Basin and resulted in small stream flooding primarily due to storm drainage system failures, though flooding affected nearly every part of the state. The Salinas River exceeded its previous measured record crest by more than four feet, which was within a foot or two of the reputed crest of the legendary 1862 flood. The Napa River set a new peak record, and the Russian and Pajaro rivers approached their record peaks. 28 people were killed and the flood cost $1.8 billion.
A series of subtropical storms, collectively called a pineapple express, struck northern California from late December 1996 to early January 1997. December 1996 was one of the wettest Decembers on record. The Klamath River on California's North Coast experienced significant flooding which led to the river permanently changing course in some areas. The Klamath National Forest experienced its worst flood since 1974. Unprecedented flows from rain surged into the Feather River basin while melted snow surged into the San Joaquin River basin. Rain fell at elevations up to 11,000 feet (3,400 m), prompting snow melt. The Cosumnes River, a tributary to the San Joaquin River, bore the brunt of the flooding. Sacramento was spared, though levee failures flooded Olivehurst, Arboga, Wilton, Manteca, and Modesto. Massive landslides in the Eldorado National Forest east of Sacramento closed U.S. Route 50. Damages totaled US$35 million (1997 dollars).
Watersheds in the Sierra Nevada were already saturated by the time three subtropical storms added more than 30 inches (760 mm) of rain in late December 1996 and early January 1997. Levee failures due to breaks or overtopping in the Sacramento River Basin resulted in extensive damages. In the San Joaquin River Basin, dozens of levees failed throughout the river system and produced widespread flooding. The Sacramento-San Joaquin River Delta also experienced several levee breaks and levee overtopping. 48 counties were declared disaster areas, including all 46 counties in northern California. Over 23,000 homes and businesses, agricultural lands, bridges, roads and flood management infrastructures – valued at about $2 billion – were damaged. Nine people were killed and 120,000 people were evacuated from their homes. 300 square miles (780 km2) were flooded, including the Yosemite Valley, which flooded for the first time since 1861-62.
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