Landslide Case study- La Canchita
La Conchita is a very small community, located on the southern California coastline between Ventura and Santa Barbara. The community lies on a narrow strip of land about 250 meters (820 feet) wide between the shoreline and abutting a 180-meter (590 ft) high bluff. The top of the bluff is covered by avocado and citrus orchards. The bluff above La Conchita has a slope of approximately 35 degrees and consists of poorly cemented marine sediments
On March 4, 1995, the hill behind La Conchita failed, moving tens of meters in minutes, and buried nine homes with no loss of life.
The County of Ventura immediately declared the whole community a Geological Hazard Area, imposing building restrictions on the community to restrict new construction. Days later, on March 10, a subsequent debris flow from a canyon to the northwest damaged five additional houses in the north-western part of La Conchita. The dimensions of the slides were approximately 120 meters (390 feet) wide, 330 meters (1,080 feet) long, and 30 meters (98 ft) deep.
The deposit covered approximately 4 hectares (9.9 acres), and the volume was estimated to be approximately 1.3 million cubic meters of sediment. The landslide slumped as a coherent mass of material.
Based on the opinion that surface water infiltration from irrigation contributed to the landslide, seventy-one homeowners sued La Conchita Ranch Co. in Bateman v. La Conchita Ranch Co. The judge ruled that irrigation was not the major cause of the slide and that the ranch owners were not responsible. The 2005 La Conchita Landslide occurred at the end of a 15–day period of near-record rainfall levels. From December 27, 2004 through January 10, 2005, the nearby city of Ventura received 378 millimetres (14.9 inches) of rainfall, only slightly less than its mean annual total of 390 millimetres (15.4 inches). On January 10, 2005, the south-eastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide. The volume of the landslide was estimated to be approximately 200,000 cubic meters with a surface 350 meters (1,150 feet) long and 80–100 meters (260–330 ft) wide. The landslide destroyed 13 houses and severely damaged 23 others. There were 10 confirmed fatalities. Subsequently, residents formed the La Conchita Community Organization (LCCO) to coordinate with government officials to determine the best way to protect the community. In March 2006, Governor of California, Arnold Schwarzenegger, allocated $667,000 for a scientific study to determine control measures to be taken to prevent future landslides.
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