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Weathering in San Diego. Beach Cliff Erosion . Beach cliffs are constantly eroding, threatening houses built on them. People erect sea walls to keep the water from eroding the cliffs, and retaining walls to keep the cliffs intact.
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Beach Cliff Erosion • Beach cliffs are constantly eroding, threatening houses built on them. • People erect sea walls to keep the water from eroding the cliffs, and retaining walls to keep the cliffs intact. • It used to be thought that the majority of beac sand came from rivers that empty into the ocean. • New studies show that beach cliff erosion is the major source of beach sand. So keeping the cliffs from eroding may damage beaches!
Landslides & Mudslides • La Jolla has a long history them.
In 1961, a landslide flattened seven houses and severely damaged another in Mount Soledad, where a hillside collapsed Wednesday. Here are some of the landslides that have done harm to San Diego homes over the last 20 years. • March 2005 – Carlsbad: A landslide caused by problematic pipes ruined eight condos, resulting in a large settlement between the city and condo owners. • February 2005 – Mount Soledad, La Jolla, Carlsbad, Oceanside: Heavy rains caused widespread mudslides, sinkholes and flooding. Countywide, 16 homes were red-tagged as uninhabitable. • January 2005 – Oceanside: Landslide forced six homes to be evacuated, one of which was condemned. • June 1996 – Encinitas: Sea erosion caused the den of an Encinitas home to break away and slide down the cliff. Residents of eight homes were asked to evacuate. • 1994 – Mount Soledad: Landslide damage in a canyon below homes on Desert View Drive was repaired by residents.
Summer 1995 - March 1998 – Del Cerro: The backyards of two houses started slipping down the hillside, due to a storm drain running between the houses. The city purchased the homes (along with two others) and later tore them down, following heavy rains in 1998. • March 1992 – Spring Valley: Mudslide forced three homes to be evacuated. • February 1990 – Cowles Mountain: Storms caused a mudslide, which flooded a home, causing over $14,000 worth of damage. • April, 1989 – Encinitas: Spurred by the collapse of a sea wall and injuries to three workers who fell down the face of a Leucadia bluff, city officials held an emergency meeting to try to save several homes threatened by the sheared-off bluff. • 1989 – Mount Soledad: Construction of a new home started a slide on Desert View Drive. • (from Union Tribune, “Slides from the Past”)
“Dry Rivers, Dammed Rivers and Floods: An Early History of the Struggle Between Droughts and Floods in San Diego “By Joseph Hill
Dry Rivers, Dammed Rivers and Floods • San Diego County has seven river systems. • All of them are dammed. • San Diego has a drought prone climate, with occasional floods. • Dams provide water during the dry summers, flood control during the rainy winters, and create lakes, used for fishing and recreation. • The population that could be supported without artificial water supply and control would be around 5,000 (based on original Native American population) • In the 1880’s and 1890’s, seven dams were built, controlling most of San Diego County’s watershed, and providing the county’s 18,000 residents with home and agricultural water supply and flood control.
Flood of 1916 • From 1900-1916 there was a terrible drought. • A “rainmaker” named Charles Hatfield was finally employed by the city. • The next day, San Diego’s largest recorded flood struck. • It destroyed Otay Dam, which “opened” like a huge gate, releasing a gigantic wave of water, 130 feet high. • This wave stripped every bit of vegetation from the canyon walls, destroyed all the structures in its path, and killed many people. • By the end of the flood, every bridge in San Diego was impassable, and it was only possible to reach Los Angeles by boat.
After the Flood • In the first half of the 1900’s, eight more dams were built. • Floods struck again in 1927, 1937, 1978 and 1980, but none were of the magnitude of the 1916 flood. • Dams have all functioned well since then, greatly lowering water flows during floods.
Mission Valley • Mission Valley is the floodplain of the San Diego River. • Mission Valley flooded completely and almost all development was wiped out in 1862 and 1916. • Land there was originally cheap because it was a flood plain, so no one built there. • Suddenly people started building, starting with the Mission Valley Shopping Center, which attracted more development, and finally housing. • There was no community plan, which would have guided and limited development, until 1985. • Resident population has grew 41.8% between 2000 and 2005, and Mission Valley is now home to 18,000 people. • There is no emergency evacuation plan. • It is generally thought that Mission Valley is subject “Hundred Year Floods.”
