SGER: Surveying the Southern California Flash Floods of January 2005

Hydrologic Research Center, San Diego CA

Investigators

Abstract

0520899 Georgakakos Extreme rainfall in Southern California in early January 2005 led to flash floods and mudslides that caused over a dozen fatalities, and extensive infrastructure damage, interrupted national commerce and stranded thousands of residents. Countless urban and rural roads, major highways, freeways, and passenger and freight railways were shut down, including freight access to major US Ports at Los Angeles and Long Beach. Thousands were forced to evacuate and hundreds lost their homes. Preliminary damage estimates topped $300 million. Regional flash flood production and development in Southern California remains enigmatic despite a history of infrequent but extreme rain events. The proximity of relatively high, steep mountain terrain along the coast makes Southern California uniquely susceptible to flash flooding when storms approach from the southwest (rather than a more typical northwesterly approach). The recent events provide an opportunity for detailed study. A field survey and data collection campaign is urgently needed before a wealth of information in the form of physical flow evidence and temporary records are destroyed or unavailable. It is planned to identify flash flood areas from radar, raingauge and our own nested high resolution simulated precipitation and surface runoff model runs, along with maps of disastrous incidents. Teams will then be deployed to survey catchments of interest targeting high water marks, occurrence of land slides or mudflows in higher elevations, and measurements of other key streambed hydrographic characteristics. Teams will also be charged with contacting Water and Flood Control Districts of various counties to gather analog data from raingauges, streamflow and other surface data not typically included in the standard operational forecast data stream. It is the main objective of the proposed research to assist in the development of a regional event database through timely field surveys and collection of all available data from Water and Flood Control Districts in the region that would otherwise be lost. The final result of the proposed effort will be a database and associated documentation that would allow the regional study of the flash floods of Southern California of January 2005.