FLOOD04413 - Laserfiche WebLink

Home Browse Search

1 Executive Summary Sacramento, California, has grown literally at the edge of the Sacramento and American Rivers and for ISO years has struggled to protect itself from periodic floods by employing structural and land management measures. Much of the population lives behind levees, and most of the city's downtown business and government area is vulnerable to flooding. A major flood in 1986 served as impetus for efforts by federal, state, and local entities to identifY an acceptable and feasible set of measures to increase Sacramento's level of safety from American River floods. Numerous options were identified in 1991 by the U.S. Army Corps of Engineers (USACE) in a report known as the American River Watershed Investigation. Due to the controversial nature of many of the alternatives identified in that report, study participants were not able to reach consensus on any of the flood control options. In response, the Congress directed the USACE to reevaluate available flood control options and, at the same time, asked the USACE to engage the National Research Council (NRC) as an independent advisor on these difficult studies. In 1995 NRC's Committee on Flood Control Alternatives in the American River Basin issued Flood Risk Management and the American River Basin: An Evaluation. This report outlined an approach for improving the selection of a flood risk reduction strategy from the many available. In March 1996, the USACE and its non-federal affiliates completed the Congressionally directed reevaluations of flood control options and submitted recommendations to Congress. In response, Congress authorized a component of the recommended plan but not an adequate plan for the reduction of flood risk for the Sacramento area. Thus, evaluations of alternatives continue. To add considerable complication to the technically and politically difficult decision process, in January 1997 the American River experienced a major flood, nearly as large as and hydrologically similar to the "flood of record" that occurred just II years before in 1986. The occurrence of the 1997 flood suggests that it may be necessary to recompute flood flow frequency relationships for the American River at Sacramento. In February 1998, the USACE published a revised unregulated rain flood flow frequency analysisI for the American River at Fair Oaks. The analysis produced a flood frequency curve that indicates that large floods are appreciably more likely than I Unregulated rain flood flow frequency analysis is conducted on annual peak flow data that have been corrected for the effects of upstr= reservoir storage. Rain flood flow is due primarily to rainfall rather than snowmelt. -