Storms, Floods, and Debris Flows in Southern California and Arizona 1978 and 1980: Overview and Summary of a Symposium, September 17-18, 1980

摘要

Following the floods of 1978 and 1980 in southern California and Arizona a symposium was convened at the California Institute of Technology in September 1980 to document the significant events of these floods and to exchange information and evaluations. The symposium laid the groundwork for a volume of proceedings, which serves as a compact permanent source of information on these floods for not only local readers but national readers as well. Special attention is given in the proceedings to documenting problems--some engineering, some institutional--and to drawing conclusions and making recommendations for research. The papers included are not intended to be research papers or to replace the much more detailed reports of individual agencies. The emphasis was on preparing and presenting the papers soon after the event in such a way as to emphasize the regional nature of floods and flood control problems. The proceedings are organized into several sections, with 35 papers altogether. Following the overview and summary, Section 2, STORM METEOROLOGY, which consists of four papers, describes the long-range weather patterns that affect the southwestern United States; the relationship of these patterns to sea surface temperatures in the North Pacific Ocean; the short-term synoptic meteorology of the storms under consideration, showing the importance of multiple storm sequences; and statistical analyses of return periods, based on historical data, for precipitation at a point. Section 3, DOWNSTREAM RIVER FLOODING, consisting of nine papers, gives an overview of the floods on the larger rivers, how the flood control works responded, and what damages occurred. Section 4, UPLAND FLOODS AND SEDIMENT TRANSPORT (five papers), focuses on the unique aspects of sedimentation in regional floods. Section 5, LANDSLIDES, with four papers, explains the problems of landslides, both large and small, that were triggered by the prolonged periods of heavy rainfall. Section 6, CASE STUDIES OF ENGINEERING PROBLEMS (four papers), gives detailed analyses of three particular engineering problems: the failure of levees on the San Jacinto River, the uncontrolled filling of Lake Elsinore to damaging stages, and the severe streambed scour threatening to undermine the Interstate 10 highway bridge over the Salt River at Phoenix, Arizona. The experiences and analyses described in these papers should be useful to engineers who deal with similar structures and situations in the future. Section 7, EFFECTS ON THE SHORELINE, consisting of two papers, illustrates the damaging effects of the high storm waves and high tides that occurred in 1978 and 1980. Beach profiles shifted very rapidly, with sand being moved temporarily offshore, which exposed many shoreline structures to direct wave attack, causing severe damages. Section 8, POLICIES FOR FLOOD CONTROL AND HAZARD MITIGATION (six papers),focuses on institutional issues. Four of these papers advocate a strong new emphasis on hazard mitigation, better flood warning systems, and other nonstructural approaches as part of the mix of society's activities to deal with floods. About 300 people participated in the symposium, and many contributed to the questions and discussion. In the closing session there was a panel discussion by Russell Campbell, Engineering Geologist with the U.S. Geological Survey; John F. Kennedy, Director of the Iowa Institute on Hydraulic Research at the University of Iowa and member of the Committee on Natural Disasters of the National Research Council; Dale Peterson, Director of Community Services with the Federal Emergency Management Agency (FEMA) in San Francisco; and Richard Wainer, Los Angeles City Engineer's Office in Van Nuys. The writer served as moderator. Since it was not feasible to digest and record all of these discussions, I am attempting in this summary to capture the main conclusions and issues.* Nonetheless, the following conclusions and recommendations are solely the responsibility of the author and do not necessarily represent a consensus by the participants at the symposium. For the record it should be noted that the following papers included in the proceedings were not presented at the symposium: "Geotechnical Origin and Repair of the Bluebird Canyon Landslide, Laguna Beach, California" by Beach Leighton and "Levee Failures and Distress, San Jacinto River Levee and Bautista Creek Channel, Riverside County, Santa Ana River Basin, California" by Joe Sciandrone, Ted Albrecht, Jr., Richard Davidson, Jacob Douma, Dave Bamer, Charles Hooppaw, and A1 Robles, Jr. The latter paper is a shortened version of the official Corps of Engineers report on the San Jacinto River levee failure , which was not available in time for presentation at the conference. Numerous brief discussions at the symposium are gratefully acknowledged, although very few are included in the proceedings.