NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.
This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.
Support for this project was provided by the U.S. Federal Emergency Management Agency under Contract Agreement EMW-94-C-4550.
Library of Congress Catalog Card Number 96-69351
International Standard Book Number 0-309-05542-3
Additional copies of this report are available from:
National Academy Press
2101 Constitution Ave., NW Box 285 Washington, DC 20055 800-624-6242 202-334-3313 (in the Washington Metropolitan Area) http://www.nap.edu
Cover credit: Alluvial fan flooding at Magnesia Spring Canyon in July 1979 caused one death and more than $7 million in damage. Photograph taken from 1989 FEMA Document 165, Alluvial Fans: Hazards and Management.
Copyright 1996 by the National Academy of Sciences. All rights reserved.
Printed in the United States of America
COMMITTEE ON ALLUVIAL FAN FLOODING
STANLEY A. SCHUMM, Chair,
Colorado State University, Fort Collins, Colorado
VICTOR R. BAKER,
University of Arizona, Tucson
MARGARET (PEGGY) F. BOWKER,
Nimbus Engineers, Reno, Nevada
JOSEPH R. DIXON,
U.S. Army Corps of Engineers, Phoenix, Arizona
THOMAS DUNNE,
University of California, Santa Barbara
DOUGLAS HAMILTON, engineering consultant,
Irvine, California
HJA
DOROTHY MERRITTS,
Franklin & Marshall College, Lancaster, Pennsylvania
Staff
CHRIS ELFRING, Study Director
ANGELA BRUBAKER, Research Assistant
ETAN GUMERMAN, Research Associate
ROSEANNE PRICE, Consulting Editor
WATER SCIENCE AND TECHNOLOGY BOARD
DAVID L. FREYBERG, Chair,
Stanford University, Stanford, California
BRUCE E. RITTMANN, Vice-Chair,
Northwestern University, Evanston, Illinois
LINDA ABRIOLA,
University of Michigan, Ann Arbor
PATRICK L. BREZONIK,
University of Minnesota, St. Paul, through June 30, 1996
JOHN BRISCOE,
The World Bank, Washington, D.C.
WILLIAM M. EICHBAUM,
The World Wildlife Fund, Washington, D.C.
WILFORD R. GARDNER,
University of California (emeritus), Berkeley
EVILLE GORHAM,
University of Minnesota, St. Paul
THOMAS M. HELLMAN,
Bristol-Myers Squibb Company, New York, New York
CHARLES D. D. HOWARD,
Charles Howard & Associates, Ltd., Victoria, British Columbia, Canada
CAROL JOHNSTON,
University of Minnesota, Duluth
WILLIAM M. LEWIS, JR.,
University of Colorado, Boulder
JOHN W. MORRIS,
J. W. Morris, Ltd., Arlington, Virginia
CAROLYN H. OLSEN,
Brown and Caldwell, Pleasant Hill, California, through June 30, 1996
CHARLES R. O'MELIA,
The Johns Hopkins University, Baltimore, Maryland
REBECCA T. PARKIN,
American Public Health Association, Washington, D.C.
IGNACIO RODRIGUEZ-ITURBE,
Texas A&M University, College Station
HENRY VAUX, JR.,
University of California, Oakland
Staff
STEPHEN D. PARKER, Staff Director
SHEILA D. DAVID, Senior Staff Officer
CHRIS ELFRING, Senior Staff Officer
GARY D. KRAUSS, Staff Officer
JACQUELINE A. MACDONALD, Senior Staff Officer
M. JEANNE AQUILINO, Administrative Associate
ETAN GUMERMAN, Research Associate
ANITA A. HALL, Administrative Assistant
ANGELA F. BRUBAKER, Research Assistant
ELLEN DE GUZMAN, Project Assistant
MARY BETH MORRIS, Senior Project Assistant
COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES
M. GORDON WOLMAN, Chair,
The Johns Hopkins University, Baltimore, Maryland
PATRICK R. ATKINS,
Aluminum Company of America, Pittsburgh, Pennsylvania
JAMES P. BRUCE,
Canadian Climate Program Board, Ottawa, Ontario, Canada
WILLIAM L. FISHER,
University of Texas, Austin
JERRY F. FRANKLIN,
University of Washington, Seattle
GEORGE M. HORNBERGER,
University of Virginia, Charlottesville
DEBRA S. KNOPMAN,
Progressive Foundation, Washington, D.C.
PERRY L. MCCARTY,
Stanford University, California
JUDITH E. MCDOWELL,
Woods Hole Oceanographic Institute, Massachusetts
S. GEORGE PHILANDER,
Princeton University, New Jersey
RAYMOND A. PRICE,
Queen's University at Kingston, Ontario, Canada
THOMAS C. SCHELLING,
University of Maryland, College Park
ELLEN K. SILBERGELD,
University of Maryland Medical School, Baltimore
STEVEN M. STANLEY,
The Johns Hopkins University, Baltimore, Maryland
VICTORIA J. TSCHINKEL,
Landers and Parsons, Tallahassee, Florida
Staff
STEPHEN RATTIEN, Executive Director
STEPHEN D. PARKER, Associate Executive Director
MORGAN GOPNIK, Assistant Executive Director
GREGORY SYMMES, Reports Officer
JAMES MALLORY, Administrative Officer
SANDI FITZPATRICK, Administrative Associate
SUSAN SHERWIN, Project Assistant
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences.
The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is interim president of the National Academy of Engineering.
The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine.
The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chairman and interim vice chairman, respectively, of the National Research Council.
Preface
People have long elected to build in flood-prone areas—whether because they sought easy access to the waterways that were once our main transportation routes, because they offer relatively flat building sites, or because of their aesthetic appeal. As the population increases and people search for desirable locations to live, they sometimes come into conflict with those who regulate construction on s. In the western United States, some of the most intense conflicts revolve around development on alluvial fans, which can be susceptible to a particularly catastrophic type of flooding. Controversy over alluvial fan flooding issues led the Federal Emergency Management Agency (FEMA) to ask the National Research Council (NRC) for help. As a result, the NRC established the Committee on Alluvial Fan Flooding with a membership composed of eight engineers and earth scientists, all of whom have experience with alluvial fan morphology and processes.
The committee was charged to revise the existing definition of alluvial fan flooding, to develop criteria to determine if an area is subject to alluvial fan flooding, and to provide examples of the application of the definition and the criteria used. The committee recognized immediately that in addition to "alluvial fan flooding," there exists a broader category termed "uncertain flow path flooding" that requires further consideration by FEMA. Confusion caused by linking two aspects of the flood hazard (i.e., land form type and uncertainty in flood processes) is part of the reason for the controversy on this subject. This committee cannot claim to have the final word on what it considers to be a complex technical and regulatory issue, hence we may not have achieved everything desired by FEMA. It has, however, provided significant guidance for characterizing how floods occur on alluvial fans and describing how FEMA might more consistently administer the National Flood Insurance Program on such landforms, which comprise large areas of the western United States and elsewhere.
In order to more fully understand the problems associated with alluvial fan flooding, the committee met at three locations in Arizona, California, and Utah, where different alluvial fans could be visited and evaluated in the field. The examples ranged from typical large alluvial fans in Arizona and California to small debris flow fans in Utah. Fans ranged from fully active, where flooding or debris flows could occur anywhere on the fan, to incised, where the bulk of the fan is not subject to flooding. Hence, not only was the varied expertise of the committee brought to bear on the problem, but the members were exposed in the field to new and different situations.
The committee benefited greatly from presentations and guidance in the field from the following people: Gary Christiansen and Mike Lowe, Utah Geological Survey; Fred Campbell, EIS Engineering, Salt Lake City; Sidney Smith, Davis County Public Works, Utah; Jeffrey Keaton, AGRA Earth and Environment, Salt Lake City; Joseph Tram, Maricopa County Flood Control District, Arizona; Terri Miller, Arizona Department of Water Resources; Philip Pearthree, Arizona Geological Survey; Joseph Hill, San Diego County Department of Public Works; Stuart McKibbin, Riverside County, California; Robert Mussetter, Mussetter Engineering, Fort Collins, Colorado; James Slosson, Slosson and Associates, California; and Joe Cook, Coachella Valley Water District. We also appreciate the support provided by FEMA personnel and contractors—especially Frank Tsai, Karl Mohr, and Ed Mifflin—who helped us understand the issues and how FEMA currently operates. We believe the hands-on perspective that all these people contributed was essential to the evolution of our thinking. In addition, the committee would like to thank the staff of the Water Science and Technology Board for their invaluable guidance to the committee, especially the insights provided by study director Chris Elfring and support from her associates Angela Brubaker and Etan Gumerman. Our thanks also to Tamera Benson for the preparation of the graphics.
Stanley Schumm, Chair
Committee on Alluvial Fan Flooding