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.

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.