WCR: The Hydrology of Extreme Floods in Mountain Watersheds

Princeton University, Princeton NJ

Investigators

Abstract

0233617 J. A. Smith The proposed research entails observational studies of extreme floods along the western margin of the central Appalachians in West Virginia . We will focus on floods produced by organized systems of thunderstorms in mountainous terrain. These storm systems have produced some of the largest rainfall accumulations in the world at time intervals less than 6 hours, including 780 mm in 4.5 hours from the 18-19 July 1942 Smethport Pennsylvania storm and 483 mm in 2 hours from the 18-19 July 1889 Rockport West Virginia storm. Our research will utilize two principal observational resources: 1) research watersheds of the Fernow Experimental Forest for examination of flood response at basin scales between 0.1 and 10.0 km2 and 2) U.S. Geological Survey (USGS) stream gaging stations and WSR-88D radar rainfall estimates for analysis of extreme flood response at basin scales between 1 and 1,000 km2. A 51-year stream-gauging record from the Fernow watersheds will be combined with 3 years of intensive field measurements to examine runoff production mechanisms and extreme flood response. Field observations will be integrated with rainfall and discharge measurements through modeling studies based on the unsaturated flow equations. Analyses of 16 extreme floods that have occurred along the western margin of the central Appalachians during the period 1996 - 2002 will be carried out for 12 drainage basins upstream of USGS stream gauging stations. Drainage area for the 12 basins ranges from 145 to 1,023 km2. The core science questions that will be examined in the project are the following: 1) What are the rate-limiting processes for extreme flood response in humid, mountain watersheds? 2) Are rate-limiting processes for extreme floods scale-dependent, and if so, how does scale dependence arise? 3) Are rate-limiting processes for extreme floods dependent on the return interval of the flood, and if so, how does this dependence arise? These science questions will be addressed through analyses of flood response in West Virginia that examine a series of hypotheses concerning runoff production mechanisms and space-time variability of rainfall. The proposed research is designed to provide the scientific basis and scientific methods for improved flood hazard management in high rain rate, mountain watersheds.