Procedures are described for estimating flood-peak discharges and flood hydrographs for extreme floods, such as the 500-year flood, to evaluate scour at bridges. These procedures are being incorporated (june 1990) in a microcomputer program called "national flood frequency" developed by the u.S. Geological survey in cooperation with the federal highway administration and the federal emergency management agency. U.S. Geological survey flood reports typically describe procedures for estimating flood-peak discharges for return periods of2 to 100 years for rural and urban ungaged watersheds. This paper describes procedures in the national flood frequency program for extrapolating design floods with return periods of 2 to 100 years to the500-year flood. This paper appears in transportation research record no. 1290, Third bridge engineering conference, march 10-13, 1991, denver, colorado, volume 2.
Abstract