Precipitation-Duration-Frequency Relationships for a Mountainous Watershed in Southwest Idaho

Abstract

ABSTRACT A procedure was developed that can be used to estimate the maximum precipitation amounts for durations of 15 min to 24 h and return periods of 2 to 50 years for a mountainous watershed in southwest Idaho. The study indicated that summer maximum precipita-tion amounts on the Reynolds Creek Experimental Watershed in southwest Idaho are primarily caused by summer thunderstorms at the lower elevations (1200 m) for durations of 15 min to 2 h. Both summer and winter storms contribute to the maximum amounts for dura-tions greater than 2 h. At the higher elevations (2100 m), the annual maximum amounts for 15- and 30-min dura-tions were caused by both summer thunderstorms and winter storms. For durations of 1 or 2 h, just over one-half of the maximum values were caused by winter storms and for 6 h and longer durations, winter precipitation accounted for about 90 percent of the an-nual maximum values. The 6- and 24-h duration precipitation amounts inter-polated from NOAA ATLAS 2 for return periods of 2, 5, 10, 25, and 50 yr were about 13 percent lower than com-puted values at the 1200-m elevation on Reynolds Creek Experimental Watershed. At the 2100-m elevation, 6-h duration values interpolated from NOAA ATLAS 2 were about 42 percent less than measured, and one-half or less than the measured values for the 24-h durations.