CHARACTERISTICS OF EXTREME PRECIPITATION AND ASSOCIATED STREAMFLOW IN THE REYNOLDS CREEK EXPERIMENTAL WATERSHED,IDAHO

Authors: Hanson, Clayton; Pierson Jr, Frederick

Submitted to: Symposium on Global Change and Climate Variations
Publication Type: Proceedings
Publication Acceptance Date: 9/29/2000
Publication Date: 9/20/2001
Citation: Hanson, Clayton L., Pierson, Jr. Frederick B., Characteristics of Extreme Precipitation and Associated Streamflow in the Reynolds Creek Experimental Watershed, Idaho., American Meteorological Society, Boston, MA., pp J2.13-J2.15, 2001.

Interpretive Summary: Knowing the duration and spatial distribution of extreme precipitation amounts is critical in the design of culverts, spillways and other hydraulic structures as well as for computing probable erosion and sediment transport rates. The USDA-ARS, Northwest Watershed Research Center operates a precipitation gauge network on the Reynolds Creek experimental Watershed (RCEW) in southwest Idaho. The 37-yr (1962-1998) record from this watershed showed that the average annual precipitation ranged from 240 mm on the low elevation to 1130 mm on the highest elevations of the watershed. The minimum average monthly precipitation occurred in July at all sites. Depth-duration-frequency studies show that short-duration, high-intensity precipitation generally falls during the summer at all sites and that the values computed for the RCEW are close to those published by the National Weather Service. This is not the case for major storms that last from 4 to 24 hr at the high- elevation sites which generally occur during the winter and produce about twice the amount of precipitation as that shown in National Weather Service publication for a 24-hr period. At the low elevation sites, about one half of the annual maximum 4-to 24-hr storms occur during the winter and the amounts of precipitation during these events agree with those published by the National Weather Service. Results from this study show that the peak runoff events on RCEW are most commonly result from rain-on-snow at the mid and low elevations, and a combination of rain-on snow and snowmelt events at high elevations. There can also be an occasional major thunderstorm runoff event at the lowest elevations of the watershed.

Technical Abstract: The USDA-ARS, Northwest Watershed Research Center operates a precipitation gauge network on the Reynolds Creek Experimental Watershed in southwest Idaho. The 37-yr (1962-1998) record from this watershed showed that the average annual precipitation ranged from 240 mm on the low elevation to 1130 mm on the highest elevations of the watershed. Maximum monthly precipitation was during the mid-winter at the higher elevation sites but was mostly uniform during the winter and spring at the low elevation sites. The minimum average monthly precipitation occurred in July at all sites. Depth-duration-frequency studies show that short-duration, high-intensity precipitation generally falls during the summer at all sites and that the values computed for the Reynolds Creek Watershed are close to those published by the National Weather Service. This is not the case for major storms that last from 4 to 24 hr at the high elevation sites which generally occur during the winter and produce about twice the amount of precipitation as that shown in National Weather service publications for a 24 hr period. At the low elevation sites, about one half of the annual maximum 4 to 24 hr storms occur during the winter and the amounts of precipitation during these events agree with those published by the National Weather Service. Because of this precipitation regime, the highest peak runoff rates have been caused by large winter rain-on-snow events. Thunderstorms produce some runoff from the watershed but they generally do not cover a large portion of the watershed and thus they do not produce the highest peak events or very large amount of runoff per event at the outlet of the watershed.