SAGEBRUSH RANGELAND HYDROLOGY AND EVALUATION OF THE SPUR HYDROLOGY MODEL1
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ABSTRACT: An excellent hydrologic record on sagebrush rangeland has been developed at the Reynolds Creek Experimental Watershed in southwestern Idaho. The objectives of this paper were twofold: (1) to analyze and describe the hydrologic record (818 years) from four sagebrush watersheds (183 ha); and (2) to evaluate the hydrology component of SPUR, a comprehensive rangeland model. The watersheds represent a gradient in elevation (11801658 m) and precipitation (240350 mm/yr). Runoff was a small fraction (> 2 percent) of the total water budget for all of the watersheds. It occurred very infrequently at the three lower elevation watersheds: Summit, Flats, and Nancy Gulch. At Lower Sheep, the highest elevation watershed, runoff occurred most years for a period of 1 to 17 weeks in the winter. Frozen soil combined with rainfall or snowmelt was associated with most of the runoff from Flats and Nancy Gulch. At Summit summertime thunderstorms produced all of the runoff. The average annual sediment yield from all of the watersheds was low (17950 kg/ha). It was highest from Summit, which had well developed alluvial channels and very steep slopes. SPUR was able to simulate runoff with reasonable accuracy only at Summit, where frozen soils were not a factor. There was poor correlation between predicted and actual annual 8ediment loss. The model tended to overpredict evapotranspiration early in the growing season and underpredict it in the late summer.
