ABSTRACT:
Runoff characteristics of sagebrush rangeland are described and related to runoff prediction by SWRRB (Simulator for Water Resources in Rural Basins). Precipitation-runoff relationships on five sagebrush watersheds located along a climatic gradient in southwestern Idaho were established using long-term records. Runoff from the two higher elevation watersheds was snowmelt-generated. With decreasing elevation, soil frost was important in runoff generation. Average annual runoff for the five watersheds ranged from 1 mm to 500 mm. The correlation between annual precipitation and annual runoff decreased with aridity of the watershed. SWRRB successfully simulated annual runoff from the highest elevation watershed where (a) runoff made up a high percentage (50%) of the water budget, (b) frozen soil runoff was insignificant, and (c) there was a strong correlation between annual runoff and precipitation. Runoff predictions were poor for the lower elevation watersheds where (a) runoff was a small part (1-7%) of the water budget, (b) frozen soil runoff was very important, and (c) there was a poor correlation between annual runoff and precipitation. For sagebrush rangeland in the Great Basin, little confidence can be placed in runoff predicted from models like SWRRB that are based on curve number hydrology if runoff accounts for a small part (<10%) of the water budget and/or soil frost plays a prominent role in runoff generation.
Footnotes
Bradford P. Wilcox is a hydrologist, Mark S. Seyfried is a soil scientist, Keith R. Cooley is a hydrologist, and Clayton L. Hanson is an agricultural engineer with the Northwest Watershed Research Center, Agricultural Research Service, U.S. Department of Agriculture, 800 Park Blvd., Boise, Idaho 83705. The authors acknowledge the efforts of Cliff Johnson, retired ARS hydraulic engineer, who was responsible for the collection of much of the runoff data used in this study. We also thank the staff of the Northwest Watershed Research Center. Material in this paper also appeared in a proceedings paper, “Modeling Runoff from Sagebrush Rangeland Along a Climatic Gradient in Southwestern Idaho,” from the Headwaters Hydrology Symposium, American Water Resources Association.
- Copyright 1991 by the Soil and Water Conservation Society
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