Rangeland Ecology & Management

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Storm runoff characteristics of grazed watersheds in eastern Oregon
Higgins, D. A., S. B. Maloney, A. R. Tiedemann, T. M. Quigley
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Rainfall and runoff data from 485 storms during the summers of 1979-1984 were evaluated to characterize storm runoff volumes (SF) and peak flows (QP) for 13 small watersheds in the Blue Mountains of eastern Oregon and to determine differences among grazing intensities and vegetation types. Based on 485 storms from the 13 watersheds, SF ranged from 0.0001 to 0.3519 inches, with a median of 0.0014 in., and rarely exceeded more than 2% of rainfall. QP never exceeded the annual peak discharges that occurred in spring from melting snow This low response can probably be attributed to low summer rainfall, dry antecedent moisture conditions due to high evapotranspirational demand, and high infiltration rates maintained by adequate ground cover in the predominately forested watersheds. Stepwise regression showed that of five dependent variables, total storm rainfall (PPT) and initial flow (QI) were the most important variables in accounting for variation in SF and peak flow above initial flow (QPI). Mean SF and QP did not differ among vegetation classes but significant differences were apparent in the relation of SF to PPT and QI, and QPI to PPT and QI. As PPT and QI increased, SF and QPI from larch-Douglas-fir watersheds increased at a slower rate than they did from the other watersheds. The lack of a strategy effect can likely be attributed to low-to-moderate grazing intensities and to maintenance of adequate ground cover over most of the watersheds.

base-flow rise rate
hydrograph separation
peak flow
surface water hydrology
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