STREAMFLOW CHARACTERISTICS OF SMALL WATERSHEDS in the BLUE MOUNTAINS OF OREGON

ABSTRACT: Streamflow data for water years 1978–84 were evaluated to identify streamflow characteristics for 13 small watersheds (0.46–7.00 mi²) in the Blue Mountains of eastern Oregon and to determine differences among grazing intensities and vegetation types. The ranges for mean annual water yields, peak flows, and 7‐day low flows for the 13 watersheds were 5.5–28.1 inches, 2.0–34.7 cfsm, and 0.006–0.165 cfsm, respectively. Two classes of vegetation were evaluated: (1) western larch‐Douglas‐fir (nine watersheds) and (2) other (four watersheds representing fir‐spruce, lodgepole pine, ponderosa pine, and mountain meadow). The means for annual peak flows and the slopes of the flow.duration curve were significantly different (p=0.05) for the two vegetation classes; differences in mean annual water yield were marginallysignificant(0.05< p <0.10). After they were adjusted for precipitation, the means for annual water yield, peak flows, and slopes of the flow‐duration curve were significantly different for the two vegetation classes; differences in the means for annual 7‐day low flows were marginally significant. The western larch‐Douglas‐fir group had somewhat lower water yields but, overall, tended to have more favorable streamfiow characteristics including lower peak flows, higher low flows, and more evenly distributed flow regimes (flatter flow‐duration curves) than the “other” class. Four levels of grazing intensity had no effect on streamilow characteristics.