| Abstract: | Much of the rangeland of northwestern North America occupies highly variable, high-relief terrain withsteep slopes, contrasting aspects, strong elevation gradients and diverse local climates. Rangeland erosionand sediment production are major concerns in northwestern natural resource management. Seasonalvariability in precipitation, streamflow and energy available for sediment rnobilization and transport ispronounced in northwestern rangeland catchments; thus, runoff and sediment yield exhibit high spatialand temporal variability. The sediment regime of such watersheds cannot be characterized by simpleindices or short-term local measurements. A long-term experimental rangeland watershed demonstratesthe need for sustained measurement programs over a range of catchment scale and topographic position, todetermine actual patterns and rates of runoff and sediment yield. More research is needed to identify andquantify the pathways of sediment from initial detachment to temporary storage and subsequentremobilization and transport through the stream system. The role of extreme hydrologic events inaccelerated landscape erosion, remobilization of stored sediment, and interaction with dynamic channel-forming processes in rangeland streams remains inadequately defined. It is necessary to better determinelandscapes and channels susceptible to treatment to reduce stream sedimentation, and to populate andparameterize simulation models for rangeland catchmenhstream systems. Such information is requiredto address emerging issues of riparian zone and water quality management in northwestern rangelands. |
