Submitted to: International Journal of Sediment Research
Publication Type: Proceedings
Publication Acceptance Date: November 2, 1998
Publication Date: October 3, 2000
Interpretive Summary: Much of the western United States is considered to be rangeland. Rangeland areas produce a diverse mix of benefits and products, and their overall health is an important national issue. Sediment yield from a watershed reflects all soil erosion and sedimentation processes occurring within the watershed. Therefore, it is logical that measures of sediment yield can be used to interpret rangeland health through soil and site stability and the overall function of the watershed. Estimated sediment discharge and yield values were calculated for two experimental watersheds in the southwestern USA. Soil and site stability at the watershed scale were assessed using the soil loss tolerance concept, in which a value is assigned to the amount of soil that can be lost from a site without jeopardizing its health and productivity. Analyses suggest that combining sediment yield estimates calculated from complex watersheds with time-space averaged soil loss tolerance values is inconsistent. Sediment yield models that can simulate distributed sedimentation processes offer promise in assessing the health of rangeland watersheds, but are dependent upon the availability of sediment concentration and yield databases. Thus, emphasis on building these databases through rescue of historical data and new sampling is required.
Technical Abstract: Rangelands, which cover much of the western United States, produce a diverse mix of benefits and products and their overall health, in an ecosystem context, is of national importance. Because sediment yield from a watershed is an integrated expression of all soil erosion and sedimentation processes occurring within it, it is logical that we seek to quantify and interpret sediment yield in the context of soil/site stabilit and watershed function as measures of rangeland health. Depth integrated suspended sediment samples were combined with runoff measured using flumes to calculate sediment discharge and yield from two experimental watersheds in the southwestern USA. Sediment yield estimates for individual runoff events were summed to produce estimates of annual sediment yield from these two rangeland watersheds. Estimated annual sediment yield data were then combined with the concepts of sediment delivery ratio and soil loss tolerance to assess soil/site stability at the watershed scale. Analyses suggest that using sediment yield estimates from distributed watershed processes with time-space averaged soil loss tolerance values is inconsistent. Thus, new distributed soil/site stability criteria are needed to replace the soil loss tolerance concept in assessing the health of rangeland watersheds. Application of sediment transport/yield models, used at interior points in a watershed to simulate distributed sedimentation processes, requires calibration and validation data and is thus dependent upon the availability of sediment concentration and yield databases.