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An accounting procedure is developed which determines a flow regime that is capable of transporting an amount of bedload sediment necessary to ensure channel stability downstream. The method allows for sediment buildup in the channel within geomorphic threshold limits during low flow periods. During periods of high runoff, enough water is bypassed to transport the stored sediment. The procedure utilizes only those flows of sufficient magnitude to maintain channel stability over the long run (25–50+ years). An example is presented which determines the volume of water and frequency of release for channel maintenance purposes downstream from a hypothetical water diversion project. Of some 1,200,000 acre feet generated...
Sediment yield from small arid basins, particularly in the Mojave Desert, is largely unknown owing to the ephemeral nature of these fluvial systems and long recurrence interval of flow events. We examined 27 reservoirs in the northern and eastern Mojave Desert that trapped sediment from small (< 1 km2) drainage basins on alluvial fans over the past 100 yr, calculated annual sediment yield, and estimated the average recurrence interval (RI) of sediment-depositing flow events. These reservoirs formed where railbeds crossed and blocked channels, causing sediment to be trapped and stored upslope. Deposits are temporally constrained by the date of railway construction (1906–1910), the presence of 137Cs in the reservoir...
The Soil Water Assessment Tool (SWAT) was implemented to determine annual sediment yields and critical source areas of erosion for the Buffalo River Watershed. Model calibrations were performed by comparing simulated streamflow discharge and sediment concentrations against measured values. Monte-Carlo simulations were performed to identify the most sensitive parameters and the “best-fit” parameter ranges. This study especially highlighted the importance of snow parameters, which, previously had not been identified as sensitive for model simulations. The cover (C) and practice (P) values for croplands had to be reduced considerably from default model values to constrain simulated sediment yields within the observed...
The primary objectives of this research were to determine SWAT model predicted reductions in four water quality indicators (sediment yield, surface runoff, nitrate nitrogen (NO3–N) in surface runoff, and edge-of-field erosion) associated with producing switchgrass (Panicum virgatum) on cropland in the Delaware basin in northeast Kansas, and evaluate switchgrass break-even prices. The magnitude of potential switchgrass water quality payments based on using switchgrass as an alternative energy source was also estimated. SWAT model simulations showed that between 527,000 and 1.27 million metric tons (Mg) of switchgrass could be produced annually across the basin depending upon nitrogen (N) fertilizer application levels...
Simulation models are increasingly used to analyze the impact of agricultural management at the watershed-scale. In this study, the Agricultural Policy/Environmental eXtender (APEX) model was tested using long-term (1976–1995) data from two watersheds (W2 and W3) at the USDA Deep Loess Research Station near Treynor, Iowa. The two watersheds were cropped with continuous corn (Zea mays L.) and managed with conventional-tillage at W2 (34.4 ha) and ridge-till at W3 (43.3 ha). The monthly runoff and sediment yield were calibrated for the two watersheds during 1976–1987 by adjusting the curve numbers, curve number index coefficient, RUSLE C factor exponential residue and height coefficients, and erosion control practice...