Author
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STRELKOFF, THEODOR - UNIV OF AZ, TUCSON, AZ |
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Bjorneberg, David - Dave |
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Submitted to: International Soil Conservation Organization (ISCO)
Publication Type: Proceedings Publication Acceptance Date: 8/28/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Surface irrigation continues to play a significant role in U.S. agriculture, with about half of the irrigated acreage under surface systems. In some areas, notably the Pacific Northwest and western Nebraska, the combination of steep slopes and soil erodibility leads at times to extensive displacement of top soil by irrigation water. Sometimes, the soil moves off the field into the surface drainage, degrading the water quality therein. In other circumstances, some or all of the soil detached in the upper portion of a field is deposited in the lower reaches. Without costly replacement, the fertility of those upstream portions can be severely compromised. A model of sediment movement in response to surface irrigation would assist in planning optimum designs and management strategies to minimize soil erosion. Existing furrow erosion models have not proved successful in application to surface irrigation. It tseems likely that process simulations and parameters therein, selected for rainfall-induced hillside erosion, are not suitable for the surface irrigation case. A simple, experimental erosion component has been developed for an existing surface irrigation simulation model, SRFR, and preliminary comparisons of results with Idaho field data are promising and suggest the need to modify the approaches. Surface-irrigation simulation models are intended for Natural Resources Conservation Service field offices, extension specialists, consultants, and others who advise growers and irrigators. Technical Abstract: In the experimental Version 4.xx series, erosion science is introduced into the surface-irrigation simulation model, SRFR. The hydraulics of water flow in furrows for individual irrigation events is predicted by numerical solution of the unsteady equations of mass and momentum conservation coupled to generally applicable empirical equations describing infiltration nand soil roughness and to a known furrow configuration and inflow hydrograph. Selection of appropriate field values for the infiltration and roughness coefficients yields infiltration distributions and surface flows (including runoff) in reasonable agreement with measurements. The erosion component consists of applying the simulated hydraulic flow characteristics to site-specific empirical determinations of soil erodibility, to general empirical sediment-transport relations, and to general physically based deposition theory to provide estimates of soil erosion, flux, and deposition at various points along the furrow as functions of time. Total soil loss off the field and ultimate net erosion and deposition along the furrow follow. At this initial stage of the investigations, a single representative aggregate size is assumed adequate for the analysis. Results are compared to measurements of sediment concentrations in the furrow quarter points and in the tailwater. For a given representative aggregate size, the results are heavily dependent on the choice of transport formula. The Laursen (1958), Yang (1973), and Yalin (1963) formulas are programmed for investigation, as are a variety of computational options. Preliminary comparisons suggest the superiority of the Laursen formulation, with the Yang and Yalin formulas significantly overpredicting transport. |
