Author
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Hagen, Lawrence |
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Submitted to: ASABE Annual International Meeting
Publication Type: Other Publication Acceptance Date: 6/27/2007 Publication Date: 6/27/2007 Citation: Hagen, L.J. 2008. Updating soil surface conditions during wind erosion events using the Wind Erosion Prediction System (WEPS). Transactions of the ASABE. 51(1):129-137. Available: http://asae.frymulti.com/techpapers.asp?confid=min2007 Interpretive Summary: During significant wind erosion events the soil surface is continually modified, however, erosion models rarely account for these changes. In this work we provide an overview of the Wind Erosion Prediction System (WEPS) model equations used to update the soil surface during simulated erosion. The objectives are to show that by periodic surface updating during events one can a) improve erosion prediction accuracy and b) determine changes in erosion control by clods, crusts, and soil roughness, so model users can improve their designs. During events, the soil surface can become armored with clods. This represents a supply-limited condition and is typical of the upwind portions of a field. Conversely, when additional mobile soil is created or uncovered faster than it is removed, the surface becomes more erodible as often occurs on the downwind portions of large fields. During an event, random roughness, ridge roughness, and the fraction of mobile aggregate cover are also updated. In contrast to models that limit erosion only by storm duration, surface updating increased WEPS accuracy both by identifying field areas that limited supply of mobile aggregates and by changing wind speeds where erosion can begin to allow simulation of intermittent erosion. Technical Abstract: During significant wind erosion events the soil surface is continually modified, however, erosion models rarely account for these changes. The objectives of this work are to provide an overview of the WEPS soil surface update methodology and demonstrate that by periodic surface updating during events, a physically-based, field-scale model can a) improve prediction accuracy and b) determine changes in erosion control by clods, crusts, and soil roughness, so model users can improve their designs. During events, the soil surface can become armored. This represents a supply-limited condition and is typical of the upwind portions of a field. Conversely, when additional mobile soil is created or uncovered faster than it is removed, the surface becomes more erodible as often occurs on the downwind portions of large fields. In this case, soil removal may be limited by the duration of the erosive winds. To facilitate surface updating in WEPS, a mass balance of the available mobile soil is maintained in two pools - one for the mobile soil on the crust and another for the mobile soil among the immobile aggregates. The net emission of the mobile aggregates is simulated in grid cells along the wind direction and the pools in each cell are updated on a subhourly basis. Partial depletion of a pool may cause cessation of erosion at a given wind speed, but permit erosion to resume at succeeding higher wind speeds. During an event, random roughness, oriented roughness, and the fraction of mobile aggregate cover are also updated. In contrast to models that limit erosion only by storm duration, surface updating increased WEPS accuracy both by identifying field areas that limited supply of mobile aggregates and by changing threshold friction velocities to allow simulation of intermittent erosion. |
