Submitted to: International Symposium on Soil Erosion and Dryland Farming
Publication Type: Proceedings
Publication Acceptance Date: 11/1/2000
Publication Date: N/A
Interpretive Summary: Conservation planning requires accurate estimation of current and future soil erosion rates. When tilled hillslopes are divided by buffer strips or grass hedges, soil movement by tillage and by water erosion/deposition processes can change slope steepness over time. Generally, soil is lost from the upslope edge of tilled areas and deposited near their downslope edges. Current versions of the erosion models RUSLE and WEPP do not automatically account for such changes. In this paper we use the sediment deposition predictions of these models and modify, outside of the programs, an approximately 250-ft long hillslope containing grass strips. We found that predicted slope changes were similar to those observed in a 7-yr old field study. Predicted erosion rates were reduced by 40 to 50% by slope shape changes observed. These results demonstrate the importance of considering landscape modification for long-term conservation planning of sloping fields containing permanent grass strips. They also demonstrate that a reasonable job of accounting for such effects can be done using existing models when simple assumptions about the location and shape of sediment deposits capture the main effects of hillslope topographic changes. The approach demonstrated will be of use to conservationists planning erosion control systems for strip cropped fields in the 21st century.
Technical Abstract: When tilled hillslopes are divided into segments by non-tilled strips, such as buffer strips or vegetative barriers, soil translocation by tillage and water erosion/deposition processes result in changes in slope steepness. Removal of soil from the upslope edge of tilled areas and deposition of sediment at their downslope margins and in the non- tilled sod areas result in the tilled areas becoming less steep and non- tilled sod areas becoming steeper over time. Such changes are not automatically accounted for in current versions of RUSLE and WEPP. In this paper we use erosion and sediment deposition predictions of these models and modify, outside of the programs, an approximately 80-m long hillslope containing grass strips using simple assumptions about the location and shape of sediment deposits. We compare the effects of these slope modifications on predicted future erosion and compare the predicted hillslopes profile topography to field observations of slope alteration over time at one field site. Our results demonstrate the importance of considering landscape modification for long-term conservation planning of sloping fields containing permanent non-tilled strips of vegetation. They further demonstrate that a reasonable job of accounting for such effects can be done without completely rewriting existing models. Simple assumptions about the location and shape of sediment deposits can capture the main effects of hillslope modification from strip cropping with grass hedges. Such accounting should be included when modeling erosion in the 21st century.