The effect of tillage-induced roughness on runoff and erosion patterns

In agricultural areas, tillage-induced roughness may have large impacts on runoff patterns and therefore on the effective slope, local contributing ar eas and erosion patterns. A model was developed to create a runoff pattern with flow in the direction of the plough-lines for all tilled fields within a catchment. The model needs a digital elevation model (DEM), a landuse ma p and the major tillage orientation per tilled field as input. Optionally. the flow direction of roads and/or channels can be superimposed on the drai nage network. The model calculates flow directions along parcel borders and creates headlands along borders that are not parallel to the tillage orien tation. The model also calculates the slope gradient in flow direction. The created tillage-controlled runoff pattern can be combined with the topogra phic runoff pattern. if decision rules are available to choose between topo graphic or tillage direction. The tillage runoff pattern can be very differ ent from the topographic pattern, leading to totally different patterns of slope and contributing area. The use of the tillage-controlled runoff patte rn rather than the topographically controlled runoff pattern in a determini stic, event-based model (LISEM). results in a much better agreement of the predicted runoff and erosion pattern with field observations. However, accu rate model predictions can only be obtained if the input DEM is sufficientl y accurate to represent local topographic variations in the fields. (C) 200 1 Elsevier Science B.V. All rights reserved.