LISEM: a physically-based hydrological and soil erosion model incorporated in a GIS

The LImburg Soil Erosion Model (LISEM) is a physically- based hydrological and soil erosion model which can be used for planning and conservation purposes. LISEM is one of the first examples of a physically-based model that is completely incorporated in a raster Geographical Information System (PCRaster). This incorporation facilitates easy application in larger catchments, improves the user- friendliness by avoiding conversion routines, and allows remotely sensed data to be used. Processes incorporated in the model are rainfall, interception, surface storage in micro-depressions, infiltration, vertical movement of water in the soil, overland flow, channel flow, detachment by rainfall and throughfall, detachment by overland flow, and transport capacity of the flow. Special attention has been given to the influence of tractor wheelings, small roads, and surface sealing: different surfaces can be defined at a sub-grid level. Vertical movement of water in the soil is simulated using the Richards' equation. Storage of surface water in micro-depressions is modelled using the concept of random roughness. The detachment and transport equations are similar to the equations used in EUROSEM (Morgan, 1994). For the distributed flow routing, a four- point finite-difference solution of the kinematic wave is used together with the Manning equation.