LISEM: a physically-bas ed hydrological and soil erosion model for basin-scale water and sediment management

Abstract

Abstract A new hydrological and soil erosion model has been developed and tested: LISEM, the Limburg Soil Erosion Model. The model uses physically-based equations to describe interception, infiltration and soil water transport, storage in surface depressions, splash and flow detach­ment, transport capacity and overland and channel flow. The model is fully incorporated in a raster GIS for ease of use. However, it is clear that although the model has several advantages over other models, the results are far from perfect. Based on the sensitivity analysis and field observations, the main reasons for these differences seems to be the spatial and temporal variability of the soil hydraulic conductivity and the initial pressure head at the basin scale. Another reason for the differences between measured and simulated results is the lack of theoretical under­standing of the hydrological and soil erosion processes. INTRODUCTION Between 1991 and 1994 a soil erosion project has been carried out in three catchments in the loess area of South Limburg, The Netherlands. The project was funded by the Province of Limburg, the water board RoerenOvermaas, the Ministry of Agriculture and 14 municipalities of South Limburg. The Departments of Physical Geography of the Universities of Utrecht and Amsterdam and the Soil Physics Division of the Winand Staring Centre in Wageningen cooperated to develop and validate a new physically-based hydrological and soil erosion model, which can be used for planning and conser­vation purposes: the Limburg Soil Erosion Model (LISEM). In three catchments, discharge and sediment load at the outlet have been measured continuously. Rainfall has been measured at six locations to take into account the spatial variability of rainfall. Furthermore, in six sub-catchments discharge and sediment load measurements have been carried out. Also, at twelve sites in the catchments along four slope profiles, continuous soil suction measurements have been done to assess both vertical and lateral transport of water in the soil. The soils in the catchments were mapped in detail to serve, amongst other purposes, as a basis for the soil hydrological sub-model. Several times during the year, land use and soil cover, surface roughness parameters, soil porosity, soil moisture content, soil shear strength and aggregate stability are measured using advanced methods. Further­more, to assess the effects of soil conservation measures and to validate the simulations