THE EUROSEM-GRIDSEM MODELING SYSTEM FOR EROSION ANALYSES UNDER DIFFERENT NATURAL AND ECONOMIC-CONDITIONS

Within the research project, nutrient losses and erosion from agricult ure are calculated. Calculations are done with an interdisciplinary mo deling system capable of predicting the effect of various policy measu res to reduce losses. This paper describes the application of the dete rministic one event based erosion model EUROSEM in combination with a digital elevation model GRIDSEM, to analyze erosion at the catchment s cale within the frame of the overall project. GRIDSEM uses a grid size of 30 x 30 m and includes a simple routine for adding up sediment los ses in the watershed. For each day during a 20-year simulation period the soil erosion level is estimated for each cell, based on: (1) the p ermanent landscape related characteristics of slope and soil type; (2) parameters determined by the agricultural management system, includin g parameters for plant height, soil covered by plants, surface roughne ss and soil cohesion; and (3) actual weather data. A distinction is ma de between rainfall and snowmelt induced runoff events. Changes in ero sion level could be estimated from the output of GRIDSEM and by analys es of the estimated erosion levels for the cells. Results show that th is method is capable of: (1) estimating changes in overall erosion lev els; (2) estimating the relative benefits of different agricultural ma nagement systems concerning total erosion; and (3) showing the unpredi ctability and importance of extreme erosion events, in both time and s pace. (C) 1998 Elsevier Science B.V. All rights reserved.