Distributed sediment and phosporus transport modeling on a medium sized catchment in Central Germany

Current research suggests that strategies to control nitrogen as well as se diment and phosphorus loss from nonpoint sources should focus on different runoff components and their spatial and temporal variation within the catch ment. Therefore nonpoint source models. especially in humid climatic region s, should consider variable hydrological active source areas. These models should also be able to consider runoff generation by saturated overland flo w as well as Horton overland flow. A combination of the hydrologic model Wa SiM-ETH and the erosion and P-transport model AGNPS Version 5 was chosen fo r this study. The models were run in the WaSiM-ETH runoff generation mode ( Topmodel and Green a. Ampt approach) and the SCS curve number mode, modifie d by Lutz (1984), to assess these different runoff calculation procedures. A medium sized catchment in the lower Hessian uplands of Germany was select ed for the present investigation. The results show that the combined Topmod el/Green and Ampt runoff approach produce reasonable results for the simula tion of runoff volume for single runoff events at the catchment outlet. The more physically based model approach computed a much more realistic distri bution of runoff and P yield producing areas than the SCS curve number meth od, modified by Lutz (1984). Reasonable results were achieved for sediment yield calculations. Particulate P calculations showed larger deviations bet ween measured and calculated values. (C) 2001 Elsevier Science Ltd. All rig hts reserved.