GIS-based catchment modeling

For the catchment of the upper Hase, with an area of approximately 700 km(2) in southwestern Lower Saxony, Germany, rainfall-runoff simulations were carried out for the period between 1989 and 1997 on a monthly basis. The subcatchments of 11 gauging stations were determined within a Geographic Information System (GIS) on the basis of a Digital Elevation Model (DEM) and river network data. The hydrological model is based on rainfall data and information about artificial discharge and removal of water. An effective actual evaporation coefficient was calibrated for one subcatchment under consideration of typical land-use pattern and used for all other subcatchments. Nitrogen loads and concentrations could be separated into point and non-point sources. Nitrate content is mainly determined by diffuse input, whereas ammonium is related to sewage discharges. Nitrate could be well correlated to subcatchment groundwater nitrate concentrations averaged from the monitoring data of private water wells for 1991-93.