Effect of land-use on the flood hydrograph of the Bauna catchment (Northern Hessen Region, Kassel Germany).

Many planning and management decisions on flood control projects made by hydrologists are based on the estimation of flood volumes and its probabilities of occurrence either directly as with flood quantiles or through the estimation of the expected flood damages. Quantifications of the flood events occurring frequently in a catchment need detailed investigation/study of all the surface conditions that might have one or more effects on the runoff value in the catchment. Much more, the physical characteristics of the catchment and its effect on the flood flow has to be examined. Though the amount of precipitation and its intensity plays a substantial part in the runoff volume estimation, the effect of the physical conditions such as land-use changes, soil characteristics, topography and other catchment characteristics cannot be underestimated. Hence a shift from the conventional method of rainfall analysis alone to a detailed and comprehensive investigations of other factors that could have substantial effect on the flood flow in any catchment. This study investigates the influence of the different external factors on the flood flow value in a particular catchment called 'Bauna' in the Baunatal area of Northern Hessen, Germany by the use of an hydrological model called Nasim. This model requires the use of different sizes of the partial catchment subareas by overlapping the different lane use map, drainage network, and geological conditions of the subcatchments. The simulation of the different areas and the volumes was done by the use of the GIS-Auto Cad-Karto software. The geographical representation of the study areas called subcatchments were digitized with these different maps overlapping one another. The selected catchment was divided into four subcatchments with three major land use types. All the geological types were defined by the appropriate parameters and these in combination with the rainfall data of the catchment area under study, temperature, evaporation and humidity data were used to analyze the various influences on the runoff volume, the infiltration and the soil moisture content of the catchment area concerned. The result of the simulation showed that the grassland has the highest runoff reduction potential with the cultivation type having the least. Forest reduces runoff more in the summer than in the winter because of the higher interception that takes place in that period.