Lutra 46(2)_John & Klein_2003

Beaver pond development and its hydrogeomorphic and sedimentary impact on the Jossa floodplain in Germany

This paper presents results of a two-year study showing different beaver (Castor fiber) induced hydrogeomorphic changes on the floodplain of the small river Jossa (Spessart Uplands, Germany). Using GIS and aerial photography, different stages of river and floodplain morphology were mapped. In addition, length of water courses, areal extent of ponds and wetlands, sediment depths, volumes and sedimentation rates, as well as erosion rates and amounts of eroded material were calculated with the supplementary aid of precise levelling. The results revealed that beaver dams create large wetlands and greatly increase the area of open water surface by dammingup ponds. Moreover, they enhance the total water flow length by diverting water onto the floodplain, resulting in a multi-channeled drainage network. The new diversion channels induced the erosion of 50 m3 of overbank fines. By reducing flow velocity within the dammed-up channel and by diverting water onto the floodplain, the dams lead to the deposition of a total amount of 1,890 m3 of sediments within the beaver ponds and on the inundated floodplain.