Bed load management Strobler Weißenbach - Monitoring, modelling, clearance concept

Research institute: BOKU Institute of Hydraulic Engineering and River Research

The Strobler-Weißenbach which is located in the Salzburger Kalkvoralpen is a part of the Osterhorngruppe. The main drainage ditch has a length of 11,3 km, a catchment area of 45.53 km2 and discharges at Strobl into the Ischler Arche River. A huge slit dam is located in the upper reach which is completely silted up with limestone gravel. To guarantee the operational reliability of the construction, clearance of the retaining capacity has to be done. However, this measurement requires high financial and operational effort. Improving the efficiency of emptying itself is only possible by mechanical means ("shoveling" of the slot openings during low and medium flow). Resulting downstream material input causes an increase in turbidity and bedload transport followed by alluvial deposition and rearrangement effects. In addition to an increase in turbidity, alterations in stream morphology in the lower reach were observed in the course of previous sediment management measures.The objective of the monitoring program is to document the actual state of stream morphology, habitats and sediment transport and to analyze its future development via an integrated measurement program.The program includes various measuring stations for water level, flow velocity, and suspended sediment load in addition to analyze the bed material and sediment migration using radio telemetry. The aim of the project is to develop a general clearance concept which is minimizing adverse effects to the lower reach concerning fisheries and flood protection. Moreover, damage potentials for fisheries as a consequence of alluvial deposition and clogging of potential spawning habitats should be determined and evaluated.