Turbidity currents in reservoirs

Abstract

This entry summarizes the physical phenomenon turbidity currents described in literature as well as the field measurements taken in a European reservoir for verifying turbidity flows. It discusses also in consequence one possibility of reducing reservoir sedimentation. The example of the Soelk reservoir in Austria has been used for demonstration to prove that measurements in nature can give evidence that turbidity currents may flow downstream to the dam. As inflows to the reservoir and, hence, suspended sediment concentrations, have been low during the measurement campaign, there has been no evident event of venting turbidity currents. However, the identification of high sediment concentrations along the reservoir down to the bottom outlet during several events has substantiated the assumption that it is possible to vent turbidity currents through the Soelk reservoir during major events. Turbidity measurements above the reservoir head, directly below the plunge point region and at the bottom outlet, have revealed a time lag in the turbid flow peaks. This observation has been supported by the results of conductivity and temperature measurements. In addition, 3D measurements of flow velocity in the plunge point region and at the bottom outlet brought forth satisfactory results even with low flow velocities. In terms of statistics, the spillway operates six times a year. Thus, it should be possible to open the bottom outlet during floods in order to provide the basis for developing an important contribution to sustainable and environmentally compatible sediment management.