Adapting reservoir flushing strategies to changing hydro-climatic conditions

Abstract

The sustainable use of water reservoirs is threatened by sediment accumulation, but loss of storage volume can be prevented or limited by appropriate sediment management strategies that work in a variety of expected conditions. The development of a reservoir flushing strategy, tested against water and sediment inflow that might occur over centuries, is presented. A typical length of water and sediment records of 50 years was used to represent the range of variability within a year, and extended by deducing longer term inter-annual variability from suitable indicators (sediment cores in natural lakes, tree-ring chronologies etc.). It was concluded that, over past centuries, water inflows over a period of 50 years could typically vary by about 10%, while sediment inflows could vary by about 20%. The resilience of flushing rules derived solely on the recorded dataset over centuries-long periods was tested using a long-term computer simulation of reservoir sedimentation. The simulations showed that some modifications to the flushing rules would increase performance over centuries-long periods. Although the approach was derived for a specific project, it is based on some generally applicable parameters, such as the discharge at which operation stops and the moving average of the annual peak flow.