Adapting reservoir flushing strategies to changing hydro-climatic conditions

Sustainable use of water reservoirs is threatened by sediment accumulation. The loss of storage volume can be prevented or limited by appropriate sediment management strategies that work for a variety of expected conditions. The paper presents the development of a reservoir flushing strategy, tested against water and sediment inflow that might occur over the centuries. A typical length of water and sediment record of 50 years to represent the range of variability within a year is used 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 the past centuries, water inflows in 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 data set over centuries-long periods was tested using a long-term computer simulation of reservoir sedimentation. The simulations showed that some modifications to the rule would increase its performance over centuries-long period. 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 moving average of the annual peak flow.