Adapting reservoir flushing strategies to changing hydro-climatic conditions

Abstract

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.