Using Reservoirs to Mitigate Nutrient Discharge

Abstract:

Reservoir management for the purpose of hydropower production alters the hydrological flow regime and can have significant impact on nutrient transport as well as ecology. Using reservoir management to reduce the nutrient load to downstream areas can be of great importance for aquatic habitats in recipient waters as well as the overall health of coastal areas. In this study the regulation of a network of reservoirs in River Dalälven, Sweden, is simulated using a multi-objective approach that accounts for both the nutrient export and power production. The optimization model is used to derive the Pareto front for the two objectives; the hydropower production and water quality objectives. The effect of regulation of River Dalälven on the nutrient transport is examined as a possible control method for limiting nutrient transport from the watershed. The cost in the form of loss of hydroelectric power is quantified. Optimization of a large-scale river network is done at great computational expense and the additional states (concentration of nutrient) increase the computational load significantly, for this reason several simplifications of the system dynamics are made. It is shown that a 50% reduction of the nutrient discharge can be achieved to a limited loss of power production (<5 – 10%), but that additional reduction is associated with a significant loss in power production.