Incorporating Sediment Management in Short-term Hydro Scheduling

Sedimentation represents a severe threat to the sustainability of hydropower. In reservoirs, sedimentation leads to the loss of storage capacity and decreases the flexibility in energy production. Sediments also results in the abrasion of mechanical equipment and increases the cost of maintenance. While the rate of sedimentation varies for each reservoir and each river in the different regions of the world, eventually most hydropower plants face the sediment problems in daily operations.

Many works in the literature study the sediment management techniques that affect operations of the hydroelectric facilities, but few focuses on the incorporation of sediment management in short-term hydro scheduling (STHS). In a cascaded watercourse where there is a combination of reservoir-based and run-of-river hydropower plants, the purpose of STHS is to optimally determine the water release of reservoirs and to attain power generation schedule of the available hydro resources during a time horizon of one day to one week.

In this paper, we present two functionalities developed for sediment management in STHS. The first functionality pertains to the discharge limits of the plant associated with the water level of the upstream reservoir. With the decrease of the reservoir water level, the flow velocity will increase if the flow discharge to the plant remains the same. Then more sediments will be carried into the penstock and damage the turbines through erosion of the oxide coating on the blades. In order to avoid this damage, new operational parameter should be included in the optimal scheduling problem. Instead of using a constant value, the maximum discharge limit of the plant should instantly vary with the water level of the reservoir.

The second functionality relates to the shifting of the operating point of the turbine. From the economic point of view, the turbine will usually run within the range from the best efficiency point to the maximum once it is turned on. However, since abrasion can be mitigated by reducing the volume of fine sediments that reach the turbine, an extra discharge cost is introduced in the optimization model to move the operating point from the peak to the low discharge area.

These functionalities have been implemented in a STHS tool used by many hydropower producers in Europe. Numerical results demonstrate the effectiveness and importance of the functionalities for daily operations.