When river flows are high, extra water can be spilled from the dams so that it does not contribute to oversupply, but too much spill exceeds water quality standards and can harm fish and other aquatic species. If water cannot be spilled, it must be passed through the hydropower turbines, thus generating electricity.
Oversupply is most likely to occur at night, when power demand is low, and in the springtime, when river flows and wind generation are high.
In these conditions, BPA may need to implement the Oversupply Management Protocol, under which non-hydro generation is displaced to protect aquatic life and maintain system reliability. Under the protocol, BPA compensates generators for their displacement-related costs. A list of BPA actions to reduce oversupply can be found in Attachment P.
Information on the Oversupply Management Protocol business practice is available on BPA Transmission's Business Practices page