Depending on expected water conditions in the fall, Brownlee Reservoir releases are managed to maintain a constant flow of 8,500 to 13,000 cfs below Hells Canyon Dam to provide optimum conditions for spawning fall chinook salmon.

In order to provide this constant outflow from October through December, the company may be required to draft Brownlee Reservoir in September. This additional reservoir space is necessary to capture inflows that are in excess of the constant outflows being released.

Spawning flow is based upon:

• A minimum reservoir elevation of approximately 2,040 feet above sea level when the program starts in October.
• Forecasted inflows so that Brownlee Reservoir is full, around 2,075 feet above sea level, by the first week in December.
• Anticipation that the minimum flow set during the spawning period can be maintained until fry emergence in the spring without emptying Brownlee Reservoir

Minimum flows below Hells Canyon Dam are maintained through fry emergence, or until the fish leave their redds, or nests.

View a chart about how many redds have been counted in the Snake, Grande Ronde and Imnaha rivers. This occurs in the spring and is established by maintaining water over the most shallow redds. Once this flow is set, it is considered the minimum flow necessary to keep fish embryos from drying out until they are big enough to leave their nests in the spring.

These operations can impact power production. The lower the reservoir elevation in Brownlee, the lower the power production capability of the plant. This, in turn, may require the company to purchase power from other sources if the demand for electricity cannot be met due to lower reservoir water levels.