What is a spillway?


The spillway is the last line of defense a dam has before water goes overtop the walls of the dam. It functions just like a drain hole near the top of the edge of a bathtub or sink by directing the flow of excess water. During a high water event, when a dam is storing water for downstream flood damage reduction, the level of the water in the reservoir will rise as water from the upstream drainage area continues to flow into the lake. The spillway provides a gradual means for water to be released from the reservoir to prevent the dam structure itself from being completely overtopped. In most cases, the spillway is located to the sides of the dam. At East Sidney Lake, the spillway is a notch located at the top of the structure.