The purpose of the spillway is to safely convey storm events, up to the probable maximum flood (PMF), around the main dam embankment. The PMF storm event estimated for Chimney Hollow incorporates recently developed climate change impacts into the estimate to make sure that the dam remains safe into the future. It is a state-of-the-art design to minimize risk of failure in the event of spillway operation. Because Chimney Hollow Reservoir is an off-channel reservoir and not on a major river system, the spillway is small relative to the main dam's size. The spillway has a 10-foot-wide chute designed to accommodate a skid steer loader for inspections and maintenance. The length is approximately 3,800 feet and contains about 12,000 cubic yards of reinforced concrete, all produced on site.
Most of the spillway will be constructed below the existing ground surface to keep the spillway on a solid rock foundation and help with the aesthetics of the site.