While excavation of the spillway channel has been ongoing for over a year, crews recently made the first concrete placements, including shear keys, a seepage cutoff wall and spillway underdrains. These features are designed to protect and stabilize the spillway structure and to intercept potential seepage from the reservoir or adjacent groundwater.

Crews began construction near the bottom of the spillway and are working their way upstream. To date, approximately 150 feet of the seepage cutoff wall system has been constructed along with 50 feet of the underdrain. Barnard Construction anticipates crews will place the first spillway slab in February.

The reinforced concrete spillway is located on the left (west) abutment of the main dam. 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 to ensure the dam remains safe in the future. The spillway includes many resilient state-of-the-art design features for safe operation during flood events. Because Chimney Hollow Reservoir is an off-channel reservoir and not located on a major river system, the spillway is quite small relative to the size of the main dam. The spillway has a 10-foot-wide chute, is approximately 3,800 feet long and contains about 12,000 cubic yards of reinforced concrete, all produced on site.  

The spillway will be constructed on a solid rock foundation so that most of the spillway will be buried below the existing ground surface.