Jan. 11, 2024

Progress Continues on Concrete Spillway

Throughout the past year, crews have been working on the reinforced concrete spillway on the left (west) abutment of the main dam. Since completing excavation, 5,060 cubic yards of concrete have been placed throughout the spillway's alignment, which includes about 74 cut-off walls/leveling concrete placements, 61 slabs and 42 box culvert sections. The completed slabs amount to 1,525 feet of its total length. Forty-two box culvert sections (the concrete wall and roof enclosures), have been placed, resulting in 1,050 feet of fully completed spillway.  

Each box culvert takes about one week to complete and is formed using a slipform system. The forms are flown in by crane, prepared with rebar, a bulkhead and water stop before concrete is placed. Once placed, the concrete must be cured to 75 percent before the slipform equipment can be removed. There are currently three slipform systems in use which are being utilized on three different headings along the alignment which will speed up production time of the culverts. 

Spillway progress at Chimney Hollow January 2024,

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.