One of the highest priorities of project managers at Chimney Hollow is ensuring the new reservoir’s infrastructure is ready for anything – even if “anything” might happen only every 500 years. Take, for example, the Chimney Hollow spillway, a recently completed structure that stretches nearly three-quarters of a mile down the north side of the main dam, dropping about 350 feet from the top of the reservoir to the valley below. 

This new 8-by-10-foot box-culvert concrete structure can carry up to 850 cubic feet per second (cfs) of water – the estimated amount that would flow downhill from the two-and-a-half-square-mile area above the reservoir during the Probable Maximum Flood. Although statistically extremely rare, such a rain event could wreak havoc on the reservoir’s infrastructure and the surrounding area without a proper way to reroute such volumes of excess water coming down the valley walls. 

The spillway is designed with state-of-practice components to make sure it can handle extreme conditions. These components include a robust underdrain system with cutoff walls, drains and cleanouts, designed to prevent uplift pressure. The spillway is founded entirely on a solid bedrock foundation. Additionally, all of the concrete joints are overlapping with continuous rebar.