Lake Ogletree Spillway - Rehabilitation in the 'Holey' Land

摘要

Lake Ogletree serves as the primary drinking water supply for the City of Auburn, Alabama. The dam and spillway were originally constructed in the 1940's and both have undergone several modifications over the years. Due to undermining of the existing overflow spillway, rehabilitation of the spillway system was considered necessary by the Water Works Board of the City of Auburn (AWWB) in order to reduce the risks associated with the aging system and protect the city's water resource interests. Alabama is the only state without a dam safety program. This provided the project with both challenges and opportunities. Most significantly, the designers had the opportunity to assist the AWWB with selecting a reasonable and justifiable design storm for the proposed spillway. The project included replacement of the existing 525-foot wide, thin slab, concrete broad-crested spillway with a 218-foot wide, 5.5 cycle labyrinth-crested chute spillway. The labyrinth spillway included four crest stages to match existing spillway outflows associated with storms up to the 100-year event. Three-dimensional computational fluid dynamics (CFD) analyses were performed to assess flow velocities within the proposed inlet channel. This modeling indicated a need for an armor-reinforced vegetation system in the inlet channel. During construction, large subsurface voids were encountered during excavation for the proposed spillway. This impacted the construction schedule and resulted in the need for coordination between the client, the contractor, and designer to plan and implement remediation strategies. Additional subsurface explorations of the site were performed to estimate the extent of the encountered voids. This exploration included the use of geophysical techniques, sonic drilling, and air track drilling. The rehabilitation work was completed in late 2017. The AWWB was selected to receive the 2018 ASDSO Southeast Regional Award of Merit for their efforts related to this project.