Onondaga County Water Authority,  Marcellus, NY

O'Brien & Gere was retained by Onondaga County Water Authority (OCWA) to replace three 36-inch sluice gates at the Ostico Lake dam. During the course of the sluice gate replacement work, a diving inspection revealed that the timber decking within each sluiceway had deteriorated. Upon opening the sluice gates to test the temporary bulkheads, water in the sluiceways was observed flowing through the deteriorated sections of the timber decking and resurfacing within the adjacent sluiceways, and at points downstream of the dam. Visible silt plumes indicated that voids existed beneath the timber decking, which could compromise the integrity of the structure. Extensive subsurface exploration was undertaken, and an underwater inspection of the dam was performed. In addition, an inspection of the downstream area was performed following dewatering using a cofferdam.

As a result of these inspections, the project scope was expanded to include replacement of the sluice subgrade with flowable fill grout above the timber decking and beneath the steel sluiceway floor, as well as reconstruction of the sluiceway inverts to mitigate future erosion. Control of water and maintenance of minimal stream flows, as required by the New York State Department of Environmental Conservation, were also key components of the project. Subsequent work performed by O’Brien & Gere for OCWA at the Otisco Lake Dam includes annual inspections, dam breach analysis, and updating the Emergency Action Plan (EAP) for the facility.