Lake Sebago Dam

Tectonic is providing engineering services to the New York State Office of Parks, Recreation, and Historical Preservation for the evaluation and rehabilitation of Lake Sebago Dam located in Harriman State Park, Rockland County, New York. Lake Sebago Dam is a 24-foot high, 950 feet long earth embankment with a 38-foot high, 197 feet long concrete gravity spillway built in 1924. Sebago Lake has a 10.4 square mile watershed and an impoundment of 5,674.0 Ac-ft.. A multi-span, 190-foot long two-lane bridge carries Seven Lakes Drive across the spillway.

Tectonic has completed the Schematic Design Phase Study that assesses the existing condition of the dam, spillway and bridge, and their behavior under loading conditions required by NYSDEC and NYSDOT regulations. The Study included review the of existing reports, stability analyses of the existing dam and spillway, and hydrologic and hydraulic analyses to evaluate spillway capacity and overtopping potential. The study also included the evaluation and rehabilitation of the Seven Lakes Drive Bridge and the stability analysis of Lake Kanawauke Dam, immediately upstream of Sebago Lake, and its impact on the Sebago Lake Dam.

Tectonic will be developing options and construction cost estimates for the rehabilitation of the Lake Sebago embankment, spillway and bridge and the construction of a new auxiliary spillway for both the half PMF. Final services will include preparation of design and construction documents assistance and construction administration and inspection.