St. Marys Dam Spillway Replacement

Location: Celina, Ohio

Project Value: $4,621,032.00

Project Completion Year: 1997

(9511)

Grand Lake St Mary was constructed in the early 1800s to provide water for the Miami and Erie Canal. It is the largest manmade lake in Ohio. Over the years, the lake has become heavily silted and the existing spillway structure constructed in the early 1900s was failing and insufficient to handle the current flow requirements.

E.S. Wagner Company served as the prime contractor on a project for the Ohio Department of Natural Resources to construct a new horse shoe shaped gravity dam extending 160 feet into the lake. It also included an 80 foot span bridge constructed for the perimeter embankment roadway. The dam itself consisted of a 15 deep 3 wide concrete keyway dug into the underlying clay subsoil and a 25 tall mass structure that was 25 wide at the base converging to 5 at the top with a parabolic face on the inside of the dam. It used a total 7,000 cubic yards of mass concrete. A 750 long steel sheet pile wall was driven from portable barges and ballasted on the inside with 20,000 tons of stone to construct the cofferdam.

A temporary spillway using two 60 inch pipes was constructed to provide emergency overflow for the lake during construction. A total of 55,000 cubic yards of silt and sediment was removed and 25,000 cubic yards of clay embankment was placed before the keyway excavation and dam construction was able to be started. Since its completion, the structure has provided relief from the chronic flooding that had plagued the lake for years.