Concerned that dam failure would jeopardize the safety of downstream homes, businesses, and a major thoroughfare, Peachtree City embarked upon its largest infrastructure project since the planned community’s founding — creating a new spillway for the 222-acre Lake Peachtree. The city selected Schnabel’s effective and exquisite piano-key weir design to bring the dam and spillway up to modern standards.

Providing flood control and recreation for residents, Lake Peachtree is the centerpiece of the community. Although the state’s Safe Dams Program classified the dam as low hazard, the city proactively elected to upgrade it and the spillway to meet criteria for a high-hazard structure. The effort involved over three years of planning, negotiation, design, and construction.

Increasing spillway capacity was the goal, but site conditions and economic considerations limited acceptable alternatives. The new spillway had to accommodate the existing peak inflows for storms up to and including the 100-year event. The ideal structure would safely discharge the runoff associated with the state-required design storm event without increasing flooding in the reservoir or the downstream floodplain.

After considering the alternatives of raising the dam to provide additional storage, widening the spillway, or replacing it with either a labyrinth weir or piano key weir (PKW), the city selected a three-stage PKW. The design met all of the project objectives related to function, aesthetics, maintenance, construction cost, operating cost, and construction schedule. Completed in June 2018, it is the first PKW put into service in the U.S. and the first known multi-staged PKW in the world.

The structural design relies on extreme environmental loading conditions, with the reinforced concrete proportioned to provide decades of reliable service. While still in design, 3D computational fluid dynamic modeling and structural finite element modeling was used to visualize spillway performance, which helped reduce constructibility issues before they emerged in the field.

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