Peachtree City is one of the first planned communities in Georgia. Lake Peachtree is the centerpiece of the community, providing water supply and recreation for residents. 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 state-required design storm without increasing flooding in the reservoir or the downstream floodplain.
Alternatives considered were raising the dam to provide additional storage, widening the spillway, or replacing it with either a labyrinth weir or piano key weir (PKW). The selected alternative was a three-stage PKW, which met all 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 United States 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. 3-D computational fluid dynamic modeling and structural finite element modeling was used to visualize spillway performance while still in design, which led to reduction of constructability issues before they emerged in the field.
2019 ACEC Georgia, Engineering Excellence Award, Water Resources Category
2019 ACEC Grand Award, Engineering Excellence Awards