The decision is in for the new spillway for Lake Peachtree. The City Council on Sept. 15 gave consensus to have staff move ahead with the design and engineering of the spillway that will feature a three-stage barrier called a piano key weir.
A topic of discussion for the past few months, construction of the spillway that will meet Category 1 dam standards is expected to begin in August 2017 and be completed by June 2018.
Seven potential spillway designs were considered prior to the recommendation of the piano key weir by city consultants Integrated Science and Engineering and consultant Schnabel Engineering.
City Manager Jon Rorie said the model selected was the most cost-effective way to fit in the existing spillway channel.
Though only one spillway in the U.S. is currently being designed based on the three-stage piano key weir concept, Fayette County Water System Director Lee Pope at the meeting said, “The design the guys came up with is ingenious. They did a great job on the research.”
The three stages pertain to the water levels to be managed by the new spillway. The lowest level will accommodate existing discharge rates while the second and third levels will accommodate much higher volumes of water flow.
Put another way, the lowest “key” will be positioned at the level of the current spillway. The middle “key” will be two feet higher to manage larger volumes of water, while the third “key,” which is significantly larger in width, will be four feet higher in elevation that the lowest key and will accommodate extreme rain events.
Meeting state Category I standards for dams, the concrete used to construct the spillway is expected to last 100 years or more, project representatives said.
The current spillway can handle eight inches of rain in 24 hours. The new spillway will be able to handle the state standard of 18 inches of rain in 12 hours.
The project also includes adding a 1.4-foot parapet wall, essentially a berm, to the dam which is situated immediately to the west of the spillway.
Also in included in the project is removing the top section of a small peninsular area situated between the dam and spillway to provide for improved inflow to the spillway. The remaining area could be used as park space.
The estimated cost of the spillway is $3.1 million, of which Fayette County will contribute $2 million. A contingency of 15 percent, or $465,000 was recommended.
The lake will have to be lowered, but not drained, during construction and a temporary dam installed immediately north of the spillway, with a significant portion of the work done during the fall and winter.
Another potential component associated with the project could be the installation of a 12-15-foot cart bridge adjacent to the spillway. The bridge would be 160 feet in length and could connect to a potential park area near the dam.
Also included in the project could be the rerouting of the cart path along Kelly Drive near the current dam and spillway driveway. There is an existing berm that, for minimal cost, could have the current cart path on the south side of Kelly Drive re-routed so that it connects to Kelly Drive near the community garden.
The estimated cost for the installation of the cart bridge, potential park improvements by the dam and spillway and cart path work totaled approximately $700,000. The bridge alone would run $400,000-450,000.
The spillway project is one of the items included on the city’s SPLOST (special purpose local option sales tax) list expected to go before voters in March.
The city will have to determine how to fund the remainder of the project and if a cart bridge should be added near the spillway.
In terms of the timeline, preliminary design is expected to be complete by December, with design development and final design done by May 2017. Bidding should wrap-up in August followed by construction running through April 2018 with project close-out in June 2018.
