Reconstruction of the breached lake Delhi dam will begin the week of April 14, leaders of the Delaware County residential area said Thursday.
The two-phase project will begin with repairs and upgrades to the flood-damaged concrete portion of the dam, said Steve Leonard, president of the board of trustees of the Combined Lake Delhi Recreational Facility and Water Quality District.
The Phase 1 contractor, Lunda Construction of Little Chute, Wis., will be moving in a crane and other heavy equipment to recondition the concrete structure and replace the flood gates and the mechanical and electrical systems that operate them, Leonard said.
A panel of federal engineers reviewing the dam breach in 2010 said the failure of one of the dam’s three flood gates to open fully may have been a contributing factor.
“We’re scrapping the original gates, with their 1928 technology, and replacing them with modern, flexible, automated gates,” said Pat Colgan, a retired civil engineer and volunteer coordinator of the rebuild effort.
Colgan said the Maquoketa River will flow over the spillway “like a waterfall” 90 percent of the time. The gates will open automatically to provide additional discharge in periods of high water, he said.
“It will be a true run of the river system with no water storage upstream,” he said.
Leonard said Lunda was the lowest bidder on Phase 1, which has an estimated cost of $4.6 million.
Phase 2, construction of an adjacent earthen dike and spillway, cannot begin until the Department of Natural Resources issues a required permit.
Leonard said a public comment period on the permit is scheduled to close Thursday. As soon as the permit is issued – which Leonard said he expects in early May – bids will go out for Phase 2, with an estimated cost between $6.6 million and $7 million.
Classified as a “moderate hazard” dam, the structure will be able to pass 69,000 cubic feet of water per second – more than double the Maquoketa River’s flow when the dam breached after two days’ heavy rain on July 24, 2010.
Colgan said a coffer dam will divert water through the gates of the concrete structure while the earthen dike is built. Earth for the dike will be trucked in from sites to be determined by the contractor, he said.
Sand and silt from the lake bed would be too permeable for dike construction, Colgan said.
Construction would be expedited by a season of normal rainfall and river levels, which might be more than lake residents can reasonably expect. Major Maquoketa River floods were recorded in 2002, 2004, 2008 and 2010.
Lake officials said they hope the project will be completed this year and the lake refilled to recreational levels by the summer of 2015.“It will be the same lake with the same shoreline,” Colgan said.