A dam sits behind the Fox Hill condominiums, fairly dry much of the time, backing up water only in times of heavy rain — and occasionally stopping enough water to create a temporary pond across Farmingville Road. The state is considering what to do with that aging dam, built almost 40 years ago across Ridgefield Brook, which becomes the Norwalk River, as part of the Norwalk River Flood Control Project.

A public information meeting about the state’s plans is scheduled for Thursday night, April 19, starting at 7 in the Ridgefield Recreation Center’s Charter Oak Room.

“They’re looking at the dam. They’re assessing whether or not they have to rehabilitate it,” said Town Engineer Charles FIsher. “They have a couple of different options, one is to do nothing.”

Another option is to get rid of the dam.

A release from the state Department of Energy and Environmental Protection (DEEP) says planning for the dam rehabilitation began in November 2017 and will continue another year and half.

”The planning effort will evaluate the following options for the dam: no action; decommissioning (dam removal); structural rehabilitation; and nonstructural measures,” the DEEP release says.

Ray Frigon of the DEEP said the examination of options was prompted by what’s happened in the vicinity of the dam more than any problem with the dam itself.

“After several decades of development in the area, the dam has a different hazard classification at this point in time,” he said. “If the dam were to fail, it has the potential to cause, certainly, destruction of property,” he said, and also “potential for loss of life, just given the acreage that drains to the Great Swamp area, which is where the dam is located.”

He added, “loss of life and loss of property, it’s under the worst imaginable scenario that you could think of.”

That’s pretty much what prompted the dam’s construction. It was built in 1979 as part of the Norwalk River Flood Control Project, prompted by the flood of 1955, which dumped more than a foot of rain on the area over two days that October.

Five flood control dams were originally planned as part of the project, and two were built — the Grea Swamp dam behidnd Fox HIll and another dam on Spectacle Brook in Wilton. Among the three that were never built — largely due to being tied up with the design of the now abandoned Super 7 expressway project — was the key flood control structure in the plan, the Miller’s Pond dam, planned off Route 7 near the intersection of Florida Hill Road. This dam would have backed up water behind it northward, towards Simpaug Turnpike and Ashbee Lane.

Two other dams were planned and never build: one on Cooper’s Brook near Candee’s Pond off Route 102 near Branchville; and one on Comstock Brook in Wilton.

As a flood control structure, the Great Swamp dam — like the others planned — has a spillway that allows the stream to flow through it most of the time.

“It meters the water out slowing through a spillway,” Frigon said.

That means it only backs up water when there’s a large amount of rain. But when there is very heavy rain, substantial amounts of water can be held behind the dam — as people driving on west end of Farmingville Road sometimes discover.

Thursday’s meeting is co-sponsored by the state DEEP and the U.S. Department of Agriculture Natural Resources Conservation Service. Staff from the two agencies as well as consultants and the Connecticut Dam Safety Program will offer an update on planning to date for the dam’s rehabilitation, the reasons for the project, and the alternatives being considered.

There will be time for public input and questions. More information is available from Ray Frigon at DEEP 860-424-3797 or Raymond.Frigon@ct.gov.