The big flood may come someday — again.

And the flood control dam by Fox Hill condominiums — while it’s in good shape by all accounts — may not be ready for the big one, a flood like the one in 1938, or the flood in 1955 that rampaged down the Norwalk River Valley, wiping out bridges and buildings, and taking at least two lives.

“Seeing houses float downstream, seeing cows float downstream, people rescued from rooftop by helicopter,” engineer Paul Well said, addressing a meeting of about 30 people at the Ridgefield Recreation Center Thursday night, Feb. 27.

Welle is with Schnabel Engineering, the consulting firm studying the dam by the Fox Hill Condominiums in Ridgefield for the state and federal governments. He said he’d heard a lot about the big ’55 floods — there were actually two — because his wife grew up in Naugatuck.

Naugatuck was among the towns hit with flooding in August 1955 following back-to-back hurricanes Connie and Diane.

But in October 1955 a tropical storm dropped 12 to 14 inches of rain over four days, unleashing a flood that devastated the Norwalk River Valley, leaving a path of destruction from Ridgefield down through Branchville and Georgetown and Wilton to Norwalk. (See related story).

The studies Welle is doing on the dam by the Fox Hill condominiums were prompted because the dam doesn’t meet upgraded safety standards, and state and federal agencies see a need to “reduce the potential” for severe flood damage or “loss of life from a catastrophic breach.”

The dam by Fox Hill condominiums is 440 feet long and 10 feet high. It is a flood control structure, built to allow normal amounts of water to pass through, but backing water up into a flood pool when rainfall is heavy — so less water rushes down the river valley all at once.

In very wet weather people driving on Farmingville Road will run into water across the road near the intersection with Ligi’s Way — that’s part of the flood pool that builds up behind the dam. That flood pool is water that would be released downstream — all at once, rather than slowly, over time — if the dam were to fail, or be breached.

Dam’s good

Officials speaking at the meeting — from the federal government, the state, the town —all seemed to agree that the dam is in good shape. None of them said the dam was in danger of breaching if it is overtopped — the time that a dam is most vulnerable — and releasing a severe flood of backed-up rain water.

“We’re not saying it’s in danger of failing tomorrow, next week, next year. We’re not saying it’s in danger of failing at all,” Welle said.

“Even a 1,000-year storm would flow through that dam without overtopping it.”

There’s a theoretical 100-year storm that’s often used as benchmark when engineers talk about drainage and stormwater control. They sometimes talk of a 500-year storm.

But the reference at the dam meeting to a 1,000-year storm was a bit unusual.

“I’d never heard of it,” First Selectman Rudy Marconi confessed later.

While state and federal officials at the meeting said the dam doesn’t pose an imminent threat, they have been looking into doing something about it.

If the dam were to fail in a big storm, they said, the breach inundation zone would include three residences, one business, and six roads and bridges would be impacted by a breach.

Traffic on the roads that would be inundated — which include Route 35 — carry 15,000 to 19,000 vehicles a day, the state and federal officials said.

According to the “estimated risks and damages” in the presentation at the meeting:

• “For these 6 roadways, it was estimated that 16 motorists would be at risk if the dam fails.

• “Three residents in one house and five people in one business would be at risk from a dam failure.

• “Total population at risk would be 24.

• “Total estimated damages from a dam failure would be about $700,000.”

Five dams?

The dam by Fox Hill was constructed in 1979 as one of five dams envisioned in the Norwalk River Flood Control Project, which had started being planned back in the mid-1950s.

Of the five planned dams, only two have been built — the one in Ridgefield by Fox Hill, called “site two” and another in Spectacle Swamp in Wilton, built in 1973.

Three planned dams in the project as originally envisioned remain unbuilt. One was to be at Miller’s Pond on the Norwalk River in Ridgefield, off Route 7 near the intersection of Florida Hill Road. Another was planned at Candee’s Pond on Cooper Pond Brook in Ridgefield near Branchville. And the third was planned on Comstock Brook in Wilton.

The two unbuilt dams in Ridgefield were designed in conjunction with the Super 7 highway project, which has since been scrapped. And a study done in 1997 found the dam in Wilton was no longer feasible.

‘High hazard potential’

Why all the studies and meetings about the dam near Fox Hill if it’s in good shape and not in danger of failing?

In 2004 that status of the dam was upgraded from a dam with “significant hazard potential” to a dam with “high hazard potential.”

The reclassification was done by the National Resources Conservation Service (NRCS) — a federal agency that’s part of the Department of Agriculture and is responsible for some 11,000 flood control dams built around the nation since the late 1940s — and the Connecticut Department of Energy and Environmental Protection (DEEP), which is technically the owner of the dam.

“It has to do with how much damage would be done if the dam fails,” Charles Lee of DEEP said of the reclassification, speaking to the Feb. 27 meeting in the recreation center.

A “project overview” document distributed at the meeting explained: “In 2004, the Norwalk site-two dam was reclassified from Significant Hazard Potential to High Hazard Potential by the NRCS and DEEP Dam Safety, due to the possible threats to life, property, and infrastructure during a potential breach of the structure.”

The presentation at the Feb. 27 meeting identified “estimated risks and damages” from a potential dam failure:

• “For these six roadways, it was estimated that 16 motorists would be at risk if the dam fails;

• “Three residents in one house and five people in one business would be at risk from a dam failure.

• “Total population at risk would be 24.

• “Total estimated damages from a dam failure would be about $700,000.”

The state and federal authorities decided something should be done.

“In 2009 NRCS conducted a dam assessment at the request of CT DEEP due to the hazard class change, updated methods, rainfall data, increased development in the floodplain downstream of the dam, land use changes in the form of residential growth in the watershed above the dam,” the project overview states.

“The assessment identified potential shortcomings in the design of the dam to withstand today’s projected storm events, namely the Probable Maximum Precipitation six-hour event (approximately 26 inches of rain in six hours), in order to meet NRCS high-hazard criteria.”

(That is, in six hours, roughly twice the 12 to 14 inches of rain reported to have fallen over four days in October 1955, causing the devastating flood.)

Two alternatives

The studies undertaken so far have looked at a variety of alternatives, but settled on two as most realistic.

* Decommissioning and removing the dam, at a projected cost of $1,605,000;

• Structural rehabilitation of the dam at a projected cost of $6,275,000.

The decommissioning and removal of the dam for $1.6 million was rated as the “preferred alternative.”

While removing the dam would mean a slightly larger area downstream would be susceptible to flooding in big rain storms, the threat of a catastrophic dam breach would no longer be there — “reducing the threat of loss of life to approximately 24 people who live or work nearby,” the meeting was told.

The project would not only mean removal of the dam, but would involve providing “local flood protection to two downstream residences” — basically, the construction of flood walls to protect two downstream properties, at 91 Great Hill Road and 4 Brookside Drive.

The other alternative studied in detail — structural improvement of the dam — would involve installing an auxiliary spillway in the dam and flood walls to protect some of the Fox Hill condominiums’ property.

The structural rehabilitation approach would also call for an “earthen berm” to protect property at 78 Farmingville Road.

$1 million? $6 million?

Whatever course of action is decided upon, it will cost money. The state and federal officials said the federal NRCS would cover 100% of the design costs and “technical costs” associated with the project.

The construction costs — whether $1,605,000 for dam removal or $6,275,000 to upgrade the structure — would be shared, with the federal NRCS cover 65% and the remaining 35% covered locally.

First Selectman Rudy Marconi said later it was his understanding the 35% local cost would be covered by the state.

“Basically ‘two thirds, one third’ between the federal Department of Agriculture NRCS, and the State of Connecticut DEEP,” Marconi said.

The studies for the project are on-going, and final decisions haven’t been made.

“We’re about three years into the study,” said Arde Ramthun, state conservation engineer for Connecticut with the U.S. Department of Agriculture’s Natural Resources Conservation Service.

The schedule calls for a draft plan to be available for public review in June or July of 2020, with the final plan completed by September of 2020.

There would then be a year and half of design work, and construction could be expected to take a year and a half after that.

Questions, concerns

“We’re here to get input from you before the study is completed,” Paul Welle of Schnabel Engineering, the consulting firm working on the project, told the Feb. 27 meeting.

Nine citizens — mostly Ridgefielders, but including two from Norwalk and one from Redding — spoke, many asking questions which were technical, or seeking clarification of points.

One man said the plan might be well intended, and justified by “federal criteria,” but he still questioned the value of the project.

“It isn’t how I’d spend my money,” he said.

Among the speakers was semi-retired town engineer Charlie Fisher, who still works for Ridgefield on a consulting basis and had looked into the dam plans.

“My recommendation is take a do-nothing approach,” Fisher said.

“It’s in good shape,” he said of the dam. ”What I do think is needed is an emergency action plan.”

First Selectman Rudy Marconi said that in recent years after major storms the town had been partially reimbursed by the Federal Emergency Management Agency (FEMA) for various costs. He wondered if the dam project — particularly if it ends up being dam removal — might alter FEMA’s willingness to provide reimbursement.

“Does this impact FEMA’s position relative to floods?” Marconi asked. “...FEMA could come back and say ‘You shouldn’t have taken that dam out.’ ”

He was told it was a matter of working together and keeping FEMA informed and involved: “We do 100% have to interface with FEMA on this.”

Marconi said later that not all of his questions had been answered by the meeting.

“I have a concern relative to the hydrology and hydraulic numbers,” he said. “I’d like to have another report on that — to verify, without the dam, what the 100-year flod line would actually be.”

Marconi also has some thoughts on the decision-making process that lies ahead.

“When the question came up: Who owns the dam? The ownership of the dam belongs to the state of Connecticut DEEP’s jurisdiction,” Marconi said.

“So, the town doesn’t own it. But when the question was asked relative to ‘who is the final- decision-maker on this?’ it kind of bounced around the room. And Chuck Lee for DEEP got up and said ‘We own the dam.’ But he talked about how they weren’t going to force anything to happen that’s not wanted.

“It’s good, because they’re saying: ‘We need local input,’ ” Marconi said.

Welle, the engineer from Schnabel Engineering who has been working on the project, said the officials overseeing the project are thinking long term..

“One of the goals,” he said, is a solution that would “last for the next 50 to 100 years.”