© 2023 WSHU
NPR News & Classical Music
Play Live Radio
Next Up:
0:00 0:00
Available On Air Stations

As flooding worsens in Connecticut, its drainage systems can’t keep up

Rising waters had completely inundated the parking lot at Great River Park in East Hartford on Thursday, July 13.
Shahrzad Rasekh
CT Mirror
Rising waters had completely inundated the parking lot at Great River Park in East Hartford on Thursday, July 13.

Raise your hand if you’ve heard this before: Connecticut has some really old infrastructure. And that includes drainage systems.

They are plagued with narrow pipes, small culverts, shallow and small waterway passages under bridges, and overburdened river outlets into Long Island Sound. Often they can no longer accommodate what climate change has created — large volumes and rates of water from intense storms that are occurring more frequently and water incursions from sea level rise, often at the same time.

While towns like Norfolk were reminded of this the hard way in July when it became apparent that the pipes put in after the 1955 floods could no longer handle the scale of floods in 2023, the problem has been on the state’s radar for at least a decade. There have been steady, though slow, groundwork improvements, the result of some serious changes to state regulations and the data informing them.

Hall Brook breaches Smith Road in Norfolk after July storms.
Town Norfolk
Hall Brook breaches Smith Road in Norfolk after July storms.

The Department of Energy and Environmental Protection has just released its latest installment: an update to its stormwater manual, which had been in the works for five years. It includes stricter regulations for how the state, municipalities and some large institutions handle stormwater by making sure more of it soaks into the ground instead of running into overburdened infrastructure.

The previous manual uses data as far back as the 1970s to calculate things like stormwater runoff volume. The new one, which is operative beginning March 30, is updated to reflect more current patterns. More important, it will encourage users of the manual to consider how climate change affects stormwater, and it provides flexibility to compensate for the kinds of extremes climate change brings.

“The major update, which is more subtle, is that we’re not trying to be static anymore,” said Kathleen Knight, an environmental analyst who was a key author of the manual for DEEP. “We’re trying to be more fluid and provide guidance documents that are living, provide direct references that are updated as we go. Both the science and technology of stormwater design and climate change are rapidly evolving.”

Manholes overflow on Union Ave in New Haven during a rainstorm. Later, when the flooding stops, city workers put the caps back on the manholes, which blow off whenever there’s a surge.
Ryan Caron King
Connecticut Public
Manholes overflow on Union Ave in New Haven during a rainstorm. Later, when the flooding stops, city workers put the caps back on the manholes, which blow off whenever there’s a surge.

Nisha Patel, who directs DEEP’s Water Planning and Management Division, said another part of the overall objective is to give those who use it specific design guidance and how-to’s for managing stormwater.

“How do you work within existing drainage systems? And what do you do to manage stormwater runoff? No. 1, in a way that’s not going to cause pollution, so that’s the environmental side. You don’t want discharge of pollutants,” she said. “But what can you also do to use small-scale, on-site solutions, so you are not always relying on a pipe to drain and take the water away?”

A key update to the manual involves something known as Atlas 14. It’s a calculation by the National Oceanic and Atmospheric Administration of precipitation amounts and duration by location. This information is used in the stormwater manual and elsewhere to determine what to plan for when designing runoff infrastructure.

Just under a decade ago, the data for the Northeast in the Atlas was from the 1960s. Under pressure from the Northeast Regional Climate Center, which is headquartered at Cornell University, and its director Art DeGaetano, the Atlas was updated in 2015 to reflect 2012 data.

“So they’re still 10 years out of date, basically,” DeGaetano said. “There is another effort afoot by NOAA, probably within the next three years, to update those data once again to as recent as possible.”

But the problem still remains that the data is historic. It does not predict precipitation in the future, which, given the acceleration of climate change-generated impacts such as rainfall rates, could mean the state is still under-preparing for storm runoff.

To that end, DeGaetano said his center has been working with New Jersey, Virginia and the Chesapeake Bay and Delaware River basins to develop adjustment factors to the NOAA Atlas 14 standard that takes climate change into account.

“I’ve heard talk about Connecticut maybe being interested,” he said. “But nobody’s coming to us, and we haven’t gone out proactively and said, ‘Hey, Connecticut, would you like us to do this for you?’

The Atlas 14 data also don’t account for shoreline-specific factors — mainly sea level rise, when more water comes towards the shoreline and storm surges push water way up Connecticut’s rivers. Those inland pushes often come during storms as precipitation creates flooding and runoff trying to go downstream — essentially bi-directional and compound events.

“There’s information on both, but they’re kind of treated separately,” DeGaetano said. He said it’s hard to tease out impacts because drainage, geology and other factors are different from town to town, making modeling difficult, not to mention expensive.

Permit changes

But the state has come up with some of its own adjustments, which it’s instituting through a few of its existing permitting processes. One involves the “General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems,” known as MS4. It is actually an EPA mandate for discharging stormwater. It presently affects about 120 cities and towns and about a dozen institutions. There’s also a specific permit for the Department of Transportation.

Flooding in Stratford town center during Tropical Storm Ida in September 2021.
Town of Stratford
Flooding in Stratford town center during Tropical Storm Ida in September 2021.

Under Connecticut regulations that kicked in in 2020 (three years after they were approved), every year municipalities that fall within MS4 parameters must remove 1% of their impervious surfaces — the kind of surface that cannot absorb water, which mostly winds up in the storm sewer — paved driveways, parking lots, sidewalks. It’s proving to be a difficult task for the bigger cities, because businesses and residents in those communities continue to add impervious surface by paving driveways and patios or extending parking lots even as their local authority is tasked with getting rid of it.

“Even if the climate wasn’t changing, just by growing the impervious surface in the state, that would have created its own problems, as far as flooding was concerned,” said Mike Dietz, who is with the University of Connecticut in several capacities specializing in stormwater management. “But now you pile climate change on top of that and the more intense storms, and it just amplifies the whole problem.”

But there are some potential holes in the removal procedure, known as “disconnection.” The state measures the baseline of impervious surface using aerial views, but it’s only done every five or 10 years, so it can quickly become out of date and underestimate the amount of surface. Another problem is that the requirement to comply with the MS4 permitting procedure is based on census tract data — basically population density in certain areas — on the assumption the fewer people, the less impervious surface there will be, so less runoff.

What it doesn’t take into account is how much flooding is likely, especially from the many inland river areas. So rural areas like Norfolk that don’t have a lot of people, but do have some serious river systems that often flood, don’t have to comply.

It’s also the municipality’s responsibility to report compliance annually. Given how new this is, the accuracy is still unclear.

But another stormwater runoff change coming in the new MS4 will also apply to DEEP’s general construction permit, which covers new public projects — local, state or federal — that disturb more than an acre and private ones that disturb more than five acres. At the moment under both permits, projects have to retain the first inch of any rainstorm. They can store it, use it, whatever; it just can’t go into a storm sewer. That one inch is about to go up to 1.3 inches, meaning even less water will be allowed into the sewer infrastructure.

Ironically, all these regulations were designed to help improve water quality, since storm runoff picks up whatever substances are in and on surfaces, impervious and otherwise. Solving water quantity problems just goes along for the ride.

For both the 1% impervious surface disconnect and the soon-to-be 1.3-inch retention requirement, green infrastructure is an increasingly popular solution. Rain gardens and retention ponds are recent alternatives to conventional stormwater runoff sewer systems, but they were originally conceived to deal with water quality, not quantity.

“There definitely is a benefit,” albeit slight, said Dietz, who also heads up UConn’s Nonpoint Education for Municipal Officials, NEMO, program, which specifically helps municipalities comply with the MS4 disconnect and provides an online guide for them. “We’re always careful to tell people it’s not going to solve the big flood problems. It helps.”

He and others point out that solving the problems would take a wide-scale coordinated system with many green infrastructure approaches. One rain garden isn’t going to do it.

DOT moving along, slowly

The Connecticut Department of Transportation, often under fire for not addressing any number of issues in a timely manner, has actually been a bright spot in retrofitting for more extreme weather. While not completing projects at breakneck speed, it can point to an array of them that feature widened culverts, minimized impervious surfaces, tidal wetland mitigation work, better fish passage, wildlife consideration, strengthened bridge abutments and more.

An executive order in 2021 required the DOT to develop a program to identify state-owned culverts in need of repair or replacement and a prioritized list to help get grant funding to do the work. DOT was already doing that, but it still faces a daunting task.


Almost all of the state’s estimated 20,235 culverts were built prior to the 1970s, according to data provided by DOT. The average age of state culverts is 62 years, and the average age of drainage networks is 59 years.

More than half of the culverts are not even mapped. Among those that are, 6,400 are not inspected. Of the 2,687 than have been inspected, 62% are in good condition, just under a quarter are in fair condition and the remainder are in poor condition or are unable to be assessed.

There are 40 active projects and another couple of dozen somewhere in the design phase.


DOT has its own MS4 parameters for how much drainage to plan for. It also monitors recommendations from a number of national organizations for how to incorporate climate changes into transportation design and policy. But DOT is faced with the reality that there’s a whole lot more impervious surface out there than when a lot of the bridges and culverts under them were put in place. And many of them are not much more than a metal pipe in the ground with only earth on top to hold it in place.

“So if the earth erodes away, that thing’s just going to pop out of the ground and then go downstream, and we’re going to lose the structure,” said Scott Hill, DOT’s chief engineer and engineering and construction bureau chief. “We’re trying to make sure that whatever we’re putting in is engineered so that it can survive the storm event.”

East Flat Hill Road over Transylvania Brook, Southbury, shown before and after work to replace the culvert.
East Flat Hill Road over Transylvania Brook, Southbury, shown before and after work to replace the culvert.

More and more, that means replacing the whole structure and using deeper and more resilient foundations to account for greater water velocity underneath. It’s not always that simple, since DOT doesn’t always own the land around bridges and roads, potentially hamstringing resiliency options. Also, municipal drainage systems often tie into state ones, so changes have to account for that.

Hill said flooding on roadways is a huge concern for DOT and in many respects more difficult to deal with than bridges and their culverts. Solving it requires figuring out what roads will flood, how badly and when. Along the coast, they must calculate which roadways might be lost to sea level rise. And then what to do. If they elevate roads, will it impede wetlands or cause other problems?

“That is all still being worked on,” Hill said. “At some point, what it’s all going to coalesce into is a statewide discussion about what are the key critical roadways that we need to keep open in case of emergency and what are the impacts depth-wise of water that eventually we’re not going to have?” he said. “On the bridge side, we can show you the hardening and all that. But on the roadway side, it’s pretty complicated conversations people don’t want to have.”

Carpenter Road in New Hartford was underwater during flooding on Sept. 29, 2023.
Stephen Busemeyer
CT Mirror
Carpenter Road in New Hartford was underwater during flooding on Sept. 29, 2023.

Launched in 2010, The Connecticut Mirror specializes in in-depth news and reporting on public policy, government and politics. CT Mirror is nonprofit, non-partisan, and digital only.