With torrential downpours in the forecast this week, Massachusetts is getting ready for a level of flooding that’s become all too familiar.
A new report from civil engineers in the state warns Massachusetts’ stormwater infrastructure is in dire need of billions of dollars as extreme rain events become increasingly common.
Heavy rain is possible through the region much of Wednesday. It could inundate city stormwater infrastructure like culverts, which direct storm water under roadways.
“When those downpours are coming down, we could see anywhere from 1 to 3 inches of rainfall in a relatively short amount of time,” GBH Meteorologist Dave Epstein said. “That overwhelms the culverts and the stormwater drains, and that’s why we see urban street flooding, which is really the primary risk from these types of weather systems.”
Midday Wednesday — some time between 10 a.m. and 3 p.m. — will likely see the heaviest downpours in Greater Boston.
“We don’t know exactly where the elements of heaviest rain are going to be,” Epstein said. “You could see 2 inches of rain in 45 minutes to an hour, if conditions are right. That’s a lot of rain. ... And so we could see something like that in a very localized area. Not everybody is going to see that kind of extreme rain.”
When it comes to managing all that stormwater, the report issued last week by the American Society of Civil Engineers and its Massachusetts chapter gives the state a “D+” grade.
“The state of Massachusetts has some of the oldest infrastructure in the country,” said Danielle Spicer, incoming regional director of the American Society of Civil Engineers. “It was designed for a smaller population, it was designed for different rainfall events. We have seen drastic changes in our climate more recently. It takes time to upgrade everything. It takes funding, it takes investment.”
These kinds of storms are becoming more common as the climate continues to change, Epstein said.
“The Northeast will see more heavy rain events as we move through the coming decades. And we have already seen an increase in the number of heavy rain events,” Epstein said.
“Much of the infrastructure, especially the things like the culverts and all those things which take stormwater, were built for 100-year floods, and those are becoming more frequent,” he said. “So they are going to get overwhelmed more as we move forward in time.”
The state has more than 25,000 culverts — but, according to the report, most of them are undersized and in poor condition.
“The culverts were designed for a specific flow through the opening that they provide. Now they’re undersized,” said Pat Tierney of the Boston Society of Civil Engineers. “Now there’s more water trying to fit through the culverts, which is causing tidal issues, water quality issues on the other side of that culvert. The systems to manage our water just aren’t designed for the rainfall that we see today.”
Intense storms have caused flooding and damaged local infrastructure like dams in recent years, including a 2023 emergency situation in Leominster.
With each major rainfall event, the state’s outdated stormwater infrastructure is also causing untreated sewageto rush into local waterways.
In nearly 200 spots around the state, stormwater systems are combined with pipes that carry untreated sewage, and heavy rainfall can lead to overflows into local waterways. The report says in 2024, there were more than 2,000 such overflows in the state, discharging nearly 2 billion gallons of water mixed with untreated sewage. In 2023, 58 beaches in 36 towns were closed due to water quality issues, according to the report.
“The state is working towards separating these combined sewer overflows,” Spicer said. “They have drastically improved a lot of them.”
But rooting out issues with the state’s stormwater infrastructure will be costly.
The Massachusetts Water Resources Authority estimates that nearly $5 billion is needed to correct combined sewer overflows across the Charles, Mystic and Alewife River watersheds, according to the report. And overall, the report says Massachusetts faces an estimated $20 billion stormwater infrastructure gap over the next 20 years.
“This gap is just mainly to bring us up to a state of good repair, not necessarily planning out for the future needs,” said Rich Matson, president of the Boston Society of Civil Engineers. “I believe the funding would be significantly more to bring us to a point where we can prepare for the future.”
For this week, at least, meteorologist Epstein warns people should at least anticipate delays on their commutes Wednesday.
“Most of us are not going to see crazy amounts of flooding, but some folks will see a lot of flooding, anywhere from the Hudson Valley of New York up through the Berkshires, east to Worcester, and even into southern New Hampshire,” Epstein said. “We’re all going to see something. It’s just a matter of who sees the heaviest.”
