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There are reasons for the more-frequent stormwater flooding of new areas in Brattleboro, ranging from more asphalt over the years to the flow of water changing as a result of rebuilding flood-torn water systems after Tropical Storm Irene.

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What happens when heavy rains meet an 1800s stormwater system? Localized flooding

With intense storms and new water-management rules, municipalities need to change how they deal with stormwater

BRATTLEBORO—Why does the section of Main Street between High and Grove streets always seem to flood during heavy rainstorms?

Intense rains easily overwhelm the downtown’s stormwater system, said Director of Public Works Steve Barrett.

It would take millions of dollars and many decades to completely replace the undersized stormwater pipes, drains, or culverts that channel rainwater and snowmelt to the Connecticut River, he continued.

According to Barrett, other factors also prompt localized flooding during intense storms, such as the one that dropped 2.5 inches on downtown Brattleboro in less than an hour on Aug. 24.

More parking lots, climate change, and a landscape altered by Tropical Storm Irene in 2011 also influence how water flows through Brattleboro.

“The pipes are antiquated,” said Barrett.

That is a slight understatement. Some of the pipes are almost 200 years old.

Cross sections of pipes pulled out from under Brattleboro’s streets line the hallway of DPW headquarters on Fairground Road. Over the centuries, the town used pipes made from materials like cast iron, lead, and even a hollowed-out tree.

A water main pulled from between High Street and Grove Street was stamped 1888, said Barrett. Some sections of Main Street contain stormwater “pipes” constructed from laid-up stone like a stone-wall water trough topped with capstones.

Stormwater pipes corral water from sources like rain or snow melt. This system is separate from the town’s two other water systems: drinking water and sewage.

Downtown has changed considerably over the past 50 to 100 years, he said.

When the system was built, the town had more green space. The open ground absorbed its share of water before the runoff made it to the stormwater system, he said.

Hannah O’Connell, highway/utilities superintendent, noted that pavement companies keep designing pavement to repel water, which can damage and shorten the life of roads and the substructures beneath them, she said.

But an increase in the area covered by impervious surfaces like paved parking lots and roads comes with the price of increasing the amount of runoff into the system, Barrett said.

High-intensity storms: a new normal

In addition, Barrett said that between his experience over decades in the DPW and data collected by the department, he can point to storms increasing in intensity and volume.

These “high-intensity” storms with a lot of running water contribute to washouts, he said.

Two years ago this month, a thunderstorm dropped 5 inches in one hour, and its runoff took out a chunk of Elm Street, he said.

These storms hit with bursts of heavy rains and “overwhelms the system,” O’Connell added.

Another significant change, Barrett and O’Connell noted, is a landscape changed by Tropical Storm Irene.

“It’s the new unknown,” said Barrett.

Four years ago, the storm caused flooding throughout Brattleboro. The Williams Street neighborhood, Flat Street and its businesses, and the housing areas around the Whetstone Brook, such as Melrose Terrace and the Tri-Park Mobile Home Co-op, all took a hit.

Before Irene, flooding in town was more predictable, Barrett said. The DPW could almost always count on West Brattleboro and the more rural areas of town taking on water in heavy storms.

After Irene, however, the DPW sees more high water on downtown streets like Flat, Main, Birge, Maple, and Canal.

Barrett attributes this shift to two factors.

First, Irene’s swift floodwaters physically changed the rivers and how they flowed, he said. And secondly, repair and mitigation efforts — such as installing bigger culverts — are working in the worst-hit areas, sending the water that would have flooded there pre-Irene to lower ground.

One phase at a time

Upgrading the town’s stormwater system will take a lot of time and money, said Barrett.

Downtown traffic and businesses couldn’t handle ripping up Main Street and its side streets in one fell swoop, Barrett said. Instead, the DPW completes work in phases or when it can fold the work into other projects.

The summer’s sidewalk rehab includes installing some “future use” infrastructure, such as sprinkler systems, he said.

O’Connell said that municipalities will change how they manage stormwater within the next five years.

The state has implemented new water-management laws and phosphorus rules, she said.

For example, the amount of potentially toxic blue-green algae blooms linked to phosphorus levels in Lake Champlain received a lot of attention this summer.

In August, the federal Environmental Protection Agency and the state announced an agreement to lower the amount of phosphorus flowing into the lake, known as the total maximum daily load, by 34 percent in the next 20 years.

Towns will also have to adapt, O’Connell said.

O’Connell said that most of the town’s stormwater runoff goes into the Connecticut River without treatment for chemicals or pollutants.

She and Barrett expect that the town might be one of many towns to move their stormwater management system into a utilities system, treating future runoff similar to the way it manages sewage.

With the sewage management system, property owners pay fees based on the amount of wastewater they send down the drain, Barrett and O’Connell said. Under a similar system, property owners would pay based on how much water runoff they contributed to the system.

For example, Barrett said, a residential house with a small driveway and roof but a lot of green space would have less runoff and pay less into the utility. A large industrial site with a lot of impervious surfaces — like a large parking lot — would create more runoff and thus would pay more.

Analyzing stormwater runoff puts town DPW staff in a different boat from their counterparts in the drier parts of the country, where municipalities channel and recycle their scarce stormwater, Barrett said.

There, he explained, they are less concerned about things like road washouts or culverts backing up because of leaves.

O’Connell laughed.

What he’s saying is that we’re lucky to have this problem, she said: Our community has more than enough water.

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Originally published in The Commons issue #322 (Wednesday, September 9, 2015). This story appeared on page A1.

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