Tour shows techniques for stormwater mitigation (9/17/09)

Sept. 17, 2009

By Tim Simard

Observer staff

The stream, a tributary of the Allen Brook, was only a trickle last Thursday morning. On the bright and sunny day, Mary Nealon, founder of the conservation firm Bear Creek Environmental, described how the calm brook located off Oak Hill Road just north of Interstate 89 becomes a raging torrent during heavy rainstorms.


    Observer photo by Tim Simard
Matt Murawski, an environmental engineer with DuBois & King, discusses a stormwater mitigation project in the Williston Hills neighborhood. Behind him used to be a deeply-eroded gully that has undergone extensive restorations in recent years.

Only three years ago, the amount of sediment pouring into the Allen Brook reached up to seven tons per year and the amount of phosphorous equaled six tons per year, she said.

“You wouldn’t know it, but there’s a lot of water that comes through here during a storm,” Nealon said.

Nealon gave one of several presentations to approximately 15 state, federal and environmental officials as part of a stormwater mitigation tour last week. Hosted by the Winooski Natural Resources Conservation District, the tour presented different models for how to best alleviate the negative effects of stormwater runoff.

The tributary off Oak Hill Road was one of the prime producers of sediment that flowed into the Allen Brook, which in turn flows into the Winooski River.

“While this is small, what I realized is that it’s a significant piece of the Winooski River,” said Abbey Willard, district manager for the Winooski Natural Resources Conservation District.

“It all adds up,” she said.

Erosion was also a problem, as the stream began to erode the edges of Oak Hill Road and Bradish Lane. But that’s changed after a massive restoration project that began in 2006.

By 2007, work crews from Williston, the Vermont Agency of Transportation and Bear Creek Environmental, among others, re-vegetated the site and constructed a flood plain in what used to be a narrow ditch. Three log jams were built in 2008 to further curb a small amount of erosion that continued.

All in all, the project was a success and an example of what other communities and conservation districts could do to stop the negative effects of stormwater, Willard said.

“The district’s goal was to do alternative analysis and find low-cost solutions,” she said.

The district organized several different stormwater projects across Williston’s Allen Brook watershed and South Burlington’s Potash Brook watershed. The projects came about with help from federal, state and local funds — notably from the Environmental Protection Agency and the federal Natural Resources Conservation Service. Willard estimated the total cost of the nine demonstration projects in Williston and South Burlington to be between $800,000 and $900,000.

The Oak Hill Road stream wasn’t  the only site visited Thursday morning. The group also looked at two rain gardens — one at the Town Hall Annex and another at Dorothy Alling Memorial Library. Rain gardens collect stormwater and filter it into the soil. They are built in small depressions to “catch” the water.

Perhaps the largest project on the tour was the extensive work done in the neighborhood around Hillside and Sundown drives. Built on a west-facing slope off Vermont 2A, rain is known to pour through the streets and into gullies toward the Allen Brook at alarming rates, said Ashley Lidman, the Winooski Natural Resources Conservation District assistant manager.

“This whole neighborhood was designed before stormwater regulations,” Lidman said, adding many of the homes were built in the 1960s.

Because of the lack of stormwater infrastructure, large gullies eroded in certain areas of the neighborhood. Three different techniques were used to limit the amount of sediment and phosphorous dumping into the Allen Brook. Vermont Youth Conservation Corps volunteers installed dams in one gully, and local construction workers stabilized a steep gully with rocks and an earthen berm at the end of Sundown Drive.

The biggest mitigation project, and one that directly impacted several homeowners, took place within the development’s primary drainage area. Heavy rains had gouged a giant gully for more than 40 years near the corner of Sundown Drive and Pamela Court. In 2008, construction crews removed brush and filled in the gully, all the while installing a large underground stormwater storage tank.

The idea is that the tank will fill up with runoff and slowly allow the water to leak out to the Allen Brook, thus ending the massive erosion, explained Matt Murawski, an engineer with Randolph-based Dubois & King Inc.

Landowner support was key in making the project happen, Willard added.

“This was quite a change in the landscape for these landowners,” she said. “The project wasn’t a go until everyone agreed.”

Lidman said Thursday’s tour demonstrated the variety of stormwater projects any city or town can initiate, from the smallest of rain gardens to the largest reconstruction projects.