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Wet Weather Tests Burlington Rain Gardens

Aug 16, 2017

Joel Banner Baird, Free Press Staff Writer 

{Stormwater carries with it all sorts of pollutants — and Jenna Olson demonstrates some of the ways to clean it as it flows. Produced August 14, 2017. JOEL BANNER BAIRD/FREE PRESS}

When rain swamps a city street, many people are relieved to see the torrent funneling down the nearest storm drain.

Jenna Olson, who manages Burlington's stormwater program at the Department of Public Works, is not among them.  

Olson agrees that deep puddles and raging streams have no place in the urban landscape. But she is also pursuing solutions that don't rely on fast-tracking water down a cast-iron grate.

{Leafy debris rushes down a storm drain at Battery and King streets in Burlington on Monday, Aug. 7, 2017. (Photo: JOEL BANNER BAIRD/FREE PRESS)}

Storm runoff is best behaved when it dilly-dallies on its way downhill, Olson and other experts say.

Their reasoning: When stormwater is allowed to seep into underlying soil, much of rain's payload of phosphorus and other mineral nutrients becomes trapped — and is less likely to spur excess algae and plant growth in ponds and lakes.

Raingardens are proven filters that mimic natural, undisturbed vegetated systems, Olson pointed out during a recent tour of the downtown watershed.

“We help rainfall flow into wetlands, where all these plants are taking up nutrients and pollutants — so when the water discharges into Lake Champlain, it’s much cleaner,” she said.

{Tropical fauna ornaments a rain garden and curb bump-out on North Avenue in Burlington on Wednesday, Aug. 9, 2017. (Photo: JOEL BANNER BAIRD/FREE PRESS)}

That raingarden strategy, pursued here and elsewhere in Chittenden County, not only has the potential to cut the cost of cleaning up the lake, but to beautify the built landscape, Olson added.

Other water-filtration features around town are less picturesque, more easily overlooked.

Among the unheralded innovations: Pavement that allows water to seep through it; and chambers beneath roads that catch and hold (or “detain,” in stormwater lingo) the first inch or so of a gully-washer.

Similarly, Burlington's Public Works and Parks and Recreation departments, has installed sub-surface planting boxes for trees that do double-duty as stormwater filters.

Often with state and federal support, the city has increasingly budgeted for so-called “green infrastructure” as a hedge against even more expensive upgrades to wastewater treatment plants.

Bottom of Form

The answer, apparently, no longer lies in miles and miles of buried pipe. 

{Jenna Olson, manager of Burlington's municipal stormwater program, stands beside a device that, when arranged in catch basin beneath city streets, helps filter pollutants from rain runoff. Photographed on Wednesday, Aug. 9, 2017. (Photo: JOEL BANNER BAIRD/FREE PRESS)}

Most of Burlington’s stormwater cascades (together with most of the city’s sewage) to the main wastewater treatment plant located next to Perkins Pier.

But removing pollutants that have been flushed into a centralized system — via relatively pure rainwater — can be energy-intensive and costly, city and state officials say.

Post-storm spikes of water arriving at treatment plants throughout the state periodically overwhelm the capacity to fully treat sewage, according to the Department of Environmental Conservation.

Acre after acre of asphalt in Burlington forms a formidable sluice, Olson said — but also might offer clues.

At the parking lot across College Street from the ECHO Center, she pointed out newer, grainy strips of pavement, Fibers embedded in that mix help maintain a strong, porous structure, Olson said, “instead of the material all congealing together and compacting down.”

Seasonal vacuuming of this asphalt has kept its pores clear — a big improvement over the pervious concrete mixes that have been attempted elsewhere in the city, she added.

{Porous asphalt, at left, allows surface water to percolate into soil, unlike the adjacent asphalt, which enables stormwater to carry nutrients and pollutants downstream. Photographed on Wednesday, Aug. 9, 2017. (Photo: JOEL BANNER BAIRD/FREE PRESS)}

The technology for asphalt has been growing by leaps and bounds,” she said.

Not your garden-variety raingarden

Olson refers water-infiltration enthusiasts to venture further north along the waterfront for a more picturesque view of stormwater management.

There, in front of the Moran plant, a broad, floral swale does the work of a coastal wetland — the sort that lined this part of the lake before it became industrialized in the 19th century.

Becky Tharp, who works as a statewide, stormwater extension agent, terms this artifical wetland as a prime example of a “paradigm shift” in infrastructure planning.

Climate studies that project an increase in severe storms are accelerating research, she added.

Tharp manages the federally funded Lake Champlain Sea Grant’s collaborative efforts with the Vermont Department of Environmental Conservation and the University of Vermont.

A promising advance in raingarden design is being tested in South Burlington, she said — a hybrid design using floating plants in existing stormwater ponds.

{Becky Tharp, a University of Vermont stormwater extension agent who works with the Lake Champlain Basin Program and the Vermont Department of Environmental Conservation, stands in the gravel wetlands near the Moran Plant in Burlington. Photographed on Thursday, Aug. 10, 2017. (Photo: JOEL BANNER BAIRD/FREE PRESS)}

Other advances Tharp promotes are more earth-bound. She offers the following advice for beginners: Raingardens fare better when humans resist the temptation to heavily fertilize them (plants are less likely to remove nutrients if they’re well fed).

Tests of raingardens’ performances suggest that even small patches can have outsized benefits downstream, she added.

To that end, Tharp has been advising a group of engineering students at UVM on improved raingarden designs.

Elle Mountain, an upcoming senior, had been developing plans for a water project in rural Ecuador, as part of the Engineers Without Borders group.

“But there were limitations on what we could do there — financial and technical limitations,” Mountain said.

With Tharp, the group turned its focus on the under-performing, overgrown and silted-up raingarden at the northern end of a two-acre parking lot along Colchester Avenue.

{A proposed re-design of an under-performing raingarden on the UVM campus was created this year by the campus group Engineers Without Borders (Photo: Courtesy Elle Mountain)}

“It was right here,” Mountain said. “We could see it, we could measure it.”

The students secured a $1,200 grant from the Lake Champlain Basin Program for the garden’s rehabilitation.

“We spend so much time in Lake Champlain — it makes a lot of sense to give back a little bit, to help with the excess phosphorus,” Mountain said. “It feels right to give back to the community in some tiny way.”

A wide variety of stormwater-treatment features 

See more: Lake Champlain Sea Grant program has created a self-guided bicycle tour of stormwater-treatment features around Burlington. Find it at UVM.edu/seagrant/GI-bike-map.

Contact Joel Banner Baird at 802-660-1843 or [email protected] Follow him on Twitter @VTgoingUp.

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