GEORGIA – A collaborative study between the Friends of Northern Lake Champlain (FNLC) and Stone Environmental has identified a handful of projects in Georgia’s South Village for mitigating runoff into a gully funneling directly into the Lamoille River watershed.
Projects recommended by the study are trained on both stymieing the amount of phosphorous-carrying sediment entering the gully in question as well as slowing that water as it enters the gully, hopefully reducing the threat of erosion.
The “Deer Brook Gully,” as the South Village gully is called, was carved into the watershed by stormwater improvements built in southern Georgia following the construction of Interstate 89 and subsequent developments.
That gully, in turn, drains into Deer Brook, which later empties into Arrowhead Lake and the Lamoille River before ultimately ending in Lake Champlain.
According to Stone Environmental’s report on the gully, that stormwater infrastructure is undersized compared to the amount of water it now handles, leading to excessive water pressure building within that system that jets water into the gully.
“The problem is that the piping system is all 12-inch to 18 inches of pipe, which is pretty undersized considering the size of the watershed,” said Stone Environmental’s Gabe Brolin during a presentation to the Georgia Conservation Commission.
“The swales will hold a lot of water and kind of create a hydraulic pressure pushing the water down into the piping network,” he said. “But that ‘hose’ is only so big in diameter, so the water starts rushing through.”
Compounding the velocity of that runoff was the height of the drainage pipe relative to the gully. With the drainage pipe set between 20 and 30 feet above the gully, water shot into the gully has an additional acceleration from its fall.
Deer Brook is cited by the Vermont Department of Environmental Conservation (DEC) as an “impaired waterway” due to erosion caused by stormwater that washes through the watershed.
DEC lists “sediment” as the primary concern for the Deer Brook watershed, which, according to the Environmental Protection Agency (EPA), can cloudy a waterway, impact abutting habitats and carry nutrients like phosphorus downstream.
Per Stone Environmental’s report, about 70 percent of the banks tracing the gully toward Deer Brook are “actively eroding.”
The Messenger previously visited the gully, observing fallen trees strewn over the then-trickle of water as it led toward Deer Brook. The banks, meanwhile, were lined with trash, ranging from bikes and drum barrels to scraps from discarded vehicles.
Stone Environmental’s report makes similar observations in the gully, noting that approximately half of the downed trees “appeared to be recent falls… with not signs of rot or weathering.”
The report describes a particular visit to the gully in the immediate aftermath of a rainfall, where, according to Brolin, water had mixed with silt lining the bottom of the gully, producing a gray sludge that drained through the gully.
“At the confluence of Deer Brook, a contrast between the gray colored gully discharge and brown flow in the brook was easily discernible,” the report reads.
Stone Environmental’s study prioritized nine improvements for stormwater infrastructure in the South Village in order to reduce the amount of runoff jetting into the gully, with a projected cost of around $400,000 that FNLC hopes to cover with grant appeals to the Clean Water Fund.
The study also provides numbers gauging the impact of those improvements, such as the amount of phosphorus it could remove from a watershed, and ranks those projects according to how easy their construction would be.
Those numbers, according to FNLC president and Georgia Conservation Commissioner Kent Henderson, should help FNLC’s grant applications once it starts pursuing those projects.
“Is really going to play nicely with the new Clean Water Act,” Henderson said. “[The state] wants a number for the amount of phosphorous you’re keeping out with an amount of money… and we have it.”
Of those nine recommended projects, seven were designed to slow and filter water entering the system and exist within the state’s right of way for Route 7:
- Four are gravel wetlands to be built near Georgia Auto Parts, Interstate Auto Services, Georgia Market and Whites Bikes & Outfitters;
- Two are catch basin risers that would raise the elevation of the catch basin’s grate to allow for slower drainage from two of the swales tracing Route 7; and
- A catch basin that would incorporate a deeper sump – a pit for collecting water – to allow for sediment in the system to settle before the water moves on.
The two catch basins described by Stone Environmental would still sit below road level, allowing the water to drain into Route 7’s drainage system rather than spill out of the swale and flood the highway.
Two improvements meant to slow water entering the gully would be built on private property.
One would see a staggered manhole system that would lower the exit pipe into the gully and dissipate some of the water’s velocity as it transfers between a pair of manholes before entering the gully.
The second improvement would be a series of log wood steps built into the gully’s channel, creating barriers to slow water and allow for sediment to build up at those steps rather than drain directly into Deer Brook.
These projects are within Georgia’s South Village, an area viewed by town officials as Georgia’s development center.
Development in the area has led to an increase in impervious surfaces throughout the South Village, leading to more water running into the area’s stormwater system.
According to the study, approximately half of the gully’s watershed is considered an impervious surface, a ratio that Georgia Conservation Commission chair and planning commission chair Suzanne Brown said would only become more challenging as projected development continues in the village.
“It’s the village,” Brown said. “It’s only going to get worse.”
Henderson said FNLC would start applying for grants to fund improvements in the watershed this fall, when the next grant cycle begins.
FNLC, a water quality advocacy group active in Franklin, Grand Isle and parts of Chittenden County, initially contracted with Stone Environmental in 2017 to study the gully’s watershed.
The study was supported by a DEC grant awarded in 2016.
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