Terry Estate Drive bioretention project targets stormwater runoff

Parking lot retrofit supports Upper Swannanoa River Watershed Management Plan

Fred McCormick
The Valley Echo
September 19, 2023

The addition of a bioretention cell and green space in a Town of Black Mountain parking lot is designed to address stormwater runoff in the nearby Swannanoa River. The retrofitting project, which began in early September, is scheduled to be completed in mid-October. Photo by Fred McCormick

A four-to-six-week project on the north side of Terry Estate Drive, designed to eliminate 339 pounds of soil and sediment from the nearby Swannanoa River each year, is scheduled to be completed by mid-October.

The $128,000 retrofit of the town-owned parking lot across from the public works and recreation building will include a bioretention system that is intended to capture, store and cool stormwater runoff on an acre of developed Town of Black Mountain-owned land near the impaired waterway.

Crews began working on the project, Sept. 5, according to stormwater technician Anne Phillip.

“This is a project that was identified in the Upper Swannanoa River Watershed Management Plan, and the goal of that plan is to identify projects that will help improve the water quality of the Swannanoa River,” she said. “The river is on the (N.C. Department of Environmental Quality 303(d) list of impaired waterways.”

A seven-mile section of the river, from the source to the North Fork of the waterway, exceeds the NCDEQ’s criteria for “fair, poor or severe bioclassification of native benthos” and fecal coliform. The addition of a bioretention cell on the west side of the parking lot, a wetland to the east and permeable grass surfaces within the property will directly address sediment, nitrogen and phosphorous before it enters the Swannanoa River, according to Phillip.

“Right now, when the rain hits that parking lot, it flows over the parking lot and washes any contaminants from there into the storm drains, which go pretty much straight into the river,” she said. “With this project, we want to capture that stormwater first and allow it soak in and slow down so the water is filtered before it goes to the river. This will help remove sediment and contaminants while allowing the water to cool before entering the river, which all impact aquatic life.”

The project is funded primarily by the N.C. DEQ, Division of Water Resources, which will cover approximately $77,000 of the cost, while the town is responsible for $51,000 of the expense. The funding was available through a partnership between the Town of Black Mountain and Land of Sky Regional Council, due to the existing Upper Swannanoa River Watershed Plan.

The reconfiguration of the parking lot will include a five-foot-wide sidewalk and designate a single entry and exit point for the lot, which will retain 50 of the original 75 available parking spaces. The system was designed by Wildlands Engineering, while the work is being completed by Asheville Drainage and Rain Harvesting.

A rooftop runoff leading from the public works and recreation building, purchased by the town in 2018 for $2 million, to a bioswale between the structure and the Swannanoa River is included in the plan.

“That will function as a rain garden right near the river,” Phillip said. “It will catch water from the roof of that building, which will keep more of that warm water out of the river by slowing it down and allowing it to cool before it enters.”

The project, which necessitated the temporary closure of the public parking lot, will be competed by mid-October, according to the town.