Blog: City Blog

Riverbank Restoration: Creative Landscape Architects and Gritty Planting Crews Create New Ecosystem

For decades, the riverbank of the South Knoxville Waterfront between the Henley and Gay Street bridges looked deceptively healthy.

Now, thanks to the creativity of Hedstrom Landscape Architecture (and the fearlessness of the Eastwood Landscaping planting crews), that section of waterfront has a better than fighting chance to become a well-functioning and aesthetically pleasing habitat with tall clusters of trees and colorful wildflowers.

As recently as just a few years back, kudzu had covered the riverbank, so it appeared to be a leafy and lush habitat. But that was misleading. The invasive species covered up a slew of environmental problems.

Unseen, water run-off spilled directly into the Tennessee River, carrying with it litter and, worse for the fish below, silt and oils. Precious soil on the steep rocky bank was being washed away.

Kudzu sends out famously long tentacles that can grow a foot a day, and the Japanese vine species is estimated to have smothered 7 million acres of the Southeastern United States. But the growth emits outward from a central root ball, sending out vines that overwhelm the native vegetation without setting down a soil-holding network of extensive roots. So among its many faults, kudzu is terrible at controlling erosion.

The first corrective step was removing the kudzu, which was done slowly, carefully and environmentally safely, over several years.

"Kudzu does a great job at hiding what's underneath it," says Chris Howley, the City's Stormwater Chief. "It didn't help with erosion, and sediment entering the Tennessee River makes it difficult for aquatic life to breed."

Getting rid of the invasive species set up the fun part: Last fall, with a kudzu-free canvas to work with, Eastwood Landscaping planted 300 trees, following a plan designed by Lucas Goodrow and others at Hedstrom Landscape Architecture.

To stop the erosion and hold the soil in place to nourish the trees, crews hydo-seeded the entire bank. In essence, they covered the riverbank with a rich slurry mix of grass and wildflower seeds, mulch and fertilizer.

The grasses you see now are annual rye grasses, which are merely making a cameo appearance to open the scene. They dependably take root and securely establish the bank, but they'll die off after a season.

Rye grasses cover what once had been a mass of invasive kudzu on the south bank of the Tennessee River downtown.

Rye grasses cover what once had been a mass of invasive kudzu on the south bank of the Tennessee River downtown.

Photo courtesy of Hedstrom Landscape Architecture

Next year, look for bee balm, goldenrod, rudbeckia, coneflowers, asters and bluestem switchgrass to take over the foothold secured by the rye grasses.

Over time, when the newly-planted trees mature, Howley says, the canopy will create shade and the habitat will support a bigger range of fish species.

One small section of riverbank by itself won't fix the entire river in downtown Knoxville, he says. "But it's an evolution of what can occur."

Goodrow, a designer with Hedstrom for 5.5 years, put a lot of thought into selecting which trees would have the best chance to thrive on the riverbank.

"We made the selections to match the dry sandy soil, or the lack of soil in some places," he says.

Maples, yellowwoods, catalpas, horn beams, tulip poplars, redbuds and plane trees are among the species that were chosen, along with sumac, beauty berry and sweetspire shrubs. Six months after being planted, only a handful of the 300 trees failed to take root.

"It was a huge challenge - a little daunting," Goodrow says. "The bank is so steep, this is my first project where we had to use drone footage to draw up the concept plan."

Justin Bullen, the project manager for Eastwood Landscaping, knows all too well about the precarious nature of the project. With no mapping of where the rock formations were, and unable to get heavy equipment onto the steep slope, crews would often start to dig a hole by hand, hit rock, then have to abandon the hole and dig elsewhere.

"This project was unique," he says. "The riverbank is a lot steeper than it looks. But - we're like goats."

Bullen says he's "definitely proud" of the project and looks forward to watching the forest and patches of colorful flowers reach maturity.

"This was very, very difficult," says Sara Hedstrom, the principal of the landscape architecture firm. "It's a testament to the team that nearly every tree has survived. Eastwood would dig a hole, and it not be suitable, so they'd dig a second, or a third. They were the right guys to do this project."

For his part, Goodrow also is looking forward to seeing how the riverbank changes next year, as the rye grass gives way to the flowers and shrubs, and the fast-growing trees start to mature.

"In the end, we hope to have a sustainable ecosystem - increased habitat for wildlife, birds, and shade in the water to support aquatic life," he says.

Look closely at the photo below - check out the hawk perched on the rock!

Check out the hawk, surveying the new wildlife habitat on the south bank of the Tennessee River.

Check out the hawk, surveying the new wildlife habitat on the south bank of the Tennessee River.

Photo courtesy of Hedstrom Landscape Architecture

Posted by evreeland On 09 June, 2022 at 3:19 PM