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After 'Grand Canyon' Project, Fourth Creek Water Tests Noticeably Cleaner

Over the years, during rainstorms, the water of Fourth Creek has been murky, at best.

The range of highs and lows for Total Suspended Solids, or TSS - basically, sediment in the water - has bounced from single-digit readings of milligrams of solids per liter of water to 175 mg/L over the last three years.

The measurements of creek water samples are collected at a station off Walden Drive, during rainstorms, for apples-to-apples comparison. The readings have run a wide gamut. But the samples have never came back with a clean bill of health.

Until this summer.

A July reading came back as "non-detectable" for TSS.

"We need more data, but that's a good indicator that things have improved," said City Stormwater Chief Chris Howley.

One plausible explanation for the improvement in water quality?

Miles upstream, Summit Medical Group and the City partnered to remediate the so-called "Grand Canyon of Knoxville," an eroded mess of roughly 4 kudzu-covered acres east of Wellington Drive, just off Kingston Pike.

The banks of Tributary 2, as it's officially named, are 30 feet tall here. The chasm is 130 feet wide.

Summit Medical Group invested more than $800,000, and the City $200,000, to minimize the decades-old erosion along this section of Tributary 2, a stream that flows on through Bearden into Fourth Creek near Weisgarber Road.

Since 2000, heavy rains have washed as estimated 8,000 cubic yards of soil downstream - perhaps the equivalent of a commercial truckload with every storm.

The elevation of the tributary channel had dropped 7 feet at one point in the stream between 2001 and 2014.

All that silt was moving downstream, and it was harming the water quality as far away as the measuring station at Walden Drive.

"This was widely considered to be the biggest erosion-control project in the city's recent history," Howley said.

In fact, it was a $1 million effort to engineer a fix to what former Engineering Director Jim Hagerman once called "absolutely the No. 1 pollutant source in Knoxville right now."

What? Topsoil is a pollutant?

In eroded watersheds, that's right. Sedimentation in a stream disrupts nature's food chain. It destroys the habitat of and smothers aquatic insects, which are an important food source for fish. Sedimentation can also impede the growth of beneficial aquatic vegetation, and it destroys fish eggs.

Summit Medical Group's Grand Canyon remediation project commenced about a year ago with assistance from Howley and Hagerman (who retired last spring, about the time when contractor S&ME was nearing completion of its design work).

It was, by all measurements, an ambitious plan to undo decades of damage.

In the 1950s, Tributary 2 and Fourth Creek in West Knoxville were quiet, unnoticed waterways. But with heavy development, especially before the Clean Water Act took effect, streams were routinely covered up or diverted into culverts and pipes. Flooding was controlled - up to a point.

By the time Tributary 2 reached Wellington Drive, it was emerging from underground piping. During a heavy storm, pressurized water would shoot out of a pipe as if it were being fired by a cannon. The sheer force would wash rock and soil away by the tons.

S&ME came up with a design to recreate a stable stream. Run-off water coming out of the pipe would first hit a rock-bottomed pond, rather than unprotected soil, so erosion is lessened.

The design required repositioning nearly 7,000 cubic yards of existing soil on the site and adding 2,300 tons of rock. Native plants were used to protect the banks.

"The Grand Canyon formed over a long time, and it's a surprising part of West Knoxville's topography," Howley said. "But not nearly as much sedimentation is moving downstream. That means fewer taxpayer dollars going to routine cleanings of downstream culverts. But much more importantly, we're seeing an immediate improvement in water quality in Fourth Creek."

Below are "before" and "after" photos of the Grand Canyon site. (The first photo, with the kudzu, shows what the area looked like a year ago. The other photos were taken this summer.)

The Grand Canyon in 2019

The Grand Canyon, 2019

The Grand Canyon, 2020

The Grand Canyon, August 2020

The Grand Canyon, 2020

Posted by evreeland On 06 August, 2020 at 5:37 PM