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Study Confirms Severe Erosion of Town Stream, and Means to Curb It

Prof. Johnson and Rogers head into the woods with their surveying equipment.
Prof. Johnson and Rogers head into the woods with their surveying equipment.

A small, unnamed stream so insignificant that it dries up in hot weather meanders quietly through a half-mile of narrow, thick woodland in the residential heart of the Town of Davidson. It originates from storm water pipes under Concord Road, emerges at a low point on Lorimer Road, and burbles along southward until it joins a fork of the Rocky River at a section of the town greenway just beyond Davidson Elementary School.

Teachers used to guide their young charges along a well-trod nature trail in the woods. PTA members even built a sturdy wooden footbridge across a swampy part of the terrain.

No more. These days the stream concludes its meandering ways across a floodplain in a waterfall that drops suddenly straight down three-to-four feet. At that point the water begins carving the soft earth beyond into a ragged, eroded ditch as large as eight feet deep and 10 feet across. A dozen or so tall trees that grew along the side of the stream have been toppled into and across the creek from water chewing away their roots. The wooden bridge that spanned the divide is broken into pieces. Some sections have washed away completely, and others hang haphazardly over the precipice.

Caught Off Guard

According to Doug Wright, public works director for the Town of Davidson, this 200- to 300-foot section of the stream ditch represents the worst case of erosion in town.

"We had watched it for 20 years, but the sudden erosion caught us off guard. We need to do something to halt it before it accelerates even further," he said.

The rapid erosion also puzzled Davidson College Assistant Professor of Environmental Studies Brad Johnson. Johnson has been working with students to monitor the health of about 20 streams in the college's ecological preserve and elsewhere around town. None showed the severity of erosion as this one.

Environmental studies major David Rogers '16 was looking for a capstone project, and eagerly accepted Johnson's recommendation to monitor the erosion.

Last May Johnson and Rogers headed into the brush for the first time, carrying a sophisticated Leica Flex Line T-SO2 survey tool. Surveying the damage was a tedious two-person job that Rogers repeated on four subsequent occasions with Johnson and patient friends. One person held a reflective survey stick, while the second person spotted it with the Leica Flex in a fixed position at the top of the ditch. Every time the Leica Flex picked up the reflection, it recorded that point on an X, Y and Z axis.

The more spots they recorded, the more accurate their results, so Rogers and friends logged hundreds of spots on each outing.

The points were processed in a program called "Surfer," which yielded a three-dimensional rendering of the eroded area. Comparing renderings gave the researchers a way to quantify the amount of erosion.

Survey Yields Surprises

Johnson was surprised by the results. He estimated the ditch had carried 190 cubic meters of sediment downstream.

"Since we first surveyed last May, the waterfall has eroded almost 25 meters back upstream, and that includes a summer that was very dry," he said. "The erosion was moving so quickly that if we hadn't started taking data when we did, we'd wish in another year we had."

Wright had followed the situation with the stream over a period of years. When the bridge washed out he had even contacted an engineering firm about a full remediation restoration. But the project was too costly and Wright put it on the back burner.

With new data in hand, Johnson met with Wright recently and suggested a less expensive "stepped grade change" solution for the stream, placing courses of rocks across the creek to trap soil by dissipating the stream's energy and creating a gentler flow downstream. Wright is now seeking a firm to conduct that work.

"We really appreciate the involvement of college faculty and students in town initiatives," he said.

Rogers said that Johnson was "awesome, and incredibly helpful," throughout the project. Rogers especially needed that support early in the past fall semester, when he faced a demanding schedule. As he worked to wrap up his capstone project, he also carried four courses and practiced and played varsity football.

"He was with me throughout," Rogers said of Johnson. "He helped me when I got stuck, and encouraged me when it wasn't going well. He was a teacher, mentor and encourager."

Rogers is one of nine students graduating in May as environmental studies majors. He and his fellow majors will present the results of their capstone projects at a poster fair later this semester.