Erosion Control March/April 2017 : Page 41

Rather than using a cast-in-place barrier on top of the retain-ing wall where a vehicle barrier was required, Superior installed ReCon’s double-sided Guardrail block, which saved money and matched the overall look of the wall. Tale of Two Railroads, Tale of Two Streams If any town needed flood mitigation, it was Johnson City, TN, (population 60,000). Floods had historically plagued the down-town area. A multi-phase master development plan for the city included Founder’s Park, which would incorporate flood control measures and upgrade a stream system, while providing an area that was ripe for economic and cultural development. Two large streams, Brush Creek and King Creek, con-verge at an intersection in downtown Johnson City. Histori-cally, these two streams have been diverted into culverts at various locations. Of course, the 16-square-mile watershed was draining to the creeks long before Johnson City and its inhabitants arrived on the scene. Then came the culverts built to transfer the creeks underground, and buildings over the culverts. Larger culverts were necessary, until they were no longer large enough to convey the heavy storm events. “Just a five-year storm would totally flood Johnson City,” says Andy Best, Johnson City’s stormwater manager. He explains that originally the streams flowed through a series of culverts, “but, in the 1970s, the Tennessee Valley Authority put in a large—a very large—box culvert.” The diverted creek ran under a warehouse, made two 90-degree turns, and then fell about 6 to 10 feet in elevation. “We wanted to make the condition smoother and better. “Historically, Johnson City had two major railroads that ran through it,” says Best. “They used steam engines that had to have water, and Brush Creek could supply that water. The railroad runs through downtown and close to the park area.” In 2007, after numerous financially unrealistic recom-mendations over the years, a downtown task force was established, made up of property owners, representatives of the downtown development group, and two Johnson City commissioners. In examining the ongoing problems, the task force determined that although flood mitigation was critical, the cost could be justified only if the solution included other improvements as well. LDA Engineering was selected to help facilitate meet-ings and provide engineering design and consulting. In 2012, the city commission approved the first project, Founder’s Park. Thomas Construction Company removed 700 feet of the Brush Creek triple-barrel box culvert under the old warehouse. The project called for an environmentally enhanced channel and construction of a 5-acre greenway along the creek banks, featuring a 200-seat amphitheater. “Founder’s Park is five acres,” says Best. “And, we have already torn down another area and put in another 1-acre pond to add on to the park.” In the design, LDA Engineering worked with Henry Benefield of Benefield Richters, a design-build company, to develop the amphitheater and retaining walls that would satisfy the challenges posed by Brush Creek. They knew that the river would, at times, submerge the walls dur-ing significant rain events. LDA Engineering knew that MARCH/APRIL 2017 Keystone Retaining Wall Systems’ retaining walls would withstand both the flow of the water and rapid water draw-down as well. The retaining wall that was built at the site has a tiered arrangement that allows for stream access when the river is at low flow and retains stability during peak flows. LDA Engineering specified Keystone’s Country Manor wall system, which met the technical requirements and also fits in with the general appearance of the downtown area. The tallest wall is 10-feet-high and the longest one 933-feet-long; the total length of the tiered walls is 2,278 feet. “The retaining wall runs the entire length of the project,” says Best. “The original bedrock was good rock, so they put the footing right on the rock.” The 200-seat amphitheatre’s walls were constructed with the same Country Manor blocks. Two 8-foot-wide Contech pedestrian truss bridges span the creek: a 25-foot-long Connector-style bridge and a 35-foot-long Continental bridge. The decking on both bridges is made from Trex, a recycled wood and plastic material. Founder’s Park now provides improved drainage and a green space for locals to gather. Best says the work will con-tinue: “Since then, we’ve bought some property upstream and will install more retaining walls there. And we still need to do some additional upstream detention ponds.” EC Linda Robinson is a journalist specializing in agriculture and land-use planning. Visit us at IECA Booth #100 EROSION CONTROL 41

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