Engineering solution assists downtown Chattanooga

February 27, 2014

By Eddie Wade, P.E.

The Citico Creek project address flooding in Chattanooga.

The Citico Creek project address flooding in Chattanooga.

Though much of our work takes place underground and out of sight, the effects of our work are felt throughout the community. LDA Engineering recently partnered on a project with Cannon & Cannon Engineering to solve overflow issues at Citico Creek. Not only was Citico Creek the first interceptor project completed under the EPA Consent Decree, but there was also additional pressure to complete the project within the strict schedule of 180 days.

Facing an extremely short timeline to bring Citico Creek into EPA compliance, LDA, Cannon & Cannon and the City were faced with quickly finding innovative solutions to three major problems:

  • The Norfolk Southern railyard is one of the largest in the country.

    Norfolk Southern switchyard.

    Problem: The interceptor included a portion of piping that ran under the Debutts Rail Yard, the second-largest Norfolk Southern switchyard in the country. The massive rail yard prevented workers from being able to reach the piping for repairs and precluded any bypass from passing over the lines. Several contractors declined to bid on the project because of this obstacle.

  • Solution: LDA and Cannon & Cannon discovered an adjacent box culvert in which a tributary of Citico Creek ran under the rail yard, and, with permitting from the City of Chattanooga, the bypass was submerged in the creek and circumvented the rail yard.
  • Problem: Immediately following the rail yard, concrete riser sections had been added on top of existing brick manholes due to the high flows in a flood zone. These “manholes within a manhole” could extend more than 10 feet into the air and were located in the creek, along steep banks or under rail structures. It was impossible to maneuver the necessary equipment to fix the manholes.
  • Solution: LDA Engineering assed the manholes and work with the contractor to apply structural solutions by hand and covered them with a polymer lining system to prevent infiltration and inflow.
  • Problem: The final obstacle was the significantly surcharged discharge of the bypass line. Because the downstream receiving line had a negative slope, the high flow was trapped in the manhole and was rising to within a few feet of the lid.
  • Solution: LDA and Cannon & Cannon developed a solution that added a 90-degree bend to the bottom of the bypass line and a pipe section extending into the downstream pipe, allowing the flow from the bypass line to pressurize the downstream line enough to counteract the negative slope and prevent overflows.

Through innovative engineering solutions and close coordination, LDA Engineering, Cannon & Cannon and the City of Chattanooga were able to solve the overflow problem on this portion of the interceptor, bringing Citico Creek into compliance with the EPA within the 180 day deadline.

This project included a multitude of unique challenges that LDA and Cannon & Cannon worked together to overcome using critical thinking, new ideas, and constant monitoring to finish the project on time and set the precedence for future Consent Decree projects.