Regenerative Stormwater Conveyances in Knoxville, TN: A Performance Analysis and Investigation of Design Feature Alternatives

Regenerative Stormwater Conveyances (RSCs) are an innovative approach to repairing eroded stormwater conveyances while simultaneously treating runoff and providing groundwater recharge. Although RSCs are increasingly being utilized as a Stormwater Control Measure (SCM) for watershed restoration, research is limited. The objectives of this research were to: 1) build and utilize a 3D computational fluid dynamics model to investigate design feature alternatives, 2) perform a groundwater analysis to determine the subsurface interactions of infiltrated stormwater, and 3) conduct a hydrologic and water quality investigation to evaluate RSC performance in terms of volume, peak flow rate, and pollutant reductions. The modeling study determined that it is possible to create a system that maximizes velocity and energy reductions. Specifically, it was determined that lower pool length to width ratios (L/W) were preferred for reducing velocities and energies, with results suggesting an optimal L/W of 0.7. The results also suggested that design of the first two pools of the system were the most critical and that a minimum number of pools was necessary for adequately dissipating erosive flows before discharging to the receiving stream. The groundwater investigation found that there were significant influences on the groundwater system resulting from infiltrated stormwater within the RSC. The degree of influence of the RSC resulted from seasonal fluxes in water table elevation, varying weather patterns, and most significantly, the presence of two buried sewer lines. Despite these confounding factors, it was discovered that the RSC acted as a source to the local water table during small to medium events, and a sink during large events. Lastly, the hydrologic and water quality investigation yielded mixed results, with hydrologic and pollutant load performance showing modest reductions, despite relatively poor reductions in event mean concentrations. The study also found that performance was best during the growing season (compared to the non-growing season), with volume reductions of 37% possible. In conclusion, RSCs are recommended as a viable SCM in the Knoxville area, given the right site conditions. Optimal site conditions include locations with lower water tables, highly infiltrative soils, treatment train applications, or as a retrofit where head cutting has occurred.