Bed roughness effects on residence time distribution (RTD) parameters of vortex-type stormwater retention ponds

Abstract. Stormwater retention ponds are used for the flood control and water quality improvement. The innovative use of vortex technology improves the hydraulic performance of these ponds which increases residence time in the pond. This enhances water quality since stormwater is allowed to spend more time inside the pond resulting in removing sediments and reducing pollutant. Using natural materials such as pebbles and cobbles for constructing vortex-type retention ponds contributes to an environmentally-friendly and visually attractive design while at the same time their bed surface becomes rougher. This investigation deals with the effect of bed roughness on hydraulic performance of vortex-type ponds via numerical tracer studies using FLOW-3D. Results reveals that bed roughness improves the pond’s hydraulic performance since residence time distribution (RTD) parameters are positively enhanced. Moreover, useful predictive equations showing the relationship between RTD parameters and bed roughness are introduced which provide valuable insights for designers.