Impact of wind on storm-water pond hydraulics

A storm water pond's effectiveness to treat particulate bound pollutants in urban runoff depends on its hydraulic behavior. Departures from the ideal plug flow, such as short-circuiting and mixing, pose hindrances to pond design. The goal of this study was to assess the importance of wind on storm water pond hydraulics. High resolution acoustic velocity measurements were conducted in a 0.3 ha, 2 m deep pond during dry weather. Results suggest that winds drive a turbulent, three-dimensional flow regime, including a lateral circulation and vertical exchange flows. A fully developed surface layer representing 1/3^d of the water depth, with drift scaling as 0.004 on wind speed at 10 m above ground, was observed in the downwind section of the pond. Wind-induced vertical mixing, short-circuiting, and basin scale mixing were estimated to occur faster than the typical nominal residence time in storm water ponds. Wind is therefore an important hydraulic driver in small water systems, which may potentially reduce their treatment performance. Local landscaping may be used as a wind mitigation measure.