Impact of Wind on Stormwater Pond Particulate Removal

Abstract

Stormwater ponds provide cost and space-efficient treatment of urban runoff via gravitational settling. The goal of this paper was to quantify different mechanisms by which wind can affect the particle removal efficiency of a shallow retention pond. An analytical bulk model was developed and validated numerically against total suspended solids (TSS) measurements in a small (0.3 ha), optimally designed oval pond during four runoff events with 7–11 m/s winds. Simulations highlighted wind as an effective mixing mechanism, lowering the removal of medium silt particles by 10–20% from ideal plug flow, and severely constraining the removal of small clay and silt particles (<6 μm). Initial background concentrations of <12 mg/L TSS were positively correlated with wind speed 5 h prior to the event, indicative of localized wind resuspension. A widespread remobilization of bed sediments was found unlikely in a 1.7-m deep, 112-m fetch pond. A stirred reactor with 60% effective volume is proposed as a first order tool to assess the treatment performance of ideally structured ponds in areas with strong, unobstructed winds.