Mixing Things Up: Preventing Short-Circuiting in Stormwater Ponds

Short-circuiting of a stormwater pond occurs when inflow to the pond flows directly to the outlet with little or no dispersion and results in the direct transport of upstream pollutant loads to the downstream receiving water body. Many municipalities and regulatory agencies implement design criteria aimed at preventing short-circuiting within stormwater ponds with the intent of eliminating direct discharges to the receiving water bodies, the most common being a minimum length-to-width ratio of 2:1. In this study, several rectangular ponds with 2:1 length-to-width ratios were modeled to investigate the effectiveness of different pond configurations in preventing short-circuiting. The theoretical stormwater ponds' inlet and outlet locations were varied to determine the most effective pond configuration. The preferred pond inlet and outlet configurations for preventing short-circuiting within the ponds were determined by measuring the time and distance traveled by the particle with the shortest flow path from the inlet to the outlet. Based on this study, rectangular ponds with inlets on the short side should provide the outlet on the closest adjacent side to the inlet and as far away from the inlet as possible to provide the longest travel path from the inlet to the outlet. Rectangular ponds with inlets on the long side of the pond should provide the outlet on the opposite side from the inlet and in the corner farthest from the inlet to provide the longest travel path from the inlet to the outlet. The results of this study may be used by agencies and municipalities in preparing or improving design criteria for stormwater ponds.