Wind effects on retention time in highway ponds

Abstract

The paper presents results from an experimental and numerical study of wind-induced flows and transportation patterns in highway wet detention ponds. The study presented here is part of a general investigation on road runoff and pollution in respect to wet detention ponds. The objective is to evaluate the quality of long term simulations based on historical rain series of the pollutant discharges from roads and highways. The idea of this paper is to evaluate the effects of wind on the retention time and compare the retention time for the situation of a spatial uniform wind shear stress with the situation of a "real" spatial non-uniform shear stress distribution on the surface of the pond. The result of this paper shows that wind plays a dominant role for the retention time and flow pattern. Furthermore, the results shows that the differences in retention time between the use of uniform and non-uniform wind field distributions are not significant to this study.

Impact of Wind on Stormwater Pond Particulate Removal

“…Accounting for the effective volume [EV, Eq. (23)], using e ¼ 0.6 from Bentzen et al (2008) numerical tracer experiments of a wind-dominated stormwater pond reduces the treatment efficiency more moderately, or by an additional 13 and 5% from the BSM model for N f ¼ 1 and 10, respectively. N f ¼ 5.6 and 30 are required to achieve 80 and 95% removal, respectively.…”

“…The key input data are (1) particle size distribution (PSD) of entering runoff; (2) hydraulic flow rates entering the pond (Q in;t ), and preferably also out of the pond (Q in;t ); and (3) effective volume, e, and background concentration, C Ã , summarizing wind-effects at bulk level. As a first order approximation, e may be taken as 60% based on Bentzen et al (2008) numerical tracer experiments. The background concentration, however, varies with inflowing TSS and biochemical factors (Kadlec 2000;Barrett 2008), as well as wind [Eqs.…”

“…Historically, hydraulic inefficiencies have been quantified in relation to structural design parameters, such as length-towidth ratios and inlet and outlet configurations, or alternatively vegetation cover (e.g., Persson 2000;Li et al 2007). More recently, numerical and field studies have suggested that wind may be an important hydraulic driver, even in very small (0.3 ha) stormwater ponds (Andradóttir and Mortamet 2016;Bentzen et al 2008). On one hand, wind-induced currents have been quantified as 10 to 100 times faster than those associated with in-and outflows, promoting short-circuiting.…”

“…Effective mixing dilutes pollutant concentrations, which may, in turn, counteract the short-circuiting. The combined effect of wind-induced extreme short-circuiting and basin-scale mixing has resulted in a 30-40% reduction in nominal residence time (Bentzen et al 2008).…”

“…The mechanisms were (1) wind stirring (WS), by which the sediments are mixed vertically over the pond; (2) basin-scale mixing (BSM); (3) short-circuiting (SC), resulting in a reduction in the effective volume (EV) of the pond; and (4) resuspension, resulting in an increase in the background concentration (BC) of fine particles. To compliment recent numerical modeling and experimental field studies (Bentzen et al 2008(Bentzen et al , 2009Bentzen 2010;Andradóttir and Mortamet 2016), this paper develops and tests a physically based analytical bulk model to serve as a simple assessment tool for event mean removal performance in wind driven shallow systems. The paper is organized as follows: first, the theory of wind in the context of particulate transport and removal is reviewed.…”