Winter flow dynamics of an on-stream stormwater management pond

The winter operation of an on-stream stormwater management pond, located in Kingston, Ontario, Canada, was studied with respect to ice cover formation and breakup, density stratification, velocity field under the ice cover, a nd the risk of sediment washout The pond freezes over in late November, wit h the ice thickness reaching up to 0.5 m. During the first half of the wint er period, the ice thickness was well described by Stefan's formula with em pirical coefficients appropriate for shallow water bodies. The pond was che mically stratified, with total dissolved solids concentrations up to 1200 m g . L-1 observed close to the bottom. The meromictic stability of this stra tification was calculated as 882 g . cm . cm(-2). Measurements of the veloc ity field under the ice cover indicated a flow pattern comprising a fast fl ow region, a small dead zone and a large recirculation zone to the north an d south of the fast flow trajectory, respectively. Such a pattern agreed we ll with that simulated by a CFD model (PHOENICS(TM)). During a snowmelt eve nt, the near-bottom velocities reached up to 0.05 m . s(-1), but were not s ufficient to scour the bottom sediment.