Simple Model for the Recirculation Velocity of Open-Channel Embayments

A simple theoretical model is presented in order to predict the recirculation velocity in river embayments, also commonly referred to as eddies, gyres, cavities, and dead zones. This velocity is important as it sets the fundamental timescale of the motion in these ecologically important regions. Using only an equilibrium torque balance, basic geometrical properties, and resistance characteristics, the eddy velocity is determined as a percentage of the freestream velocity. The model is restricted to the single-gyre case, placing modest limits on the embayment aspect ratio. The result compares favorably with recent experimental, computational, and field studies of river embayments.