Mixing in Overland Flow during Rainfall

Abstract

A method is presented for estimating vertical mixing coefficients in overland flow with rainfall using laboratory data and using a mathematical model of shear‐flow convection, rainfall dilution, and vertical mixing. The laboratory data consist of concentration‐time measurements downstream from an injection of a conservative dye into overland flow during rainfall over a smooth impervious surface with constant slope, without sediment and with flow in the laminar Reynolds number range. Results of the mathematical model are compared to the concentration time measurements to calibrate values of the vertical mixing coefficient. The calibrated values of the vertical mixing coefficient were most highly correlated to slope and a Reynolds number related to rainfall intensity. An analysis of the calibrated vertical mixing coefficient values using equations for eddy turbulence did not prove satisfactory.