Spreading of a River Plume: Field Observations, Integral Model Analyses and Numerical Experiments

Abstract

Physical processes of gravitational spreading of the Akashi River discharge are discussed by means of field observations, including aerial surveys, integral model analyses and numerical experiments. Various types of plume patterns have been observed, from a potential-type one to a jet-type one, depending on the river discharge. The analyses based on an integrated conservation equation approach indicate that the outflow patterns can be classified into four flow regimes as functions of the parameter, Sd = E _v (2B/H)/(dB/dx), and the densimetric Froude number, Fd. Field measurements correspond closely to the theoretical classification and they also agree with the integral model predictions, thus suggesting that river plume expansion is intimately related not only with the vertical entrainment rate but also its aspect ratio. Finally, three-dimensional numerical experiments illustrate the hydrodynamics of the actual flow deceleration and plume dilution.