Red Tide and the Fluctuation of Conservative Concentrations at an Estuary Mouth

A set of observations of the conservative concentration, salinity, at an estuary mouth in a Red Tide region is generalized by an extension of the mixing length theory of tidal flushing for steady state to one for transient state. The river flow and tidal current are taken as functions of time, but not of space. The solution confirms the expectation that the intensity of the zone of rapid transition of conservative concentrations is greatest during high river flow and low tidal ranges. The solution also indicates that the tidal advection and diffusion reinforce each other.