Salinity Effects on Velocity Distributions in an Idealized Estuary

Abstract

An experimental and analytical investigation of the two-dimensional (i.e. longitudinal and vertical) convective-diffusion processes in an idealized laboratory estuary. The estuary is idealized to obtain steady-state salinity and velocity distributions. The mixing effect of tidal motion is produced by homogeneous turbulence generated by vertically oscillating screens. A fresh water inflow at one end and the introduction of saline water near the other end produces an estuarine salinity intrusion condition. The cyclic convection motion of the tide is not reproduced. The investigation was conducted in three phases which are outlined below. (1) The need for an accurate determination of the salt concentration distribution led to the development of a highly sensitive conductivity probe suitable for measurement in situ. (2) In order to predict the vertical diffusion coefficient from a knowledge of the turbulence intensity, a vertical column was built, and the diffusion coefficient was determined from measurements of the one-dimensional, time dependent, non-convective diffusion process. The horizontal diffusion coefficient is known from previous studies. (3) The horizontal and vertical distribution of salinity was measured in a long, horizontal flume. With an assumption as to the distribution of vertical velocity component, the longitudinal velocity profile was determined. The local value of the bottom velocity was found to correlate with the local, densimetric Frounde Number. The discussion of the experimental investigation concludes with some speculations on the engineering applications of the results.