Intruded Salt-Water Wedge in Porous Media

A laboratory model of a two-dimensional, confined aquifer containing an isotropic homogeneous, porous medium was used to investigate the gravitational convection and dispersion of salt water. An equation for the rate of movement of the intruding wedge toe is presented and experimentally verified for the case of zero net fresh ground-water flow to the ocean. The earlier work of Henry in defining the equilibrium position of the intruded wedge is experimentally confirmed. The extent of the zone of dispersion at the salt-fresh interface due to the steady fresh-water flow to the ocean is treated analytically, and reasonable agreement is found experimentally. The additional interfacial mixing due to tidal effects is shown to be governed by a longitudinal and a lateral coefficient of dispersion that are functions of the pore system geometry of the medium and the tidally-induced seepage velocities.