Methods of estimation of the location of a sharp fresh water-salt water interface with hydraulic heads or pressures are relatively simple and are widely used. Progress has been made in the recent decade toward the mathematical relations describing the position of the sharp interface using hydraulic heads or pressures in coastal zones. This paper reviews several methods for estimation of the location of fresh water-salt water interface in coastal aquifers, including the classical Ghyben-Herzberg relation. The location of the fresh water-salt water interface in a coastal homogeneous, isotropic unconfined aquifer can be estimated based on piezometric heads at two points in the same vertical line tapping respectively the salt water zone (including the interface) and the fresh water zone (from the water table to the interface) when the groundwater flow system is in a steady state and satisfies the Dupuit assumption. If pressures are measured at two points in the fresh water and salt water zones in the same vertical line in the coastal aquifer under the same assumption, the position of the interface can still be estimated with the pressure data. If the Dupuit assumption is not met in coastal aquifers and the vertical fresh water head gradients can be approximated with a straight line, the position of the interface can roughly be estimated by using the water level data in a partially penetrating well during drilling of the well.
This work was supported by the Fund for the Special Research of Doctorate Subjects of the Ministry of Education of China （20070491522）
School of Water Resources and Environment, China University of Geosciences,School of Water Resources and Environment, China University of Geosciences