Potentiometric Maps and Subsurface Water Flow

Abstract

A potentiometric surface is a calculated imaginary surface, the topography of which reflects geographic variation in the fluid potential of the formation water within a particular aquifer or subsurface reservoir. The elevation of the surface at any point on it reflects (but does not exactly equal) the height to which a column of water would rise above a reference datum within a vertical tube (ignoring capillarity). This is an approximation of the “head,” (H_w), as has been explained earlier. The hydraulic head reflects the level of potential energy of the water at the point concerned, and the height of the column mirrors the pressure within the aquifer at that point, as well as the salinity (since pressure is a function of density) of the water. The heavier the fluid, the shorter the column required to balance a particular internal pressure. For example, the height of a column of dense brine required to offset a given pressure in a formation might be only 90% that of a column of fresh water.