Toward a coastal ground-water typology

Although submarine ground-water discharge is recognised as being of physical and ecological significance, direct measurements are rare, and calculations are hampered by a lack of offshore data. Classification of the world's coast with respect to its potential, submarine ground-water contribution would help to focus attention on the most important areas and to extrapolate existing data. A classification may be based on relevant physical/climatological parameters (e.g. precipitation, soil type etc.), or geologic/geomorphic classes (e.g. karst, coastal plain, etc.), or on a collection of state parameters. State parameters for a coastal ground-water typology may include aquifer thickness, onshore hydraulic gradient, anisotropy and fractal dimension of the shoreline. Topographic gradient can serve as a surrogate for the hydraulic gradient. A fourth type of classification may be based on the distribution of salinity in the subterranean estuary but adequate subsurface data are not yet available.