1 - Assessment methodologies for submarine groundwater discharge

Abstract

Submarine groundwater discharge (SGD) in the coastal zone is recognized as a potentially significant material pathway from the land to the ocean. This chapter provides an overview on several methodologies used to estimate SGDs. Measurements of SGD using “manual seepage meters” show that consistent and reliable results can be obtained if one is aware of and careful to prevent known artifacts. New “automated seepage meters” help understand the hydrological and coastal oceanographic processes with longer-term and higher-resolution measurements. Direct measurements of SGD by seepage meters and piezometers in local areas may be scaled up to a regional basis by use of natural geochemical and geophysical tracers. Water balance estimates, although useful for rough estimates, are usually not very precise because the uncertainties in the various terms used to construct the balance are often on the same order as the groundwater discharge being evaluated. Estimates of SGD via analytical and numerical methods depend mainly on the evaluations of the thickness of the aquifers and representative hydraulic conductivities, of which well-constrained values are usually difficult to obtain.