Author(s): V. Kaleris; G. Lagas
Linked Author(s): Vassilios Kaleris
Keywords: Groundwater Discharge; Density Effects; Numerical Modelling
Abstract: Submarine groundwater discharge can be a source of pollution in coastal environments. Its estimation requires the thorough understanding of the outflow conditions at the sea bottom. In this study groundwater outflow in pockmark areas has been analyzed by means of a numerical model. The objectives are: (a) To investigate under which conditions outflow of pure fresh groundwater occurs at the sea bottom and when outflow is a mixture of groundwater and saltwater invading the aquifer in the pockmark area (mixed exchange conditions). (b) To assess the portion of the outflow at the sea bottom, which is of marine origin. For the investigation a vertically two-dimensional flow configuration has been used and three cases of permeability distribution for the aquifer have been considered (homogeneous, anisotropic and layered aquifer). It has been found that the transition from pure groundwater outflow to mixed outflow and vice versa occurs for a critical value of the ratio between the Rayleigh number Ra and the Peclet number Pe. The value of this ratio is influenced by the ratio between the width of the pockmark and the thickness of the aquifer as well as by the anisotropy ratio and/or the characteristics of the layers of the aquifer. For Ra/Pe-values, which are larger than the critical value, outflow at the sea bottom is a mixture of groundwater and seawater, which invades the aquifer in the pockmark area, recirculates and discharges back into the sea. For the cases of mixed exchange investigated here, the minimal portion of the outflow, which is of marine origin, varies from 25 to 65%. The analysis shows that numerical simulations of the density driven flow at the sea bottom are crucial for planning of measurements to estimate submarine groundwater recharge as well as for the interpretation of such measurements.
Year: 2003