The Dynamics and Evolution of a Coastal Water-Table Aquifer Under a Regime of Slowly Rising Sea Level

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This project addresses the problem of the dynamics and evolution of the freshwater - saltwater interface in ground water along the forest - marsh boundary in South Carolina. The position and expression (i.e. clarity versus diffuseness) of this interface is governed by short-term forcings (diurnal tides, daily ET cycles and rain events), episodic storm surges and long-term sea level rise. Prediction of the fate of contaminants released on land and their impact on adjacent marshes depends on a clear and quantitative understanding of the movement of ground water at and near this interface. Because of the complex forcings and boundary conditions, presently available models for coastal aquifers are too simple to adequately simulate such systems. In addition, adequate field measurements of head and salinity are not available to test complex numerical models that might be used. As a remedy to this problem, the objectives of this project are to collect long-term measurements of head and salinity along transects across the forest-marsh boundary and to use the data to develop, calibrate and validate a numerical model of the system. A spatially dense network of piezometer along each transect will be equipped with recording pressure transducers (assembled in house) that will gather data on the effects of short-term forcing. Based on geomorphic and stratigraphic criteria and C-14 dating of tree roots found in high marsh soils, transects will be selected to represent stages in the conversion of a forested, pleistocene beach ridge terrain into a Holocene salt marsh under a regime of rising sea level. This will provide a unique opportunity to test our numerical model against truly long-term data. The results of this project could be used by regulatory agencies for environmental impact assessment and planning and by ecologists interested in interactions between forest and marsh ecosystems.