Tidal along-shore groundwater flow in a coastal aquifer
Cross-shore interactions between the ocean and a coastal aquifer have been studied extensively, whereas the corresponding along-shore case has seldom been examined. This paper presents a numerical model that simulates two- dimensional groundwater flow averaged over the thickness of a coastal aquifer. The model is used to examine the essential features of tide-induced, along-shore effects on an aquifer adjacent to a cross-shore river. The results show that the tide, which fluctuates the water level in the river, induces groundwater table fluctuations and oscillating flows in the along-shore direction. This occurs even at locations much further inland than tidal cross- shore fluctuations can propagate. However, the magnitude of along-shore water table fluctuations and flow velocity at a given cross-shore distance decreases with the distance from the river in the same manner as cross- shore tidal fluctuations. The along-shore groundwater flow, together with the cross-shore flow, forms horizontal circulation and increases mixing of solute in the aquifer. Over a tidal period, a large amount of water exchange occurs at the river-aquifer and ocean-aquifer interfaces, leading to increased transfer of chemicals between the three water bodies. These results have implications for the management of waste discharge in estuaries and coastal aquifers.
Record created on 2005-12-09, modified on 2016-08-08