1.6 Coastline Exchange

The generalized conceptual models of exchange are applicable to coastal settings. However, the presence of the more-dense brackish and seawater adds complexity to the exchange process forming a boundary to freshwater flow (Figure 9). Sea level stages, and groundwater heads and rates of groundwater flux control the locations of the groundwater-seawater interface. For example, groundwater discharges when the water table near the shoreline is higher than the ocean stage, effluent conditions (Figure 9). When ocean levels rise higher than the groundwater levels along the shoreline, sea water infiltrates into the shallow groundwater system, influent conditions. Flow-through conditions are not applicable in coastline settings but zero-exchange occurs temporarily in portions of the flow system when sea level and groundwater heads are equal. Many research efforts focus on the development of water supplies along coastlines and how extraction of freshwater influences the nature of the sea-water interface/transition zone (e.g., Fetter, 2001; Jiao and Post, 2019). This book focuses on groundwater-surface water exchange associated with rivers, lakes and wetlands.