Spatial analyses and repletion of Gargathy coastal lagoon

Coastal lagoons and bays vary in shape and size in response to antecedent topography, geologic processes and sea level rise. Variations in shape and environmental conditions of coastal basins are believed to influence the distribution of benthic subenvironments and the exchange of water with the ocean and other adjacent coastal systems. Gargathy Inlet and its coastal lagoon vary spatially from the inlet, where the greatest depths are observed, to the mainland, dominated by shallow intertidal areas, colonized by marsh. Hypsographic and hydro-hypsographic analyses of Gargathys coastal lagoon were the primary techniques applied to understand the relative distribution of the benthic and pelagic surface areas at different elevations. Using these techniques, four benthic sub-environments, upper intertidal benthic environment, lower intertidal flats, shallow sub-tidal lagoons and sub-tidal channels were differentiated. The Hypsographic curve of Gargathy Lagoon illustrated that 80.81 % of the total surface area is colonized by marsh; however, only 27% of the basin volume occurs over the marsh. Water exchange and flushing characteristics of this marsh-dominated system were associated with volume-hypsography, the hydraulic turn-over time and the repletion footprint. The volume-hypsographic curve for Gargathy lagoon, illustrated that about 77.3% of the basin capacity is completely exchanged with coastal oceanic waters with each tidal cycle. If repletion water completely mixed with residual water between tidal cycles, then, hydraulic turn-over time (HTT) could be as low as 1.29 tidal cycles. Mixing between residual water and repletion water is strongly influenced by hypsometry. Repletion patterns are strongly influenced by the presence of marsh during the last stages of the tidal cycle when water spreads over the marsh surfaces after filling the tidal channels. This study provides spatial techniques and methods that allow for a better understanding and characterization of coastal basins.