Geomorphology of Tidal Courses and Depressions

Abstract

Wetlands are unique environments along the coasts of the world since their origin, andtheir preservation is required for the conjunction of a series of factors. First of all, the geomorphologyof the initial coast must have enough accommodation space to allow the retention,minimizing the bypass, of the sediment being provided by the various possible sources. Sedimentsupply must also be important; therefore, the sources must provide a continuous inputto build the wetland both vertically and horizontally, and keep it in equilibrium with the energyconditions proper of the coast, and potential modifications due to mean sea level variations.The location of the coastal setting should be such as to minimize the energy of the sea;for instance, protected coasts have a better chance to retain sediment than those found in theopen shores. Furthermore, progradation and/or aggradation of the wetland, as it happens indeltaic coasts, requires a positive balance between the sediment input from the different sourcesand the material removed by waves, tides, and their corresponding currents (Perillo andPiccolo, 2011). This balance must also be positive for longer periods because the wetlandneeds to aggrade at least to the same rate to counterbalance the potential compaction/subsidence of the sediments and the increase in mean sea level.Tidal courses and depressions are incisions or negative elevations in an otherwise level orslightly seaward-inclined surface represented by a typical coastal wetland. From the initialstage of wetland formation, courses and depressions are common features of the environmentmorphology. Even the smoothest topography has depressions where tidal water is retainedduring low tide. In fact, the irregularities of the surface when connected develop coursesthat, for a part of the tidal cycle, conduct the water and the substances and organism thatit mobilizes. Therefore, courses are necessary features for the circulation of water and sedimentduring the preliminary stages of the formation of the wetland.