Morphology of Coastal Lagoon Entrances: Waves Versus Tides

Abstract

Lagoon inlets and river entrances on sandy coasts are shaped by waves, tides and freshwater outflows interacting subject to geological constraints. In dimensionless terms the relative importance of fresh water discharge Qf versus peak tidal discharge is quantified simply by , where the tidal peak discharge may be taken either as the actual corresponding to the actual bay tidal amplitude aB or the potential , which is based on the ocean tide amplitude aO. ωtide is the tidal angular frequency and AB is the bay surface area at mid tide. The quantification of the relative strength of waves versus tides is less obvious and has not previously been clearly resolved. The case is made here for it being quantified by . denotes the average offshore significant wave height and g is acceleration due to gravity. More comprehensive data may lead to the inclusion of the wave period as well as the wave height in future formulations.

The daily‐scale entrance dynamics of intermittently open/closed estuaries

“…In situations characterised by cross‐shore transport, entrance closure is related to onshore sediment transport under long‐period swell conditions when ebb‐tidal currents are weak (Ranasinghe and Pattiaratchi, , ). Cross‐shore closures are most common on embayed beaches (FitzGerald, ; Treloar et al ., ; Cooper, ; Ranasinghe et al ., ) and have only been described for IOCE which open and close on a regular seasonal basis (Ranasinghe and Pattiaratchi, ; Vu et al ., ).…”

On the Tidal Prism: The Roles of Basin Extension, Bottom Friction and Inlet Cross-Section

“…Furthermore, tidal inlets are fundamental in the morphodynamic processes of the nearby coast and of the lagoon itself. In fact, they act as both sources and sinks of the sediments which are suspended from the bottom by the wave motion, which is locally generated inside the basin or outside in the open sea [2][3][4][5][6][7][8][9][10]. Sediments are then transported by currents that transfer the material into the network of tidal channels or along the shore in the surf zone.…”