Wind influence on the orientation of estuarine landforms: An example from Lake Illawarra in southeastern Australia

Abstract

We propose a type of a quasi‐equilibrium, which describes a convergence of the estuarine system towards a form whose planimetric orientation is along the prevailing winds. By using the microtidal Lake Illawarra in southeastern Australia as an example, we describe sediment convergent and divergent processes that induce such an equilibrium controlled by the complex configuration of the shoreline relative to the prevailing winds. For a complex estuarine sedimentary system with a mixture of non‐cohesive and cohesive sediments, alongshore distribution of fluvial or marine sand deposition and associated subaqueous morphology reflects alongshore redistribution of sediments from rivers and the tidal inlet. The orientation of the second‐order polynomial trend surface of estuarine morphology is consistent with prevailing wind directions. Along the lake shore, there are extensive narrow flats mainly covered by fluvial or marine sands shaped by the prevailing winds. The implementation of the Delft3D flow model coupled with the SWAN wave model driven by idealized prevailing winds indicates the potential of sediment convergent and divergent transport at the embayment and promontory shoreline, which appears to be similar to the alongshore distribution of sandy sediments and the nearshore flats. Alongshore transport of sandy sediments is primarily induced by the wave refraction on the shore, while the currents are more effective in transporting fine‐grained sediments such as mud or clay. Finally, we suggest a conceptual model that describes potential sediment transport of convergence and divergence on the embayment or promontory shoreline that is normal to the prevailing winds. Orientation of the estuary follows the convergence centre of sediment transport driven by the prevailing winds with the largest fetch. A quantitative threshold for such sediment redistribution may be determined in the future. © 2018 John Wiley & Sons, Ltd.

Holocene evolution and depositional model of a bayhead delta, Lake Illawarra, Australia

“…The remaining intersections are associated with two small channels north of Penterong Point and at Duck Creek (Fig. 2) where they form a near‐shore band of sandy silt extending south towards Macquarie Rivulet delta under the action of north‐easterly winds in summer (Deng et al ., 2018). FA6 consists predominantly of dark olive to grey, poorly sorted, weakly laminated, sandy silt with the mean grain size gradually increasing upward from about 38 to 155 µm (Fig.…”

Coastal wetland responses to a century of climate change in northern Sahara, Morocco

“…At Venice Lagoon, Italy, winds were found to influence the equilibrium elevation of tidal flats as a result of the relation between wind stress and depth (Fagherazzi et al 2007). Although processes such as continuous sediment input, varying hydrodynamic and climatic changes prevent the basin's morphology from reaching a long‐term stable equilibrium, a relatively large‐scale stabilization is expected to be achieved (Deng et al 2018). In this case, a dynamic equilibrium may be observed between the longitudinal axis of the estuary and the prevailing wind direction (Deng et al 2018).…”

“…Although processes such as continuous sediment input, varying hydrodynamic and climatic changes prevent the basin's morphology from reaching a long‐term stable equilibrium, a relatively large‐scale stabilization is expected to be achieved (Deng et al 2018). In this case, a dynamic equilibrium may be observed between the longitudinal axis of the estuary and the prevailing wind direction (Deng et al 2018). Thus, explaining the NE position of the Khnifiss Lagoon in consequence of the NE winds, prevailing for the region.…”

“…In shallow microtidal basins like the Khnifiss Lagoon, characterized by extensive tidal flats and salt marshes, prevailing winds appear to be important in constraining sediment stabilization and erosion (Fagherazzi et al 2007; Deng et al 2018). Tidal flats elevation results from a balance between sediment deposition and resuspension by tidal currents and wind waves (Fagherazzi et al 2007).…”

“…This process is valid for winddominated systems. For example, at Lake Illawarra, Australia, a similar process occurred, where the estuarine system reached a quasi-equilibrium state, and a planimetric orientation along the prevailing winds was observed (Deng et al 2018).…”