The remaining 13% of progradation proceeds through settling of suspended sediments however the rate at which this can occur under the mobilising effects of shallow wind waves is poorly understood, and the role played by vegetation is still debated. Shoreline classification of 20 SE Australian estuaries shows that delta growth is responsible for 87% of all lateral progradation and is therefore the primary mechanism for fetch reduction. Depths at specific points within an irregularly shaped SE Australian estuary have also been correlated with total fetch and wave energy arriving at those locations. The control exerted on estuary depth by fetch distances, a proxy for wave base, is evident in the physical dimensions of SE Australian coastal lagoons. The stage of inhibited deposition, therefore, represents a “dynamic equilibrium” of basin shape with driving forces, where vertical accretion cannot proceed until the depth of the effective wave base is reduced. However, the notion of estuarine basins existing in equilibrium or possessing a limiting depth for deposition is misleading, since many basins have completely filled and evolved towards their most mature forms, deltas. Estuarine basins at this stage of development are often described as being “in equilibrium”. The depth at which deposition becomes inhibited corresponds to the effective wave base, the depth at which shallow water waves are able to mobilise bottom sediments. Water bodies may infill to a certain stage of maturity, but locally generated wind waves will thereafter prevent further sediment deposition. A relationship exists between the physical dimensions of coastal lagoons and the sediment distribution forces operating within them. Coastal lagoons: geologic evolution in two phases. For full publication, not just conference paper see: Adlam, K., 2014.
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