Regional variation of coastal morphology in southwestern Australia: a synthesis

Abstract

The morphology of landforms on the south coast of Western Australia is determined predominantly by wave refraction around discrete headlands and islands. Wherever offshore structures protect the shore from the direct effects of swell, sheltered sandy beaches have developed in association with cuspate forelands and tombolos. In contrast to this open coast setting, the nearshore waters of the west coast are protected by semi-continuous reef systems, which significantly modify the morphology of large-scale accretionary landforms, beaches and foredune sequences. On the south coast, foredune plains occur primarily as fill in sheltered embayments and storm built ridges do not occur. Foredunes on the west-coast include washover ridges and low aeolian dunes on the backshore of embayment and inset beaches. The form of high wave-energy beaches of the south coast fluctuates between reflective and dissipative morphodynamic states, and most commonly between transitional and dissipative states. Sediments are mainly fine grained siliceous sands. In contrast, the low-energy west-coast beaches are composed of medium to coarse grained, calcareous sands. The beaches are planar in section, characterised by lines of debris deposited by tidal and longer-term fluctuations in sea-level and their form does not alter with short-term changes in the wave regime. Despite the very low energy micro-tidal conditions experienced by the coasts of southwestern Australia, systematic variation in the morphology of coastal landforms does occur. As protection to the coast increases from the open-fetch south-coast environment to the reef-protected west-coast setting, swell energy decreases, there is an increase in the relative importance of locally generated wind waves, wave set-up and tidal forcing of currents, and forelands become increasingly asymmetric due to the strength of longshore sediment transport.