Wave processes in shore platform development: interactions between waves and morphology

The interactions between waves and morphology on shore platforms were investigated at four platforms located at Kaikoura Peninsula, New Zealand and the Otway coast, Victoria, Australia to determine the role of waves in shore platform development. Waves were measured over six tidal peaks of a spring tidal sequence at each site during a six month period (February 2007 - July 2007). Investigation of the offshore wave climate showed that over 90% of offshore wave energy was attenuated before reaching the platform. Direct measurement of waves on the platform found that wave attenuation was not dependent on platform width. An important fording of this study is that the depth of water on the platform exerts a primary control on wave heights on the platform during energetic conditions. Spectral analysis was used to assess how wave energy was transformed across the platforms. Although widely used on coastal landforms including beaches and reefs, the use of spectral analysis on shore platforms has been limited. This thesis reports the results of an investigation into how wave energy is transformed on shore platforms and the impact of platform morphology on the type of wave measured. Analysis of the capacity of breaking waves to cause erosion indicated that during the study period these were ineffective agents of erosion as waves broke before reaching the platform. The role of broken waves in shore platform development was assessed through comparing compressive strength of the lithology to shear stress, hydrostatic pressure and dynamic force exerted by waves directly measured on the platform. This showed that these forces were not mechanisms of erosion on the shore platforms investigated in this study. Through the investigation of wave interactions on shore platforms it is shown that complex hydrodynamic patterns form on shore platforms. The interactions between waves and morphology could not be explained using existing models of platform development and therefore a broader morphodynamics approach was discussed. A conceptual model of wave and morphology interactions on shore platforms is also presented