A field study of morphodynamics at "North Bay Beach", Kaikoura.

Abstract

Morphodynamics, the latest approach to surf circulation dynamics and beach morphology, is used as a framework for analysis of a mixed sand and gravel beach fronting Kaikoura, east coast of the South Island, New Zealand. Within this analysis, a model for morphodynamics developed in Australia is utilized and assessed. The morphodynamics model is a model of morphological sequences thought to result from variations in energy dissipation over the surf zone. The model combines both circulation theory and morphology together and the beach is analysed in all three dimensions. The major aims of this thesis were to determine whether the behavior of North Bay Beach can be described by a morphodynamic model, and whether variability alongshore at North Bay Beach is explained by morphodynamics. Aims were achieved by specific measurement and observation of the process environment, beach profiles, and beach cusps of North Bay Beach, Kaikoura. Methods include littoral environment observations (LEOs), beach profile surveys, documentation of cusp , occurrence or extinction and wavelengths, sediment sampling of cusp horns and bays, and the compilation of wind and weather data. Morphodynamic beach state was indicated by way of a surf scaling factor. Results indicate a relationship between beach cusps and wave approach, explicable by the edge wave theory utilized by morphodynamics. Beach profile results show North Bay Beach as morphodynamically reflective - reflecting rather than dissipating wave energy at the shore. Surf scaling factor analysis indicates that North Bay Beach experiences intermediate morphodynamic beach states as well, although this is not reflected in the morphology of the beach as a whole as the model predicts. Due to these inconsistencies, the specific morphodynamics model presented proved inconclusive. However, it is clear that North Bay Beach is more reflective than it is dissipative. On this point, the conceptual basis of morphodynamics proved appropriate. It provided a link between the known morphology, sediment, and morphological responses of North Bay Beach, and the lesser known, difficult to measure, process environment. However, the morphodynamic model needs "fine tuning", i.e. possibly more defined beach states in the sequence to adapt highly reflective, mixed sand and gravel beaches such as North Bay Beach.