Abstract:
Examining the complex process-form relationships of coastal systems across multiple spatiotemporal scales is integral for understanding the cumulative coastal changes related to large-scale coastal behaviour. The high energy environment of the west coast of the North Island is subject to high rates of sediment supply and, therefore large fluctuations of the shoreline position. This has translated into non-linear behaviour dependent upon the interplay between environmental conditions such as sediment supply, accommodation space and hydrodynamic forcing, with site-specific geological frameworks. The connection between short-term variability and longer-term morphological responses and the drivers of these changes remains poorly understood. This thesis investigates the shoreline development and onshore sediment storage in the context of morphodynamic change at multiple spatiotemporal scales at Whites Beach. To address the spatiotemporal disconnect, data were obtained at different scales including: short-term beach profile behaviour; multi-decadal scale analysis of planform changes in shoreline position using remotely collected imagery, and; longer-term interpretation of coastal development using ground penetrating radar, radiocarbon dating and sedimentological analysis. The data were combined with findings from other research within the west coast littoral cell. Results show transgression of aeolian-driven sand formed over a basement facies, depositing approximately 81824 m3 after 413 yrs. BP (± 25 yrs.). Geophysical signatures and compositional analysis of sediments show that deflation occurred most likely as a consequence of foredune instability. Between 1940 and 2013 shoreline analysis reveals a shift in the depositional style at Whites Beach to one of progradation, where net shoreline movement at an average of 35 m has added approximately 83709 m3 to the modern dune system. However, shoreline analysis between 2001 and 2013 describes a trend towards recession. No apparent trend was found from changes in beach profile volume and the link between beachface and shoreline has not been established. However, results indicate large quantities of sand are exchanged in and out of this zone at extrapolated yearly rates of change 76% greater than that of multi-decadal change. Comparisons with other studies highlight a general pattern of progradation during the last century, with cyclical phases of rapid accretion appearing to relate to fluxes in longshore transport. However, evident irregularities in coastal change between beaches emphasises the importance of understanding the roles of geological inheritance, sediment supply and foredune stability. Significantly, smaller embayments like Whites Beach appear to be more sensitive to shoreline change and sediment budget variability. Keywords: Large-scale coastal behaviour, morphodynamics, shoreline change, dune transgression, progradation.