Shoreline Variation and Beach Rotation of Pauanui Beach
Foster, R. A. (2012). Shoreline Variation and Beach Rotation of Pauanui Beach (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from http://hdl.handle.net/10289/6472
Permanent Research Commons link: http://hdl.handle.net/10289/6472
Shoreline variation over short, medium and long term time scales is well studied and documented. Rotation studies however have only focused on the phenomenon occurring on embayed beaches. This type morphological change is known to be caused by variations in wave climate such as wave approach direction and energy flux. Rotation studies on other beach classifications are limited, specifically on the potential of harbour adjacent beaches to rotate. Given the highly variable nature of estuaries and their impact on sediment supply to these flanking beaches, rotation could be exacerbated and aggravate existing localised erosion as a result. This thesis uses a video imagery shoreline dataset to determine the shoreline variation and beach rotation of Pauanui Beach, a harbour adjacent beach. Comparisons are then made to neighbouring Tairua Beach, an embayed beach. The shoreline over 2002, 2003 and 2004 displayed variation at short, medium and long term scales. Large wave events exceeding 4 m in significant wave height eroded beach profiles until accretion occurred during lull periods. Alongshore uniformity of this erosion pattern was not consistent throughout the timeseries at both beaches indicating the phenomenon of beach rotation. Pauanui transects moved in unison with each other, while an out of phase relationship existed between the Tairua transects. Seasonal changes in wave climate also influenced shoreline change however consistent cycles were not evident at both Pauanui and Tairua until 2004 where summer accretion and winter erosion dominated. The effects of ENSO were also observable in the long term where the shoreline gradually accreted with the long term negative ENSO index. Pauanui accretion quantity was much larger than Tairua over the same period. Rotation phenomenon at Pauanui was caused by a strong variation in cross shore shoreline position while Tairua demonstrated a strong out of phase behaviour at either end of the beach. Wave models were generated to determine the effect of islands inshore of the generating conditions. Shadowing effects were highly noticeable on the wave climate projected onto the beach, affecting the rotation and mean shoreline position. Alongshore currents were generated which affected the sediment transport to these rotated areas of beach. Based on these results, the two beaches responded similarly during erosion, accretion and rotation events. Alongshore uniformity does not exist alongshore of the two beaches as wave climate variations are created by the offshore island.
University of Waikato
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