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Decadal Shoreline Stability in Eastbourne,  Wellington Harbour

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thesis
posted on 10.11.2021, 11:10 by Olson, David

Mixed Sand and Gravel (MSG) Beach research in recent decades has overwhelmingly focussed on open-oceanic environments, however, those found in fetch limited settings remain poorly understood. This thesis has examined spatial and temporal morphological change through such a system in Eastbourne, Wellington Harbour, New Zealand. This site has only recently prograded following several decades of erosion. This accretion has been the result of a northward migrating gravel front, which is introducing gravel sized sediment into the previously sandy system resulting in significant changes in beach morphology and volume. The aim of this study is to quantify these spatial and temporal changes and to assess shoreline stability on a decadal timescale. Additionally it aims to ascertain whether the current progradation is a long term change to the system or the result of a short term sediment increase. This assessment has been conducted in the form of topographic surveying, grain size and aerial photograph analysis. The topographic surveying and grain size analysis provides an accurate description of beach morphology. This is compared to the established MSG beach morphology models for the open coast, but operating on a smaller scale because of the lower energy fetch-limited environment of the study area. Aerial photograph analysis is used to show the longer term changes in beach width and the northern migration of the gravel fraction of the sediment supply regime. The spatial analysis results show that the beach morphology is highly variable. In the embayments that are more exposed to oceanic swell waves beach profiles are broad and steep, and in the beaches in the northern sections of the coastline which are more sheltered from oceanic swell waves, profiles are flat and narrow. The temporal results show that the coastal accretion observed through the study area has been initially rapid, followed by sustained increased beach width. These results suggest that the morphological variation on this coastline is part of a long term adjustment to a change in sediment supply, initiated by tectonic uplift and subsequently driven by longshore sediment transport. The observed mechanism of longshore transport has been suggested to be a function of sediment properties, relative wave energy and bathymetry/topography. The findings of this research are used to develop a conceptual model of shoreline evolution for the study area in response to changes that have occurred over the last 154 years.

History

Copyright Date

01/01/2010

Date of Award

01/01/2010

Publisher

Te Herenga Waka—Victoria University of Wellington

Rights License

Author Retains Copyright

Degree Discipline

Physical Geography

Degree Grantor

Te Herenga Waka—Victoria University of Wellington

Degree Level

Masters

Degree Name

Master of Science

Victoria University of Wellington Item Type

Awarded Research Masters Thesis

Language

en_NZ

Victoria University of Wellington School

School of Geography, Environment and Earth Sciences

Advisors

Kennedy, David; Dawe, Iain