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The Geomorphology of Farewell Spit and Its Sensitivity to Sea-Level Rise

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posted on 09.11.2021, 18:53 authored by Tribe, Helen M

Sand-dominated barriers are highly sensitive coastal systems which alter their morphology in response to rising sea level, undergoing extensive sediment reworking as wave activity reaches further inland. Farewell Spit, South Island, New Zealand, is a sand-dominated barrier spit which extends 25kms eastward from the mainland, enclosing the northwestern corner of the macro-tidal Golden Bay. During spring tide cycles low-lying areas of the Spit become completely inundated. The aim of this study is to establish the morphological stability of Farewell Spit and its potential response to the latest IPCC projected eustatic sea-level rise of 0.48m (A1B scenario) by the end of this century. GIS analysis of aerial photographs and the identification of 137Cs signatures within the dunes have shown a high degree of mobility in the Spit's features over the past 55 years. Vegetation increased by 75%, mainly due to the introduction of A arenaria, which has also led to the development of foredunes prograding up to 142m over the tidal flats. Barchan dunes on the Spit are also highly mobile migrating at up to 30m/y. The high amount of sediment movement along the spit is reflected in the sedimentology of the tidal flats, which show layers of aeolian transported fine, well-sorted sand several centimetres thick. The predominance of medium sand shows that reworking appears to have occurred on these flats due to storm events in Golden Bay, and like the dunes, 14C dating indicates they are very young features Projected sea-level rise was modelled to assess the vulnerability of low-lying areas of the Spit to tidal flooding. Deeper water levels in the two tidal channels which currently flood across the Spit are expected and there is a risk of additional channels opening, one being very near to the contact between the Spit and mainland. The mobility of the dune systems may however buffer some of these processes by providing natural defences against the sea. Barrier roll over does not appear to be an important process as it appears to be too wide to allow for washover. It is concluded that under current sea-level rise predictions Farewell Spit will not transgress landward but will be subject to exacerbated erosion.

History

Copyright Date

01/01/2008

Date of Award

01/01/2008

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