Episodic, seasonal, and long term morphological changes of Coromandel beaches
Wood, A. (2010). Episodic, seasonal, and long term morphological changes of Coromandel beaches (Thesis, Master of Science (MSc)). The University of Waikato, Hamilton, New Zealand. Retrieved from http://hdl.handle.net/10289/4345
Permanent Research Commons link: http://hdl.handle.net/10289/4345
The Coromandel Peninsula was subject to subdivision and development primarilysince the 1960's. Much of the development that has occurred now rendersprotection from the existing beach systems which have typically been altered bydevelopment. Coupled with huge populations during summer, the region is ofnational significance therefore an understanding of coastal impacts is paramount.Analysis of the spatial and temporal variation of beaches along the easternCoromandel Peninsula from Whangapoua in the north to Whiritoa in the southprovided results ranging from single storm events to decadal scale oscillations.Beach similarity was determined by measuring parameters such as beach length,beach connectivity to neighbouring beaches, aspect, and beach slope. The analysisof variability in beach face volumes was undertaken using an extensive beachprofile database collected by R. Keith Smith, Ron Ovenden and a monitoringprogram maintained by Environment Waikato since 1978. The database had ahigher-resolution sampling interval from 1996 until present (a maximum samplingfrequency of approximately bimonthly).Results showed that short term beach volume changes were explained by thebeach classification devised from the Wright and Short (1984) model andavailable planform morphology data. Intermediate beaches overall had a greaterrange of variation, but had a higher frequency of low magnitude of change events.Reflective beaches had a higher frequency of large magnitude of change eventsand subsequently greater short term volume changes. Beaches adjacent toharbours and two outliers were identified which did not accord to theclassification. The classification model maintained its applicability for seasonalscale beach response. Embayed beaches on the Coromandel Peninsula alsoexhibited beach rotation to varying degrees. Beaches with similar planformmorphology showed similar long term beach rotation characteristics. A biennialoscillation related to the El Ni o Southern Oscillation (ENSO) was evident aswell as an interdecadal oscillation related to the Interdecadal Pacific Oscillation(IPO) was evident across the Peninsula. In particular, no beaches north of theKuaotunu Peninsula showed a strong ENSO signal, and the strongest IPOresponse was on beaches north of the Kuaotunu Peninsula. The IPO appeared toenter a long term negative phase indicating decadal scale persistence of La Ni aevents, therefore Coromandel beaches are likely to exhibit erosion dominanttrends for the next 20 to 35 years.Based on these results, 3 sediment transport and behavioural cells were defined,they were: beaches located north of the Kuaotunu Peninsula from Whangapoua toOtama with northerly orientations; Mercury Bay beaches including Opito Bay;and, easterly orientated beaches south of Mercury Bay.
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