Show simple item record  

dc.contributor.authorBear, Alison Louiseen_NZ
dc.date.accessioned2009-02-05T12:00:12Z
dc.date.available2009-07-30T09:33:10Z
dc.date.issued2009en_NZ
dc.identifier.citationBear, A. L. (2009). Erosion and Sedimentation Processes at Northern Waihi Beach (Thesis). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/2783en
dc.identifier.urihttps://hdl.handle.net/10289/2783
dc.description.abstractThe northern sector of Waihi Beach is an example of chronic erosive tendency. The sediment deficit along the area of beach fronting the seawall means that there is often no beach at high tide. This existing situation, and the various remedial options suggested, has created an emotive issue for beach residents. Accordingly, the current study was undertaken to identify and evaluate the fundamental coastal processes impacting upon the erosion at northern Waihi Beach. Methods used to investigate this problem included: beach profiling and shallow water hydrographic surveying; mapping of sediments and the distribution of bedforms on the inner shelf using side-scan sonar, identification of nearshore sediment transport pathways from sediment textural analyses; collection and analysis of nearshore wave and current data; and numerical modelling of wave refraction and sediment transport processes. A side-scan sonar survey, ground-truthed by surficial sediment analyses and underwater video and diver observations, indicated that the shallow inshore zone is characterised by a relatively featureless seabed dominated by fine sands. Large shore-normal sand ridges (η=0.4-2.5 m, λ=300-1400), with crests oriented northeast to southwest were identified between 15-30 m water depth offshore northern Waihi Beach. These very pronounced features consist of coarse megarippled (η≈0.12 m, λ≈1 m) sediment. Sediment textural analyses revealed that offshore sediments vary from fine to coarse sand, showing a seaward-coarsening progression. Beach sediments consist of predominantly fine sands, with a slight inferred fining in grain size that occurs towards the northern end of the beach. This is possibly a result of lower wave energy when subject to swell and sea waves from the north, due to sheltering in the lee of Rapitiotio Point. 80 days of wave and current data were collected offshore northern Waihi Beach, during two separate deployments in Nov/Dec 2007 and May/June 2008. The summer deployment was characterised by waves from a northeast-east origin (Hs=1.09m; Ts=7.13s). Similar conditions were exhibited during the winter deployment (Hs=0.95m; Ts=6.79s). Observed relationships between wind direction and near-bed current direction, combined with calculated sediment entrainment rates, enabled predictions of the frequency of shoreward sediment transport by bottom currents to be made. Onshore currents, associated with winds from the southwest, prevailed during the deployment period. However, observed current velocities alone were generally incapable of inducing sediment motion. Analysis suggests that wave properties are likely to govern the frequency of sediment transport in the nearshore, as their presence is required to lift sediment into suspension for dispersal by ambient background currents. Onshore movement of sediment was estimated to be ~11,800 m3/year or 2.6 m3/m. Monochromatic wave statistics measured during the field study were used to calibrate a numerical wave refraction model. The wave refraction influence of Mayor Island was found to be the major feature influencing the distribution of wave energy along the shoreline, which is likely to contribute to localised accelerated beach erosion and dune setback. Wave energy focusing at northern Waihi Beach is maximised by swell waves, resulting in greater wave heights along eroding sectors of the beach. Potential sediment transport rates were investigated. Results suggest the littoral drift direction was bi-directional at northern Waihi Beach, although net littoral drift was southeasterly during the study period. An estimated net loss of 46,200 m3/year or 10.3 m3/m was predicted for northern Waihi Beach during the present study. Longer-term drift patterns were examined using a five year record of wave data collected offshore Pukehina by Environment Bay or Plenty from 2003-2008. Similar patterns but with lower magnitudes of sediment transport were obtained, with net annual drift rates estimated to range from 1,300-58,000 m3/year. A conceptual model of nearshore sediment dynamics is proposed for Waihi Beach to identify the major factors contributing to long-term erosion in the northern sector. Approximately 115,000 m3 of sediment was estimated to be moving within the defined northern Waihi Beach littoral cell during the study period. The derived sediment budget produced a net deficit of sediment of approximately 36,000 m3/year or -8 m3/year during the year commencing November 2007. The net southeasterly littoral drift was determined the major contributor to the net erosion rate during the study period, with alongshore transport rates exceeding available supply to the beach from diabathic movement of sediment onshore. Several aspects of the erosion problem at northern Waihi Beach are recommended to be researched further to identify what coastal management options are required.en_NZ
dc.format.mimetypeapplication/pdf
dc.format.mimetypeapplication/zip
dc.format.mimetypeapplication/zip
dc.format.mimetypeapplication/pdf
dc.language.isoen
dc.publisherThe University of Waikatoen_NZ
dc.rightsAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.
dc.subjectErosionen_NZ
dc.subjectSedimentationen_NZ
dc.subjectWaihi Beachen_NZ
dc.titleErosion and Sedimentation Processes at Northern Waihi Beachen_NZ
dc.typeThesisen_NZ
thesis.degree.disciplineScience and Engineeringen_NZ
thesis.degree.grantorUniversity of Waikatoen_NZ
thesis.degree.levelMasters
uow.date.accession2009-02-05T12:00:12Zen_NZ
uow.date.available2009-07-30T09:33:10Zen_NZ
uow.identifier.adthttp://adt.waikato.ac.nz/public/adt-uow20090205.120012en_NZ
pubs.place-of-publicationHamilton, New Zealanden_NZ


Files in this item

Thumbnail
Thumbnail

This item appears in the following Collection(s)

Show simple item record