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Paleogeomorphic reconstruction of the Omokoroa Domain, Bay of Plenty, New Zealand

Omokoroa Peninsula, located on the shores of Tauranga Harbour, has undergone major land use changes with associated shoreline modifications; becoming increasingly urbanised since the 1950s. A low-lying area on the northeastern side of the peninsula, referred to loosely as the Omokoroa Domain, is important to the community for recreational use and as a location for a vehicular ferry service to Matakana Island. Sedimentation issues in the vicinity of the boat ramp have created problems regarding access to the boat ramp, as well as requiring protection works to deal with shoreline erosion. The primary aim of this research was to determine the geomorphic evolution of the Omokoroa Domain and assess the processes that contribute to the long-term stability and future evolution of the shoreline. A range of different techniques were used to assess the prehistoric and historic geomorphic changes and interpret the driving processes; and also to quantify modern processes operating around the Omokoroa Peninsula. These have included analysis of historic photos, particularly aerial photographs; examination of LIDAR and mapped information, such as the underlying geology; field observations of the stratigraphic units in the cliffs and shore platforms around the peninsula; collection of sediment samples from potential sources, transport pathways and sinks, and associations lab analyses to characterise the sediments; shallow coring to determine the near surface stratigraphy of coastal sediments; and the deployment of a range of instruments, and subsequent analysis of the collected data to define the hydrodynamic processes around the Omokoroa Peninsula. The various lines of evidence analysed indicate the Omokoroa Domain can be classified as a cuspate spit, which enclosed a tidal lagoon that was infilled with landfill during the construction of roads on the Peninsula. The spit has developed in an area of low sedimentation, with a low potential for sediment transport. The sediment comprising the shoreline around the Omokoroa Domain is primarily derived from local sources, specifically from mass-wasting from the peninsula and predominantly from debris from landslides in the immediate vicinity of the Domain. There is evidence of both a tsunami event and rapid deposition of most of the sediment after 1,652 ± 20 BP. This appears to be associated with a local earthquake that also produced a tsunami deposit at Waihi Beach. It is possible that ground shaking and vertical movement triggered landslide events around Omokoroa Peninsula. Continuous tidal action and episodic wind generated waves are the primary factors influencing sediment transport, redistributing sediment around the Peninsula, and forming the cuspate spit and tidal lagoon. More recently, landslides have mostly formed on the western side of the Omokoroa Peninsula, with the sandy debris being transported around the peninsula to accumulate on the northern flank of the modified cuspate spit. This sediment is a minor contribution to the sedimentation problems at the boat ramp; the major issue being settling of fine sediment within the turbid fringe that has been enhanced by the shape of the present boat and vehicular ferry ramps, and associated wharf.
Type of thesis
Christophers, A. J. (2015). Paleogeomorphic reconstruction of the Omokoroa Domain, Bay of Plenty, New Zealand (Thesis, Master of Science (Research) (MSc(Research))). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/9606
University of Waikato
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