Littoral Drift on Delta Fans, West Coromandel

A series of gravel delta fans occur along the fault line scarp of the western Coromandel Peninsula. This thesis involved a study of the nature, source and stability of sediments on four delta fans at Te Puru, Waiomu, Tapu and Te Mata. Abstract from thesis: West Coromandel delta fans are composed of a mixture of sand and gravel sized material. Gravels are typically small cobbles of bladed form and of greywacke or andesitic origin. Sands are dominantly rock fragments of coarse to very coarse size. Textural and mineralogical evidence suggests that almost all sediment on the deltas is derived from streams backing the deltas which drain the Coromandel Ranges. Gravel tracer experiements at Te Puru and Te Mata indicate that the direction of net littoral drift of sediment along the western Coromandel coastline is southwards. The average rate of drift decreases southwards from 63 m/yr at Te Mata to a negligible amount at Te Puru. Attrition rates of 4.4% and 2.7% per annum are calculated for greywacke adn andesitic gravels respectively. Computer simulation of wave action within the Firth of Thames shows that the study area is exposed to short period (3.6-5.1 s) low amplitude (1.5-2.5 m) waves from the northwest, west and southwest. Refraction of these waves is only significant within 500 m of shore due to the conditions of limited fetch and gently sloping bathymetry. A longer period (8-10s) swell wave which enters the Firth from the Hauraki Gulf was also noted. Aerial phtoograph analyses and repeated surveys of beach cross-sections suggest that all four deltas are prograding into the Firth of Thames. Rates of +0.06 m/yr, +0.12 m/yr, +0.66 m/yr and 0.23 m/yr were measured for Te Puru, Waiomu, Tapu and Te Mata respectively with the approximate volume of mobile sediment on each delta calculated as being 17,200, 22,400, 25,500, and 8,800 cubic metres respectively.

Grain size analysis of gravel sediments at four deltas (see above) Wave simulation and calculation of littoral drift. Investigation of shoreline change with aerial photography and field data. Assessment of littoral drift rates. Gravel tracer experiment at Te Puru and Te Mata.

Thames Coast deltas, Te Puru, Waiomu, Tapu and Te Mata.

Study undertaken in 1987-1988

Transect lines (23) spaced 200 m apart at Waiomu, Te Mata, Tapu and Te Puru. Sediment samples taken. Long, short and intermediate axes of pebbles taken. Grain size analysis undertaken. Limestone tracer placed and movement monitored. Auckland Met Station wind data used to generate wave spectra for storm events. Wave refraction and proagation simulation modelled (Black, 1983)

Discussed in full in thesis.

Presented in hard copy thesis.

Assessment of shoreline change, sediment transport processes and coastal hazards on Thames Coast deltas.

Thesis available in Waikato University library. No confidentiality.

Study completed. Data archived.