Shoreline Movements in New Zealand

The study outlined patterns of shoreline erosion and accretion, and observed that over the past century, about 56% of the open exposed part of the New Zealand coastline had remained static, 25% had eroded and 19% had accreted. The most important driver of shoreline change in the last 65,000 years is thought to be fluctuations in sediment supply and the resistance of coastal rocks to erosion. Findings relevant to the Waikato Region: This study (Gibb, 1979) summarised patterns of long shore transport on the New Zealand coastline. A net northerly longshore drift was noted on the west coast of the Waikato Region. It was also recognised that the sheltered nature of the Bay of Plenty, Coromandel and Northland coastlines meant that longshore drift was likely to be oscillatory and the net northerly drift existing in most other areas of the coastline was unlikely to exist. The thesis discusses in some detail the various geological and geomorphic signals useful for interpreting littoral drift direction. Purpose: This data is associated with a study that investigated the advance and retreat of the shoreline in New Zealand during the Late Quaternary and considered the dominant factors causing the shoreline change.

Contents include: Chapter I: An introduction to shoreline movements. Chapter II: Longshore drift around the coastlines of New Zealand and geologic methods for determining the net drift direction and rates of transport. Chapter III: The direction of net longshore drift around the coastlines of New Zealand. Chapter IV: Rates of longshore transport around the coastlines of New Zealand. Chapter V: Coastal erosion and accretion in New Zealand during the last century. Chapter VI: Late quaternary eustatic sea level changes from New Zealand. Chapter VII: Conclusions – shoreline movements in New Zealand. There is a brief discussion in Chapter III of sediment characteristics on the Coromandel Coast. There is a brief description of littoral drift patterns in the Firth of Thames. The study observed net drift southwards along both coasts of the Firth of Thames, with small down-drift asymmetric deltas at the mouths of the Tapa, Waiomu, Te Puru and Tararu streams. Figure 3.28 is a sketch map showing directions of net longshore drift around the coastlines of New Zealand, based on the study. The figure also includes the main oceanic currents. Useful figure: Figure 5.1: Diagram showing seven different reference shorelines used by New Zealand land surveyors to define MHWM on cadastral plans over the past century. Shows dune and cliff scenarios. This study includes a discussion of the challenges and pitfalls associated with determining shoreline change from cadastral plans and aerial photographs. Figure 5.7: Sketch map showing the present extent (ca. 130y.) of eroding, accreting and static coastline in the North Island for the nine rate classes (slow, moderate, rapid, extreme erosion/accretion, or static shoreline). The only assessments on the map within the Waikato Region are at Matarangi (extreme erosion) and southwest Firth of Thames (extreme erosion). Extreme erosion is classified by this study as being in excess of 8m/yr. While these large rates of erosion are indicated on the map, there does not appear to be any discussion in the text explaining this.** Check with author?? Chapter IV contains some discussion of sea level patterns and the development of coastal plains, including those at Miranda and Kaiaua. Thesis includes printed records of sediment samples (collected from the North Island between 1974 and 1976) and analysis, including textural analysis, magnetic separation, detrital grain counts and bulk density analysis. In the Waikato Region, beach samples were collected on the Coromandel Peninsula, and from the Waikato River bed. Appendix includes details of collection date and grid reference.

All of New Zealand, including Waikato Region.

1974-1976

Study included literature review, field observations and sediment sampling. Bulk samples were collected of approximately 800g from the North Island west coast beaches and from the east coast of Coromandel Peninsula on or about the time of low water spring tides. Cut a linear series of channels each about 2 m length by 5-10 mm depth, and spaced 5-15 m apart. Methods and data very well recorded in Appendices of thesis.

Completeness: Study complete.

limited to content of thesis. Digital Format: University of Victoria provide electronic access to thesis for students and staff only.