Development of the Kaiaua-Miranda Chenier Plain

The study was undertaken to improve the understanding of of the development of the chenier plain on the Miranda/Kaiaua coast. Taken from thesis abstract: A conceptual model of chenier ridge formation was developed for the Kaiaua - Miranda chenier plain on the western coastline of the Firth of Thames. The model associates fair weather and storm induced sediment transport with different phases of chenier ridge building processes. The predominant fair weather environment contributes to the vertical building of the chenier ridge. Storms cause increased sea level, wave height and onshore sediment transport, which contributes to the horizontal (landward) development of the chenier ridge. The frequency and intensity of the storm events during the formation period of the chanier ridge controls the dimensions of the ridge. A high frequency of storm events produces a wide, flat ridge, whereas a period of sustained fair weather increases the vertical development of the ridge. A numerical model was used to compare current patterns during fair weather and storm conditions to help understand surficial sediment distribution in the Firth of Thames, which influences sediment flux for the prograding chenier plain. A clockwise movement of currents in the southern Firth caused by the south-east orientation of the flood tide has induced the movement and accumulation of fine sediments from the Waihou, Piako and Waitakaruru Rivers. The sediments from these rivers are transported by the currents mentioned above to form extensive intertidal flats along the southern and western coastline of the Firth of Thames, ending north of Kaiaua. The sediment transported along the western coastline is also acted on by wave transport processes moving sediment onshore to contribute to the development of the chenier plain. Coastal erosion encroaching on public infrastructure and private property along parts of the Kaiaua-Miranda coastline is a short-term problem associated with storm events. The long term trend of the coastline is progradation, as evidenced by the continuing development of cheniers. Existing coastal protection measures (groynes) along the coastline are recommended to be removed as alongshore transport is negligible during fair weather conditions. The groynes also exacerbate storm effects, and result in the loss of natural character along the coastline. The Kaiaua-Miranda chenier plain is a unique landform which holds valuable information for present and future generations and must be allowed to continue to form naturally.

Numerical modelling of Firth of Thames using 3DD (model used for NOSEX programme by NIWA). Fair weather and storm conditions modelled. Implications for sediments discussed. Weather station was erected at Waitakaruru.

The Kaiaua/Miranda coast on the western shore of the Firth of Thames. Also looks at processes within the Firth itself.

Weather station data collected 9/12/96 to 18/7/97. Wave and current data collected 27/3/97-23/4/97 and 10/4/97- 23/4/97. Sidescan sonar survey 15/2/1997 offshore from Miranda.

Weather station used to gather wind data. Numerical modelling used to simulate fair weather and storm conditions. Sidescan sonar used to gather information about surficial sediments. Frequency of collection: One-off study.

Physical trace of sidescan sonar. Sidescan data stored digitally as well as hard copy (ISIS)

3DD data file printouts in thesis. No confidentiality known.

Study completed.