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Raglan Monitoring

Location: Raglan, New Zealand

Type of Project: Coastal Sediment Transport Monitoring

ASR Projects- Raglan Monitoring

The Raglan BarCam GUI is used for monitoring the movement of the ebb-tide delta during various wave events.

Project Overview:

The use of rectified video imagery is a powerful tool for studying coastal processes. Automated photogrammetry techniques were developed and put to use monitoring Raglan’s Bar – an iconic ebb-tidal delta subject to high-energy wave conditions. By comparing images collected over long periods of time valuable insight can be gained relating to morphological changes as well as factors contributing to changes.

Project Outcomes:

The BarCam project consisted of writing several specialized algorithms to automatically process the thousands of images collected since October 2004. The selection, averaging, rectification (transformation from a perspective view to a planar view) and detection of the bar were automated via a Matlab code and applied to the image database. This resulted in a set of images depicting the evolution of the bar over the 5 years.

Observations of the observed morphological changes on the ebb shoal have led to hypotheses on the wave driven sediment transport over the shoal. The bar detection algorithm provided a basis for calculating wave peel angles (for surfing) and a means to estimate the bathymetry. The extensive set of imagery will be used for future validation of numerical models of sediment transport amidst high-energy wave conditions.

Ebb tidal sandbars formed offshore of a harbour mouth are observed throughout New Zealand, however there are very few studies on their large scale morphological changes. Consequently, gaining an understanding on the factors inducing these would be highly beneficial for the management of many harbours as well as useful for boating safety and recreational planning.

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