Mapping beach types & hazard assessment

An explanation of how New Zealand beach types are classified and mapped and how the different beach types and their associated hazards are identified.   

What is beach type?

Beach type refers to the prevailing nature of a beach, including the waves, tides and currents, the extent of the nearshore zone, the width and shape of the surf zone, including its bars and troughs, and the dry or subaerial beach. The beach types that occur around the New Zealand coast are products of the forcing by waves, the tide range, beach morphology and beach sediment characteristics.

The hazard rating for beaches

There is a beach hazard rating associated with each beach type for the most commonly occurring (or modal) wave conditions. The beach hazard rating takes into account hazards such as rips, surf zone currents, deep water and holes nearshore and how changing breaker height affects the hazard rating for each beach type. Currently some 270 New Zealand beaches have been classified and assigned a hazard rating.

The classification and mapping of beach types and hazards

The classification and mapping of beach types involved identifying modal wave conditions (breaker height), tide range and beach morphology (the configuration of sand bars, and rip channels, beach slope) and sediment characteristics (grain size). This was carried out by undertaking site visits to numerous beaches throughout New Zealand, supplemented with information from literature search, aerial photographs and using numerical models to generate tide and wave information.

An assessment of beach hazards as they relate to water safety was also conducted during site visits. This identified hazards such as rip currents, submerged rocks and reef, stream mouths, along with features that influence the level of risk associated with the hazards, such as the type of access to the beach via tracks or road and facilities at the beach such as Surf Life Saving Clubs and public toilets.

The mapping began as a collaborative project with Professor Andy Short of the University of Sydney and capitalised on his 17 year effort mapping, classifying and applying hazard ratings to more than 10,000 Australian beaches. In addition mapping undertaken of additional beaches by Surf Life Saving New Zealand was assimilated into the database.

References

Short, A D. 2006. Australian Beach Systems - Nature and Distribution, Journal of Coastal Research, 22: 11-27.

Short, A. D. 2006. Beaches of the Western Australia Coast: Eucla to Roebuck Bay. Sydney University Press. 433 pp. 

Beach hazards. [NIWA]
Large rip visible as blue-green coloured deeper water cutting through the surf zone at North Piha Beach (image SLSNZ).
Screenshot from Coastal Coastal Explorer of a beach report card for Piha Beach .