This indicator measures shoreline change (erosion and accretion) since 1979 at a number of sandy beaches in the Waikato region.
Sandy beaches are often the site of housing development and are used by the public for recreation. Sandy beaches are naturally prone to changes in shoreline position. These movements occur in response to major storms and changes in climate patterns over longer time periods.
Fluctuations in the position of the shore can create risk to houses and infrastructure that are too close to the sea. Engineered structures placed on the beach to protect at-risk assets often degrade the natural and recreational values of the beach and can put nearby property at risk. By understanding of the extent of natural beach change, councils can guide existing and new developments on these coasts.
Reducing, and where possible avoiding coastal hazard risk is a key focus of the New Zealand Coastal Policy Statement (NZCPS 2010) and of regional and district council plans. Waikato Regional Council has a responsibility to provide information to district councils about coastal hazards and hazard areas. Shoreline change information is one tool that can be used to understand which areas of coastline are at risk from erosion due to natural changes in the shoreline.
This indicator reports changes in the location of the dune toe, which provides the best illustration of the type of shoreline change that can threaten coastal development.
Individual storms can cause the dune to erode by several metres over periods of hours or days. This erosion generally recovers naturally in the following months. A trend for erosion or beach building can also occur over several decades, usually in response to climatic cycles, such as ENSO ("the El nino - La nina cycle"). Widespread long term (permanent) shoreline change has not yet been recorded on Waikato beaches, but could occur in response to accelerated sea level rise and/or climate change.
Changes measured in the position of the dune toe show that Coromandel east coast beaches have undergone periods of erosion and dune building since 1979. During the early 1990s, there was a period during which most dunes were accreting, or growing toward the sea. After about 1996, and in particular during the last few years of the 1990s, many of the dunes eroded, some quite severely. Many of the dunes reached their most eroded state between 2000 and 2003. Most then recovered gradually until further severe erosion occured at some locations in 2008. Some dunes have since recovered, while others still have not completely rebuilt since the erosion in the late 1990s.
The results of this indicator show that shorelines don’t all respond in the same way to any one storm. In particular, the northern beaches (north of the Kuaotunu peninsula) respond differently to those on the rest of the Coromandel coastline.
This indicator is updated every two years, with the next update scheduled for 2019/2020.
Coastal Scientist - Science and Strategy Directorate
Updated 9 May 2018