Coastal developments at risk
Why we monitor coastal developments at risk
In many areas on the Coromandel Peninsula people’s properties and dwellings are at risk from coastal hazards, such as erosion and flooding. Waikato Regional Council and Thames Coromandel District Council have developed development setbacks for most developed beaches on the Coromandel Peninsula. Coastal erosion hazard has been divided into two categories: the hazard under current conditions (“CCEL”), and the hazard that is likely to occur over the next 100 years as a result of sea level rise due to climate change (“FCPL”).
The CCEL identifies the area currently at risk from coastal erosion associated with natural shoreline changes and current sea level. These are temporary fluctuations in the shoreline position as a result of natural processes. The CCEL is between 10 and 45 metres from the toe of the frontal dune, depending on the beach.
Coromandel beaches don’t currently show a trend for permanent erosion. However, rising sea levels and increased frequency and intensity of storm events are predicted to occur from projected climate change. This is expected to worsen coastal erosion and flooding hazards and may drive a trend for long-term erosion. The FCPL identifies the total area that might be at risk from coastal erosion associated with predicted sea level rise over the next 100 years. This line provides some insight into the long-term management implications for coastal settlements. The FCPL is different at each beach, and is 30-75 m from the toe of the frontal dune.
At a number of locations, one or both of these setbacks overlap significantly with private properties on the beachfront. This is likely to influence future development along many beaches these beaches. The proposed Thames Coromandel District plan contains development controls that apply to the CCEL and FCPL, which will restrict and place conditions on development within the two hazard areas.
Sandy beaches are constantly changing. The shoreline on a sandy beach will naturally move, depending on whether sand is being deposited or eroding away. In many areas on the Coromandel Peninsula coastal development has occurred very close to the sea. Where this has occurred the natural movement of the shoreline may threaten beachfront properties and houses.
Where coastal erosion occurs, residents and land owners may want to build protection works, such as seawalls and groynes, in an attempt to stop the erosion and protect beach-front properties. Erosion protection works can have a number of effects on the beach. For example, when a seawall is placed on an eroding beach, the beach in front of the seawall becomes lower and narrower, often to the point that there is only a dry beach at low tide, or none at all. This affects the beach’s appearance, natural character and beachgoers’ ability to enjoy the beach.
Waikato Regional Council has a responsibility under the Regional Policy Statement (RPS) to gather and communicate information about coastal hazards to territorial authorities. This indicator monitors the extent of coastal development within the existing coastal development setback zones. This information allows us to identify areas most at risk from coastal erosion and those requiring long-term coastal erosion management strategies.
This indicator also allows us to develop and monitor the success of coastal management practices. Successful management practices should result in decreasing levels of coastal development within hazard lines over time. The data suggests that this is occurring slowly in the high risk area, but that the number of houses in the long term potential risk area is increasing.
Beaches on the Coromandel Peninsula have been heavily developed over the last 50-60 years, mostly for private residential use. In some areas properties have been developed very close to the sea, within the active beach zone. Shorelines undergo natural changes in position, so there is a width of coastal margin that is at risk from natural coastal erosion.
Frontal sand dunes reduce the risk to coastal properties from coastal erosion. However, in many areas on the Coromandel Peninsula, sand dunes have been removed to improve views. This has increased the risk to property from erosion and coastal flooding.
Development setbacks have been developed to manage land development adjacent to mobile beaches on the Coromandel Peninsula. They identify areas of risk and define the space should be left between a building, such as a house, and the shoreline. The aim of the development setbacks is to reduce risk to property from coastal erosion or flooding in the long term. Setbacks have been used on the eastern Coromandel since the early 1980s, but were most recently reviewed in 2009 and 2012.
There are two coastal development setbacks for beaches on east coast of the Coromandel Peninsula. The first setback is the Current Coastal Erosion Line (“CCEL”), which represented the width of coastal margin at risk from coastal erosion under current climate and sea level conditions. This area is therefore at relatively high risk from coastal erosion.
The second setback is the Future Coastal Protection Line (“FCPL”), which identifies a further area of coastal land that is likely to be at risk from coastal erosion in response to sea level risk over the next 100 years. This setback is not applied on the western coast of the Coromandel Peninsula, where long terms coastal flooding hazard has greater management implications than erosion.
This indicator reports the number of properties and dwellings located in each of the two coastal development setback zones. Results show that over time there has been a small reduction in the number of dwellings that are at risk with current sea level. This is likely to be due to implementation of development setbacks, so as new houses are constructed, they are moved outside the hazard zone. There has been only a very small increase in the number of properties currently at risk, which reflects council controls on subdivision in hazard areas.
When this indicator is updated
This indicator will be updated when new aerial photographs areavailable (generally every 5 years).
Contact at Waikato Regional Council
Coastal Earth Scientist - Waikato Regional Council