While the rate and magnitude of future sea level rise is uncertain, we do know that rising sea levels and coastal hazards will have increasing implications for development and infrastructure in coastal areas along with environmental, cultural and societal effects.
By coming together to look at what we know about sea level rise and coastal hazards in Tasman, and the options we have for responding, we’ll be better prepared for making decisions in the future.
Following release of our coastal hazards and sea level rise maps (in 2019), and preparation of a coastal risk assessment (in 2020) we are now focusing on how we can respond to sea level rise and coastal hazards by identifying high-level options that enable us to adapt. The options are grouped into four categories – accommodate, protect, avoid, and retreat.
At this stage, our focus is to raise awareness and develop a common understanding about what we know and the options we have. These are complex issues, so it is important we start the conversations now because the decisions we make over the coming years will affect generations to come.
Long-term adaptive planning work will take several years to complete and the community conversation will be ongoing.
The conversations we are having now are at a broadly regional level, to understand the range of possible coastal management options.
It’s important to note that our key legislation, the Resource Management Act 1991, is currently being reformed. Central government-led work to develop a proposed a Climate Adaptation Act, and release of a National Adaptation Plan (due August 2022), will inform future phases of our Coastal Management Project. The work we do together now will stand us in good stead for responding to future central government direction.
Next steps in the Coastal Management Project will be to consider specific options at the local level around Tasman. This will include considering their respective costs, benefits, and potential adverse effects - and which are acceptable or not.
Long-term adaptive planning work will take several years to complete and the community conversation will be ongoing.
In July 2019, we wrote to all landowners and long-term land occupiers to let them know if their property was included in the extent of the mapping. For some properties, the house was not included in the map, only part of the driveway, or a small area of garden or land.
As a landowner, you do not have to take any action as a result of receiving this information.
We’ve made this information and maps available as part of our ongoing conversation with our communities on coastal management. Long-term adaptive planning work will take several years to complete and the community conversation will be ongoing.
The maps simply show land at or below the elevation of the particular scenario being viewed.
The actual extent of the land flooded will be dependent on its connectivity and distance to the coast.
Low lying land not directly connected to the coast may appear on the maps due to its low elevation, but may not be subject to seawater flooding.
These low lying areas may be subject to stormwater, river flooding and/or elevated groundwater levels that may become more prevalent as sea levels rise.
Implications of the mapped information will vary from site to site and we’re not able to determine whether there will be any effect on property values.
In the first instance you can contact your insurance provider to discuss your specific policy.
The Council cannot advise property owners about the implications of this mapped information on your ability to obtain insurance or on insurance premiums.
We do know that the insurance industry uses local government-produced natural hazards data, along with their own assessments, to quantify natural hazard risk to help determine insurance coverage and/or premiums.
Deep South National Science Challenge has developed an easy-to-read infosheet for homeowners, with important frequently asked questions about how insurance companies might respond to increasing climate hazards.
At this stage, we don’t know what the implications for Council rates will be – that will depend on what future mitigation or adaption options the community chooses, and the costs of these options over varying timeframes, alongside future Council and central government decisions.
How you are rated varies depending on where you live, what services you can access and the value of your property.
The annual rates requirement for each rate type is determined through the Council's Annual Plan or Long Term Plan process.
View our Common Rates Questions for more information on how Council sets rates.
When you’re selling a property, you and your agent are legally obliged to share all relevant information about it to buyers. It’s also important that potential buyers do their own due diligence on any property they wish to buy.
Under the Local Government Official Information and Meetings Act 1987, councils have an obligation to make natural hazards information available.
District and unitary councils also have specific obligations under the Building Act 2004. This allows people to access information held by council about their property or any property they are interested in.
The data used to prepare the maps is applied to Land Information Memorandum (LIMs) and Project Information Memorandum (PIMs).
The LiDAR derived elevation data used in the mapping is also publically available via Tasman District and Nelson City Councils’ Top of the South Maps service or Land Information New Zealand’s (LINZ) website.
There are some properties close to the coast that are not included in the extent of the mapping because their land elevation is higher that the extent of the sea level rise and storm-tide elevations that we’ve mapped.
However, this doesn’t mean that these landowners and residents are not affected.
Rising sea levels will have increasing implications for ‘everyday life’ activities in our coastal communities, for example road access to individual properties or into townships, the ability of our utilities infrastructure to function, access to coastal recreation reserves, and loss of scared sites or coastal habitats.
There may also be other natural hazards that should be taken into consideration, such as stormwater, river flooding and/or elevated groundwater levels that may become more prevalent as sea levels rise.
As part of developing a long-term adaptive strategy we will need to consider the wider implications and a ‘whole of community’ response.
The Coastal Management Project currently focuses on the District’s coastline of Tasman Bay/Te Tai o Aorere and Golden Bay/Mohua. This project currently excludes the west coast of the District from Kahurangi Point (including Whanganui Inlet) to Farewell Spit and Port Pūponga as there is limited hazard information, sparse population, limited access and minimal pressure for coastal development in this area.
As a Council, we are looking to better prepare our communities for the impacts of climate change and coastal hazards.
There are statutory and legislative requirements for Councils to manage the significant risks from natural hazards and the effects of climate change. An important document is the New Zealand Coastal Policy Statement 2010 (Objective 5 and Policies 24-27) which directs councils to identify areas that may potentially be affected by coastal hazards over a timeframe of at least 100 years.
This aim of this project is to enable communities across most of Tasman District to work towards long-term adaptive planning for sea level rise and coastal hazards.
In developing our adaptive strategy, we’re following the process set out in the Ministry for the Environment’s Coastal Hazards and Climate Change Guidance (2017).
We're following the Ministry for the Environment's 10-step decision cycle
| Technical term | Definition |
|---|---|
| Annual exceedance probability (AEP) |
An AEP is the chance or probability of a natural hazard event (such as a storm tide) of a particular size or greater occurring or being exceeded annually. It is usually expressed as a percentage. For example, a 1% AEP event has a 1% chance of occurring in any year. |
| Coastal accretion | Occurs when there is a net gain of sediment (such as sand) at the immediate shoreline area, resulting in the beach profile elevating/advancing seaward. |
| Coastal protection structures | Are structures that have the purpose or effect of protecting land from a coastal hazard including inundation or erosion. Examples includes stopbanks, seawalls, rock revetments and causeways. |
| Inundation | Freshwater or seawater flooding of land or buildings. Coastal inundation specifically relates to flooding from seawater. |
| Mean high water springs (MHWS) | The mean level of spring tides at standard atmospheric pressure. MHWS-6 is the 94th percentile of spring tides (i.e. 6% of spring tides are higher than MHWS‑6). |
| Representative Concentration Pathways (RCP) | A standard set of scenarios (pathways) which describe different climate futures, all of which are considered possible depending on how much greenhouse gasses are emitted in future years. The different pathways include different global responses to greenhouse gas emission controls. |
| Sea level rise (SLR) |
The rise in the level of the sea. Relative (or local) sea level rise includes both the change of the level of the sea (such as from global warming) and movement of the land (such as from earthquake subsidence) for the relevant coastal area. Tidal gauges measure relative sea level rise. |
| Storm surge | The rise in the level of the sea caused solely by a storm; this is caused by wind and wave action and low barometric pressure. |
| Storm-tide |
The observed seawater level during a storm. |
The rate and magnitude of future sea level rise is uncertain, particularly later this century and beyond.
Scientists advise that sea levels will continue to rise and that levels are likely to rise at an accelerated rate over time, meaning changes could happen sooner than predicted.
We’ve based the sea level rise information in the coastal hazards map viewer on the Ministry for the Environment’s Coastal Hazards and Climate Change Guidance (2017).
The Guidance outlines the approximate years, from possible earliest to latest, when specific sea level rise increments (in metres above 1986-2005 baseline) could be reached for various projection scenarios of sea level rise for the wider New Zealand region, as shown in the table below.
| SLR (metres) | Year achieved for RCP8.5 H+ (83%ile) | Year achieved for RCP8.5 (median) | Year achieved for RCP4.5 (median) | Year achieved for RCP2.6 (median) |
|---|---|---|---|---|
|
0.5 |
2060 |
2075 |
2090 |
2110 |
|
1.0 |
2100 |
2115 |
2170 |
>2200 |
|
1.5 |
2130 |
2160 |
>2200 |
>2200 |
|
2.0* |
>2150* |
>2195* |
>2200* |
>2200* |
*extrapolated out based on MfE’s 1.9m sea level rise scenario.
The representative concentration pathways (RCPs) listed are four comparable scenarios used to predict how future global warming may contribute to climate change and sea level rise. The lower scenario (RCP2.6) represents the rise in sea level if the Paris Agreement measures was achieved, namely to keep the global average temperature well below 2° C above pre-industrial levels, while pursuing efforts to limit the temperature increase to 1.5° C. The upper scenario (RCP8.5 H+) represents continuing high emissions and no effective emissions mitigation, plus runaway instabilities in polar ice sheet melting. The other two scenarios (RCP8.5 and RCP4.5) are in between those two different futures.
For example, based on current information we may expect 1m sea level rise by the years 2100 (RCP8.5+), 2115 (RCP8.5), 2170 (RCP4.5) or beyond 2200 (RCP2.6) depending on the rate of future global warming and climate change. Given that the rate and magnitude of future sea level rise is uncertain, we will need to consider all four RCP scenarios when developing our long-term adaptive planning approach.
Consideration of sea level rise and coastal hazards has been embedded in the Council’s work programmes for a number of years.
We use this information in:
Through Council’s activity management plans we already identify Council infrastructure and assets that are at vulnerable to the impacts of climate change.
View our Activity Management Plans
A Local Government New Zealand’s 2019 report quantifies and values local government infrastructure exposed to sea level rise (increments of 0.5, 1.0, 1.5 and 3.0 metres).
The report identifies Tasman roading, ‘3 waters’ infrastructure (water, wastewater and stormwater), green spaces, and other facilities which are vulnerable to rising sea levels.
Vulnerable: the quantum of local government infrastructure exposed to sea level rise (2019)
Nationally, climate change and any adaptation response will present new challenges (as well as new opportunities) for iwi, hapū, whānau and Māori enterprise.
Eight iwi are tāngata whenua in Te Tau Ihu (the top of the South Island). Tasman District also covers the northern part of the Ngāi Tahu takiwā (tribal area/territory).
These iwi have all been through Treaty of Waitangi settlement processes and the resulting statutory acknowledgement documents contain information on the cultural, spiritual, historic and traditional associations each of the iwi have with the coastal areas in Tasman District.
VIew Te Tau Ihu Statutory Acknowledgements
Some iwi authorities have also lodged iwi management plans with the Council. These plans are a written statement identifying important issues regarding the use of natural and physical resources for the iwi and are lodged with councils under the Resource Management Act 1991.
These information sources provide a starting point for our discussions with iwi on responding to climate change.
Several other agencies have also started to quantify New Zealand-wide risks and vulnerabilities to climate change and sea level rise and their reports include Tasman-specific data.
The Parliamentary Commissioner for the Environment identifies that in Motueka approximately 1,043 homes, 117 businesses, and 41km or roads lie less than 1.5m above the spring high tide mark (MWHS level).
Preparing New Zealand for rising seas: Certainty and Uncertainty (2015)
The Department of Conservation’s report identifies the Abel Tasman Coast Track as one of seven ‘icon destinations’ which have 10 or more vulnerable assets and/or more than 5% of vulnerable track.
Risk exposure of Department of Conservation (DOC) coastal locations to flooding from the sea (2019)
We’ve mapped the extent of low lying coastal land that corresponds to a range of sea level elevations. The sea levels include projected sea level rise scenarios and/or calculated storm-tide elevations.
Sea level elevation is mapped from the present day mean high water springs mark (MHWS6) with either:
A storm-tide is the combined effect of a storm event and the tide, resulting in a higher sea level than the tide alone. A 1% AEP storm-tide is the sea level reached by the effects of a storm event in combination with the prevailing tide that has a 1% chance of occurring or exceeded every year.
Mapping is based on present day ground topography derived from LiDAR (flown summer 2015 onwards). LiDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the earth. We used ARC-GIS software and a LiDAR-derived digital elevation model to map the spatial extent of land at or below the level for each extreme water level scenario.
We’ve categorised and mapped historical rates of coastal erosion and accretion, described as:
We’ve mapped existing coastal protection structures, described as:
We’ve mapped coastal protection structures known to Council to highlight the existing extent of our coastline that is currently actively being managed using structures such as stopbanks, rock revetments or seawalls.
In many cases, the coastal protection structures have been erected to manage erosion, rather than to hold back seawater and prevent flooding. Even now, and increasingly over time, storm-tide levels cause coastal protection structures to be overtopped by waves or high tides.
In some coastal areas of our district, coastal protection structures manage seawater flood hazard from present day high tides. Often these protection structures have limited life durations (via resource consents) or are privately owned structures. This means there are no guarantees that existing structures will continue to provide protection in the future.
The coastal hazards map viewer shows all land below a particular sea level or storm-tide level and ignores the ‘blocking’ presence that these structures provide.
In reality the land behind these structures would only become flooded once the sea level exceeds the top of the structure, or freshwater inundation occurs due to the elevated seawater restricting stormwater flows to the coast.
The coastal hazards map viewer also illustrates broad scale erosion rates along the coast in combination with the presence of coastal protection structures.
The shoreline erosion trend in these areas is indicative of the underlying 30-year average erosion rate at that location and prior to structural intervention taking place.
For example, a section of coastline adjacent to the Sandy Bay-Marahau Road is shown as being subject to a high erosion rate, however, this is currently mitigated by the presence of a rock revetment wall.
Wave runup is the maximum vertical extent of wave ‘up rush’ on a beach or structure.
This can result in seawater reaching land higher than the adjacent level of the sea. Where large waves are running up onto the shore and exceed the height of the shoreline, the overtopping seawater can then flow and pond inland, particularly if flow paths back to the coast are blocked.
The amount of such overtopping is dependent on the nature and form of the coastline, including its height and gradient. Typically, such overtopping is limited to a period across the high tide.
There are some areas of the Tasman Bay and Golden Bay coastline where the seawater inundation hazard is dominated by wave runup and overtopping. Such inundation was particularly evident at several locations in Tasman Bay during ex-tropical Cyclone Fehi (2018), including Mapua/Ruby Bay, McKee Domain, and Kina Peninsula.
The coastal hazards map viewer currently does not show areas prone to wave runup. This is due to the lack of location-specific modelling required to determine the rate and volume of seawater overtopping for each sea level scenario.
Not including wave runup is consistent with how other councils have mapped inundation, including Auckland Council and Waikato Regional Council.
The Coastal Management Project currently focuses on the District’s coastline of Tasman Bay/Te Tai o Aorere and Golden Bay/Mohua.
This project currently excludes the west coast of the District from Kahurangi Point (including Whanganui Inlet) to Farewell Spit and Port Pūponga as there is limited hazard information, sparse population, limited access and minimal pressure for coastal development in this area.
The coastal area is the interface between land and sea. It is a dynamic environment where a number of natural hazard processes can occur, either individually or in combination.
In addition to the coastal hazards shown in the coastal hazards map viewer, there are other natural hazards that may impact the coastal area. The combined effects of these natural hazards (where known) need to be considered holistically when considering options for future growth and development.
Many of our coastal communities are located on river flood plains (e.g. Collingwood, Riwaka, Motueka, and parts of Richmond) that include low lying areas susceptible to stormwater flow and/or ponding (e.g. Ruby Bay). Often the same low-pressure weather systems which result in significant storm-tide events on the coast will be accompanied by rainfall. The combined effects of coastal storm-tides and rainfall runoff events can be greater than the effects of one or other of the individual hazards.
As sea levels rise, coastal groundwater levels (the water table) will also rise.
This can reduce the capacity for rainfall to infiltrate to ground, potentially resulting in increased stormwater ponding. Low lying land close to coastal margins is the most vulnerable. Rising groundwater levels may impact areas of fine grained silts and sands. When these areas become saturated they may be susceptible to liquefaction, if an earthquake of a sufficient magnitude were to occur.
Both Tasman and Golden Bays are susceptible to tsunami hazard from various local, regional and distant sources. As sea levels rise, the areas potentially affected by tsunami will increase. Nelson Tasman Civil Defence have published a series of tsunami evacuation maps on their website which will be periodically updated as required.
Council staff produced the maps using a combination of peer-reviewed calculations, data and mapping tools.
In mapping the potential sea level elevations for each scenario, key data was derived from a ‘coastal calculator’ tool developed by National Institute of Water and Atmospheric Research (NIWA).
The calculator is based on local tide and wave climate data, to assist in calculating wave climate and sea level elevations along the Tasman and Golden Bay coastlines for a range of different scenarios for open coast sandy beach sites. For sheltered estuarine environments (such as Waimea Inlet and Parapara Inlet) we used a methodology consistent with that used by other coastal practitioners such as Tonkin and Taylor Ltd.
The techniques used to determine the sea level elevations was peer reviewed by NIWA to ensure that our methodology is consistent with national best practice.
We then took the data and produced the interactive map in-house.
The map uses Council’s most recent LiDAR derived digital elevation model and applies the derived sea level elevations for the various scenarios across Tasman and Golden Bays.
The method is sometimes referred to as the ‘bath tub’ model (the line that a bath tub would fill to), and is consistent with how other councils have mapped inundation, including Auckland Council and Waikato Regional Council.
The methodology used to develop the coastal hazards information shown on the map viewer is described in the accompanying report:
Coastal Hazard Assessment in Tasman Bay/Te Tai o Aorere and Golden Bay/Mohua (2019) (pdf 2 MB)
Climate change is happening now and the impacts will worsen over time.
Across Tasman District we’re already experiencing extreme weather events, such as cyclones, intense rain events and severe droughts, with increasing frequency. These events cause damage to properties and infrastructure from flooding, landslips, erosion or fire.
It is widely accepted internationally that the costs of inaction or delayed action outweigh the costs of acting now.
In recent years we’ve implemented a range of initiatives in response to climate change.
Examples include:
Council adopted the Tasman Climate Action Plan on 12 September 2019.
The plan's focus is on the things that Council can influence or control now.
It sets out goals, targets and actions relating to three key areas:
Our coastal management project is one of several Council work programmes which contributes to the ‘adaptation’ theme.
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