What is coastal inundation?
Coastal inundation is flooding from the sea. Coastal inundation modelling shows which areas might be flooded in the event of a storm surge and to what depth they may get flooded.
Where are coastal inundation areas identified?
The District Plan maps identify coastal inundation areas along the open coastline at Waihi Beach, Bowentown and Pukehina.
You can view these maps below.
Search your property - current natural hazard maps
To show the natural hazard map for your property please enter a valid Address or Parcel ID below and click the launch button. Or you can browse the natural hazard maps.
Tips for finding your property:
- Type the address in full such as 10 Example Road or 10 Example Street, instead of using street name abbreviations (Rd or St etc)
- If there are identical addresses in other parts of the District, you'll need to type in community abbreviations e.g. Beach Road (KK), Beach Road (MAK) or Beach Road (WB). Help with identical addresses
- If searching by Parcel ID, recent letters from us about natural hazards show your Parcel ID number.
How has the mapping been done?
For Waihi Beach, Bowentown and Pukehina the modelling is based on a 1% Annual Exceedance Probability (AEP) storm surge event. A 1% AEP event is something that has a 1% chance of occurring in any year. This means it is expected to occur on average once every 100 years, however it could actually happen at any time. The modelling also takes into account the effects of climate change on sea level rise. It shows us what a 1% AEP event will look like if it happens in 100 years’ time including climate change.
To generate a coastal inundation map we build a computer model of the area (also known as a catchment) and use specialised software to show the effects of storm surge.
We take into account different criteria including:
- What will the sea level be in the future?
- What if the storm surge happens on a high tide?
- How long will the high tide last?
- For how long will the storm surge last?
- What is the contour of the ground?
- What obstacles are in the way as the water moves inland i.e. stopbanks or increases in elevation?
Each model calculates how, when and where the sea water will flow and tells us which areas are likely to be covered by water and to what depth. Flooding less than 100mm isn't shown.
Here is the report supporting the coastal inundation areas on the District Plan maps:
|Waihi Beach, Bowentown and Pukehina||Tonkin and Taylor Coastal Protection Areas Stage Two Report 2015 (PDF 7.6MB)|
What further work is coming up?
Council together with the Regional Council and Tauranga City Council are modelling coastal inundation along the entirety of the Tauranga Harbour. This review will take into account climate change and will show us what a 2% AEP, 1% AEP, 0.2% AEP and maximum credible event will look like if they happen in 100 years' time.
Draft results from this project are expected in mid 2018 and will be peer reviewed. Final results (including maps) are expected in late 2018. When the mapping is completed, risk assessments and changes to the District Plan will also be required.
Council and the Regional Council will also need to start a review of the existing coastal inundation areas along the open coastline at Waihi Beach, Bowentown and Pukehina in the near future as well as identify any other areas that may need to be investigated.
Frequently asked questions about coastal inundation
What is an Annual Exceedance Probability (AEP)
This is a statistical term referring to the likelihood of a natural hazard event occurring in any year. As a generic example, the event might be 300mm of rainfall in 24 hours. If such an event has a 2% chance of occurring in any year it would be described as a 2% AEP rainfall event. This means it would be expected to occur on average once in every 50 years. Although this is sometimes referred to as a 1 in 50 year flood, it could actually happen at any time. For example, it might not occur again for 80 years or it could even occur twice in one year.
AEP terms associated with coastal inundation include:
- 2% AEP event = expected to occur on average once in every 50 years
- 1% AEP event = expected to occur on average once in every 100 years
- 0.2% AEP event = expected to occur on average once in every 500 years
What are the requirements if I am constructing a habitable building or shed/garage?
You will need resource consent. If you are constructing a habitable building you will need to have a minimum floor level of 500mm above the identified inundation level for the property. If you are building a shed or garage, you could be allowed to build at ground level if you enter into a legal agreement with Council waiving any rights to complain if inundation occurs. For all of these buildings, you will also need to ensure they don't interfere with natural flowpaths or ponding areas. These will also require building consent.
What about additions to existing habitable buildings or shed/garages?
These will be treated in the same way as any new habitable building or shed/garage (as described above). For habitable buildings, this is the case even if the additions will be higher than the existing building.
I have a resource consent / a consent notice registered on my title which specifies minimum floor levels for habitable buildings. does this mean i can go ahead and build to these levels?
No it doesn't. Council is still required through the building consent process to use the most up-to-date flooding information available to set minimum floor levels. If we have new information, the levels are likely to have changed.
What are the requirements for minor structures?
You will need resource consent for any closed boarded fences, retaining walls, raised gardens and concrete and block walls. Other structures may also need resource consent if they are defined as a structure in the District Plan e.g. carports and some decks, pools and tanks. Minimum floor levels are generally not applicable for minor structures but you'll need to ensure the structures don't interfere with natural flowpaths or ponding areas. These may also require building consent.
What if I want to do earthworks?
You can only do up to 5m³ without having to let Council know. If you go above this, you will need resource consent to ensure the works don't interfere with natural flowpaths or ponding areas. Also check with the Regional Council as it also has rules for earthworks.
How do I know whether buildings and/or earthworks will have effects on natural flowpaths and ponding areas and how can I mitigate any effects?
This assessment needs to be carried out by a suitably qualified expert such as a stormwater engineer. They will be able to identify any potential problems for you and recommend solutions.
What is the inundation level for my property?
For this, please contact Council on 0800 926 732 or at email@example.com.
If I have a building site approved from a previous subdivision can I go ahead and build?
Yes, but only if the subdivision has addressed all identified natural hazards, and building works are in accordance with the requirements of the subdivision. If new natural hazard information has become available since the subdivision, this will need to be addressed when you go to build.
Will I be prevented from doing any new subdivision?
Being within a coastal inundation area is unlikely to stop you from subdividing if you would otherwise qualify. However, there will be additional requirements such as raising building sites above the identified inundation level or avoiding interference with natural flowpaths or ponding areas.
Where can I find the District Plan rules for coastal inundation areas?
Within Section 8 - Natural Hazards.
My property has never been flooded by the sea; does this mean the maps are wrong?
No, coastal inundation is something that is projected to occur more often in the future as sea level rises.
Got a different question?
If you have any other questions, please contact Council on 0800 926 732 or at firstname.lastname@example.org.