What is flooding?
Flooding is the covering of normally dry land as the result of extreme rainfall. Flood modelling shows which areas might be flooded in an extreme rainfall event and to what depth they may get flooded. Council's natural hazard maps show a number of different types of flooding (from extreme rainfall) including:
- Ponding This is when water builds up and forms ponds or puddles. This happens on flat land, or within dips in land, where rainwater can't drain away quickly. This is more common in low lying areas but can also happen in elevated areas.
- Overland flowpaths These are the routes that rainwater will naturally follow on the way to a permanent waterway e.g. a stream or river. Overland flowpaths are generally the lowest point on a property. Most landowners will already be familiar with where these flowpaths are on their property.
- River and stream flooding This is when a river or stream exceeds its capacity and overtops its banks and begins to flood onto land.
- Harbour and estuary flooding This is when the harbour or an estuary exceeds its capacity and begins to flood onto land. This type of flooding is most likely to happen at a high tide when there are also large amounts of rainwater coming into the harbour or estuary from rivers and streams.
Climate change is expected to worsen the effects of flooding (from extreme rainfall) over time. See why under the FAQs below.
Where are floodable areas identified?
The District Plan maps identify floodable areas in most urban areas as well as many rural areas.
Council also holds other floodable area maps (not shown in the District Plan) for some locations as the result of recent projects:
- Waihi Beach, Athenree and Bowentown
- Wairoa River (downstream of the Ruahihi Power Station)
You can view the District Plan maps and other 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 'Find my Property' 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.
Urban areas - how has the mapping been done?
Flooding in urban areas is modelled for a 2% Annual Exceedance Probability (AEP) rainfall event. A 2% AEP event is something that has a 2% chance of occurring in any year. This means it is expected to occur on average once every 50 years, however it could actually happen at any time. We have not mapped less extreme rainfall events, but this does not mean flooding during such events will not occur.
For Waihi Beach, Athenree, Bowentown and Te Puke, which have undergone recent reviews, the modelling takes into account the effects of climate change such as sea level rise and the increasing intensity of rainfall. It shows us what a 2% AEP event will look like if it happened in 100 years' time including the effects of climate change.
For the settlements along the Tauranga Harbour and at Paengaroa, Maketu, Pukehina and Little Waihi, the flood modelling hasn't taken into account climate change yet and therefore only shows what a 2% AEP event will look like if it happened today.
To generate a flood hazard map, we build a computer model of the area (also known as a catchment) and use specialised software to show the effects of different intensities of rainfall.
We take into account different criteria including:
- How hard is it raining?
- How long has it rained for?
- What is the contour of the ground?
- Where will rainwater soak into the ground (e.g. grass)?
- Where will rainwater flow over hard surfaces (e.g. roofs, concrete)?
- How long will it take for rainwater to flow from one part of the catchment to another?
- What stormwater systems are already in place?
Each model calculates how, when and where the rainwater 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.
Rural areas - how has the mapping been done?
For rural areas, the mapping was historically done based on the best estimate of the engineers at the time. In some cases, the Regional Council has undertaken flood modelling to identify flood prone areas in rural catchments. This information has also been used to update some of the floodable area maps in the District Plan.
Council's primary focus is on updating floodable area maps in urban areas however the Regional Council are progressively re-modelling various catchments around the District based on latest information. In many cases, rural properties within a floodable area in the District Plan will require an individual assessment by a qualified engineer to determine a suitable minimum floor level.
For the Wairoa River catchment (downstream of the Ruahihi Power Station) recent modelling has been done for low-lying land adjoining the river. The draft report identifies the possible extent of flooding that may occur in the year 2130 if a 1% Annual Exceedance Probability (AEP) rainfall event and a 5% AEP storm surge event were to happen at the same time. The modelling takes into account the possible effects of climate change that may be present in the year 2130 such as sea level rise and the increased intensity of rainfall.
Here are the reports supporting the floodable areas on the District Plan maps:
Here are the reports supporting the other identified floodable areas not shown in the District Plan:
|Waihi Beach, Athenree and Bowentown||Tonkin and Taylor Waihi Beach Stormwater Model Report 2017 (PDF 8MB)|
|Wairoa River (downstream of the Ruahihi Power Station)||DHI Wairoa Stormwater Catchment Modelling Report 2016 (PDF 4MB)|
What further work is coming up?
Council and the Regional Council will be reviewing all floodable areas in the District's urban areas over the next two or three years. These reviews will take into account climate change and 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. When the mapping is completed, flood risk assessments and changes to the District Plan will also be required. The floodable areas at Omokoroa and Katikati are currently being reviewed.
Frequently asked questions about flooding
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 flooding 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
How does climate change affect flooding?
Climate change is expected to cause sea level rise as well as bring much heavier rainfall than what we are currently used to. Therefore, whether you live near the coast, or further inland, or up on the hills, climate change could worsen flooding on your property. Here are some of the ways that climate change is expected to worsen flooding (from extreme rainfall):
Sea level rise (in low lying areas):
- Higher tides would prevent rainwater from draining into the ocean, leaving ponds and overland flow to stay on land for longer.
- Higher tides would increase the chances of river, stream, harbour and estuary flooding.
- Higher groundwater levels would cause land to get saturated faster when it rains (meaning flooding would begin and worsen quicker).
Increased intensity of rainfall (in low lying and elevated areas):
- More intense rainfall means a greater amount of rainwater going into ponding areas, overland flowpaths, rivers, streams, the harbour and estuaries.
- More intense rainfall would cause land to saturate faster and any drainage systems to reach capacity earlier (meaning flooding would begin and worsen quicker).
What are the requirements if I am constructing a habitable building or shed/garage?
If your property is identified in the District Plan maps as a floodable area, you will need a resource consent. If you are constructing a habitable building you will need to have a minimum floor level of 500mm above the identified flood 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 flooding occurs. For all of these buildings, you will need to ensure they don't interfere with natural flowpaths or ponding areas. You will also need a building consent.
If your property is identified in a floodable area map outside of the District Plan, Council is still required to impose controls to protect people and property from flooding based on the new information. Although we can't require a resource consent just because of these maps, we may be able to impose controls if a resource consent is required for another reason. Otherwise, this will be done through the building consent process.
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?
If your property is identified in the District Plan maps as a floodable area, 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 structures may or may not also require a building consent.
If your property is identified in a floodable area map outside of the District Plan, Council is still required to impose controls to protect people and property from flooding based on the new information. Although we can't require a resource consent just because of these maps, we may be able to impose controls if a resource consent is required for another reason. Otherwise, this can be done through the building consent process, if such a consent is required.
My property is shown as floodable in the District Plan, however the new flood maps (for Waihi Beach, Athenree, Bowentown and the Wairoa River) show that it isn't floodable. What does this mean for me?
The District Plan permits buildings/structures (instead of requiring resource consent) if there is evidence showing that the District Plan maps are incorrect. The new flood maps would be considered as evidence. The new flood maps would also be considered when processing any building consents.
What if I want to do earthworks?
If your property is identified in the District Plan maps as a floodable area, 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 flood level for my property?
For this, please contact Council on 0800 926 732 or at email@example.com.
I want to build or renovate an existing building in an area that I know is susceptible to flooding but isn't currently identified as floodable. Will this affect my building consent?
If Council has no information showing that the property is floodable (e.g. maps or complaints about flooding on the property file) your building consent is unlikely to be affected. However, if you know the area is actually prone to flooding, it would be in your best interests to choose to build in a way which reduces risk e.g. building to minimum floor levels.
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 floodable area (District Plan or other) is unlikely to stop you from subdividing if you would otherwise qualify. However, there will be additional requirements through the resource consent process such as raising building sites above the identified flood level or avoiding interference with natural flowpaths or ponding areas.
Where can I find the District Plan rules for floodable areas?
Within Section 8 - Natural Hazards.
My property has never flooded after rain; does this mean the maps are wrong?
Most maps are based on a 2% AEP event. This is something that has a 2% chance of happening in any given year so it is likely that such an event hasn't occurred while you have been at the property. However, there are cases where flood maps are incorrect e.g. a property is clearly higher than the flood level. In these cases, we can have maps corrected.
Why does Council have information about flooding outside of the District Plan?
The recent modelling we did for Waihi Beach, Athenree and Bowentown was necessary because some of the flood mapping hadn't been reviewed since 2001. The recent modelling for the Wairoa River (downstream of the Ruahihi Power Station) was done by Tauranga City Council and passed onto us. Normally, we would change the District Plan soon after modelling a flood hazard. However, under Change 2 to the Regional Policy Statement (RPS), we must also identify other less frequent events (e.g. 1% and 0.2% AEP events) and do risk assessments before we can do a Plan Change.
What is Council doing about flooding?
Through our 2015-2025 Long Term Plan consultation we sought feedback from our communities on a number of stormwater and flooding related issues.
After reviewing feedback, we decided to roll out a $20m District-wide stormwater flood prevention programme over the next 10 years, using a combination of infrastructure and planning tools, and including an offer to waive the house-raising consent fee for flood-prone properties.
This District-wide flood mapping will also help us combat flooding by providing up-to-date, accurate information. This enables us to plan stormwater management in the most efficient and cost-effective way.
Got a different question?
If you have any further questions, please contact Council on 0800 926 732 or at firstname.lastname@example.org.