Flooding

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 mapping been done?

District Plan
All urban flood maps are based on a 2% Annual Exceedance Probability (AEP) 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 events, but this does not mean flooding during such events will not occur.

Only some urban flood maps (Waihī Beach north of Two-Mile Creek and Te Puke) also include the effects of climate change such as sea level rise and increased intensity of rainfall. This is because they have undergone recent Plan Changes. These maps show us what a 2% AEP event will look like if it happened in 100 years' time.

For the remaining areas, the flood maps don’t yet include the effects of climate change and therefore only show us what a 2% AEP event will look like if it happened today. This includes Waihī Beach (south of Two-Mile Creek), settlements along the Tauranga Harbour, Paengaroa, Maketu, Little Waihi and Pukehina.

For rural areas, the mapping was historically done based on the best estimate of the engineers at the time (without flood modelling). In some cases, the Regional Council has undertaken flood modelling to identify flood prone areas in rural catchments which has been reflected on our maps.

Maps outside of the District Plan

Council is in the process of updating all of its flood maps for urban and rural areas to include the effects of climate change and to meet other new requirements. As we review each area, new maps will become available. We have new maps for most areas already.

Most of these new maps are now based on a larger 1% AEP 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.

For Katikati, Ōmokoroa, Wairoa River (downstream of the Ruahihi Power Station), Te Puke, and Rural Areas and Small Settlements, the new maps show us what a 1% AEP event will look like if it happened in 100 years' time including the effects of climate change.

For Waihī Beach, Athenree, Bowentown, the new maps show us what a 2% AEP event will look like if it happened in 100 years' time including the effects of climate change. We will need to update to a 1% AEP event in due course.

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.

Technical reports

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:

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 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 Waihī Beach, Athenree, Bowentown, Wairoa River, Ōmokoroa, Katikati, Te Puke, and Rural Areas/Small Settlements) show that my property 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.

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 1% or 2% AEP event which means they only have a 1% or 2% chance of happening in any given year. This means it’s unlikely that such an event has 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?

Council is in the process of updating all of its urban flood maps to include the effects of climate change and to meet other new requirements. Normally, we would change the District Plan soon after identifying a natural hazard. However, there are now further steps we must take before doing a Plan Change (including risk assessment) as required by the Regional Policy Statement (RPS).

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.

What is the flood level for my proposal?

If you are looking to subdivide or build in a floodable area, you’ll need to know what the flood level is in order to plan your proposal.

To find out the flood level, you will please need to provide the following information to the customer service planner at info@westernbay.govt.nz:

• The address of the property
• Your proposal. Is it a new dwelling and/or shed? Is it an addition to an existing dwelling and/or shed? Where on the title are you proposing to do this?

The customer service planner can then confirm your requirements. It may take a couple of days until you receive a response.

Got a different question?

If you have any further questions, please contact Council on 0800 926 732 or at info@westernbay.govt.nz.