Natural hazards management questions & answers

Waimakariri District is susceptible to a number of natural hazards such as flooding, earthquake faults, liquefaction and coastal erosion. The most likely hazard for our district is flooding.

The Council has information on natural hazards including areas subject to flood risk, location of fault lines, areas susceptible to liquefaction and coastal erosion. This information is being used to review the Waimakariri District Plan so that the impact on people, property and the environment can be assessed and managed.

Much of the hazard information is of a technical nature, and the proposed plan provisions have a significant bearing on individual properties in parts of the district, especially around requirements for building and development.

If your query is not covered in any of these questions and answers, or for further information, please phone our Natural Hazards Hotline 0800 639 000 or email districtplan@wmk.govt.nz.

Download a copy of all the questions and answers (pdf, 131.6 KB), or view them below.

Why is the Council proposing to make this change to its District Plan now?

The Council now has access to improved information for natural hazards affecting the district, including flooding, fault line location, coastal erosion and liquefaction areas. The Council now needs to update the District Plan provisions for natural hazards to protect people, assets and infrastructure.

What is a draft plan change?

A draft of proposed changes to the District Plan have been prepared and released for public consultation and comment as a step to inform and allow discussion before any formal notification and submission process.

It gives a chance for people to view and comment on the draft changes and the background information on hazards at an early stage and gives Council an opportunity to take these views into account before finalising the proposed changes.

Comments can be made on the draft changes for Council to consider. These are not formal submissions.

How do I find out if my property is affected?

Use our interactive map and see how your property may be affected. Hard copies of the plan change and maps are also available at any Council service centre or library, or you can phone us on our Natural Hazards Hotline - 0800 639 000 to talk through what the proposed changes may mean for your property, or email districtplan@wmk.govt.nz

Please note that the interactive map was developed using pixels that show 10 or 12 m2 units when viewed at high resolution. These show the area within which a hazard is modelled, but at the individual property level it will not show the detailed outline of the hazard. 

What other high hazard areas are there?

There are high hazard areas for land that is likely to be subject to coastal erosion and inundated by sea water in the next 100 years. Sea water inundation along the extent of the Waimakariri coastline has not been specifically factored into the draft plan change.

There are also high hazard areas for land that is subject to liquefaction and earthquake fault lines. These are shown on the interactive map.

What if I am in a high hazard area?

High hazard areas will need assessment prior to building or adding to an existing building to determine if mechanisms are available to avoid or reduce the effect of the flooding.

Why have some areas been excluded from the high hazard flood area on the maps (being the red hatched areas shown on the District Plan map series A1-E4)?

Some areas have gone through assessments for flood risk – normally through a plan change or subdivision process, and have either had resource consents approved that set out floor heights or identified works that must be done to mitigate flood risk.  For areas that have been through a plan change process, there are rules in the District Plan that set floor heights or other methods for these particular areas.  As a full assessment has already been carried out that allows for development to have occurred, these areas are proposed to be excluded from the new provisions.

What does 0.2% and 0.5% Annual Exceedance Probabilities (AEP) mean and how/why have these levels of risk been used?

The figures are used to describe the probability of a flood of a certain size occurring in any one year.

A 0.5% AEP is another way of saying a one in 200 chance of a flood occurring in any one year. 0.2% similarly means a one in 500 chance that a flood of this type could occur in any one year.

The AEP levels come from the Canterbury Regional Policy Statement. The Council is required to give effect to the Regional Policy Statement and therefore has to use these events in its assessment of risk.

Aren’t the Council’s flood protection works supposed to protect us from flooding? Why do we need this plan change as well?

The Council provides some flood protection works that are designed to provide protection to property and infrastructure from moderate to heavy rainfall events, but are not designed to cope with extreme flood events. The rainfall that flood protection and drainage works are designed to cope with is at a level that could be expected once every 10 years to once every 50 years.

The District Plan change is required to provide protection to human life and to houses in extreme rainfall events that result in flooding. In events of this nature it is expected that existing drainage systems including streams and rivers would be overwhelmed and some damage would be caused to infrastructure and property.

What is displacement and diversion of floodwater and why does it matter?

Development of a site, for example through earthworks or placement of structures, can in some cases affect the flow of floodwater, or how deep the water is.

As an example, a new building may be placed so that it redirects the flow of floodwater onto roads or neighbouring properties where they can adversely affect traffic, drainage and the damage or risk from floodwater for other people and property. Moving the path of floodwater is diversion.

Displacement relates to the level of floodwater, if earthworks raise the level of one site, it may mean that other adjacent sites take more of the floodwater as a consequence. In an area, displacement can occur if the intensity of building development increases, leaving less area for floodwater to pond, which can result in higher water levels.

What is ‘freeboard’ and how has it been assessed?

Freeboard is a distance between the height of floodwaters and the floor level of a building.  For new buildings a minimum floor level height may be required to provide a safety factor to avoid buildings becoming inundated with water during a flood event.

How have the floor height measurements been calculated?

The minimum floor heights that  in each case have been calculated using a mix of information/data sourced from a number of models.  Information that is factored into determining the measurements required comes from aerial photos of the sites, LiDAR (Light, detection and ranging information) and the topographical contours of the land where the building is. This information is brought together to create a digital elevation model, that is then factored into the overall flood modelling to determine minimum height requirements.

How has climate change been factored into this plan change?

It is recognised that climate change will lead to a rise in sea level over time and that this will affect coastal processes, and flooding in coastal areas and further inland.  The information has been used within flood modelling and includes an allowance for sea level rise and changing rainfall as a result of ongoing climate change.

Will this stop me putting any more buildings on my land?

The proposed plan change is not trying to stop development. It seeks to more appropriately manage effects and risks of natural hazards as it applies to flooding and earthquake effects. There are some instances when a resource consent will be required, particularly within high hazard flood areas.

What does this mean if I want to renovate or extend my house?

If you are located on or near a fault line, or liquefaction area, you may need specialist geotechnical advice for any new building foundation for house extensions. This has been the case for some time, particularly in terms of subdivision and building consents.

In Low or Medium Hazard Area for flooding, you can extend your house by up to 20 m2 without a raised floor level. Any larger extensions would require the floor level to be 300 mm above the 0.5 AEP flood level at the building platform or building location.

In a High Hazard Area for flooding, extensions are also limited to 20 m2. Larger extensions would require resource consent approval.

Internal renovations and second storey additions to dwellings are not restricted by the proposed plan change (but may require a building consent).

Will this stop me subdividing my land?

You will still be able to apply to subdivide your land. The natural hazard risk associated with the land will be taken into account during the assessment of any application for subdivision. You would still need to comply with minimum lot areas as set out in the District Plan.

How will the plan change affect the assessment of floor levels that will be done for a building consent?

The Building Act, Building Code and the District Plan (or a resource consent condition) may require minimum floor height levels for buildings.

The Building Code requires minimum floor levels to provide protection from an event having a 2% probability of occurring annually, usually defined as a 1 in 50 year flood event. Where inundation is considered a natural hazard (the threshold for a natural hazard has been determined by Court decision to be a 1 in 100 year event in relation to flooding), building work must not accelerate or worsen the hazard on the property on which the building work is being carried out or any other property. Where building consent is granted in an area that is considered a natural hazard under the Building Act Council must identify and register the hazard with the Registrar-General of Land.

If the floor level requirement in the District Plan is less than that of the Building Act, the Building Act requirements will still need to be met. If the District Plan has a higher requirement, then that will need to be provided even if it is higher than that required by the Building Act. This is because the District Plan can impose a greater level of protection in areas where higher flood levels could be expected.

What information will be needed to get a resource consent?

You will need to provide detailed plans of your proposed building including a site plan, and provide an assessment of effects appropriate to the level of risk associated with your property. For example this may involve getting a flood hazard or geotechnical expert involved. There will also be an application fee.

Will information about flood hazard be included on my LIM?

Yes, and this has previously been the case. A Land Information Memorandum (LIM) is issued by the Council and contains important Council information relating to a property. It is an important part of the due diligence process that helps people make a decision about whether to purchase a property or not.

The property zoning and its location within any areas that have special requirements, such as a Hazard Area, will be noted on the LIM to ensure that the owner, or prospective owner, is aware of the location of the property in regard to hazard risk and that there may be special requirements or restrictions that apply to the use and development of the site.

What is a fault awareness area and what does it mean?

The fault awareness area is located on either side of an identified active fault line, and is mapped to ensure that land owners and service providers are aware of the presence of a fault line before they decide to build.   Within the awareness area special consideration should be given to geotechnical investigation and the design of building platforms.

 

Why is the liquefaction area included in the plan change?

The liquefaction area is mapped to ensure that owners are aware of the risk from liquefaction and lateral spread prior to building to allow for evaluation and design in these locations. This has been included on LIMs for some time. This is consistent with the Canterbury Regional Policy Statement, which sets high level policy direction that Waimakariri District Council must give effect to.

What effect will the plan change have on my property values?

There are many factors which affect property values. The risks posed by natural hazards are one of them. A registered property valuer may be able to advise on any enquiries regarding property value.

What effect will this have on my insurance?

The Council cannot provide guidance or indications of potential consequences for insurance resulting from the draft proposed plan change.  If you would like to know more about this, you should contact your insurance provider for further information about any insurance implications.

Why has the Council previously allowed development to happen in new residential areas that are at risk to flooding or liquefaction?

Since the previous rules were developed the Council has received hazard and flood modelling information which increases the understanding of risks posed by natural hazards.

The information that is available about natural hazards wasn’t available to the extent that it is now. Now that this information is available, the Council has a responsibility to manage and minimise risks to protect people and property. The District Plan needs to be updated to respond to this new information and plan for management of risk situations.

What is the Canterbury Regional Policy Statement?

The Canterbury Regional Policy Statement (CRPS) sets the strategic policy direction for resource management in Canterbury, and has been developed by Environment Canterbury (ECan).  The district plans of the Councils within Canterbury must give effect to the direction set by the CRPS. The CRPS can be viewed on Environment Canterbury’s website.

How does the hazards information and the draft plan change relate to the Waimakariri Red Zone Recovery Plan process?

The Preliminary Draft Waimakariri Residential Red Zone Recovery Plan acknowledges the preparation of a draft District Plan change relating to natural hazards as it applies to the regeneration areas in the Recovery Plan. The draft plan change on natural hazards must not be inconsistent with the approved Recovery Plan. Both the Recovery Plan and the draft plan change are currently in process. The Recovery plan is intended to be supplied to the Minister on 1 August for consideration. The timing of both processes is interrelated. It should also be noted that the Recovery Plan and the draft plan change have data sets in common relating to potential flooding and its effects.