The Council will help property owners who've had frequent above-floor flooding, where their flooding has been worsened by the earthquakes, and planned flood mitigation schemes will not offer a timely reduction to their flood risk.

The Council will work with these property owners to determine the most appropriate, cost effective option for their property, which might be reducing their flood risk through localised drainage works or house raising, or the Council may offer to purchase the property. A purchase offer would be voluntary.

Flockton is the first area where this policy is being applied, having been through a long process of investigation and flood mitigation design, and understanding which properties will benefit from timely area-wide mitigations, and which won't.

In other high priority flood risk areas, once the Council’s Land Drainage Recovery Programme has completed flood risk investigations, if there are still properties at high risk that won't benefit from timely area-wide mitigation, the Council will offer the same assistance to these property owners. 

The process the Council will go through to identify properties that are eligible for this assistance

The Council will offer assistance to property owners whose homes are at risk from flooding during regular rainfall events, where the earthquakes have worsened this risk, and the home will not benefit from timely, area-wide engineering works to reduce the risk.

Step 1

house with water level rising around itHigh flood risk areas prioritised

for flood risk investigation and mitigation works – areas include Flockton/Dudley Creek, Heathcote Valley, lower Heathcote and lower Avon.

Thorough investigations into flood risk in each of these areas (or catchments) – extensive detailed modelling, floor level surveys etc.

Step 2

digger moving dirt aroundArea-wide engineering options

explored and developed explored and developed – looking to offer the most benefit to the most people.

Step 3

sketch of planners and engineersProperties within a catchment are assessed

to determine the benefits of the area-wide mitigation works.

Step 4

a house fixedMost properties

identified as benefitting from timely, area-wide mitigation.

Flockton / Dudley Creek area are at this point.

or

work being done at a propertySome high flood risk properties

have flood risk alleviated by timely area-wide mitigation works and meet criteria which includes a risk of floor level flooding in 1/10 year rainfall event (a flood that has a 10% chance of happening in every given year, so a probability of happening once in every 10 years), risk increased by the earthquakes, and not a rebuild.

Council will offer assistance to these property owners. Options will be explored on a property-specific basis, and may include localised drainage improvements, house-raising, or voluntary property purchase.


This process will take time to complete across all high risk flood areas.

The Council is fast tracking flood investigations to understand the risk, prioritise those most at risk, and develop sensible area-wide solutions that offer the most benefit, to the most people. The Council has committed large amounts of funding and resource, but it will take many years to implement the flood mitigation works across these priority areas. We will work with communities to keep them informed of what we are doing in their area, and give timeframes wherever possible.

To be eligible for the assistance:

  • The property must be residential, and within the Christchurch city urban area.
  • The habitable floor (excluding garages, laundries, sleep outs and utility areas) is at risk from a one-in-ten year flood event, (a flood that has a 10% chance of happening in any given year, so a probability of happening once in every ten years) as confirmed by Council modelling and a survey of the floor level.
  • The earthquakes have worsened the flood risk - assessed by eligibility by Council flood modelling.

The policy excludes tidal/coastal inundation flooding. Homes will not be eligible if catchment works will eliminate the risk of flooding to habitable floors in a 1-in-10 year rainfall event; or they are to be rebuilt; or foundation repairs will see the floor level raised to comply with the Building Code.

The policy will be funded from the Council's Land Drainage Recovery Programme budget.

Further information

More on what’s happening in other areas to reduce flood risk.

Intervention options

Our first consideration is reducing flood risk to the property to enable people to stay in their home. We are committed to keeping communities together wherever possible.

We will work with property owners to undertake further investigations into the flood risk for the property, and look at the viability and potential impact of localised drainage works or house raising. Voluntary property purchase offers will be explored if neither of these prove to be workable or cost effective options in reducing the flood risk to the property.

If a purchase offer was accepted, for most properties, the existing house would be demolished and the land would go back on the market. In some cases, the sale may be delayed until flood mitigation works reduce the risk. Any new house or development on the site would need to meet the floor level requirements of the Building Code and the replacement Christchurch District Plan.

So far, the Flockton area within the Dudley catchment is the only area where we have been through the process of investigation and flood mitigation design to know which properties may be eligible for this assistance.

We still have to work through the most appropriate assistance for each property. So we don't yet know how many properties in this area we may end up purchasing. 

For other areas, investigations and flood mitigation design work will need to be completed before it will be evident which properties in these areas may be eligible for assistance.

LIMs and hazard notices

The Council is legally required to note natural hazard information on a LIM, if it is known to us.

Properties at risk in a 1:200, 1:50 and 1:10 event already have this information recorded on the LIM where the Council has that information.

When the new flood model is rolled out across the city, (expected to be in the next 12 months) we will have this information for almost all of urban Christchurch across the flat lands. At that stage, 1:10 flood risk will be recorded on the LIMs of properties across all catchments of the city where that risk has been identified.

The flooding information on the LIM will change for many properties when mitigation works are carried out and reduce this risk. The works will generally reduce the depth and extent of flooding, although not for every property.

If house raising or local drainage works are done this will also appear on the LIM. If a purchase offer was made on the property, and declined, this would be noted on the LIM.

For properties marked as eligible for this policy, a hazard notice may be placed on a property when there is an application for consent under the Building Act. So if the properties are sold as an empty section there will not be a hazard notice on them. However the appropriate comment would appear on a LIM.

A new building on the affected properties may have a hazard notice depending on the depth of flooding and any on-site mitigation measures. This will be determined for each site when a building consent application is received.

One-in-ten-year rainfall event

When we talk of a 1 in 10 year flood, we are talking about the probability of a flood of that size happening.

A 1 in 10 year flood has a 10% chance of happening in any given year, so a probability of happening once in every ten years.

This is sometimes talked about as AEP, standing for ‘Annual exceedance probability’. For example, a 20 per cent AEP rainfall has a 20 per cent chance of occurring or being exceeded in any one year, so a probability of occurring once in every five years. This is often called a “1 in 5-year-flood.”

The confusing aspect is that this does not mean that a 1 in 10 year flood will happen regularly every 10 years, or only once in 10 years. In any given 10 year period, a 10 year event may occur once, twice, more, or not at all.

We cannot predict when these flood events will come in any given period, we can only predict the probability, or likelihood of how often they may come in a given period.