Flood Hazard Mapping FAQ's

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Click here to view the flood hazard maps. Flood mapping is also shown in the Waipa District Plan.

Waipā District Council flood hazard modelling has been completed in four urban areas. The four areas are Te Awamutu (includes Kihikihi), Cambridge (includes Leamington), Ohaupo and Pirongia.

Absolutely. You can call 0800 924 723 to speak with our district planning team, building team or duty planner. You can also email your enquiry to info@waipadc.govt.nz and we’ll get back to you

Yes. The Waikato Regional Council also has a Waikato Regional Hazards Portal which includes river flood information for Waipā District.

This depends on how high off the ground your house is built and the depth of the water. If your house is built higher off the ground than the surrounding floodwater, any flooding impacts would be minimised. Any areas that lay below the depth of the surrounding water may be affected by floodwater. Council are contacting property owners where habitable floor levels may be at risk of flooding during a 1 in 100 year event. We encourage you to get in touch with us to discuss flooding on your property as well as any floor level data for your property. You can also request this via our freephone number, 0800 924 723 or send an email to info@waipadc.govt.nz

No. However, flood hazard mapping information may affect changes to your property such as new subdivision, use and development (such as new buildings and extensions to existing buildings). We encourage you to get in touch with us to discuss flooding on your property as well as any floor level data for your property. You can also request this via our freephone number, 0800 924 723 or send an email to info@waipadc.govt.nz

If part of your property is affected by a flood hazard this means that areas of your garden or non-habitable floors (such as garages and sheds) may be impacted by flooding. Flood hazard mapping information on your property may affect changes to your property such as new subdivision, use and development (such as new buildings and extensions to existing buildings). We encourage you to get in touch with us to discuss flooding on your property as well as any floor level data for your property. You can also request this via our freephone number, 0800 924 723 or send an email to info@waipadc.govt.nz

No. While it indicates that a property is not subject to an identified flood hazard, this does not mean it is totally free of any risk of flooding. As Council’s Flood Viewer shows the best available flood hazard information for catchments that have been modelled, this information is based on computer modelling which relies on data inputs and assumptions that have been captured at a point in time (currently 2019) - there will always be some uncertainty associated with modelling.

Flood hazard mapping is only for an event that has a 1 percent risk of occurring or being exceeded in any given year (a 1 in 100 year flood event) . A larger flood event may have wider impacts and be to a greater depth than that shown on the flood layers.

The District Plan identifies flood hazard areas and has objectives, policies and rules specific to each flood hazard area. These provisions set out the requirements to be met, whether resource consent is required, and the criteria to be used to assess whether to grant or decline resource consent.

New subdivision, land use and development should avoid areas subject to flood hazards, if the level of risk is unacceptable. Please check the relevant section in the Waipa District Plan for more information.

A property that is shown on the flood viewer as having a flood hazard but not on the District Plan would be due to new information becoming available post the District Plan becoming operational.

Under the Resource Management Act 1991 (the RMA), Council may refuse subdivision consent, or may grant a subdivision consent subject to conditions, if it considers there is a significant risk from natural hazards. Council may include a condition of the resource consent that provision be made for protection of any land against natural hazards from any source. In the case of land not forming part of the subdivision, this means natural hazards arising or likely to arise from subdividing the land.

The RMA states the management of significant risks from natural hazards is a matter of national importance that Council must recognise and provide for.

Under the RMA, when considering an application for a resource consent, Council must have regard to:

(a) Any actual and potential effects on the environment of allowing the activity; and

(b) Any relevant provisions of a regional policy statement, proposed regional policy statement, a plan, or proposed plan.

Policy 13.2 of the Regional Policy Statement is to manage subdivision, use and development to reduce risks from natural hazards. Section 15 of the Waipa District Plan and related policies aim to manage activities to avoid or mitigate adverse effects on, and minimise risk to, people, property and the environment from natural hazards. Consequently, even though flood hazard maps are not yet included in the District Plan, regard can be had to them when considering a resource consent application for an activity in that area.

Building consent applications for sites that are subject to a flood hazard will need to demonstrate that the proposed buildings and site work will protect the outfalls of drainage systems and safeguard people from injury or illness, and other property from damage, caused by surface water. Refer to ”Building Consents” for this information.

As this differs between insurance providers, you should discuss this with your individual insurer. Insurance policies often include a clause requiring policy holders to advise the insurer of any new information about natural hazards on an insured property. This information is available to the public, including insurance companies, on Council’s Flood Viewer.

Council cannot advise you about the effect flood hazard information may have on insurance premiums or the ability to obtain insurance.

Property valuations reflect sales evidence up to the valuation date. Over time, property sales evidence will reveal any effect the flood hazard information has on property values.

Council cannot make any comment about whether or how flood hazard information affects property values. Council is required to produce the best available flood information and make it available to the public, including those considering buying a property in the area.

Councils are responsible for controlling any actual or potential effects of the use, development, or protection of land to avoid or mitigate natural hazards through the Resource Management Act 1991. In addition, Waipā District Council’s Comprehensive Stormwater Discharge Consent requires Council to avoid as far as practicable and otherwise minimise adverse flooding of land, property and stormwater receiving water bodies. Mapping flood hazards helps Council fulfil these requirements.

Council requires a new stormwater comprehensive discharge consent in 2022 and a requirement of this is to provide Catchment Management Plans. To develop these, flood hazard maps must be developed.

Council undertakes dynamic 1D and 2D (computer) modelling which takes into account the landuse, terrain, detailed survey information and information collected about the stormwater assets. This information has been sourced from 2019. The modelling adopts several standard assumptions around climate, rainfall, ground information and runoff.

The model has been independently peer review which means it is deemed accurate enough to be made available to the public through Council’s Flood Viewer.

The District plan is reviewed periodically on a needs basis. At the present time, the Flood Hazard data in the viewer is complementary to that already shown in the District Plan.

Where new flood hazard maps overlap areas already identified through flood hazard mapping in the District Plan, the new maps will represent the best available information.

Feedback about the flood maps will be considered and may result in changes to a flood hazard map. If you wish to discuss this further, please call 0800 924 723 or email info@waipadc.govt.nz

Yes, flood hazard maps will be updated as new information becomes available. As modelling can be a lengthy exercise, this may be infrequent due to the length of time and cost involved.

Changes to the flood viewer will only be made once verified flood data is available and it has been modelled accurately. Council will communicate changes as appropriate through various public notification pathways.

Along with rivers or streams, flooding may also occur from:

1. Pipe network overloading or present overland flow paths.

2. Rain falling and flowing over land (for example, water flowing downhill, through channels and gullies).

3. Ponding in localised depressions or low points.

Some ground may appear to be flat, however it is often very difficult to see gradual or subtle changes in the surface that would create low points or overland flow paths on a property.

The 1-in-100-year flood results are based on an extreme rainfall event that, on average, would only occur once every 100 years. Such an event has a 1% likelihood of occurring once or more in any given year.

The 1-in-100-year event is required by the Waikato Regional Policy Statement (20 May 2016) under the Implementation method 13.2.6 (a).

To model a 1-in-100-year event, Council uses a flood event computer model as there is insufficient historic and observational information to define the extent of land affected. The quality of the modelling result relies on the quality of the information used to build the model. To start with, we divide the district into catchments. Each catchment collects rainfall which flows downhill to its end point or outlet. The factors taken into consideration include:

• The shape of the land (topography). Contours on the land represent the terrain. Water drains downhill, therefore it will drain in the direction where contours are found within the land. This is provided from LiDAR (Light Detection and Ranging) data. Flood hazard mapping completed prior to 2019 is based on LiDAR data obtained at the end of 2008. New LiDAR data was received for the district in January 2020.
• The amount of rain that falls. A 1-in-100-year storm event is made up of rainfall volume, intensity (mm/hr) and duration. We have considered flood modelling data with and without the effects of climate change on rainfall depth and duration.
• The ground surface conditions. The type of ground the rain falls on affects how much water is absorbed and how fast it flows over land. For example, more rainwater is absorbed in grassier areas than on concrete, and rainwater flows faster over concrete than grass.
• The capacity of stormwater infrastructure, such as culverts, are also included in the model.

The modelling tells which parts of the catchment are likely to be covered by floodwaters, the depth of floodwaters, and how fast it is likely to flow.

While the words Hazard and Risk are related, they are different. Let’s explain further. In this instance, flood water is the hazard. Modelling identifies hazards only.

The risk is the effects of the hazard combined with the impact it may have on people, property and the environment.

Along with rivers or streams, flooding may also occur from pipe network blockages or overloading. The flood hazard areas that result from rain falling and flowing away do so over land (for example, water flowing downhill, through channels and gullies), or ponding in localised depressions or low points. Some ground may appear to be flat, however it is often very difficult to see gradual or subtle changes in the surface that would create low points or overland flow paths on a property.

No. Whenever stormwater runoff exceeds the drainage capacity of the stormwater network, ponding and/or overland flow is expected. It would be extremely expensive to provide a drainage network that avoids all ponding and overland flow. Within existing development Council plans to maintain the following levels of service for the stormwater system: 1-in-2-year event for residential, 1-in-5-year event for commercial, and 1-in-10-year event for industrial1 . On the other hand, the Regional Infrastructure Technical Specifications (the RITS) requires all new primary stormwater systems2 to be designed for the 1-in-10-year rainfall event for residential, industrial and commercial areas.

Council considers all verified, currently available flood information and modelling when managing its assets and planning future stormwater network improvements. Decisions on the priority and timing of stormwater upgrade spending are made via Council’s Annual Plan and 10-Year Plan processes.

Council will use the flood information in the District Plan and on the web viewer to manage new subdivision, development and use of land to help mitigate future flood risk.

We recommend you to seek professional advice about ways you can reduce the risk of flood damage to your property. Anything you do must not however worsen the occurrence of flooding of any other property.