Flood hazard mapping
Lower Hutt is the most densely populated flood plain in New Zealand. The city has a history of flooding, and the projected effects of climate change makes flooding a complex and difficult natural hazard to manage.
To give us a clearer understanding of stormwater flood risks in Lower Hutt and better prepare for the future, Wellington Water (which manages water services for the Wellington Region’s councils) is modelling the likely impacts of extreme rainfall on the urban areas of Lower Hutt.
Computer modelling identifies areas that are affected by heavy rainfall draining from the hills into urban areas, from roofs, roads, footpaths and the water's overland paths to drains, streams and rivers. This information is converted into maps.
The computer modelling:
- is done to best practice standards,
- takes into account the forecasted impacts of climate change out to 2120 and
- is being peer reviewed by independent experts.
The resulting stormwater flood hazard maps depict flooding in 1 in 100 year and 1 in 10 year floods. They show:
- where waterways are most likely to breach their banks,
- where water moves across land during flooding and
- areas of ponding.
The work represents the most comprehensive flood hazard mapping in the city’s history. It is expected to be completed by the end of 2021. The modelling of urban Wainuiomata is the first model to be completed. This is now being followed by Stokes Valley, Petone and Alicetown. In the coming months, the Waiwhetū catchment, which includes most of the Te Awa Kairangi/Hutt River valley floor, will be completed.
The maps will help reduce the impact of flooding by giving council, the community and government agencies a better understanding of future flood events. This means we can improve infrastructure, our urban planning and our responses during extreme rainfall events.
An important part of finalising the maps is asking local people about their experiences of flooding on their properties and in their neighbourhoods. Wellington Water and council staff will be showing draft maps to residents and seeking their observations and photos of past events at public drop-in sessions to ensure the maps are as accurate as possible.
What will Council do with the information?
The main aim of this project is to protect life and property.
The information provided by the maps will be used in the review of the city's district plan, which includes the land use rules for Lower Hutt. This review is now underway. Council has a responsibility to ensure future developments avoid flood prone areas and do not make flooding risk worse for existing properties.
All councils are required to make natural hazard information public. Any property with a history of flooding, or identified as flood prone through this process, will have this information added to its Land Information Memorandum (LIM).
The flood hazard maps will provide crucial information for the forward planning of stormwater and other infrastructure in Lower Hutt. They will also be an important resource for local civil defence planning.
What happens next?
The first modelling to be completed is of urban Wainuiomata. To ensure the maps are as accurate as possible, Wellington Water and Hutt City Council held two public drop-in sessions.
This enabled residents to view the maps, ask questions about the project and provide their observations and photos of past flooding events. This information was used to fine tune the maps, which are now finalised.
A similar rocess is now underway for the rest of urban Lower Hutt. Please see venues and dates at the top of this page.
For more information on the flood hazard mapping project, see the frequently asked questions or contact Wellington Water at: firstname.lastname@example.org