People in Wainuiomata will soon be able to view completed stormwater flood hazard maps of their suburb, as part of the most comprehensive flood mapping programme in Lower Hutt’s history.

The maps, created by Wellington Water Ltd on behalf of Hutt City Council, identify flood prone areas caused by stormwater flooding in Lower Hutt’s urban areas. Wainuiomata is the first area to be completed. And Greater Wellington Regional Council (GWRC) is now reviewing flood maps of the 22 kilometre long Wainuiomata River.

Hutt City Council Director of Environment and Sustainability Helen Oram says Lower Hutt is the most densely populated flood plain in the country with a long history of flooding. The mapping programme will help reduce the impact of flooding by giving council, government and Civil Defence a better understanding of future flood events.

"The main aim of this work is to protect lives and property," she says.

"So to build resilience in our communities, this information is vital in showing where we can safely develop land, place infrastructure and where to focus our stormwater investments."

The stormwater flood maps use computer modelling to depict what areas 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.

The draft stormwater flood maps were taken to Wainuiomata at the end of 2019 for residents to view, ask questions and share their recollections of past flooding. Around 60 people attended three open days.

This local information - which verified many flood-prone areas, blockages of drain intakes and culverts, water quality issues and the impacts of development - was used to fine-tune the maps.

GWRC is now updating its 2012 flood hazard maps of Wainuiomata River. GWRC is urging local residents to share their knowledge of past river flooding. This information is critical in getting the maps as accurate as possible.

GWRC Flood Protection Department Manager Graeme Campbell says the river’s meandering course has changed in some places. GWRC will update its flood hazard maps over the next 18 months using the latest computer modelling software and more extensive data.

Wainuiomata residents can provide their recollections of flooding of the Wainuiomata River to GWRC staff and view the completed stormwater flood hazard maps at the Wainuiomata Community Hub on:

-Wednesday 23 June, 3-5pm

-Saturday 26 June, 11am-2pm.

The stormwater flood maps depict flooding in one in 100 year flood events, or events that have a 1 per cent chance of happening in any given year, and one in ten year floods. They take into account the latest climate change projections and are peer reviewed by independent specialists.

All councils are required to make natural hazard information public. Any property shown to be at risk will have this information added to its Land Information Memorandum (LIM).

The information provided by the stormwater and river flood hazard maps will be incorporated into the review of Hutt City Council’s District Plan to ensure future developments take account of flood risks and don’t increase the risk to existing properties. This information is used to help set floor levels for house developments to ensure they will not be flooded.

In the coming months, draft stormwater flood maps of Stokes Valley, Petone, Alicetown, Moera and the Te Awa Kairangi/Hutt River valley floor will be made available for residents to view and provide their observations and photos of past flooding.

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