The Hutt River/Te Awakairangi burst its banks in 1840, forcing the fledgling European settlement at Petone to move to Thorndon soon after its establishment. In 1858, a flash flood took the lives of 12 settlers. A succession of floods prompted the first construction of stop banks on the river in 1898, the year the entire valley floor was inundated and two people died.
More recently in 1976, 153 mm of rain in 24 hours caused $167.5 million of damage in today’s money, with Stokes Valley being particularly hard hit. In Petone, workers had to be rescued from a factory roof by helicopter as around 20 cars floated under the nearby motorway over-bridge.
In 2004, extreme rainfall caused the Waiwhetu Stream to breach its banks driving 50 households from their homes. The Wainuiomata River hit record levels. The roads to Wainuiomata and Eastbourne were blocked, and Lower Hutt was effectively cut off with the closure of state highways one and two and train services were halted. Surgeries at Hutt hospital were cancelled or postponed. Two people drowned in Wellington Harbour.
Today, Lower Hutt is the most densely populated flood plain in New Zealand. While hazard planning, stop banks and other engineering initiatives have dramatically improved flood management, the risk remains, aggravated by the projected effects of climate change.
Wellington Water, which provides drinking water, waste water and storm water services to the Wellington Region on behalf of its councils, is modelling flood hazards across urban Lower Hutt.
The resulting flood hazard maps depict flooding in one in 100 year and one 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 takes into account the projected impacts of climate change out to 2120, including a sea level rise of one metre and an increase in rainfall intensity and volume of 20 per cent.
This work will be completed 2021. The first modelling to be finalised is of urban Wainuiomata. The resulting maps will go out to the Wainuiomata community shortly for feedback.
Information from the maps will be detailed in the District Plan to ensure future developments take account of flood risks and don’t increase the risk to existing properties.
Hutt City Council Chief Executive Jo Miller says the maps will be critical to the management of flood risk in Lower Hutt, improving the city’s resilience and helping determine priorities for infrastructure investment.
“It’s also data that’s vital as Lower Hutt plans for its long-term future. Managing the impacts of climate change is a central aspect of this so this information will be invaluable as we begin discussions with the community on climate change mitigation and adaption over the coming year.
Next week, Wellington Water staff will take the maps to Wainuiomata to get the community’s perspectives of past flooding.
Ben Fountain Chief Advisor Stormwater for Wellington Water says the feedback from Wainuiomata residents is an important part of finalising the maps.
“Ensuring the maps are as accurate as possible relies on local people with local knowledge telling us where water flowed or settled in their neighbourhoods and properties during past flooding events.”
Public drop-in sessions where people can view the maps, talk to Wellington Water staff and provide their observations will be held at the Wainuiomata Intermediate School hall on:
- Thursday 5 December 6pm-8pm
- Saturday 7 December 2pm-4pm.