Te Kāuru Upper Ruamāhanga Floodplain Management
Masterton is a river town with the Waipoua running through our urban area. It’s an important natural asset that gives us identity and connection to our environment. It also means Masterton faces a risk of flooding.
A key role of local authorities is to work with communities to protect them from the effects of hazards including flooding. To do this, we all need to understand the flood risk, put affordable and acceptable flood protection in place and ensure inappropriate development doesn’t create new problems.
In 2014, Greater Wellington Regional Council shared its understanding of the spread of flooding across urban Masterton in one of these 1% annual chance floods.
Thanks to access to better information, technology and local knowledge we now have a more accurate picture of what a significant and infrequent flood would look like in Masterton. The modelling has been revised and updated in collaboration with Masterton District Council.
The new modelling now available shows a future 1% annual chance flood is likely to have less impact on the Masterton urban area than initially thought. The modelling is still in draft stage pending an independent audit.
Impact on Masterton
The maps, which are still in draft stage, show some areas of the Masterton urban area are likely to experience flooding in a 1% annual chance flood. This is mainly around Oxford Street and areas bordering Akura Road. The depth of flooding varies depending on the scenario being considered; most is likely to be below 30cm but some areas experience flooding up to two metres.
The spread of flooding increases when other potential scenarios are factored in. For example, assuming a greater amount of debris collects on the railway bridge, assuming greater river flows, or a “rougher” river channel.
Work has also been done to model what a flood would look like in the future (2090) with the impacts of climate change factored in. In this scenario the flooding spreads across the urban area to the south west of the Waipoua River, including the central business district. However, this flood spread is smaller than what was initially thought in 2014.