New flood modelling shows less impact on Masterton

New research has found a large and infrequent flood is likely to have less impact on Masterton than previously thought.

Masterton District and the Greater Wellington Regional Councils have collaborated on draft maps which indicate the likely spread of flooding in the urban area. The focus has been on modelling a 1% annual chance/1 in 100 year flood - that is, a flood that has a 1 per cent chance of occurring in any given year.

The maps, which are still in draft stage, show some areas of the Masterton urban area are likely to experience flooding should a 1% annual chance flood occur. These areas are mainly around Oxford Street and parts of Akura Road.

Overall, the spread of flooding is greatly reduced from predictions released in 2014.

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 flood spreads into larger areas of urban Masterton including the central business district with most of the flooding likely to be 15-30cm.

Chair of the Te Kāuru Upper Ruamāhanga River Floodplain Management Subcommittee, Bob Francis, said better information had improved the accuracy of the modelling.

"Part of the role of local authorities is to work with communities to protect them from the effects of hazards, including flooding. To do this, we need to understand the likely hazard a flood will bring," Francis said.

"Gaining this understanding relies on modellers having the best information available, including local knowledge. The next step is to put affordable and acceptable flood management in place and ensure inappropriate development doesn't create new problems."

Masterton District Deputy Mayor Graham McClymont is also a member of the Te Kāuru Upper Ruamāhanga River Floodplain Management Subcommittee.

McClymont said the subcommittee had made positive progress and it was an important milestone being able to release updated draft maps.

"This research has important and significant ramifications for the people of Masterton - I'm glad we have reached a point where we have a more accurate picture of the likely flood spread across Masterton," McClymont said.

"Our focus should now be on how we mitigate the flooding impacts for areas likely to be affected. I'm looking forward to the Masterton community providing input as to what mitigation options are preferred."

The maps are still in draft stage, pending an independent audit. The audit is expected to be carried out over the next few months with the maps confirmed as final in early 2019.

The maps will support the development of the Te Kāuru Upper Ruamāhanga Flood Plain Management Plan.