Tens of thousands of Wairarapa homes at risk from 100-year flood
With the ground sodden after months of high rainfall, now information has shown tens of thousands could be affected across Wairarapa in a severe flood. The Greater Wellington Regional Flood Exposure Assessment obtained from Greater Wellington Regional Council under official information legislation has revealed more than 43,000 people and almost 18,000 properties, in Masterton, Carterton and South Wairarapa could be affected in a one-in-a-hundred-year flooding event. Wairarapa has been hit by major flooding in the past, notably in 1947 and 1976. More recently, Cyclone Gabrielle tore through the small settlement of Tinui earlier this year, causing widespread damage. The report showed 700 commercial properties were at currently risk; 100 in Carterton, 400 in Masterton and 200 in South Wairarapa. Additionally, 17,100 residential properties were at risk; 3,000 in Carterton, 9,000 in Masterton and 5,100 in South Wairarapa. The risk was expected to increase, with numbers rising by 2110. Lian Butcher, Greater Wellington Regional Council group manager, environment, said modelling showed all except one of the main towns across the region were likely to be significantly impacted. We anticipate the major towns of Masterton, Carterton, Greytown, and Featherston to be most at risk from major river flooding. We also anticipate widespread flooding of rural land from the Ruamahanga, particularly in the Lower Valley, Butcher said. While the town of Martinborough itself was not specifically mentioned, rural South Wairarapa was. The report applied population projections from Statistics New Zealand to compare the number of people exposed to flooding now and by 2110 in an undefended scenario. It assessed flood risk across the wider Wellington region, with territorial authorities analysed separately. In all instances the undefended scenario has been considered. This is considered a true flood exposure as continued investment is require to maintain defences and schemes, it said. When applying the population projections provided by Stats NZ, the number of people exposed to flooding across the Wellington Region by 2110 in the undefended scenario could increase further to approximately 260,000. The Waohine catchment, primarily located in Carterton District, was assessed with the greatest proportion of people exposed to flooding at 64%. Up to 7800 people could be affected in Carterton, 23,000 in Masterton and 12,600 in South Wairarapa. By 2110 this was estimated to rise to 10,700 in Carterton, 28,400 in Masterton and 13,400 in South Wairarapa. By 2110, both the South Wairarapa and Masterton districts have nearly 50% of all buildings exposed to flooding, [approximately 6,100 and 10,900 respectively]. This represents approximately 60% of the commercial buildings in South Wairarapa and 70% of commercial buildings for Masterton. Both councils have nearly 50% of all residential buildings exposed to flooding by 2110, the report said. The risk assessed a 100-year flood means that there is a 1% chance this type of flood could occur in a given year, possibly even multiple times. Butcher explained GWRC managed risk from major rivers across the region, and communities were also likely to be at risk from surface water/stormwater flooding managed by the district councils. Coastal flooding was a further hazard. Climate change was expected to worsen the current risk. The impacts of climate change do not result in any new catchments having significant increases in flood exposure. Climate change is therefore expected to exacerbate issues that are already being experienced across the region, the report said. Public Interest Journalism funded through NZ On Air