New data gathered after 20 years of research, using aerial photos, surveys, electronic flood mapping tools and other analytical techniques has greatly updated flood risk information.
Huge chunks of Masterton's housing area from Akura Road/Upper Oxford St in the north to the Homebush sewage ponds in the south would be expected to go under water in the event of a big flood.
Flooding would be especially evident in areas close to the Waipoua River.
Publication of the new data led to an open day being organised earlier this month so people who had concerns about the likely effects of a flood on their property, and the impact on property values, could discuss these with civic leaders.
More than 200 people took the opportunity to do so.
In a meeting between Mr Borren and GWRC at which the flood data was presented, the issue of including flood information on LIM reports at each of the affected Oxford St houses was discussed.