The Waikato District Council is expected to this week advise the owners of around 920 Tamahere properties of the re-calculated flood risk of their land.
The update and amendment of a study into the drainage patterns of the Tamahere Country Living Zone follows a release of information in July last year that proved very controversial.
“The letters being sent to property owners within the Tamahere Country Living Zone this week is the culmination of what is best described as a challenging process,” Tamahere councillor Wally Hayes told Tamahere Forum.
“They represent the final stage in the development of the Stormwater Catchment Management Plan model, and are a further opportunity for ratepayers to double check the maps to see if the model has taken into account drainage on or around their property.
“The upgrade of the model has, in some instances, produced significantly different results to the initial version.”
The original study used outdated aerial contour mapping data known as LiDAR (Light Detection and Ranging), dating from late 2007 and early 2008. The latest study uses LiDAR data from late 2012.
The updated study also includes further information on the stormwater infrastructure system and there has been a change to the modelling methodology to provide a more accurate picture of the potential impact of ponding.
“This is mainly due to both a change of method around how the NIWA weather numbers were applied to the model, which now more accurately reflects the reality of the situation,” Hayes said. “It is also because the council has checked to see if the drainage assets actually in the ground were accounted for accurately in the model.”
The council should never have publicly released the initial results from the model in July 2012 without validation of the model in the first instance, Hayes said.
“These models will never be a perfect science as there are many assumptions applied to them. However, the facts on the ground need to be checked against the model to see if they have been taken into account, before releasing the information onto property files.
“Councils should not be able to place unvalidated information on to property files and the integrity of information linked to property files should be of the highest standard,” he said.
Hayes believes the district council was panicked into releasing the early information, which occurred around the same time as the Hamilton City Council caused similar outrage in Hamilton by sending “vague” letters to residents warning of possible flood risks to their properties.