Papamoa East - A Humdinger of Catchment

After the flood events of 2013 Tauranga City Council embarked on a programme of 2D modelling and flood hazard mapping of the whole city. This was to enable Council to determine problem areas and inform the most cost effective way to mitigate them.

Papamoa East was an area which experienced property flooding in 2013. It is also an area designated for significant urban growth. Development of a model for this catchment by Aurecon has therefore been made a priority by Council.

The aim of this paper is to be of interest not only to modellers but to all professionals who use model outputs as a tool. This paper describes some of the issues in developing models – focusing on Papamoa East as an example. This will allow users of model outputs to understand both the advantages and limitations of the methods employed including rain on grid.

Papamoa East is a real humdinger of a catchment and has a little bit of everything. This includes an extensive stormwater reticulation network but also a significant open channel. The open channel is also unusual in that it is basically flat with limited ocean outfalls and currently acts as a bathtub with base levels often controlled by the groundwater table.

In the future the catchment is to increase in size by about 30% with the major urban hub of Wairakei to be built on greenfield land that is to be drained into the catchment. As part of this development the bathtub drain is to given a high level overflow to the Kaituna River. How relevant is model validation when the catchment is to change this much?