Natural Hazards

 

Te Aroha FloodCase Study

Te Aroha Flood, 1985*

 

Te Aroha experienced severe flooding on 17 February 1985 when floodwaters and debris inundated the township. The flooding occurred after a period of high intensity rainfall in the Kaimai-Mamaku Range catchment area behind Te Aroha.

 

Prior to the flood event, it had been very dry with no rainfall for the previous three weeks. The ground was very dry and cracking had allowed water to infiltrate and ‘grease’ the slopes making them very unstable. Steady rain for 24 hours prior to the flooding had saturated the ground increasing its weight on underlying slopes.

 

After the initial period of rain, an unpredicted 600mm fell between 6pm and 6am on the 16/17 February. StrongTe Aroha Flood winds which characterise storms in the Te Aroha area added to the potential hazard by uprooting large trees on the upper slopes of the catchment.

 

As the level of the streams draining out of the catchment, through Te Aroha and into the Waihou River increased, the trees felled by the strong winds acted as bulldozers and pushed tonnes of mud and debris down the overflowing streams and through the township.

 

In 1988 Council commissioned a flood hazard assessment of Te Aroha which made a number of suggestions for reducing the flood hazard risk. These included additional drainage works and a recommendation to implement some planning controls on development in flood hazard areas. The district plan identifies areas of Te Aroha that are subject to flood hazard and has developed standards for these areas such as minimum height for floors, to mitigate adverse effects on economic well-being and life.

Te Aroha Flood

*Howarth, Merle, 1986: Town in Trouble, Te Aroha, Thames