Matata LIDAR 1m Contour Awatarariki
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If no specific structural works were constructed to control future debris flow events, then clearly many properties will remain at risk in an event similar to May 2005.
A public meeting was held on 3 November 2007 to present the options being considered for the Awatarariki catchment.
Five options, which would stop and manage future debris flow have been investigated in some detail. All options presented (drawings of each option can be found under Recommended Options) would mitigate the risk of devastation to the community should an event of similar size to 2005 occur
Of the five options, the two most cost effective were the more conventional debris embankment dam and another option called a flexi-net barrier
The embankment dam is not your traditional dam (in terms of a water retaining structure or a hydro scheme), the purpose of an embankment dam is to stop the debris, such as large boulders, from going further, but still allow water and silt to run through.
The flexi net barrier system was developed in Switzerland, where they have been used extensively. The flexi net barrier comprises of large interlocked rings, which are much stronger than ordinary steel. The concept is that during an event, the net traps the large debris behind the barrier forming a natural dam, while allowing the water and silt to flow through. The effect of the rocks piling together helps slow down and stops the larger debris following behind. Refer to photos.
In normal conditions the water from the catchment is able to flow naturally through the flexi net.
It is estimated that each structure would cost approximately $2.2-2.4 million to construct, which is considerably less than the original estimate of $3.2 million.
See the video which shows how the flexi net works in an debris event (Wmv 18.4MB).