Matata LIDAR 1m Contour Waitepuru
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If no specific structural works were constructed to control debris flow events, then many properties will remain at risk in a similar event.
A debris flow bund is to be constructed on the fan head of the Waitepuru Stream upstream of the railway. The bund height will be up to approximately 5 m to divert the design debris flow. In conjunction with this bund will be an engineered solution to return the Waitepuru lower flood flows (up to Q5 – 5 year flood level event) back through the township. This stream works will include the increasing the improving erosion protection and slope stability (reinforcing the stream where there are identified weaknesses), and increasing culvert capacity where appropriate.
Debris flows during the May 2005 event were substantially contained upstream of the railway embankment. As part of future mitigation works an area for deposition will be excavated to maximise storage potential behind this embankment.
Debris bunds will be constructed to prevent lateral movement of any debris flow into adjacent properties and maximize the developed land area protected by the works. It may be necessary to raise the level of Manawahe Road to lower the risk to properties to the west of Manawahe Road. This could be accomplished in conjunction with low retaining structures built along Manawahe Road and the railway to increase the deposition area freeboard. Capturing material in this location will reduce the deposition risk to downstream properties that were significantly affected in 2005.
It is likely that access to Manawahe Road from the town would be severed as a result of debris control works.