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Protecting our flood control scheme

Opinion Piece

There is a full council meeting on Thursday. We have two public presentations, one from Mary Clarke about flooding potential from forestry planting, and one from Mathew Laing about the introduction of carbon pricing.

We have a report on the Waipaoa Water Extraction Infrastructure Policy. With new stopbanks being constructed over the existing stopbanks to accommodate for a 1-in-100-year flood event, it has become apparent that private irrigation pipelines which cross over or under stopbanks increase the risk of physical failure of the council’s flood control scheme.

There are 13 known pipelines intersecting the Waipaoa stopbanks; some have council permission and some do not. It is estimated that with full allocation of the surface water resource in the Waipaoa river, we could reach 40 pipelines in total.

A pipeline through a stopbank increases the risk of a stopbank breach during a flood event by creating a pathway which water may travel through. This can cause erosion from within the earth mass, which can result in catastrophic collapse of the stopbank.

Piping erosion along a pipeline occurred in Cyclone Bola in 1988 in which a catastrophic failure was narrowly avoided with significant emergency sandbagging.

A pipeline over the stopbank, buried in the surface, has potential to float and damage the stopbank surface during a flood event, causing erosion.

To minimise the risk of failure of the flood control scheme, the council is seeking to strictly control irrigation pipelines crossing stopbanks. Five engineered solutions have been assessed and consulted on with representatives of pipeline applicants.

Option five, a pipe over the stopbank which can be removed easily in the event of a forecast flood, is recommended and is suitable to all parties. This option is low-risk to the flood scheme, with low installation and decommissioning costs.

Irrigation is typically required for 90-120 days per annum, therefore option five allows removal of the pipe for much of the wet season. The pipeline owner will be responsible for removal, at the request of the council’s flood warning duty officer.

Some of my colleagues and I have recently had a tour of the new stopbank construction site, and it is very impressive. Some huge, high-tech machinery is moving an incredible amount of soil to form this new flood control scheme. These big tractors have laser levelling systems installed, along with the most modern technology, so the new stopbanks are much higher and wider, with absolute perfect alignment.

There is much road construction happening around the region at the moment. The good news is there is now extra government funding to assist in getting our roads back into a respectable state. A report to the council asking for approval of the variation to the existing northern road contract for an additional $9.2 million, and a variation to the existing western road contract for an additional $13.8m, will help fund this urgent work programme.

Awapuni Road has just been asphalted to a nice, smooth surface which should last for a long time. There have been many positive comments from residents along Awapuni Rd saying the noise and vibrations from trucks has greatly reduced. Some are saying it has been transformational for that area.

Our CBD is going to get an ashphalt makeover this week. It was last done 20 years ago before the year 2000 celebrations. Construction starts Thursday on the Customhouse St and Lowe St block. It will be done block by block, each block taking at least two days to complete, weather permitting.

Larry Foster