Erosion puts water supply intake at risk

The erosion of banks along the Waitaki River has Waimate District Council staff weighing up options for the future of a water intake plant situated nearby.

Council water and waste manager Paul Roberts raised concerns at Tuesday’s infrastructure committee meeting.

Staff have been monitoring erosion of the Waitaki River bank, 500 metres up from the Lower Waihao intake plant, after initial erosion was noted on December 20, with peak flows hitting 1190 cubic metres per second on December 8, his report states.

‘‘Environment Canterbury has completed some erosion protection by wire roping tree trunks to the bank in an effort to reduce the amount of erosion.’’

A second warning of high flows was released before Waitangi Weekend with flows reaching 1201 cumecs on February 6, the report states.

‘‘There has been some more erosion during the last event, but currently it is not threatening the intake.

‘‘Staff have assessed the risk to the treatment plant as low, and will continue to monitor the river bank.’’

Roberts told the meeting there were plans to upgrade the plant.

‘‘It would be good if Meridian Energy and ECan were part of these discussions,’’ he said.

Council chief executive Stuart Duncan said it could be a ‘‘good idea to look at preliminary work in changing that intake’’.

Council asset group manager Dan Mitchell said ECan was aware of the problem and the council could move gear quickly if it had to.

Duncan replied ‘‘I think we have to move quickly rather than wait for an emergency’’.

Waimate District mayor Craig Rowley said he was concerned about the water intake plant.

Mitchell said an intake upgrade for Lower Waihao was in the Long Term Plan.

ECan regional lead river engineer Shaun McCracken said staff had been on site with the affected landowner monitoring the situation and had informed council staff on December 20.

Physical work started on December 20 when bulldozers and diggers diverted the bulk of the flow away from the eroding frontage, he said.

‘‘This had some success, but the sustained high river flows restricted what could be achieved, trees have been anchored into the eroding bank and a large rock has been strategically placed to provide erosion resistance.

‘‘ECan staff are continuing to monitor the situation. Further inriver channel works will occur when river levels drop to safe levels for the machinery,’’ McCracken said.