Coastline to get ‘mattress’ protection work


Coastal protection work from just north of Oamaru Harbour up to Oamaru Creek got the green light to go ahead at last week’s meeting of the Waitaki District Council.

Up to $800,000 has been budgeted for the work.

This coastline has been subject to erosion at an average rate of about half a metre a year, with potential short-term erosion of up to 15m from a single storm event.

In a report to councillors, it was outlined that if this rate of erosion was left unchecked, it would threaten the penguin nesting area and the recently capped contaminated land site.

The recommended option involves placing a ‘mattress’ over the erosion prone area. The mattress is a filled protective covering that is placed at a gentle slope matching the adjacent land. A significant amount of shingle beach material is placed on top.

The mattress creates a gentle sloping beachfront that allows the energy of the waves to run up the beach rather than being reflected back.

Mayor Gary Kircher said he believed it to be an acceptable solution within the allocated budget.

Councillors voiced their concerns, firstly about whether this type of coastal protection had been used in New Zealand before and with what results, and secondly about the frequency of bad weather events and its effect on the mattress.

It was noted in a memorandum from council management that the mattress may be exposed every five-to-seven years following severe storms. Estimates to place new shingle over the mattress sit at about $50,000.

Mr Kircher said it was decided that this was still the most cost-effective option.


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