Sea eroding farmland at river mouth



Glenavy coastal dairy farmer Robert Smith is losing part of his farm to erosion as the sea pounds in through the Waitaki River mouth, which has shifted north by almost 3km - its furthest move for about three decades.

And there is nothing Environment Canterbury - the Christchurch-based regional council responsible for the river - can do until it can get a resource consent to create a new mouth.

In the meantime, Mr Smith estimates he has lost about half a hectare of land from the coastal 5km strip his farm occupies between Glenavy and Morven.

Over the past six months, the river mouth has shifted progressively north, flowing through a dead arm lagoon. At its furthest, it has been about 3km north of where it usually is, although it has gradually started shifting south again.

The shift has been caused by stable, lower flows in the Waitaki without any major floods to keep the mouth open directly at the end of the river.

Yesterday, it had moved south again by about 500m, flowing through a gap of about 400m.

This has left the protective shingle bar in the lagoon and the 10-metre high cliffs exposed to heavy sea swells or waves pounding into the shore.

Mr Smith said yesterday the erosion was not threatening any buildings on his property, but he had removed a portion of a fence along the coastal cliff.

The fence will not be put back until he knows what is happening to the mouth.
‘‘I don't want to lose a new fence to the sea. Every day I'm losing a bit more of the farm,'' he said.

The erosion has removed a big boulder bank which used to sit between the lagoon and the bottom of the cliff. The sea eats in to the cliff face, particularly during prevailing northeast swells.

Mr Smith has been on the Glenavy farm for 14 years, since moving down from the North island. In that time, he said he had never seen the river mouth that far north.
Others had told him the only time they could recall a new mouth being opened after it had shifted dramatically was in the former Waitaki Catchment Commission days - prior to 1989.

Environment Canterbury senior engineering officer Bruce Scarlett, who is based in Timaru, said his council was aware of the problem and had been keeping watch on the river mouth, visiting it last week.

However, he said that until the council had a resource consent which would enable it to open a new river mouth where it should be, nothing could be done.

The situation did not qualify as emergency work. The council had applied to itself for a ‘‘global consent'' which would give it the right to do work on the mouths of major rivers throughout its region. That would include the Waitaki, he said.

Mr Scarlett said the new northern river mouth was causing ‘‘a lot of erosion'' because its width let seas into the cliff base.

‘‘It has been further north, but now appears to be heading south again,'' Mr Scarlett added.


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