Culvert blocked month before

LETTER

Re: Major erosion caused blowouts, Sept 5 column.

Yes, I was there Deane, just before the blowout occurred, so I feel compelled to make a comment. I am talking about the major washout at the headwaters of the Tikiwhata Stream.

I first tramped down the Tikiwhata Stream in December 2008. At that time, the entrance to the large square culvert under the railway was marked by a vertical iron chamber with slots cut in the side, and a wide open top approximately 2 metres in diameter, which allowed water to enter. We were able to climb down this shaft, walk along the culvert and exit at the other end.

When I again visited this location in early February 2012, the iron chamber was completely covered by debris. Water was slowly making its way down through cracks but the culvert was completely impassable. You could see a tide-mark of flotsam where water had previously reached partly up the side of the embankment before slowly receding. The capacity of the unrestricted culvert was large, given its wide opening and slotted sides. With that amount of blockage, the gully upstream of the culvert would have filled very quickly in any significant rain event.

The question that needs to be asked is, is there any record of that significant blockage being cleared between early February and approximately a month later when a massive blowout swept away the railway and left a large chasm?

If not, then one can only conclude that lack of maintenance was responsible for this failure.

Paul Ericson

Re: Major erosion caused blowouts, Sept 5 column.

Yes, I was there Deane, just before the blowout occurred, so I feel compelled to make a comment. I am talking about the major washout at the headwaters of the Tikiwhata Stream.

I first tramped down the Tikiwhata Stream in December 2008. At that time, the entrance to the large square culvert under the railway was marked by a vertical iron chamber with slots cut in the side, and a wide open top approximately 2 metres in diameter, which allowed water to enter. We were able to climb down this shaft, walk along the culvert and exit at the other end.

When I again visited this location in early February 2012, the iron chamber was completely covered by debris. Water was slowly making its way down through cracks but the culvert was completely impassable. You could see a tide-mark of flotsam where water had previously reached partly up the side of the embankment before slowly receding. The capacity of the unrestricted culvert was large, given its wide opening and slotted sides. With that amount of blockage, the gully upstream of the culvert would have filled very quickly in any significant rain event.

The question that needs to be asked is, is there any record of that significant blockage being cleared between early February and approximately a month later when a massive blowout swept away the railway and left a large chasm?

If not, then one can only conclude that lack of maintenance was responsible for this failure.

Paul Ericson

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