EROSION AT KAIRAKI

Press, Volume LXXIX, Issue 23946, 13 May 1943, Page 3

EROSION AT KAIRAKI

“ COSTLY PROTECTION ; NOT WARRANTED ” i 1 REPORT TO RIVER TRUST ) A request by owners of huts at Kai- ■ raki, the Kaiapoi Borough Council, and I the Kairaki Sailing Club, for the instal- ; lation of protection work to prevent furi ther erosion at the Kairaki settlement, was the subject of a report by the engineer (Mr H. W. Harris) to a meeting of ' the Waimakariri Riiver Trust yesterday. Mr Harris produced a plan showing the present alignment of the Wafhtakariri river along the Kairaki frontage above and below Saltwater Creek, and the position of the Kaiapoi council's 1 low stop-bank across the southern end of the Kairaki settlement. He stated that the present river-bank is, at its closest, within half a chain of the stopbank over -a stretch- of about three chains laterally. Further erosion by the river might result in the boatshed and four cottages being carried out to sea. “The only effective permanent protection," said Mr Harris, “would necessitate the driving of light piles, faced with fascines, and backed with clay filling, at, an estimated cost of £SO a chain. At present about Hi chains would be required, costing £575. This would include five chains of protection along Mclntosh's frontage (west of Saltwater Creek), which is still being eroded, to prevent the river getting behind any protection put in on the eastern side of the creek. The first four cottages on the landward side of the bank are valued at about £350, and the cost of removal of these to new positions would be £IOO. The low stop-bank could be reconstructed some five chains back (if the cottages were removed) at a cost of £65. "It is pointed out that if people will persist in erecting buildings on unstable areas, in close proximity to a river's mouth,” said Mr Harris, “it is hardly equitable that they should expect expensive works to be put In for their protection. when no beneficial result would accrue from a river control aspect. The stoppage of erosion on this frontage would be detrimental to the retention of the present northerly position of the outlet to the sea. From a flood discharge and flood level point of view, the retention of this northerly position is an aspect that should outweigh most other considerations,” Mr Harris said that unless expensive training walls were put in to divert the river .flow into the upper end of the lower cut, it was desirable that the erosion at Kairaki should continue in order that the outlet to the sea should remain in a northerly position. By putting in protection as requested, the trust would be tacitly fixing a definite northern line ' beyond which it would endeavour to prevent the river passing, and this would result in requests for increased extension and maintenance of the protection work. If the required protection were installed, added Mr Harris, it would be detrimental to flood control of the river In its lower reaches. No cheap form of protection would be effective, and the estimated cost of protection could not be justified when .weighed against the benefits that would accrue by its installation. Mr F. W. Freeman said that when the scheme was originally outlined, the river mouth was considered to be free country, through which the river would burst. Conditions had developed which could not be harnessed, and the tendency of the river to move back to Kairaki could not be stopped by groynes. “It would pay to shift the cottages further back, to give the river more play,” said Mr Freeman. "Unless we are prepared to go on with the lower cut any attempt to put in stop-banks will have the same result as former attempts." Mr C. Morgan Williams, M.P., suggested that some form of cheap protection should be tried at Kairaki as an experiment. “It is a fair assumption, if we do anything, for the residents to think we have assumed the responsibility of maintaining the north boundary of the river,” said Mr W. Mgchin. On the motion of Mr Williams, it was decided to reply to the Kaiapoi Council and the deputation, in terms of the engineer's report.