Halswell flooding difficult to treat

Press, 22 January 1982, Page 9

Halswell flooding difficult to treat

The best way of dealing with flooding problems in the Baisweil River catchment would be to produce an overall scheme for the river. Lake Ellesmere and the sur-

rounding farm areas. This was the opinion of several speakers in a panel discussion on land use in the Halswell River's catchment area held at Lincoln recently. The New Zealand Institute of Agricultural Science organised the discussion, which was held after a bus trip around the catchment area.

A number of alternative schemes to deal with the serious surface flooding, which affects about 1000 hectares of farmland and housing in the river's catchment area, were proposed by the North Canterbury Catchment Board in September. 1978. However, subsidy money from the Government was not made available because a survey by the Economics Division of’ the Ministry of Agriculture showed the scheme would not provide an internal rate of return of at least 10 per cent. This is the minimum figure set by Treasury.

The member of the divi

sion who compiled the report. Mr S. M. Hadfield, said his evaluation was done from the national viewpoint. Basically the scheme would, at a cost of about S2M. provide a system of clearing surface flooding, which otherwise lay about for a number of days after heavy rain.

He stressed that the proposed plans for the catchment were not for drainage but to facilitate water runoff.

The gains from the scheme would be fewer stock losses

and a reduced amount of damage to fences and buildings.

It would also open up horticultural possibilities and make more land available for urban development.

But the internal rate of return, as determined about two years ago. would onl}' be seven per cent and that figure was considered optimistic. Mr Hadfield said.

He said the scheme would cost about $350 a stock unit. Other schemes which had been considered by the Government during the last two years had been considerably cheaper. He said if the water runoff was improved this would allow for the development of more industrial and residential land in Halswell and Hornbv. but it was likely the development of residential land would occur anyway. None of the farmers surveyed during his divisions investigations had indicated an interest in horticultural production, but that would have changed and there would be some interest now. Mr Hadfield said. Mr W. P. Studholme, of the Selwyn Plantation Board, said about two-thirds of the water in the Halswell catchment came from the surrounding hills.

The strategic planting ot trees could be very useful for reducing peak flows because of water absorption and improved erosion control. Tree planting would be profitable. It would give a 14 to 17 per cent internal rate of return and gross about $7500 to $lO,OOO a hectare after 25 years.

He suggested that most farmers would be able to plant out about 10 per cent of their farms without seriously reducing stock numbers.

Mr B. Dwyer, deputy chief engineer for the North Canterbury Catchment Board, said the board had already established a drainage scheme for the Halswell catchment — what was needed was better flood protection.

The board had a working group looking at several matters in the area, including improving the drainage of the whole area.

Installing a permanent outlet from Lake Ellesmere would cost a lot of money, but would probably be very useful in improving the drainage of the surrounding area.

Mr Dwyer said farmers needed the coniidence to do on-farm drainage work. A system was there to connect farm drainage to and this would help over-all drainage in the catchment, he said. Some of the comments made at the seminar underlined the point that farmers were not aware of the benefits they could gain from improved drainage and flood protection. One farmer said the benefit from improved flood water run-off would be long term and farmers 100 years hence would still be appreciating the work done.