Flaxton flood protection scheme a top priority

Press, 16 April 1982, Page 18

Flaxton flood protection scheme a top priority

A 51 million flood protection scheme for the low-lying Flaxton and Ohoka swamp areas of North Canterbury could increase stocking rates on nearby farmland by about 27 per cent. A start on the scheme by the North Canterbury Catchment Board is dependent on tbe amount of money allocated by the Government for 1982-83 for new water and

soil projects. But the scheme, which would improve drainage on 23 farms, is one of 14 first

priority schemes proposed by the Soil Conservation and Rivers Control Council for a start this financial year if finances allow (see accompanying story). The district, just north of the Waimakariri River and west of Kaiapoi, is renowned for flooding with the lowlying areas which can be seen from the Skew Bridge over the Main Drain, being under water three or four times a year. The whole ...$1 million scheme as defined by the -I catchment board includes the Cam River and its tributaries, the drainage networks of the Flaxton and Ohoka swamps, and the Cost Main Drain and its contributing side drains. The Main Drain was first cut in the 1860 s and the surrounding swampland at Flaxton and Ohoka dropped one or two metres. It has all been farmed since that time. The Cust River, which has an upper catchment area around Oxford of 80 square kilometres, once terminated in the swamps but is now conveyed by the Main Drain,

along with the water from the side drains south of Rangiora, to the Kaiapoi River.

The Cam River, north of the Main Drain and the Flaxton area, overflows in high flood conditions and the water, after passing over a large area of gently sloping land, ends up in the low-lying swampy areas surrounding the Main Drain, particularly around the Skew Bridge. High water levels in the Cust River also prevent the inflow of flood water from its tributaries, resulting in more water ponding in the swamps and backing up along the most easterly of • the seven side drains which go into the Main Drain. The Cust River, particularly in the lower reaches where it becomes the Main Drain, is elevated by banking which results in flood water levels being higher than adjacent ground levels, according to a report prepared by the North Canterbury Catch, ment Board. The threat of a breakout from the channel was very real and the consequences

would eclipse the problems which already existed, said the report. The inflow of foreign water from overflows compounded the difficulty of removing ponded water from the swamps. The scheme is expected to allow a further 1534 hectares of land to be farmed in a more productive manner. Ail but 60 hectares of this land is grazed because of the danger of flooding.

Au extra 5600 stock units could be carried by farmers when the scheme was completed, according to an economic survey done by the Ministp' of Agriculture and Fisheries. In addition, an extra 140 hectares would be used for cropping. Flooding has not been a serious problem in tbe last two years because of low rainfall, according to a local farmer. In normal seasons, paddocks could be flooded three or four times and pasture could be under water for three weeks to a month. On one occasion 25 hectares of crop was submerged under water and was a total loss.

Drainage would allow farmers to plan their farming operations with confidence. Good quality pasture could be established and cropping would be an alternative.

Flooding cost an estimated $7OOO each year in stock losses and $3OOO in damage to fences, according to the M.A.F. The annual cost of oversowing drowned pasture was $15,500.

The scheme involves upgrading the upstream section of the Cam River near Rangiora and improving the drainage network of the Flaxton and Ohoka swamps. Two pumping stations will be installed, one at the Boys Road floodgate and the other on the Cust Main Drain near to the discharge point into the Kaiapoi River. The Cust Main Drain will be widened from No. 6 drain to the Kaiapoi River and sections of No. 6 and No. 7 drains will be upgraded. Provision will be made for the regular removal of gravel from the Main Drain to allow the level of the bed to remain constant.