WAIMAKARIRI RIVER

Press, Volume LXXVII, Issue 23445, 27 September 1941, Page 10

WAIMAKARIRI RIVER

♦ INCREASED MARGIN AGAINST FLOODS MUCH WORK TO PROTECT CITY COMPLETED By concentrating labour and machinery on the necessary work, the Waimakariri River Trust has in the last 18 months been able to provide a considerably greater margin of safety against dangers disclosed by the record flood of February last year. Measures lor giving embankments vital in the protection of the city area the extra strength they were shown to require are virtually completed, and, except for stabilisation or the mouth and work in the lower reaches, steps for the general control of the river are approaching completion. Within the 18 months, the trust has employed men varying in numbers from 200 to 400 (largely under Scheme 13) on jobs ranging from clearing to tree-planting (an average of 500,000 trees are planted each year), and groyne and bank building. Speed has been attained on heavier aspects of the work by the use of a bulldozer, two draglines, and a fleet of trucks. One of the major operations for improved river control has been the blocking of- the cutting between Coutts Island and Kaiapoi Island, through which floodwaters last year threatened the Chaneys district. To avoid damage and delay by flooding, the work had to be undertaken in the winter. It will be finished on Tuesday, 12 weeks from the time when preliminary clearing started. To block the cutting, 37,000 cubic yards of material had to be shifted, completing the lOi chains between the stopbanks. _ Beneath this new embankment, which is GO yards wide at the base and 21 feet from the riverbed level at its highest point, clay was laid to a depth of nine feet below the shingle level to prevent seepage. The embankment is sufficient to allow a 32-feet road on top, eliminating the Coutts Island bridge, 250 yards 'down the cutting. It is expected that a repetition of the danger which (his cutting constituted last year will be eliminated, as it will in future carry only ponded water entering from the lower end, near White’s bridge. Important Improvement Another important protective improvement pver which a reporter of “The Press”' was taken yesterday by the engineer to the trust (Mr H. W. Harris) is the mile and a half long crossbank running through McLean’s and Templar’s Islands to the .head of Coutts Island. It was in this crossbank that a breach was forced last year, leading to concern lest Papanui and northern city areas should be flooded. The bank, one of those vital to the city’s protection, has been strengthened, and is being raised in height. It contains in all about 250,000 cubic yards of shingle and other material, most of which was excavated and moved by manual methods. The 40,000 cubic yards used in strengthening were entirely excavated by shovel and manual labour, unlike the Coutts Island cutting embankment, on which 85 men have been assisted by the full use of mechanical methods. Stopbanks and groynes have been substantially strengthened also atHalkett. at the upper and lower race intakes, and there is considered to be a greatly diminished risk of trouble such as that of 1868, when floodwater at the lower intake site broke through down one of the old river channels leading to the back of Fendalton. Ad* ditional groynes and tree-planting have been used to afford the bank on the southern side of the river extra protection in places where natural changes in the course of the rivers flow have demanded precautions, and where a breach would result in water going down the old south channel and flooding the Belfast, Styx, and probably Papanui afeas. , , ~ On the north side of the river, the main work in this period •has been directed towards preventing flooding of lands immediately surrounding Kaiapoi. Repairs are being made to about 14 miles of embankment (over a seven-miles length of the Kaiapoi and Cam rivers) found to be inadequate in last year’s flood. So far, eight and a half miles have been repaired, and realigned where necessary. At the junction of the Kaiapoi river with the old south branch of the Waimaka-i-iri, a nest of floodgates and culverts will in future prevent the backing-up of water. Extra fall will also be provided for the farmlands behind the Kaiapoi township.