THE WAIMAKARIRI.

Press, Volume LVI, Issue 16854, 7 June 1920, Page 6

THE WAIMAKARIRI.

FLOOD DANGER PERMANENT.

Past experienco and the opinion of experts seem to support the proposition that tho body charged with the duty of protection from floods from the Waimakariri river should have control and should concern itself -with the protection of areas on the north as well as the south bank of the river. The Board at present in existence —the South "VVaimakariri River Board —concerns itself practically with the protection of tho city of Christchurch from the effects of floods in tho "VVaimakariri. This is very dearly set out by the late Mr Edward Dobson, in conjunction with Mr A. Dudley DoT>son, at present city surveyor and engineer, in a report submitted by them in 1880 to the Kaiapoi Borough Council and the -Eyre- J ton, West Eyreton, and Mandevillo and: llangiora Road Boards. That report stated:—

"It is very desirable that, in future, the whole of the river from bank to bank, should be under one management, the object of which should be, not the protection of any one district, but the establishment of a permanent channel which will carry down the floodwater from the back-country to the sea without injury to its banks, and without flooding the low-lying lands on the coast, and at the same time to concentrate the whole drainage of the district in such a way as to assist the navigation of the estuary, and without in j any way reducing the extent of the present backwater." There is little doubt that these remarks are as true and as important to-day as when they wore written. Despite the protective works built by the South Waimakariri River Board, the menace of the Waimakariri to Christchureli, and to Kaiapoi, is almost as great now as it was in ISBO. There are three overfalls of the river—one into the Halswell, one into the Avon, and tho third into the Styx —and the energies of tho existing Board have been directed to strengthen these points' and the points between them. The result has been, apparently, to divert the course of the river to the northern bank, with the consequence that considerable erosion of the lands on that bank has taken place. This is shown by the fact that since 1875 Kaiapoi Island has been j divided, owing to the river seeking a! new channel, and by the erosion of j lands on tho northern bank. One of! the recommendations made by the; Messrs Dobson in 1880 was "to estab-j lish a system of groins along tho north j bank above Kaiapoi Islnnd, to check! the scour, and protect tho land from; further scouring.-"' j

In 1880 the new channel in Stewart's Gully was in process of natural formation," but despite the completion of this new outlet, the silting up of the riverbed has continued. In 1900 the water area at Empire Bridge was 5705 feet; but that is now reduced, owing to silting up, to 324G feet, consequently, in the event of a topping flood, there must be an overflow, which could only find an outlet to the southward, possibly by way of Irishman's Flat. It is of considerable importance that the data of 1875 regarding the river-bed. as checked by the observations made for the Rivers Commission, show that the river-bed has been raised, in the vicinitv of the islands, at least five feet.

"The general effect of the protective works made by the South Waimakariri River Board appears to be that they have increased the danger of erosion of the lands on the north bnnk, and the danger to the town of Kaiapoi being flooded.