THE WAIMAKARIRI.

Lyttelton Times, Volume LXX, Issue 8552, 4 August 1888, Page 2

THE WAIMAKARIRI.

MR LAMBERT’S REPOET. The following is Mr Lambert’s report on the Waimakariri River Protective Works, near No. 14 embankment, as read at the meeting of the Board of Conservators on Tuesday:— I visited the upper protective works yesterday, in company with Mr .Teal, who expressed himself as being pleased with my coming, as I would see the effect of the flood on Friday last on the new (or Jubilee) groin. The water on that occasion rose only three feet, but it did considerable damage to this work, as it had scoured under the last placed concrete blocks, and consequently they had fallen into the torrent, and the remaining ones .were gradually being prepared to follow them, as they are inclining considerably over from the vertical. The scout under, and the embankment behind, will soon accomplish the rest. The .bank has also been scoured away for six feet behind , where the last concrete was placed. I much fear we shall not be able to keep this point, on account of the enormous volume of water impinging against it at an angle of about seventy degrees, and the consequent erosion of the friable bank, which is lower than the shingle in the bed of the river, a few chains distant, at right-angles. I was much surprised at the altered appearance from the time I last it, when a member of the Board about four years ago. The torrent now setting in being almost the entire stream, has, during that period, scoured away to a width, of ten chains, at the said groin, and about fifteen chains lower down, at the weakest point, in all about an average of, say, six chains for more than a mile, or, say, about fifty acres. Mr Jeal agrees with these measurements. The worst feature of it is that less than a chain further from the water’s edge are the old gullies, leading into the head waters of the Avon, at the point where it overflowed on Dec. 25, 1865, which the shingle hank of No. 14 will not intercept. Referring to the proposed cutting, I find the river has commenced to make a channel in the direction I have suggested. A bank of shingle, formed apparently by the embankment at No. 14 checking the velocity of the river, has gradually commenced to form a fan moving in a South-west direction. The propose is intended to try to break up this fan, by making a channel through it in the original line the river took until a few years ago. The decline at this part would be very considerable, as I estimated with the appliances at hand that the fall from where the water leaves the comparatively level bed several chains North, to rush in a South-east direction on the before mentioned groin down to No. 14 is over 80ft, and I would also suggest that an anchored spar should be placed in the stream to wear the water into the cutting to give it a start. I am thoroughly convinced that if such a cutting were made as shown on the accompanying plan, although it is tentative, still I think the experiment is worth trying, as it would, if successful relieve the water from the weak point, and would enable the necessary groin of a permanent character to be placed in position to meet such a contingency on a future occasion. I would further suggest that the shingle dyke from No. 14 should also be continued up in a South-west direction for some distance, to intercept the gullets above referred to, so as to form dead water and return it again into the stream at No. 14. These two works, in my opinion, ought to precede any permanent works that will undoubtedly have to be taken in hand at this point at an early date, as it is useless to disguise the fact that this weak point is a source of real danger, and must he attended to. According to Mr deal’s statement on the occasion of the Jubilee flood, the water rose to within a few inches of the top of the shingle dyke referred to. If it had made a breach it is impossible to say what damage would have resulted, as it is about 400 feet above Christchurch; and, inasmuch as the volume of water was to the full capacity of the wall, if the current could be directed through the fan referred to it would go past instead of lodging behind and endangering the valuable and expensive piece of work. In arriving at the above conclusions, I have consulted the various maps of the river by Messrs Doyne and Cameron in 1865, and other subsequent ones as to datum, and they all materially agree. With regard to the cutting that was tried some years ago at Chaney’s, the conditions were totally different, as I saw them on several occasions, as also works on other rivers. Butl have considered this on the altered general appearances, and the environment of this undisputably weak point. Before coming to a conclusion on the matter, I would suggest that the members should see and judge for themselves, and I have little doubt but that they will generally agree with me as to the importance of immediate action at this the most suitable season of the year, when there is the greatest immunity from floods, and labour is plentiful and cheap. Mr deal's estimate of Is per yard for shifting the shingle with a Yankee scoop a few yards, is, to my mind, about double what it ought to cost, or would if tendered for. TO THE EDITOR. Sir, —As I have been asked by several persons interested to give my opinion on the proposals now before the Board of Conservators, I do so, especially as by giving them publicity in the columns of the Lyttelton Times, the members of the Board will have an opportunity of considering them before visiting the spot on Monday next. Mine was no hurried visit to the works yesterday. Far from it. A week on the ground could not have shown me more than I then saw, as the damage the flood had done on the Friday night was apparent, and showed where the weak spot exists. What I then wrote was the outcome of a study of this class of work gained in the northern district, where the action of the Ashley river was practically the same as that of the Waimakariri, but the circumstances much more in favour of the former river being worked. The drawbacks in protecting the banka of the Waimakariri are numerous. First, there is practically no solid bottom. The late Sir Julius von Haast made no secret of it, that the river is running on a bed of loose shingle not less than 900 feet in depth. This of course accounts for the total disappearance of the water from the surface during portions of the year, as also for the grand artesian water supply we have in Christchurch. Numerous wells have been sunk in the locality, and nothing has been found in sinking them but pure shingle, even as far as 300 ft below the level of the river-bed. Hence, pile-driving for protective purposes is rendered futile. Secondly, the force of the flood-water in the Waimakariri is much greater than in the Ashley; and thirdly, in consequence of the nature of the ground, there is much more difficulty in securing the growth of willows or any root-bearing class of tree. At the Ashley willows grow on the clay banks profusely, piles can be driven into the stiff soil in the bed of the river, and consequently protective works are easier of construction there. But a serious bite having taken place just to the eastward of the bridge across the river on the North road near Saltwater Creek, some protection was required, or valuable property would have been sacrificed. Large sums of money were expended to effect the protection, but the most simple means were found the most effective in the end. The channel system, exactly similar in form to that so enthusiastically advocated by Mr Lambert, was adopted. A strong groin, portions of which remain still, though constructed fifteen years ago, was built to lead the stream into this, but proved of no avail, though carried out under the superintendence of two of the best engineers of the day, and it was only by willow staking, facing with gorse, and wattling with willow branches, that the remedy was effected. Once completed, it has remained a success ever since, and the property has been rescued from destruction. In the Waimakariri nothing seems to have answered except using heavy blocks of concrete, large quantities of which have

J wtsro»saraaw^^»«i a ”* ll, *” aata * ~1, ” ,wi^^ had to be sunk and are still sinking, - making a firm foundation for the upper structure, whfch is thus enabled to stem the torrent, arid cause an accumulation of silt on which plantations of willows, &c, t can he made. That a quantity of money must be spent before any show is made is very apparent from the fact that the wool-bales used in the last new groin between Nos. 9V and 14 are now out of sight, but are maSVing an excellent bed for others to he dumped on them. In my opinion this groin i s n eeded to be made quite as much as any that have been made, and if a similar emb'ankment to that in the continuation of No. 14 is carried out from it to about twenty chains hack, where there is some rising ground, a basin would be formed, which, in the event of an overflow, would hold the dead water and make it act as a force to divert the main current. It is an acknowledged fact in river engineering that dead water is t\he best factor in turning storm water, and this object would be attained in causing the bank to be made, as in heavy floods the proposed basin would hold an immense quantity of dead water, and a heavy deposits of silt would result in the reclamation of\ several acres of good land for plantation purposes, which, must in time prove a complete preventative against further overflows. It is clear, however, that as fihe shingle brought down by the river .in large quantities every flood must lotlge somewhere in the vicinity of these works, there is a never-ceasing amount of work to be done, and attention to be paid to the condition of the banks. As to the proposed channel, I am convinced that the wcfck is impracticable; firstly, because the bed of - the river after the top crust of shingle is broken, is too soft for horses to work'in ; and, secondly, because the stream has such a decided “ set ” in to the bank that'it could not be led into such a channel even.Xf made, as the first action of the water in i\ flood would be to deposit shingle in its\ mouth, and render it totally useless at ", once.—l am, &c., R. AHEENE. Christchurch, July 31,1888.