WAIMAKARIRI RIVER CONTROL.

Press, Volume LXIII, Issue 18896, 11 January 1927, Page 11

WAIMAKARIRI RIVER CONTROL.

TO ZRt ZDITOJt Of Till TEISS. Sir,—ln Jii- H. M. Cluystall's letter of to-day on the above subject, ho quotes what you refer to in your leader as "inconsistencies in the statements of the engineers behind the Trust's plan." Mr Chrystall criticises the scheme of river control by endeavouring to discredit its authors and trying by methods not too suupulotis to belittle theij- capabilities. I will refer briefly to the six points raised by 3lr Chrystali. . No. 1. Diversion of Eyre. This diversion would net have been recommended l'y mo or approved by Mr Eurkert if certain definite precautions were not to bo taken to obviate all possible danger to the Waimakariri by the introduction of detritus. No. 2. The scheme adopted by the "rust is entirely in accord with Mr Wood's statement and not contradictory to it, as Mr Chrvstall would suggest.

No. :j. The shingle now coming through the Gorge is not the chiet cause of the trouble in die Waimakariri and by itself will not cause an aggradation of the ted of the river when the scheme is carried out." No. 4. Mr Chrystali is wide of facts —the throttle has not been abandoned and a grab-dredge has not been borrowed from the Lvttelton Harbour Board.

No. 5. Mr C'hrystall's statement is quite erroneous—the Trust's work at liyroton is to prevent erosion and the consequent filling up of the bed of the river lower down with shingle, and it is successfully doing so. The Trust is carrying out works for the protection of Coutts Island, and this very scheme which Mr Chrystali so consistently disapproves of will, when carried out, give Coutts Island as well as the rest of the district perfect immunity from flooding. No. (3. The protective works at Kaianga were done before I had charge of construction, and in any case are not. part, of the scheme which is the subject of criticism. That Mr Chrystali should criticise this scheme without being sure of his facts is not surprising when I toll your readers that Mr Chrystali has never yet examined the plans and design. He has Vtover availed himself of the opportunities so'freely offered by the Trust to get air the facts'and figures bearing on the scheme. ~ T do not wish, to discredit Mr Chrystali in the minds of the community hut surely some knowledge of a scheme is necessary' before" it can be criticised, and if Mr Chrystali will not qualify for the role of "expert" critic, he has only himself to blame if His ignorance of the engineering principles involved on which the scheme of flood control is based, leads him into a position where nothing but ridicule will reward him. — Yours, etc.,

. I<\. C. HAY, Christchtireh, January 10lh.

On receiving this letter we informed Mr Hay that in the circumstances we could not print it without such brief comment as Mr Chrystali might make upon it. Mr Chrystall's comment is as i'o'lows :

"I emphatically deny that I am for a moment questioning the capabilities of the authors. On the other hand. I do not deny that I am seek'iug to discredit the scheme on facts—facts which have never been answered. My list of published inconsistencies, is taken with rigorous care from the published statements and writings of the authors and therefore must stand. To anyone who read my letter the most striking feature of Mr Hay's is the fact that lie altogether avoids making any attempt to explain inconsistencies, established by textual quotations, from his and Mr Wood's, statements, which were astounding. The item grab-dredge, etc., is from a report of a Lyttelton Harbour Board meeting. "Mr Hay's statement that I have never yet .examined the plans is incorrect. Some time ago, per Mr Manhire, I spent an hour with Mr Hay and his plans, and finally in order to avoid any misunderstanding, I said: 'Mr Hay, T .fundamentally differ with you in regard to your'principles of river control, which are not based on hydraulics.' His reply was 'Come and have a spot.* The same afternoon I went in the same car up to the works at Eyreton when I saw/ I looked, and, I listened. My principles of -river control are based on recoCTiising that' the enormous amount nf'travelling shingle (only to be stopped bv a dnni) is the crux of the whole problem, but the authors completely disregard it." . . " ■ O

TO THE IDITO* Of TBI PBESB. Sir, —There has from tirho to time been mention of tho Waimakariri taking the gravel travelling down it out to sea. When tho writer was making enquiries about the depth to the gravel about the estuary, I was informed by householders who had had bores put down for a water supply that- it was 120. feet to the _ gravel. 'This' of course settles tho question of a Port Cdiristchurch on the estuary. It also settles the question, of a deep narrow cut.to carry the Waimakariri and gravel-out to sea. It is perhaps not generally known that tho bottoni of a large number of tidal rivers is considerably lower inside the bar -at_ the mouth than at the mouth at the river, and further, they continue lower a good distance up the river—many miles in some cases. Every tide, gurgitation takes place and scours the bottom. What is wanted'is to-get gravel down to where the tide reaches. The tide will then.deal with what is brought down. Why I mentioned dredging, below, the bridge was that by taking a cut up towards the bridge, the Railway Department or the Highways Board, whoever is responsible for the bridge would soon get a hustle on to alter the bridge. Otherwise they might find it going down the river. The chief reasons for the river bottom rising above Coutts Island and in the upper reaches is the obstructions caused bv. the scrub and M-illows, and the fact that the Tiver was allowed to split above Coutts Island. The river lost its force and tho, break-away should have been repaired at once, and the bed of the river on this south side should have been kept clear, and the situation would not occurred in our time. However, the dredger, or the dredger working.up this side of Coutts Island and tho grab going ahead up the river removing the willows and other rubbish would soon alter this. There is one fact Mr Furkert may have learnt in Italy: that is. tho jrravcl was tak<?n out of the bottoms of the rivers to make tho roads with, also to repair the banks, etc., etc. They did not buy land to get the material to do repairs with. It seems the height- of folly when the river is ri*»ne --higher to cart gravel, etc., to it.—Ynnrs. ot<\, GEORGE LEE. Templeton, January 10th.

TO THE CDITOB Of TBI rttSSS Sir, —Shortly and simply, dredge the shingle from Hie lower river, otherwise it must continue to accumulate and the bed to rise. Granted this removal from lower roaches, prevention of erosion and flooding will bo obtained by, groins and stop-banks. The Trust's expert advisers, it is presumed, have obtained sonic definite knowledge of the amount of detritus passing down, say through the Gorge bridge, so that it can be estimated roughly what quantity is settling at the lower levels. That quantity has to be dredged and carried out to sea. There is no other way, unless they arc prep.rod to go on building up groins and stop-banks until the river is lifted so high that it will soon be

a. res J, and not a possible menace to Ckristehureh,_and more so to the farms it will override.

Groins and stop-banks arc alwavs accessary in such p. river where slight obstructions, such as tree stunios". bunches of willows' 1 , or even large stonesj quickly causa diversion, but unless the ever-accumulating shingle be removed, these protective works will simply create greater trouble. Let 500.000 yards ot' shingle annually bo guessed at, of which the sand and lighter material, say at least one-third, now goes out to sea. This would mean about 350.000 yards dropping where the current is unable to take it further. That quantity yearly must be mechanically removed, a first step being to shift part of past accumulations.

The ordinary type of gold saving bucket dredge would do the lifting admirably and exceedingly cheaply, discharging the shingle into self-emptying barges, towed or self-propelled, of whatever size and draught the mouth of the river allows, carrying it out to sen and dropping it each side of the entrance. No doubt in the work of straightening and deepening the engineers will find that a very great deal of the accumulated shingle need not be taken to sea, but be advantageously dumped in different places inside. With the deepening of the channels the river would not wander so much. Spits formed or starting to divert the regular stream could be put out of action at once by sucli dredges, which mounted on pontoons of light draught, and given a moderate supply of water can move themselves anywhere.

Plenty of reliable data is obtainable as to the cost of such bucket dredges and self-emptying, self-steaming barges, and of operating them, and given the average distance the shingle so dredged would have to be transported, a near estimate of the cost per yard can be easily arrived at. Such a method would also gradually produce solid and valuable foreshore each side of the mouth of the river, and, although this is outside of the n.ain question, a permanent safe little port of moderate depth be provided for Xaiapoi. The foregoing, together with my two preceding references to the responsibilities cf the Commission;') s and the influences affecting tho Waimakariri's discharge are with all respect commended to the consideration of tho Board about to be appointed.—Yours, etc., WAIMAIEI RATEPAYER. Christenurch, January 10th, 1927.