WAIMAKARIRI.

Press, Volume LXVII, Issue 20366, 13 October 1931, Page 9

WAIMAKARIRI.

THE NEW CUT. EXPLANATION BY TRUST CHAIRMAN. 10 THE KDXTOI& 01 Tit* PRESS. Sir, —Referring to the leader in your paper of the 6th instant, which I have just seen, I agree with you that if the public of Christchurch do not understand the proposals of the Waimakariri River Trust below the railway bridge, they should be clearly informed as to their purpose and their cost. This I will try to do in this letter, and give you also the reasons why the Trust considers that the work should be undertaken as soon as possible. As you are aware, the scheme for the control of the Waimakariri river includes the making of two river diversions, generally known as "cuts," and for the purpose of making my statements clear I will refer to the one already done through Wright's property as the "upper cut," and that below the railway bridge as the "lower cut." The work below the railway bridge consists of two parts, the lower cut and the concrete block training wall at the river mouth. Both of these works are designed for the purpose of shortening the course of the river. This is necessary, not only to enable sufficient velocity to be generated to safely pass flood waters, but also, and this is really the more important function, to facilitate the transporting of shingle to the

It would be as well to explain liere that the upper cut, which is much the i more important cf the two, does not! at present act as a complete diversion of the river. It is for the time being a spillway; that is to say, it only carries the flood water which the present or original river channel cannot safely pass. When the willows on either bank are sufficiently grown to act as an adequate protection to the stopbanks, the pilot channel through the cut will be opened up to allow as much flood water as possible to pass down the cut and so develop and enlarge it as to convert it gradually into a total diversion of the river, capable of earrying shingle at a velocity sufficiently great to transport it to the open sea. This action may not be possible, or rather advisable, i'or a few years yet, but when it does take place large quantities of silt and shingle, not only from the cut itself but from the shingle deposited for very many years above the cut, and which will still be deposited until the cut ia opened, will bo carried down the river into the reaches below the upper cut. With this explanation I should now be able to make it clear to you why for one reason it is not wise further to delay the work of shortening tlic river's course below the bridge. The length of the river from the lower end of the upper cut to the sea, when the river mouth is in its most unfavourable position, that is, when it is furthest south, is 6J miles. When the lower cut is made, and the mouth stabilised where now proposed, the length will be miles. To express it in another way, the flood grade of the river at present in the most unfavourable position of the mouth is only 2$ feet per mile, whereas it will be feet per mile when the Trust's operations are completed. The present flood grade of the river between the upper cut and the sea is quite insufficient, I can assure you, to allow the river to develop sufficient energy to carry dven its ordinary shingle load to the sea. Supposing now the upper cut were permitted to develop before anything were done in the lower reaches, not only would the river thereby be devoid of sufficient energy to transport the enormously increased load of shingle obtained from the cut, but the present sinuous course of the river would in itself assist rapid deposition of this load along the course below the upper cut. You might say to me here: "Even granting the shortening of the river below the railway is necessary when the upper cut develops, why do ' the work now?" The reason is that the lower cut, like the upper one, will take some considerable time to develop a channel of sufficient capacity to carry shingle, whereas to fulfil its functions as I have outlined them to you above, it must be ready to 'act to its full capacity immediately the upper cut starts to develop. The Bame reasoning applies to the work of stabilising the river mouth. You will see that each portion of the control of the river must be synchronised, and I trust you will believe that the problem has been carefully thought out with this end in view.

So far, I have dealt with the worls below the railway as a scheme for the removal of the menace caused by shingle deposition, but it has, of course, an important function in tho diminution of the flood menace. Calculations made show that if the shortening of tho river below the railway be not made, the flood will, when the mouth is in its worst position, and floods have a habit of reaching their maximum on just such occasions, rise two to three feet higher than they would under the improved conditions at the highway bridge, and the banks there ■ would be overtopped. This would be disastrous enough, but the position might be made even worse if much shingle had deposited here from the upper cut. To obviate this, it might have been possible to raise the banks, of course, but the least we could Jiave thought of raising them would be four feet, and this would have cost as much or more than the works we now propose. Moreover, every foot on a high stopbank is an element of increased danger in the event of the floods overtopping them. I can assure you, Sir, that this was very carefully gone into and the Trust did not feel justified in adding to the dangers already existing. I am in a better position now to answer more directly the points yon have touched on in your leading article, and will* try to make my answers as brief as possible, as I am afraid I am making this letter too long. . First, with regard to cost, the work at the mouth has been estimated to cost £9OOO and the making of the lower cut and stopbanks £4900. To this must be added about £6OOO for purchase of land and £6OO for clearing land anrl tree planting. A further sum of £3OOO was put down for futnre protection of the banks, but this will bo spent over a period of years, and is much in tho nature of maintenance. Second, tho work was authorised by the Trust soon after the first flood waters had passed through the upper cut, I think c-'mut April last when the i annual estimuu s wore under considers-

tion. The decision of the Trait is tho matter was unanimous. I think I have already explain*! as fully as I can within the limits y<* will probably allow me, the relatkus this work has to the work above the railway. The benefit to the City of Christchurch is contained in tie prevention of the deposition of shiagl* along the course of the river Led. Of what use would it be to scour away shingle in one place and transfer th« menace to another place by allowing deposition to take place there? The prevention of shingle deposition* prevents the raising of flood levels- the inundation of land around or even La the City of Christchurch, and, not least, tie danger of the whole Waimakariri river leaving its present course, cutting ofif lines of communication and destroying much valuable land and property. This, however, is all old ground I am going over, and I know you have followed tie progress of the scheme closely enough to need no further explanation heir, though I am only too willing to give it if you wish. You say that it was understood that the Trust would not proceed with tbe second cut until the success of tke first cut was established, and yon ask if th» situation has since changed. Tie situation has never changed, bat so alio has the necessity of the second «»t never changed. We have no doubt now as to tho success of the first cat, and I have explained that its success It likely to be very much impaired if tbo second cut is not made. Surely y©» will admit after this explanation that the Trust has waited as long as it dared before putting in hand the "work below the railway bridge. I trust, Sir, you did not do me tIM injustice to think that I would take advantage of the depression to adroott the doing of any work that I did net think was- a necessary 'part of tho scheme. "The Trust certainly is gettiag its work done more cheaply by unemployed labour than it would have dan* otherwise, but the chief reason for doing so has been the desire of the wear bcrs to help in the unemployment problem. This is clearly shown by the fact that any gain to the Trust by using th* ! unemployed will be paid back to tka funds of the Unemployment Board sad will be allocated to tbe Christehnrch district for further relief to tbe employed in Christchurch. It has been difficult to explain a* briefly the salient points of a seheaM N comprehensive as that which tbe Tmt has undertaken, bat I can assure yoa that the inclination of tbe Trait fcaa never been to withhold any information desired by the public, and aay further explanation yon wish X mm nsccra than willing to supply.—Yours, «t&» J. WOOD, Chairata% Waimakariri Biver Trust. Wellington, October 9th, 1931. £Wo refer to this letter in our Leader columns.—-Ed. The Press.] FLOOD WATERS SUBSIDING. FURTHER RISE EXPECTED. Although the flood waxeis is tlia Waimakariri have been subsiding steadily since the rise reached Its pMk at about 4 p.m. on Sunday, iiHinafa a* the River Construction Cusp last evening that a farther alight M* could be expected this morning, following heavy rain which fell in the watMV shed at Arthur's Pass and at tto Bealey on Sunday and yesterday. The** was two inches of rain at Arthur 7 ! Pass on Sunday, it was stated, to* owing to there having been no report received about the state of ths xvtv at the Gorge, tho extent of the expected rise could not be. foretold, was sure to be only a slight Hooding* h °By V eight o'clock last evening tha river had fallen five feet at the «"QP at Stewart's Gully, since the Bfffc «» the rise. By 10 o'clock it wasftiUo*** three feet six above its msmaliaweiTlie flood-waters were still over t» low-lying portions of . Co . u , ttß . L^S r yesterday, but the depth of water Wi the road, giving epess was not anient to block the app*«¥ft to the bridge leading to tho max*la Tbe engineer to the River Trust. Mr H. W. Harris, stated last eveningtbat the only loss of stock that he bad beard of had been the drowning of a f«S and a cow on the Island, petp a«» been no serioiis damage to tne 5 protective works.