THE WAIMAKARIRI.

Lyttelton Times, Volume XXX, Issue 2376, 4 August 1868, Page 2 (Supplement)

THE WAIMAKARIRI.

gkograi'iiicalj rki'out on tiii: itivKn w.uJIAKAMKI, RY JAMKS IiiXTOIt, M.1)., F.U.S., COLONIAL GKOMItJIST, J[;'XK 20, 1805; Cliristchurcli, June 20, issj. Sir,—l have tlie honour to report the results of an examination of the Waimakariri river, which I undertook, at your Honor's requi.st, during the past week, and which lias ltd me to the following conclusions First—There is_ every reason to believe that Cliristchurcli is in imminent danger from the recurrence of flood* like those which have so frequently occurred of late in the Waimakariii river, and that the works at present executed would prove quite insuffi'ii-nt to avert the calamity. Second—That means can he adopted at a moderate cost that will tend greatly to diminish the risk of the flood-waters re-tciiing Cliristchurcli, and others that will at any rate reduce the extent of damage done in the event of a recurrence of an inundation. Third—There is no reason to believe that the proper or permanent channel of the Waimakariri has ever passed through the district now occupied by Christehurch, or tlwt it tends to acquire such a course at the present time. The inundations hitherto have been exclusively due to flood-water, which escipes from the river bed through gaps in its rigiit bank. Previous to the settlement of the country, the escrpe water would seem to have been distributed over the extensive swamps which then occupied the district, and was slowly absorbed, whereas since the clearing of the land, and the formation of surface drains, it flows ofE with too great a rapidity for the capacity of the present water courses. Fourth—The present works above the Sandy Knolls are directed rather to prevent the transference of the water courses from one part of the river-bed to another, than to resist the overflow through the gap leading to Cliristchurcli. At the above point, the iiver is bounded on the north by high cliffs or shingle, which, being undercut during floods, yield a larger supply of loose material than can be carried forward. The river tends, therefore, to form a concave bend under the opposite or smith bank, at a point where that bank is very imperfect, owing to the divergence of the old watercourses leading to the ilalswell. The river is thus forced into channels which it had previously abandoned, in favour of the shorter course under the north hank. The south ban!;, below ilie point where the old watercourse leads to tlie Halswell, hough low and imperfectly defined, wnul! be nevertheless quite sufficient to resti.in the hiuhest floods which take pi .ce, and to lead the wat,-r which overflows hick to the river again, were it not for two breaks or gaps, one leading to the head of the Avon, tlie other to the Styx. The whole of the 11 aid water which readies Cliristchurcli from the Wnimnkuiri during floods appears to pass through the former of these gaps, and if this ga;> can he efl'ectnaih closed, and a proper fall afforded to tin- flood water that will lead it on towards the river, or towards the Styx, floods of an extent quite equal to that of February Ik would be pre vented from reaching Chrkcimrch. The most favourable loiitim fT closing this is a short distance above Mr Tempter's house, mi l 1 pointed out on the grmnd the exact locality and ppnml direction* of the promised works tn Mr Tbornuuijllie Ae:ir.g Provincial Knuiiiwv. The work would be part cu«;tn.; :nl pari embankment, and would not exceed. l;a!f-a----mile iu length. Hut levels would have to he taken before the exact line can be determined on. Tlio sliingl'j in this part of the river-bed consists of larger-sized stones than those at present travelling in the proper channel of the river; and as the floods hitherto appear to have exercised no scouring effect, the stability of any works executed is rendered more hopeful. If the llood water can he carried past the gup leading to the Avon, by means of the proposed works, it will then have to travel for a long distance owr loose shingle, and a greater proportion of it will be absorbed than hitherto, so that, except iu excessive floods, only a small quantity will reach the Styx ■, and, moreover, as that slre'in h's ",e!idefine I banks a ••• .i . •• g tviuv, 1 .!.»s anticipate lli.u a darns w is likely !o aeeru, to oiiier districts.is ihc result oi the suggested works. Although f think the construction of wing dams of shingle, takui from the neighbouring river bed, like iln'se alove the Sandy Knolls, will prove futile as « means of preventing the river courses from being form! to the south side of the valley, and so reaching (he abandoned channels winch le.nl towards the Avon, nevertheless a great deal may he done by watching the changes of the river, and assisting it by simple means in its endeavour to form a defined terrace on its south bank. In addition to any works executed for the purpose of restraining the Waimakariri river, immediate facilities should he provided for the escape of the water from the lower puts of the oily, should another inundation unfor tuniitely take place. A great ileal mielit be done at once, and at small expenditure, by removing such obstacles to tho course of the Atou through the town, which, experience Ins shown, cause the inundation of property during Hods, such as the embankment leading to Colombo-street bridge, the narrow bend of the river opposite ; the lioverninent Buildings, and other places which are well-known. But the greatest ; security would lie attained by cutting a wide storm-channel along the North To mi belt, , between the sharp bend which the Avon makes at the llagley park bridge, and the ] bend below the Church of England cemetery. By placing' n sluice gate on the Avon, at the upper end of this channel, all llood water

could be diverted frmn the tnrtl " narrow part of the Avon, wl, ere through the city, anil returns to it ,7 s whore its channel is wiJe, and its banks'!^ The detail plan of such a work is , for the advice of an engineer, but : «fhl" a:t ' r fully considering the level,, to lie an effectual provision against ,n n;? damages caused by the inundation's y a" 1 ' 1 moreover, as it would nearly ahvavVt i'' except the local drainage, which couW !!„ , ry ' bly he carried in a box drain, such, J. l ' might be converted into a vtrv orn^'"""'' 1 feature'in the city. J """""nt,! I will communicate further with Honor on the subject of the indications J-"f iv study of the deposits of the WaimJ ' afford, as to its probable course in the ,i:? ri future, and also giving more fully the rr ,. for my making the foregoing 5(1 ,,• Meanwhile, I would strongly time should he lost in commciici.v»V r .." I '' t r ° works of some kind,as otherwise"! ri-.'' " of the late floods, (l nd probably' h, ',"' ' tl,,n disastrous extent, is, in my opining I have the honor to be, sir, Your olieditnu-ervan' JAW* !fi;cr. )a .