RIVER PROTECTIVS WORKS.

Colonist, Volume XXXVIII, Issue 8328, 16 August 1895, Page 2

RIVER PROTECTIVS WORKS.

Ode readers will readily oall to mind th« ' exceptional downpour experienced in the ! Waitiess on the SeoOnd of January fasf, ' when considerable damage was done to the Nelson-Belgrova railway line in places while ' a quantity of land waa carried away, and the river Wai-iti made such encroachments as to threaten serions damage should flood waters again reach a eitni'ar height, at Lines's Creek on tin Nelson side oE tho Wai-iti r&i'wey bri'go, the piers of *be small bridge were bo considerably undermined by t <c rushing torrent, that when the waters subsided, the foundations were lefa hangtcg between earth and sky, supported by the superstructure, and it was evident, thai had a train attempted to pas 3 over the bridge, a dicudful aooident must have eventuated. Under one cf tbe piers a boy oft. ia hfight oculd have st ood, though under the other there was only aepaca of about a foot. Seeing that the foundations consisted of seventeen ton blooks of cement, it is appa r ent that the bridge stood a pretty severe Btr*in. As soon as possible after the damage work waa commenced, r*nd ne.v conorele foundations were put io, while since then the bed of thy crdek has been pitched with bou'ders so that eeour may be prevented, and the wat c r, instead of backing up as it did on the occasion referred to, when a length of embankment was only saved from being sluiced away by reason of its sides being protected by a thick growth of grass, may flow onward practically unimpeded. A little further up the line than the point just referred to, is the bridge across the Waiiti river a substantial structure on the girder principle, the girders being of ironbark timber with ties of iron and it is worthy of mention that although this portion of the line has only been open for traffic some twelve years the present is the second bridge over the river at this spot. Enquiries, have elicited the fact that not one of the birch bridges originally constructed along this line is now standing complete, although there is one birch bridge left that has had two new tops and a third is about to be placed. The bridge referred to crosses the Wai-iti at an angle and on the occasion of the flood alluded to a deep hole was scoured out for some distance above the bridge along the right bank, looking down stream, and it was evident that further scouring would endanger both bridge and railway embankment. To avert the danger threatened considerable skill and ingenuity were called for, as well as expenditure of money. By way of a first protection, iron rails, each 21 feet long, were driven from the bank of the river, and behind these stones and willow branches were filled in to prevent further encroachment. The depth to which the scouring out took place may be judged horn the circumstance, that only about four feet of these rails aie tow to be sten. But afler temporary protection had been provided it waa necessary to further safeguard the line as the rivsr was threatening to uut in at the back ol the bridge. With this object opsra t:oaa were commenced from where the Wsiiti washes toe base of a steep blu3 above the residence of Mr Bright, .tfrom tLi* point a groin was pui io, its dir. o ; .ion being from tbe bluff mentioned towards lbs bridge, its object being to divert the ourrent from thebr. ach whiah threatened to become enlarged Bnd as the construction o? this and olher groins is both new and iogacious a description of the one, which W:ll also 'serve for all, may here be made. The groia is practically a bank or wall of river holders so encased that they cannot be waabcd away, and a3 an additional protection Ggainst the scouring action of a Etrong and eidying ourrent, light willow branches have been laid beneath the bank ia such a fash oa that the tops lie on tbe river bod, o.nd thesss will doubtless grow and break the force of the water. As to the wail howev , r — itg course and size baviog been laid off and dvtarminei. lengths of iron wire netting, kn^wn an pig netting, each sufficiently long to lie un^er the wall about to be erected, and to be brought up on eisner side so that the end 3 may be brought together and fattened on top when th? wall h-*s been constructed, are laid at right angles to the course of tue wall. ThaEe leag h3 of net-ing are e»eb three feet wide, but eaoh width is laced together by a length cf stout fenoing wire being threaded between each two widths, and when the V/ire is pasted alternately between the meßhes of each width of netting, tua i eoftons are firmly fixed together. The wall is then erected of boulders, which cannot pass between the mesh of the mttiug, for tbe required heighs and as tha wall proceeJß the enos of tbe neting ara brought up over both faces of the wall and the stout fencing wire having been made taut eaoh seation cf svire is farther laced together with wire of similar size to that in tbe netting. Thu?, when the section of wall is completed the whole is bound together by the netting whioh eaaaae3 it and jet not so rigidly that the wall may not give sufficiently to at onoe counteract aay undermining action of the water. This form oE wall for tue protection of rivr bank* has been successfully employed ia va ious parts of the Colony, and with matkel success, but in the work on the banks of the Wai-iti, an improvement has been introduced iv the lioicg cf the netting with stout wife, whioi enables the whole to be bound together more tightly. From behind the groin referred to a bank has been built to protect the weak part that had been encroached upon, and the more exposed por.ion of taia wall ia coc" structed in like manner to the s>roin w*li, and behind the whole, for a length of eoina tea chains willows bava been plintnd an a distaaoa of only four feet apart each way, and ih«se, a3 they grow op, wiU oi themselves form a completa proteo'ion to the banif. Alongside the more exposed portion of the wall, and near the centre cf ihe weak part a 8m?lt obannol waa cuttorough a shingle bank in the river bed to carry tha water away from the breach, bu* siacs that work was done a freshet occurred which widened the channel conc-idsrabiy, and served to Bhow whit the sc ion of the groin above wi 1 be, as where tbe currant was slopped by its ac ion a quantity of silt was deposited, and with successive freahes, more biU will be deposited at the back of and below the stone wall, thus filling up tha weak piao? 3 . Although a considerable amount cf work bal to be done at this place, it was bui small in comparison to whati was nee ssary further up tha line. At Hollana's creek an additional length of 26 feet bad to ba aided to the railway bridge, while no le=s that 150 tons of stone were used in filling up a hole that was scoured ia the creek bed. Then, too, at rreity Bridge 200 tons of baulders - ere needed to fill in a hole thera that hai been cut by the water. By Mr Holland's hop garden the river Wai-iti had so considerably enorosched on Mr Holland's Und, earrvi-g away the rich soil, thas le?s than two chains remain in one placa between tae*railway and river, and tje pro?peoi; o! further enoroachments rendered L imperative that protective works on a considsrabla scale should be provided at this point. On the sama principle as that adopted above the railway bridge and explained above, a wall 100 yards in length, with a height of Eix feet, ii being eight feat wide at the bo: torn and four feet wide at the top, has been constructed to proteot the breach. Here, too, a channel has been cut to carry the water near the centre of the wide river b^d, arid with the aid of the thick growth of willows which may be expected to result from the planting, tbe river will be called upon to make up a bank whera it previously made a breach. At - Morrison's paddock the river had onoroaohed to within 40 fe?t of the line, and before the flood that did the mischief had subsided run were put on to prevent further damage being done. iNow this gap is also protected by a

setting encased wall. In the vioioifcy of the Bolgrove station, commenolng at a point several chains above the horse bridge, there ure three > imilar wails, designed to protect the rail way property, and for about half a mile willow plantations have been made as a defence behind the walls, and these, in caoh plao?, have to be f need t"> keep the cattle from injuring the willows b?fore they become firmly established. When they do become established there will be a d n -e growth, for the trees are only four f et apart, and at Belgrove, ft the narrowest point, the plantation is half a chain wide, though it would average very considerably more than that. | We understand thftt the work was designed and laid off by Mr Lo*\ the chief engineer of the depa^rnent, after consultation with Mr Christophers, the general manager of thp line, but the whole of the work ha* been carried out uncle: the auperviei: n of the lastmentioned gentleman, to whom, too, the detail work fell. As we have Baid, Mr Christophers devisel a method for making the casing of the netting stronger, and the whole work has been very carefully carried out. The emoaey of the plan adopted will be watched locally with very considerable in'erest, morn so because it provides a cheap method of protecting the banks of mers such as the majority in this district. It will, of course, be i bserved that the planting of willows is. to provide a permanent check against eneroaebnfents, for tbongh the wire netting which holds tbe walls together will last for a considerable number of years, it cannot be expected to last for ever. So far as we have gathered, the flood of January last necessita'ed work that has cost the Kailway Department something like £600, but if tbis work chows that river encroachment may be prevented without costly applianoes, and by a method which any settler cculd himaeif adopt, the advantages will be considerable, rod as in other places such work has done ill that was expected of it, a like result may be expected here.