THAMES NEWS.

Thames Star, Volume XLVII, Issue 10380, 6 December 1912, Page 4

THAMES NEWS.

THAMES HARBOUR IMPROVEMENT

I th& step produced by exclavatin|g one foot below B will be scoured ffway when, the new water course is turned upon it, and a gen-1 eral scouring of the present channel 8 leading to the 18in line may ba ex- i pected. Practically the new bottom- at , Bi will be in terms of the 18in line before referred to. The distance from , |B to this line is some 57 chains ttir- [ ther seaward. If however found necesi.saiy thie channel from B seaward ! could be deepened In the centre in * encourage' scour. 1 I It will be apparent that no'satix- | factory permanent improvement can j < '; be achieved unless works, are under- 3 . taken that will be veiy materially ns.sisted by taking advantage of-, the • scour that the %auaeranga river c.f- < fens, and' as tins scour must be on- i jder control it necessarily follows that : I some description nf training- wall ] : must be employed. ' ' i i The chief object of the wall menjtionecl afoove would be to ke«p the major portion of new channel fre.-r from gravel and other silting. . It would of course be desirable to cany the proposed wall right out to the end) of the dro^img, but the cost of same would be very heavy. It is considered that if the wall is carried from present" wharf to the lamppost, a distance of 1860 ft, that this is albout as far as possible to cany it .taking into cionsideraition! tine limitations of j the scheme 1. The proposed wall would be on' tihie north.side of the channel and would prevent any encroachment jof silt from the north west while at the same time serving to maintain • the lull - depth of water along fhfl south side of. same. It is proposed to carry the top of this wall on a level ■ with the top of the existing reclamation, so that at any time fresh, re- | clamation dan 'be gone on with. It is j undesirable to cv-rv.the wall'pofet ithe- , lnmjpi-posfc in view of a future possible ! comprehensive scheme of harbour j and foreshore improvements being ' ! taken in hand by yoiu- board', but , ! the portion suggested will at any rate form part thereof and can well be . used' in connection with paddoekmig \ off areas to the northwards for rectaj j mation "purposes. , .--. --.- i As regards the; class of wall it would [be desirable to -construct I may say jthab this has "been seriously consid-; , ! ered, and, taking into consideration ;the limited scheme. proposed, a com-' . i-paratively cheap style Is suggested. /[Any of "the usifal type of detaining [walls would be too costly and not ..j-wa.rran.ted under the circumstances. ,:and the one allowed for niow is slrn-' > ply one of "concrete steel sheet'!piling." .. ••■ _ ' I estimate that the cost of this wall . | will be about £-7560, while the' cost- , of one in hard wood would of course . jbe less, but its ultimate durability J wiould nloit reooininemd it. I have ali lowed for tflain piles being 3'2in in ■ length, with the sheet piling 24in in length. • • ' j Anchor pile* and a' coping throughout have also been allowed for. .Such a length of piles as has been j allowed for would ensure a sound <-n- ' choragß, a, froeuess from scour, ond the seas would hit the wall practically end oiii, as the prevailing seas are from the north west. » Without having bores put down it is impos-eible_to_-say under what conditions the

piles would have to bet: driven, but, if the 'shinprle if? very dense probably a -Vater jet, would have to be use.cV.lo drive the piles. It will be as Avail to note tiia.fc the present .slip-way will be interfered with,. but this ea.n lie easily provided for. The nisw flianuel will of course cause a lowering: of water level at _wharf basin and it will necessarily empty more quickly thaai 'beforehand it is certain tlmt portions of the 'basin now providing anchovn.o"e for launches will not be available

for the purpose onJ atecount of the shallowing that will follow. In- connection with the bottom width of 60ft provided for in i-•••-•• channel it will be as. yell to note that this will attain niaturally another 10ft on account of the scour alongside the proposed Wall. The approximate iimiouut of .m/aterial thiit will be dredged from the new channel is alwuib 16,500 uibici yards, and 1 the approximate

- cost, of depositing the spoil behind ■ -tho walL will- ibe' about as follows: " (^ If projected oiv'eir the waill by • suction dredge, £350; (b) if spoil ••.has. to bo. delivered into hoppers turd > •tiliebc© deposited behind wJaJI, say ; .£IOOO. Neither of the* estimate^ billows for hire of dredge, and in • this conuectioiii I rnia.y ®wy that it ■ is very unlikely that any class of 1 dredge could be hired in the Dominion at the present time, as most harbour workj are in full swing. I have reason to believe that a-'small suction dredga and fittings eouild be : unade hi Niew Zealand -for - about : £7000, that would allow of your jfoard doing yciry usefuil work,'and Tiia' amount of reolainntion that could be mad-> would very soon re ' pay, .the- outlay. .-Mi.tw^Jy*. t-he,. form. ' of dredge 1 allude to'ivouJd wb. she.uncle*'. Her own steam, j. 'ha|vfe considered the possibility of .■ -.using a Priest-man Vab-diredjsreir! for .'the work, halving it fitted with, "oliutes" to discharge . direct over the-wall, I ■ am hoivyieiver, of the opinion that there would be grave risk of damage to both plaint and mien, employed upon same, on account of the probaibility of "chutes" fouling' thetop of wall when discharging' the spoil. ' Elven if there was no dhanoe of fouling the wall, yet the efficiency of thedredge is greatly discounted by-. the faic'b that its area of action in conjunction with-tih© "chutes" would not ■control the 60ft out from one. side. Of course a "Priestnmn'.' could disohaiigje focm :graibi-b.uc!keti intiG] a suitftblo hopper pontoon",