NELSON HARBOUR

Nelson Evening Mail, Volume XLVII, Issue XLVII, 6 November 1912, Page 3

NELSON HARBOUR

REPORT OF ENGIXEER-IN-CHIEF. Following is a fuller report than that appearing m last night's issue of the Engineer-:n-Chief (Mr. R. W. Holmes) report on harbour improvements, presented to the monthly meeting of the Harbour Board yesterday afternoon : ilt appears that owing" to continual increase in the size of vessels trading between New Zealand, Europe and other countries, the accomcrcdation considered sufficient when the present improvements were planned will not now enable the class of vessel required to visit the port, or only to do so under great difficulties, increased risk, ar.d expense ; the position being further complicated by some silting which has since taken place inside and outside the new entrance. Ths .matters requiring principal attention in order of importance are: — (1) The deepening cf the entrance channel ; (2) The widening of the berthing apace and its entrance beyond end of the wharf; (5) The widening of the entrance channel; (4) The widening of the channel frc--r the entrance to the vicinity of ths wharf. (1) Nearly all the vessels taking frozen meat and other produce from. New Zealand draw, when loaded, from 30 feet to 34 feet, and when in coasting trim from--20 to 24 feet. .... It will therefore be necessary to provide at neap tides a: high water at least 26 feet, .... at low water neaps 19.6, and at lo%v water springs 16.9. The imaximu-rr depth at high water springs will be 28 feet 9 inches The depth of 25 feet mentioned, only allows at neap tides for a minimum range at sea .... and would not provide for vessels cf the Athepic class The depth of 26 feet entails the vessels making Nelson the first port cf loading, which way nor be convenient or desirable, ao that if possibl.3 it should be increased to, say 28 feet at high water neaps. (2) The space in front of the wharf should be sufficient to allow of the largest vessel being turned with ease; this space should extend beyond the wharf and a short distance to the rear of face of wharf at each end to allow scope for eit.her end of a vessel when swinging on a line attached to an end ibollard. As •the larger class cf vessels will only work the port at, or very near, high water, it is not essential that this area should be any deeper than the entrance channel, except as regards a sufficient area close to- the wharf forming the vessel's berth, which must provide for them safe flotation at low water spring tides, say 26 feet. That is to say, an area extending the whole length cf "the face of the wharf and about 200 feetTbevond at earfo end, for a width cf about 90 feet, shculd hav e a depth at low water spring tides of not less than 26-feet. - (3) Fcr the 'safe .handling of vessel?', •in the light condition in which they" must be when visiting Nelson, under present and proposed conditions as regards depth of water, the new entrance .... it not .wide enough. It is therefore ! strongly recommended to increase its | width, measured between low water crarks spring tides to £CO feet. . I (4) Inside . the entrance the channel i • • • • is at present somewhat narrow for .the safe handling of large vessels. It is therefore strongly recommended that, it be widened on the convex, north, or seaward ..side, as scon as the Board is in a position to do so. This work can be left to the last. (5/ .... There is no doubt but that accumulations will take place in the entrance channel due to wave action along the Boulder Bank, and also in the shallow water on each side of the entrance, outside particularly during flood t:des, but to- what extent it is impossible to say. Dredging is the o nlv means of coping with this difficulty, which occurs _ t at all harbours where" the natural conditions -will enly permit cf an" insufficient depth being iraintained. However, accumulation inside cannot be extensive It remains now to consider the best means of carrying out the work recommended. . . ~ ." Assuming that the Board has only sufficient funds to rrrroye recent accumulations outside and inside, then in the event of the liuibi Seddon proving unsatisfactory, . . . . the Priestman dredge appears to be the only solution of the difficulty. To carry out the dredging by Priestman machine's .plant to the value of £SOCO would be required to be purchased. The working expenses are estimated at per annum cf 313 days, with 75 per cent, actual working davs at dredging | a* - • • • £44 CO ' This plant will be able to deal with the whole of the dredging both inside and outside the harbour. .... The quantity to be removed to obtain sarre depth (20 feet low water spring tides) will" be rather more than bv ,Mr. Young, . a total quantity of" 200,000 tons requires removing, which the Priestman plant can deal with in about 20 months. At the expiration of this time the Board may be in a, position by reason of the ccirparatively small annual rate of the expenditure to continue*the dredging- out of revenue, and thus avoid having to raise a loan to execute work, a considerable portion of which is reallv maintenance \vork. . . . . In view of the Board's already possessing a ladder dredire, the purchase of additional plan! wculd > r.npear superfluous, but as the Board's dredge cannot work in a seaway • and if the Rubi Seddon cannot deal economically with the light fine sand, there is no other plternative but to obtain t the Priestman plant mentioned. This plant will be at all times a valuable asset, and one which.can be easily disposed of at a mmi.rrum cf loss The Board's ladder dredge is capable of dealing with the whole cf the inside dredg mg m a cheap manner, providing some more hopper barges are obtained" and, it necessary, a more powerful tug. The drrdge is in a -Trout disgraceful condition, so that a considerable expenditure will now be necessary to place her in working order . . '. . .and the Board should at once have her plac-' ed on ways and raised clear of the water .for inspection, repairs and painting of £. • - ■ • • There are several" com,i n€ J ev and P I,Tr P ho PDer dredges in the Dominion which would be suitable tor dealing with th = whole of the dredging inside in a speedy and economical manner provided the Board had sufficient funds to carry out at once -he whole of the dredging required, and worked double shifts with the dredge, lney would .not be suitable, however, for the outside work, if the Rubi Seddon ennnefc deal with the light sand. . . . ihe quantity of dredging to be carried out at present, c r that is likelv to be required in the future, is not sufficient he Bonrd spending the sum of £25.000 or £30,000 in obtaining a modern comb.ned sea-going dredge solely for its own work. • . . . It has been

nentioned that the Board's dredge is suitable to execute the inside dredging; out'to enable it to be done economically, it will be necessary to provide at least four 100 cubic yard hopper barges to enable the spoil to be removed with suficierit rapidity to keep tV dredge workng up to full capacity. In addition a tug will be r?quircd sufficiently powerful to tow two barges 6 knots per hour. Dredging at the wharf.-y-To provide berths along front cf wharf with a degih ;£ 28 feet at low water spring tides, a width o.f 90 feet and winding 200 feet irom end up stream requires .the removal if about 30,0C0 cubic yards cf material, which can be rTroved and taken to &ea for about £2OCO by means of the Priest-' nan plant recommended. The dredging jlong the wharf can be economically dealt with by the Board's dredge, if the -poil can be placed in the area "at the i-_"k of the wharf, the reclamation 'of J wnich has been authorised, as the dredgeis provided with the necessary pump a'«d pipe line for such work, and if _ She ..rachine can be placed at work with little delay and at small cost, .otherwise the Priestman method is without doubt the best way. Removal of dredging.—The most economical; -.method of T-nrroving material raised by a ladder dredge is by means cf attendant hopper baiges, either, to\yed or self-propelled, but where it is re quired to deposit the dredgings on shore, | tne plan is of ten adopted of dumping the dredgings in a hole, from, which, they can, be again lifted by means of a centrifugal pump nlaced either on shore or afloat .as may be the - more convenient; but as there is -not scope for this method in Nelson, further consideration-may be dismissed. - ; , ~ Priestman Plant.—ln Addition to the rcixarks made previously as to the value of this • plant as a convertible asset, it may be as well to point out'Lhat &nere.. will always be small quantities of accu T •mulations to remove from time to time by dredging, particularly in the' outer part of the, entrance channel and along the front of the wharf, the cfornrer due to wave and current actionj the latter to detritus brought down by the Malta: river, and to disturbances in the shallow waters adjoining caused by steamers' propellers. To Temove Ithese accumulations a handy plant is required which will not require a large initial outlay each time to place it in commission, or that must be incurred by hiring a.plants '-The Priestman type of dredge is the only type what has so far been developed to ;rree.t these conditions. It also has the particular advantage of being able to dredge close up to the face of a wharf, also in confined spaces, a.nd is capable of removing any form cf obstruction within its power to lift. Recommendations.—l recommend that at attempt be o-ade to remove the outside and inside recent accumulations by means of the Rubi iSeddon, and if her work prove unsatisfactory, a Priestman plant be obtained and that final consideration '.b& deferred until the trial by the Rubi Seddon has been made: and firrther that no work beyond a trial of the Rubi iSeddcn be undertaken until the Board is in possession of, or has in ■ view sufficient funds to execute a considerable part of the dredging required , in order that the preliminary expenses, may be reduced to :the lowest possible pro rata'rate. (As stated in last night's issue, the Board, after a short discussion, resolved to hold a special •rreHing en 15th inst. to consider the report.)