THE TIMARU HARBOR.

Temuka Leader, Issue 2610, 20 January 1894, Page 4

THE TIMARU HARBOR.

The Shingle Question. The following is the continuation of the report to the Governor of Meßsrs Ussher and Hay, who were appointed a Royal Commission " on the proposed extension of the mole of the south breakwater for the purpose of giving greater facilities for the removal of the shingle accumulation on the south side of the breakwater" : " Referring now to the arguments advanced by the Board in support of its request to have the construction of the proposed works sanctioned, to (a) and (e), it may be replied that the proposed works are only necesary if it can be shown that there is no other method of dealing with the shingle without their aid. The Board has made no attempt to prove this, (b) (d) (e) and (f) may be generally accepted. They effect the question at issue in bo far as (b). There would be a possible loss of revenue if the new dredge while at work occupied a berth at the wharf to the exclusion of a vessel paying dues. This possible loss is difficult to determine, for the dredge should only require two or three months a year to remove sufficient shingle, and much of the work could be done while the berth was not engaged, possibly oneeighth of the annual value of a berth—say £3O0 —would be an ample sum to allow if the nonconstruction of the proposed works meant the occupation of a berth at the wharf by the dredge, which we are not prepared to admit (d). Protection to 300 to 400 feet of the breakwater would no doubt be given, but at the expense of nearly as much more to maintain, also considerable shelter would no doubt be given at the outer berth at the wharf in a few S.E. gales. (e) A slight diminution of the evil effect of seas breaking over the breakwater might be hoped for, but not to such an extent as to be of much practical value, (f) It may readily be conceded that three years'cost of shingle dredging will be saved by the construction of the works, whatever such may, by experience, be found to be. As to (g), no Buch length of time as three years «an be required for internal dredging by the new dredge, at least for the present, if it proves as efficient as should be expected from its size and cost. To deepen say 40 acres, to the extent of three feet only, means about 150 days' work of the dredge at five loads per day. As a much less area than this will meet present needs, the argument has little force, in view of the present volume of trade at the port, (h) By putting a high value on the laud that would be reclaimed by the shingle, it might be held that a large portion of the cost of the proposed works would be covered by the proceeds of the sale or lease of the increased area reclaimed. This area, between the breakwater and the Rock Island now is about 19J acres, and by allowing the shingle to accumulate as proposed it might be increased by 11 acres. As the board, however, would not be able to realise on all this land for many years, we do not feel justified in attaching much importance to the argument, more especially as the reclamation of a given area at Timaru by detention of shingle, no doubt for the future carries with it the destruction of possibly a much greater area of fertile land along the beaches to 'the northwards. Also to enable the full value of the reclamation i to be realised, it would be necessary to ' spend considerable sums of money in reising the general level and in protecting it from the sea. " The proposed works being only part of a plan for checking the advance of the shingle accumulation along the south mole beyond a certain limit, the question really at issue in their authorisation is : Are they necessary for the most efficient ' working of the plant for shingle removal now at the disposal of the board ? "The board has a new dredge on its way from Britain, its dimensions are, length 145 feet, breadth 30 feet, draught, I loaded, 10ft 9 inches, hopper capacity 267 cubic yards, about 400 tons. It has two I engines and twin screws, the engines are to develop together 450 indicated horse power. The starboard engine can be used either for propulsion or for driving the centrifugal pump for dredging, the horsepower for which may therefore be taken as 225. No definite data are yet to hand as to the amount of material the pump may be expected to lift, except that it is stated by the makers to be capable of lifting 2000 cubic feet of pure water per minute. The delivery pipe is located 11 feet above the loadline; the Buotion pipe is 20 inches in diameter, and for the above discharge, the velocity in the pipe Would be a little over 15 feet per second, a velocity which could not be maintained ove* any groat length of pipe through which the flow is maintained by atmospheric pressure. The hopper doors of the dredge drop 4 feet 0 inches, therefore if quickly opened a depth of 22 feet Would be necessary for the safe discharging of the dredge when loaded; if the doors were only partially opened, the safe depth for unloading may in most cases be taken at from 18 to 20 feet ; tbe drapghi pf the dredge unloaded will be between f aud # feet. The dredge has only one suction pump, and it appoars thai ft can only be driven from one engine. In the case o"" breakdown of either pump or engine, the board will therefore be left without means for coping with the shingle until such time as repairs are effected. As the dredge will only be required to work at the shingle for, say, about one-fifth of its time, usually there should be abundant time for repairs due to any such contingency j nevertheless the possibility of a breakdown at a critical period after a severe S.E. gale has to ba borne in mind in fixiog the safe limits within which the shingle must be kept. These remarks are made on the supposition that all the board's present dredging and tug plant is sold as is intended. The dredge is designed to act as a tug, and in addition will be constantly engaged in dredging to deepen and maintain the depth of wai-@r within the harbor. "After carefully considering various possible methods of utilising the new dredge without having recourse to the construction of works for retaining the shingle, we believe that the further advance of the shingle deposit can be arrested by the following plan : " We would locate the dredge at the curve, A 3 proposed by tho board, because at this fetation it would be able to work without interruption, Slid also because there seems to be greaioi' probability of being able to avoid tho evil effects likely to arise from tho ranging and possible rolling of the dredge while at work ; to work the dredge from this station a suction pipe would bo laid under the wharf for a length of about 300 to 350 feet from tho end of the wharf; then it would be can ied across the breakwater and connected by a swivel joint with a pipe carried by a crane projecting, say, 70 feot from its centre, at which distance the pipe would descend vertically to whatever depth under the water it is desired to remove the shingle. The dredge suction pipe would be connected to the fixed pipo by means of a ball and ftoctot »u d telescopic, joint, carried, oy »

small trolly to allow of ea«y movement and fitted with mechanism for rapidly making the connections. The swivel joint (at A on sketch plan) would enable the crane to be rotated through any angle, and enable the suction nozzle to command an arc of about 168 feet clear of the upper random blocks; the joint at B would euable the length BC of the pipe being elevated to the position BCi, and allow the vertical pipe to be lifted clear of the surf or swung in over the breakwater as might be desired. The vertical portion of the pipe CD could be lengthened at will by putting in a telescopic joint, but any extra length that might be wanted for deep dredging could be bolted on and removed as occasion required. There would be a universal joint in the vertical pipe AC, which would enable the nozzle easily to command a distance of, say, seven feet on each side of its mean position. The vertical pipe would be controlled by four steel-wire guide ropes; these would be useful in checking excessive swaying of the pipe when empty, and the longitudinal ones for increasing or diminishing the radius of action of the nozzle. The crane would be carried by massive blocks of concrete in masß built on the breakwater, and be placed at such a height above the HWM as to be reasonably beyond the reach of heavy seas. It would probably be advantageous to use steam or preferably hydraulic power for rotating the crane, and raising and lowering the suction pipes. The guide ropes would be controlled by hand gear, as this would probably be found most convenient, but the whole workiug of the crane could also be done by manual power if desired, as all the requisite motions would be very slow. The suction pipe would be about two feet in diameter, and the uptake pipe probably a little less, but the exact size can hardly be fixed without knowing what the discharge of the pump is likely to be when lifting shingle or sand as determined by trial, nor I can the details of connection of the dredge to suction pipe be decided without full information as to joints of the suction pipe fitted on the dredge. In the design of the crane, etc., we have endeavored to keep the velocity of the water in the pipes as low as possible, consistent with the power to trausport the shingle; to expose a minimum area of the suction pipe to the breaking waves; to arrange that the suction pipe could, if required, be lifted beyond the reach of heavy seas; aud to enable the suction nozzle to command sufficient area to ensure complete control of the toe of the shingle bank. Also by passing the pipe, as shown, under the ooncrete, all the rails will be left clear, so that no obstacle is i put in the way of urgent repairs being executed if required at any point of the breakwater beyond the pipe crane. If this be deemed to be of no importance, the pipe can easily cross the mole above rail level. Assuming the nozzle to work at a depth of ten feet below LWM and the lines of the toe, HWM and LWM of the shingle to be as shown on the sketch, the orane in one sweep would enable about 2700 cubic yards to be be excavated, taking the slopes as 2 to 1. If the »ction of the waves made the slopes much flatter, as would probably be the case, a much greater quantity of shingle could be removed at one time. Over part of the arc greater depths could be reached, and the toe of the bank consequently held better under control than it probably would be by dredging by the Priestman grab. The proposed fixed pipe crane is admissible, because the experimental dredging by the "Priestman" proved that dredging over a length of 80 to 90 feet held the toe of the shingle stationary, as long as the dredgiug proceeded. As the nozzle of the pipe crane shown would command a length of about 136 feet along the line of upper pell-mell blocks, and reach much further out and to greater depths than was possible in the experimental dredging, considerable margin is allowed for the contingencies of possible breakdowns, and rapid accumulations which take place during severe storms. Mr Marchaut states that he has known a storm carry the toe of the shingle Lank out as much as 80 feet, aud a receuf. fivedays' storm added the greater part of the advance of 50 feet which took place between the 15th of May and 15th of August last. ■ Some small alterations to the suction pipe on the dredge would probably be necessary to give it greater freedom of motion and also to stiffen it. The cost of initiating the scheme above described would be approximately—Concrete, £100; crane, £600; machinery, £200; pipes and junctions (including fixing in position), £700; total, £I6OO. " We do not anticipate that any trouble will be experienced in working the suotion pipe in the waves and surf, nor any very serious difficulties in working the dredge when attached to the fixed ■uotion pipe, as there should be generally plenty of suitable weather to choose from;'* « Mt f, W, Marchanij M. Inst., C.E., late engineer to the Board, very Mudly gave us a description of a method he thought out for working the Priestman grab and the new dredge in conjunction. Ag Mr Marchant haß given a great amount of attention to the subject, we give his descnptVou veifjatfn} ;—■ ' i ( Proposed method of workiug at shingle removal :—The first Byetem was to remove the shingle from Ob"i.?t . breakwater by dredging with a Priestman crane working ou the breakwater and discharging into a raised hopper, also standing on the breakwater. From this hopper an iron baud conveyor was to carry the shingle from the hopper to the dredger moored alongside the wharf, the conveyor being worked by a small engine obtaining steam from the Priestman crane boiler by weans pf a flexible hose. The objections to tho scheme were that the hopper on the breakwater could not be constructed to contain more than 200 tons of shingle, which would not be a full load for the veseel, and which consequently would have to fill up by dredging the of load required. Also this system requires the use of the wharf for a Considerable time, which during tho busy season could not be arranged, as the speed of delivery is governed by the working capacity of the Pristmau crane, and which does not exeed say 000 tons a day, or 400 cubic yards, equal in all to hut l£ loads for tliG dredger in fine weather. Likewise the baud conveyor 1 supports must project beyond the face of the wharf; this part miißt be made telescopic, which makes the thing difficult, and the projection is liable to daniago from a vessel ranging about at the wharf. Hoeing all the above objections, and that it may bo assumed that a berth beside tho wharf could only be given when not required for shipping, say a total of SO to 100 days in the year, after considerable thought over tho problem, I hit upon the following simple expedient." " That, under tho wharf a very large bin or bunker should be constructed, enclosing by sheet piling a space under the wharf, nay 40 feet, lung by l.'O feet (the width of the wharf) by 38 feet (the appropriate height), and which would contain 2000 cubic yards of shiugle. If needed, the enclosure could be made even longer—-to any 9steut. Aioug the face

of the enclosure and at the bottom of the ' same on the harbor Bide, there would be , 3 iron sluices worked by screws above ' H.W. I enclose a cross sectional outline sketch of the proposal. The method of working would be this ■:—The shingle would be raised by the Priestman crane working on the breakwater and discharging each bucketfull of shingle into a shoot, down which it would slide into the enclosure under the wharf, the enclosure, containing 2000 cubic yards or more, equal to 5 days' or more continuous work of the crane to fill. When the bunker was full, or when this part of the wharf was unoccupied by shipping, the dredge would come alongside. The sluice doors would be opened one at a time, and as the shingle flowed out, so it would be sucked up by the suction pipe of the dredging pump, and discharged into the vessel's hopper. When one sluice had run empty, the vessel would be hauled ahead or astern as the case might be, and another sluice opened. I cannot conceive the slightest objection to such a plan, and it seems to me to completely dispose of the argument that' the wharf cannot be spared for Bhingla shifting.' Day after day and week after week at certain times of the year, this wharf is only partly occupied by shipping, and it is only a question of arranging the vessels so that this particular part of the wharf could be left clear when the wharf was only partly occupied. Care could always be taken to clear up any shingle from the harbor's bottom, so that no shoaling occurred for working operations, and, as illustrated on sketch, the harbor bottom could be deepened 8 or 10 feet along the face of the enclosure, and even then if the sluices were left open, the shingle would stop itself, as soon as it had attained a certain slope outside the sluice. The dredger could probably remove in this manner 1000 to 1500 cubic yards a day, and thus at my computation of an average quantity of shingle to be removed of 57,000 cubic yards per annum, this particular part of the wharf would be occupied only from 40 to 50 days in the year. This small quantity could be reduced still further by working longer hours if need be. This system leaves the floating machinery and arrangements entirely distinct and unconnected with the gear ashore, which I consider is a sine qua non to successful working. It provides for continuous workiug or nearly so on the part of the Priestman crane and the inexpensive storage of the shingle until required. The only objection that could be urged is, that it occupies part of the wharf for a few days iu the year, but, as I have tried to show, there is nothing in this. " This is the scheme I was thinking out for permanent working when my appointment was terminated by the board. It provides for the solution of the shingle difficulty at a minimum of capital expenditure, aud as far as working cost is concerned, I can conceive of no practical scheme that could be cheaper."