HARBOUR DEVELOPMENT.

Wanganui Herald, Volume LIII, Issue 16044, 7 February 1920, Page 5

HARBOUR DEVELOPMENT.

SURVEY OF WORKS. PROGRESS DEPENDENT UPON SUPPLIES OF STONE. ENGINEER’S SPECIAL REPORT. A report giving a survey of the development works in connection with the harbour was made to the Board last night by the engineer, Mr H. M. Haszard. His report was as follows; STONE FROM QUARRY. “It must be clearly understood that the progress of practically all construction work about the harbour is entirely dependent on the rate at which stone can be obtained. At the time the quarry was shut down in 1918 there was a good working face of stone from 30 to 40ft high with only a few feet of underlying sand j soon after resuming operations in June, 1919, a serious fault developed, the bottom of the stone rising steeply until there was ultimately only about Bft depth of stone and over ,30ft of sand underlying this to the floor of the quarry. So it was decided to run a narrow bench along to carry the stone, etc., until a better depth of stone and less underlying sand would be met with, thus the work of the last few months has been almost purely developmental. The depth of solid stone is now gradually increasing, being 30 ft, but there is still underlying over 30 ft of compacted sand entailing much dead work. There is every indication that the depth of stone will continue to increase and the amount of sand decrease.

I do not consider it practicable to do much more than at present to increase output, as owing to the narrow face only a limited number, 27 to 28 men, can be conveniently placed. In three to four months the face should have increased in depth and been, widened sufficiently to admit the working of two cranes, when it is hoped to maintain an output of 2000 tons per month. Two 15-ton cranes have been on order since July, 1919, unfortunately the delivery of these has been much delayed through the long drawn out strike of the ironmoulders in When delivered and erected the handling of stone will he facilitated, besides allowing the use of much larger stones in making np the moles, a factor which should do much to lessen the maintenance of Hie moles at a satisfactory height.

CONSTRUCTION OP NORTH AND SOUTH MOLES. 'The provision of deep water over the bar is intimately connected with the condition and length of the motes. It is very questionable whether a deep channel could be dredged and maintained without the extension of the moles, so this must be looked upon as the most important constructional work to be undertaken. Of the extensions already authorised, 1400 ft of the north mola and 1100 ft of the south mole remain to be constructed, but before this work can be proceeded with it is most necessary that the present south mole, Which has settled in places, particularly at the outer end, should be made up to its former height, or even a little higher. This mole is supposed to be built up to half tide, but owing to the large and unavoidable interstices through the stones, the effect as far as scour is concerned is somewhat less than a true half-tide wall, a considerable body of water escaping outwards at ebb tide over and through the stones, and, of course, to a much greater extent where the mole has sunk. This, I have no doubt, is responsible, as on former occasions, for a reduction in the depth on the bar from 22ft 6in to 20ft. As a matter of fact, there is at the present time a channel over the bar with 25ft of water, but this is too close to the south mole for navigational purposes. This movement of the channel to the south is certainly due to the “pull” of the ebbing waters getting .away over the south mole- 1 feel certain that if the present south mole is well made np a depth of from 22 to 24 feet will be "restored to the navigable portion of the entrance. This, if for no other purpose, is most desirable for the more efficient working of the Kaione, for the greater the number of loads that can be discharged at sea when working in the basin and approach, tho lower will be the unit cost of dredging. With only 20ft of water on the bar, the Kaione can scarcely cross prior to half tide.

Preparations are just about complete for commencing tipping stone at the south mole. One more punt-load of large stone ■will be deposited on 'the north mole, and then the locomotive, etc., will be moved across to the opposite side. The crane has already been, overhauled. I estimate that a minimum of 40 punt loads or, say, 5000 tons of large stones are required to make up the present south molo, and probably nearly as much again oould not be used to better advantage. When the south mole has been placed in a satisfactory condition, the extension of the north mole ahonld then be proceeded with. Timber sufficient for COOft of staging has been contracted for and a good deal delivered. Thirty-five tons of rails and fastenings have also been ordered from Australia.

A start could be made with the extension di the north mole staging as soon as the wooden training wall has been completed, but it is nob desirable to do this until the making-up of the south mole is well under way, as tho risk of staging in deep water, without any supporting stone, being destroyed in rough weather would be considerable.

The boiler of on© of the two piledriving outfits requires re-tubing, and tbis should be undertaken immediately, though there may be some difficulty in securing the necessary maiterial. Should it not be possible to get this repaired in a reasonable time, an effort should bo made to get another boiler, as an accident to the other outfit might cause considerable delay. It is difficult to say how much stone will he required td carry on the authorised extensions, as it is so largely dependent on, the amount of settlement that occurs during construction. Taking the assumed settlement line as shown on Mi - Howorth’s plan, the quantity would be about 156,000 tons, but as this degree of settlement would only obtain after a number of years, probably from 80,000 to 100,000 tons would be required in _ the first construction, the, balance being mad© up in after years in the form of maintenance. "Some repairs must be undertaken at the loading stage. If possible this will be postponed until the arrival of the cranes, to avoid double movement of plant. Also when the diving suit on order arrives, some stones in the river at loading stage must be removed. DREDGING OF RIVER CHANNEL. “1 understand the Kaione when ordered was primarily intended for dredging ithe basin and approach thereto ah