THE HARBOUR MOLES

Wanganui Chronicle, Volume 77, Issue 25, 30 January 1934, Page 4

THE HARBOUR MOLES

RE-CONDITIONING WORK CONTRACT PROCEEDING. USE OF SHELL-ROCK BLOCKS Progress is being made with the con* tract of re conditioning the Wanganui Harbour entrance moles, which are to be built up to full tide height with shell rock. Messrs. W. R. Rope, Ltd., the successful tenderers, secured the contract with a tender of £12,810, and the expiry date is June 8 of this year. Present indications suggest that the work will not bo completed before then, but will be fairly well forward. Six thousand tons of rock have been specified as the quantity to bo placed on the north mole, and 14,000 tons on the south. Specifications provide for rock in blocks not less than 2j tons. Work is now proceeding on the north mole. The contractors have obtained their supply of rock from the quarries up-river, and have brought it down stream by punts, which are moved with a launch. At Castlecliff the blocks are lifted off the puntj on to trucks on the

wharf by the Harbour Board’s big crane near the cool stores. A locomotive takes the trucks out to the moles and export workmen see that the rock blocks are placed effectively so as to build tho mole upward and outward to its far end. The work has proceeded a certain distance, and it is already noticeable that the beach to the north of the north mole is “making” steadily as the strengthening of the rock wall moves further seaward. Mr. R. R. Dawson, engineer to the Harbour Board, who is supervising the work, contends that the use of smaller pieces of rock can bo made full use of in creating a watertight mole. He has pointed out to the board that every hole left between the larger pieces of rock permits an. avenue for sand to find its way into the navigation channel. Acordingly, he is filling the spaces in with smaller stone and using the larger to provide solidarity in general frame work of the mole. The fact that the beach is “making” proves that a great deal of sar.d that would otherwise move into the channel is being banked up along the mole. Engineering theory holds that the volume of water will keep this in check, and when both moles are at full tide height tho entrance to tho. harbour will automatically scour. It is quite evident from the operations of the sea on the south side that a great deal of sand roa*hes tho channel. The south mole is very much below high tide level, and, in parts, cannot be seen even at iow tide. Operations of sea and wind have almost uninterrupted sway, and what was intended to bo a barrier guarding the entrance is of very little use. Whom the current contract Is completed and both moles are at full tide height, and are holo proof, there is every possibility of tho harbou* reaching the goal long aimed at. It is certain that when the moles aro up to specification the first operation will be to nicve a groyne of bluegum poles that has been erected off the south mole near the entrance. When this creciion was agreed to nautical opinion opposed it. Advice of engineers, however, favoured its establishment on tho ground that it would effectively check the making of a sand spit that was developing near the junction of the south mole with the shore inside the harbour. Operation of the elements subsequent to the erection of the groyne has not quite borne out engineering theory, however, and once the entrance to the harbour is guarded by two full-tide moles the structure will be pulled out. Interest in the work of improving the harbour is quickening in view of the work being done on the moles. Progress has been slower than was anticipated, but if plans bring forth the fruits of engineering anticipation all will be well with the Wanganui harbour in the future.