HARBOUR IMPROVEMENT

Otago Witness, Issue 4028, 26 May 1931, Page 21

HARBOUR IMPROVEMENT

WIDENING OF QUARANTINE GUT SUCCESSFUL BLAST CONDUCTED. The discharge of over 20001 b of blasting gelatine on Saturday afternoon marked another stage in the advancement of Otago Harbour from the shipping point of vi ew, explosion demolishing the rock shelf jutting from Quarantine Island into the gut at the entrance of the Victoria channel.. This shelf, which had been an obstruction to shipping ever since large vessels have come up to Dunedin, was about 150 feet in length and extended about 50 feet from the shore, the rocky in ass, which at its shallowest portion was about five feet below the water, proving a potential danger to shipping. Those who travelled to the scene of operations on Saturday in the hope of witnessing a terrific upheaval, such as might have been expected when over a ton of explosive was touched off, were disappointed in that the blast was far from spectacular. Had it fulfilled the expectations of the spectators and blown

tons of water high into the air the blast would probably not have achieved the object for which it was intended, for such a spectacle would have indicated that much of the force of the explosion was badly directed. The heavy, shaking explosion. with its attendant upheaval of water to a height of about 12 or 15 feet, however, proved that the blast was an unqualified success, as it indicated that practically the whole force of the explosion had been directed downwards and outwards, thus exerting its greatest effect on the rock ledge. The contract was let in September of last year to Mr F. Goodman, and the first of the 72 holes was drilled on January 14. Since then, despite adverse 'Lather cont l*lions and the ever present difficulties attendant on working in a channel through which a seven-knot tide inns, the contractor made excellent progress, and on Friday night the last canister ot explosive was lowered into place and the wires were connected. The 72 charges were so placed as to hav e a pulverising effect on the ledge in order that the spoil might be easily removed. As each hole was drilled to a depth of 35 feet below low water mark, it is hoped that there will be a mean depth of at least 30 feet at low tide at that section

of the channel, thus giving a working channel of 300 feet in width, but not until full soundings are taken will the exact result of the blast be known. Immediately after the explosion the small steamer Maroro steamed through the channel towing an iron rail suspended horizontally at a depth of 30 feet in order to ascertain that no obstruction had been placed in the channel bj- the blast, whilst a large number of private launches, which had been kept at a safe distance bv the Harbour Board's pilot launch before the discharge, sailed through the gut to view such results of the explosion as could be seen on the surface. Reports from the engineers as to the actual result of the blast will be awaited with interest. A diver will descend to the ledge, and if the rock has been properly shattered the Harbour Board’s 222 will probably dredge out the material. Both the Harbour Board and the contractor are to be congratulated on their work, for the destruction of this ledge will remove the most serious obstacle to shipping in the Otago Harbour. Mr Goodman’s planning of the work and his boring operations, culminating in a splendid disruptive _ explosion, must be considered as a highly meritorious performance.