OTAGO HARBOR.

Evening Star, Issue 15138, 20 March 1913, Page 10

OTAGO HARBOR.

' WHY" 1 THE ENTRANCE' MUST ’Bt KEPT OPEN. ; [B~S,] The problem at the entrance of our harbor, briefly put, is whether the Mole, in its present state, is capable of maintain-' ing the deep-water channel which at present gives such ready access to the port 6£. Otago;

Let ns look into the position a little. What needs to bo considered first and foremost, in order to make this discussion anywise profitable, is whether our harbor entrance needs attention in the way of improvement or whether it does "not. Everybody admits that the Mole at the Heads is responsible for the present deepwater entrance to the harbor. 'The Mole having accomplished that useful work, the query arises ; Is it capable of maintaining that depth of water or is it not? Thai is really the crux of the position. Some say the Mole is capable, as it is, of maintaining tho depth of water; others say it is not. .Some of those who say it is also say that the .Mole is as good as ever - it was —a statement that does not seem to lie demonstrable, because a large portion of the woodwork has disappeared, and because stonework placed on tide-swept sands, such as is the case at the Mole, tends to sink down into the sand on which it is placed. Those, on the other hand, who say the Mole needs attention recognise that the woodwork has largely gone, and that the stonework, if it has not already sunk into the- sand, is nevertheless incapable of diverting tho tidal scour so as to maintain as it should- be maintained the deep-water channel which constitutes the entrance to the harbor. Now, what can wo learn from the Kowhai mishap? The reply is that a deal may be learned. Had the stonework of the Mole extended up to high-water mark, the ebb tide would not have combined with the wind to drag the vessel out of tho channel. The ebb tide was rushing across the Mole instead of rushing down the entrance channel and thereby helping navigation, as well as assisting to maintain the depth of tho channel. The tide was halfebb when the Kowhai leapt the Mole, and as her draught must have been about 10ft at least, that shows clearly what an immense volume of water was sweeping over the Mole instead of being directed down the entrance channel, "which extends for a considerable distance beyond the Mole. The ebb tide, in its outward rush, strikes Harrington Point and shoots right over to the Mole, where, instead of being diverted down the channel, it sweeps across tho Mole, and the scour value of the ebb tide is thus almost wholly lost where it is most needed.

_ Now-, has this escape of the sweep of the tide across the Mole wall, or, rather, the foundation of a wall, any deleterious influence on the entrance channel and the position of the big, shalloyv sandbank through which the channel extends? It does not require the trained observation of an expert to see that if the enormous volume of yvater which at present syveeps over the Mole yvere directed down the channel—and that could be accomplished by building the Mole yvall up to highwater mark—the deep-yyater entrance of the harbor yvould be better maintained than itis. That is self-evident. If the yvall yvere merely built up to loyv-yvater mark, the extra scour thus secured in the entrance channel yvould be enormous. These are some of the arguments of those who assert the Mole requires attention ; and when it is further remembered that a vessel, yvhen entering the harbor “on the line of beacons,” is only barely her own breadth distant from the danger zone of surfbreaking bar on her port beam, then one can more_ easily understand yvhy some people think the Mole merits attention. That is not all. Evidently the scour at the Heads yvill be further detrimentally affected by the proposed reclamation at Anderson Bay. Expert opinion, says so. In his recent report to the Harbor Board in _ connection with the visiting engineers’ opinions on the matter of the reclamation at Anderson Bay, Mr Blair Mason stated s that “ the intensity of scour at the Heads is principally dependent on the area of the harbor, so that all reclamation must he pernicious in its tendency, and render more difficult the maintenance or further increase of the channel depths. Referring to the channel from the Mole seayvards, it is of the utmost moment that the scouring effect be maintained, not only to ensure a good depth of yvater, but, what is no less important, that it should maintain its present direction o<’ floyv. Any diminut’on of the tidal scour yvould permit of the bank on the seaward side of the channel groyving shore-wards, and thus force the deep yvater further yvest, rendering the channel in heavy weather dangerous for navigation. . . . It should also be home in mind that it is not altogether a question of holding and maintaining tho present entrance depths and widths of channel, but of increasing them, if the port of Otago is to rank with the other ports of the Dominion and of the yvorld in its accessibility for the largest classes of shipping.” The above was written in protest against reclaiming a certain increased area in the Upper Harbor. 'Therefore, if the amount of tidal scour at the Heads is to be diminished in consequence of harbor reclamation, that seems to accentuate the need that exists for building up the Molo in stone, and thereby ensuring that the scour shall do what Mr Mason says it is indispensable that it should perform. On the yvbole, it seems that the Mole at the Heads requires attention, and that the Harbor Board understand the position, as it was explained so lucidly in the report quoted from above.