OUR HARBOUR.

Evening Star, Issue 2890, 24 May 1872, Page 2

OUR HARBOUR.

To the Editor. Sir, —f notice that this harbour is gradually filling up ; the channels are getting shallower every day, and there exists an appreciable difference on the depth of the bar at present. It is only {natural tn .suppose that as this silting up mation works are proceeded wjthja&itftslllPper portion of this, comparativefy" speaking, shallow basin of water, that tbedepth ofrtoe bar will decrease, owing to the want of space to receive from the flood-tide the natural quantity of water originally intended to keep[ the entrance at its . natural depth, by efluxion. The effect of this.will become more apparent at the inner bar at the sand spit than at the outer bar, where the action of the ocean tends to keep it, more or less opda. The reason of this is obvious, viz., that as the water and space-in the upper harbour are contracted it cannot receive the natural volume of water fr- m the ocean with the flood tide, and consequently the force of the ebb tide is enfeebled. The action of the flood tide during the first f.ur hours of flood being rendered stronger or more preponderating in the lower portion of the harbor bythe resistance present* d by any reclamation that takes place in the upper, and as so, disturbs the mud and debris otherwise brought down, so the ebb tide being enfeebled, does not scour out any of this disturbed matter, bat distributes it over the banks and around any natural or artificial groins existing on the sides of the channels. Moreover, the numerous beacons erected alongside The channels tend in this direction, i.e„ they act at "groins, and the banks grow round thfeift.*’ Following this process of reasoning, we may infer that a very serious amount of silting up will take place all over the harbour, until a series of pools and shallows obtain unices counteracting means a- e resorted to. At the inner bar the effect will become more and more apparent every day arid fraught with disastrous consequences. The roll of the ocean comes up to this point, and as the force of the ebb tide becomes diminished so will the roll the mo e counteract any existing scouring effect of the ebb and effectually shoal up the entrance to such an extent as shall only be necessary to let' PUt : the daily but surely dimishiug quantity of watei which can be admitted. It being therefore apparent that there is less water coming into our harbor everyday, owing, as I have said, to the effects of reclamation and the contraction of the space originally desigued to contain the influx fr|m the ocoan, so it must be observed will die scouring action of the ebb tide decrease as reclamation goes on. The deposit from the Upper Harbor will be distributed over the whole interior of the harbor space, and tho shoaling of the bar will inciea&c as indicated, until the consequences become rather serious to this port of Otago. Now what is the remedy for all this ? A detailed survey of the harbor should be made, more particularly of the bars and their vicinity, the Quarantine Island channels, 1 and the Upper or Dunedin basin, with proas to high and low Water at these placvS, and at the Ocean Beach. And a competent engineer should then lie found to prescribe the remedy. Trusting you will deem this matter of sufficient importance to give it ventilation in your paper, —I am, Ac. Utopia, Dunedin, 23rd May.