KAKANUI HARBOR WORKS.

New Zealand Times, Volume XXX, Issue 4369, 22 March 1875, Page 3

KAKANUI HARBOR WORKS.

Kakanui, in the province of Otago, has not, up to the present time, occupied a prominent position in the history of the colony, either as a seaport or a settlement. Hitherto its name has been associated with an extensive meatpreserving establishment located near the entrance to the Kakanui river, hut of the progress of the district, its resources, its increasmg population, and the commercial activity and enterprise of the settlers, little has been known except to those ever-watchful business men of Otago, who are always on the look-out for trade. Kakanui, too, has been somewhat overshadowed by the proximity of the port of Oamaru, which, being only some seven miles distant northerly, might be supposed to be able to supply all the wants of Kakanui; but the Kakanui people think differently, and having a river at hand, and having the means —or a good prospect of raising the means, which amounts to much the same thing—they have determined upon constructing artificial harbor works to facilitate and extend the trade of the district. It should be mentioned that, in addition to the meat-preserving works already alluded to, there is ft pretty extensive township at Kakanui, so that there is every justification for the proposed outlay. The local Harbor Board, it is understood, has already applied to the Otago Provincial Council for power to raise the money necessary for carrying out the work, but the proposal was allowed to stand over, in order that the Provincial Government might fortify themselves with a professional opinion upon the matter before entering upon an expenditure which might in the end turn out to be futile. Whether these latter facta are or _ are not strictly accurate matters little. It is certain that Mr. Macandrew, as Superintendent of Otago, Bought the professional advice of Mr. T. M. Hardy Johnston upon the subject, and his report is doubly satisfactory, its primary affirmation being that the construction of a harbor at Kakanui, by deepening the channel and keeping the mouth of the river open for the entrance of small vessels at all times, is practicable. It is satisfactory also, because it is the most able report upon marine engineering prepared in this colony since the decease of the late Mr. Balfour. The report is long persons not interested in the work might consider it unnecessarily long—but Mr. Johnston has been compelled to deal in first principles simply because no data of any kind as to soundings or borings existed. Therefore, there was no opportunity of discovering, by comparison with previous soundings, the effects of tide-set, the quantity of detritus brought down by the river, and the changes that may be wrought by the varying influences of wind and weather upon the shingle banks, this being information of the utmost consequence in conducting a survey of the kind. Simple data of this kind has now, however, been placed before the local Board, in the form of a report accompanied by a set of plans—the latter presenting a clear insight into the nature of the proposed works, and the former explaining its engineering features with great perspicuity. Had Mr. Johnston not shown such intimacy with his subject, one might have felt disposed to offer him a word of caution in regard to the treacherous nature of the shifting banks at tbe entrance to New Zealand rivers. The Hokitika river forms a good illustration. There these hanks "come like spirits, so depart.” A bank that could not be moved by human hands in twelve months, or twelve years, suddenly makes its appearance at the entrance of the river after a storm, and is, perhaps as suddenly, swept away by the next storm; but Mr. r Johnston’s plan seems certain to obviate the possibility of such an occurrence in the case ®f Kakanui, although the shore in both cases is exposed to the roll of the ocean.. He proposes to construct two piers to be carried out into the roadstead transversely to the set of the prevailing current, so that once having cleared the channel, by gathering and concentrating the force of the river itself, the piers, or rather the northern pier, will prevent tho set of the seaward current from silting it up again. By this means a permanent channel, 100 ft. in width, will be obtained. The south pier, estimated to cost £2500, will terminate at tho line of low water spring tides, hut the north pier, to cost £BSOO, will be carried out a distance of 250 ft. further, to check the passage of shingle and sand across the entrance. The north pier, in addition to

bearing the brunt of, the weather, will also provide wharfage acoommod ition, hence its increased cost. The total cost of the undertaking is put at £II,OOO, bur. this, of course, con only be taken as the approximate cost of the work. However, it ii not probable that the estimate will be much exceeded, as Mr. Johnston in one part of Us report says:— “It will be seen that timber, stone, and-con-crete, compose nearly the whole of the materials to be employed in the works, all of which are easily and expeditiously procurable; especially shingle for concrete, and the best of stone for the purpose, are so close at baud, and in such abundance, that they may be said to be already delivered on the ground and almost ready for use. There are also quarries of fossil limestone in the neighborhood, within a mile from the lagoon, and by the ai d of a tramway, at comparatively small cost, the stone could be conveyed by its own. gravity nearly, the whole way to the new harbor, and thus become not only valuable as furnishing ballast for shipping, but as an article of commerce, whenever greater facilities are afforded for its transport. It is also likely to prove useful in carrying out masonry works at some future time in connection with the further extension of harbor improvements, and of the township generally.” As might be expected, Mr. Johnston shows a thorough knowledge °f hydraulics and dynamics generally. In speaking of the means of keeping the liver free at its entrance he expresses the clear couvictiou* that the scouring power available is the only means.to be employed, and he is equally clear that this power is sufficient for the purpose'if judiciously employed. Then he goes on to say ; “ In considering the relative power of the two scouring agents to be dealt w tli, namely, the fresh, water and the tidal flow, I need hardly say that it is not by the former we can hope to keep a navigable . channel open, but mainly—indeed, almost entirely —by the latter, if once given freer access to the lower compartment of the river and thus made the means of doing important service by not only maintaining but increasing the present scanty depth.of water within the estuary. By the erection of piers in the position shown on the plan, the effect will be .to increase the rise and fall of tide within the estuary and lower the present shallow bed of the lagoon in its approach to the piers, where I understand it consists of soft mud and sandy deposit of considerable depth. The steepening action in front of the tidal wave will therefore be considerably diminished, and thus admit of its freer - propagation up the river. I must add, however, that it is strictly a, matter of ealeu: lation as to what volume of tidal water entering the estuary would, by its daily scouring properties, be sufficient to maintain an efficient channel of any considerable depth between the proposed piers.” Mr. Johnston very properly connects the harbor improvements with their probable effect upon trade. Even ’ without the aid of .the engineer the trade of the placo has increased from a tonnage of 2151 tons for the year 1873 to 5861 tons for ten months' in 1874 (January to October), and what the ratio of increase would be were vessels able to enter at all times and not delayed occasionally for weeks by a “.bad bar,” it is nut difficult to foresee. To compare big things with little, we have the cases of the Danube and the Scheldt, in Northern Europe, where, trade increased threefold after the construction of necessary harbor improvements, and if such were the results in the cases of old-established ports, it is justifiable to look for more encouraging results in new ones. Attention is directed to this subject not somuch on account oi Kakanui,asto show the importance of permanent improvements of the kind being effected in other harbors of New Zealand.