THE TIMARU HARBOR.

Temuka Leader, Issue 2609, 18 January 1894, Page 3

THE TIMARU HARBOR.

The Shingle Question,

The following is the report to the Governor of Messrs Ussher and Hay, who were appointed a Royal Commission " on the proposed extension of the mole of the south breakwater for the purpose of giving greater facilities for the removal of the shingle accumulation on the south Wle of the breakwater." The Commissioners met in Timaru on the 7th November, and left again on the 11th.

KEFOBT.

" The work* for the construction of which the Timaru Harbor Board now seeks approval consist of an extension of the ,mole or first straight portion of the southern breakwater, the proposed extension to star* fron the commencement of the curve, and to consist of a junctioa length of concrete in bwjsb or monolith of varying breadth built oa the extisling breakwater, or on random blocks now in position, or yet to be laid, also an outer length of 97ft, consisting of concrete blocks get in position with a monolith mass of concrete restiDg on them, and contiunous with the junction monolith. The maximum breadth of the proposed extension is 24 feet, and the height of the full section 39 feet. The total length of the works is given as 300 feet, but it appears that to fuMy attain the objects the Board 'has in view in their cousti action, a further length of about 200 feet of the full section just given will require to 1 e constructed. The bosrd propose 3 the above described works as part of a plan for dealing with the shingle accumulating to the south of the breakwat )r. This plan appears to be to prolong the south mole in a straight line, to enable it to act sb a retaining groyne for the shiugle, to allow the shingle to accumulate until its low to high water face advances abreast a berth to be prepared for tho new dredge at the curve just beyond the end of. the wha'f, aud then to begin to lift tho shinglo—at such a rate as wi'l arrest its farther accumulation —over the breakwater by Pritjstman grabs or other mejins, into hoppers, whence it can be ian into the new dredge, or d" ectly iuto tho dredge itself, by which it will then be taken to aea, and deposited on the beach opposite the Washdyke of Waimataitai lagoon. In support of this plan of deal "-ig with the shingle, and the proposed a 20S&o\y works, it lwi been urged, cither by the board 111 writing, or by the chairman and officials in our interviews with thein, (ft) that the proposed works aro essential for the preservation and fi:ifot.y of the harbour ; and to provide fac'itioi for dealing v Ith the shingle. (/<) That the only avai'able berth for the now dredgo is along tho inne? faces of curvo of tho breakwater, where it can lio with the least, possible interference with tho working of tho port, (c) That as the shinglo can only be effectually dealt with between low and water mark the proposed extension of the inolo is necessary to control the shingle when tho low to high water face of the shirglo is allowed to advance opposite the selectc 1 station for tho new dredge, (d) That the accumulation of shinglo tathe extent will pre:ewe tho breakwater, »ud afford considerable protection to the

wharf and shipping, (e) That the extension of the mole wi l ' diminish the seas breaking over the in bad weather. (/) That the shingle o n be allowed to accumulate without any neces3ity for its removal for at least tr-ea years longer than if works were not constructed. (g) That during the:e three years th new <?-edge could be profitably employed in much needed dredging inside the harbor, (/i) That the area of land reclaimed by the shingle w."'. be considerably increased. "The proposed new mole iB only to have a thickness of 24 feet, or two-thirds that of the existing breakwater. It will therefore have much less stabi'ity than the latter, though iu quite as exposed—if not more exposed—a position. It has been advanced in support of the diminished thickness, that the Manora breakwater at Kurrachee, India, is only 24 feet thick, and also that the outer portion of an unfinished length of 166 feet of the Timaru breakwater, only two blocks thick, ie. 24 feet tlr.ck, resisted the force of a great storm in May 1882, though it is admitted that the inner portion of the unfinished length gave way. As regards the reference to the Manora breakwater, it is remarked iu Vernon Harcourts " Harboura and Docks," page 324, thatthe design was found to be only just sufficient; further the I set block work is only 24 feet high, as against 39 feet proposed by the board for the extension of the Timaru south mole, and only reaches up to the level of high water, and also an exactly I similar breakwater was wrecked at Madras. These facts, together with the partial failure of the unfinished portion of the Timaru breakwater above referred to, and the breach made iu the Oamaru breakwater, which was 36 feet thick and only 30 feet high, appear to us, apart from other reasons, to clearly show that the proposed width of 24 feet would be found to be quite ihsufficieut: and if for economical and convenient methods of de iling with the shingle accumulation we had been able to recommend the construction of the proposed works, it would only have been on condition that the tb ; .ckness of the mole would be the same as that of the existing work, viz., 36 feet. It is proposed to back up the new mole with shingle to a height of about 22 feet from the sea bottom, but the outer or more exposed portion could receive no assistance from such shingle backing, which must necessarily rise with a gradual slope from the sea bottom till it attains its full height. It is improbable that shingle deposited in the V space between the proposed and existing mole would remain there in heavy N.E. seas; it is more than likely that it would be swept over the breakwater into the harbour by the intensified power of the waves trapped by the converging walls. " The estimated cost of the proposed works appears to us to be too low. Comparing the rates for the labor of u,ixing and placing the concrete in position per cubic yard, we find only two shil i; igs and sixpence (2s 6d) allowed in the estimate, against nine shiUiugs (9s) in the latest contracts carried out under the board, taking the cement as costing thiiteen stagings (13s) per cubic yard. Allowing the board, by doing the work themcelves, can save ordinary contractors' profits, a considerable margin must be left for contingencies in works of this nature. We are of opinion that the proposed work', taking into account the extra thict aess of mole that we would insist on, could not be executed for a less sum than £7500, nor the total length of 500 feet that would be nect ssai./for less than twenty thousand pounds (£20,000). In addition to this there would certainly have to be added the coßt of pe'l mell protection, possibly on both sides of the mole throughout its length, at any rate a large number of these blocks would be requi-e i between the moles at the junction, to prevent damage from the piobable intensified wave action in the acute angle. We consider taat the proposed apron blocks shown on the drawings are insufficient. " If the idea of being able to utilize the proposed works as part of a possible extension of the harbor into deeper water were given up, the object the board now has in view—the construction of a groyne to retain the shingle —could be attained more cheaply by building such a groyne at right angles to the breakwator. As only about 80 feet in length would be saved we do not think this sufficient to justify its adoption. (2b be continued).