POWER HARBOUR.

Otago Daily Times, Issue 15748, 26 April 1913, Page 4

POWER HARBOUR.

ENGINEER'S REPORT ON IMPROVEMENTS. ' The engineer (Mr J. Blair Mason) submitted the following report to last night's meeting of the Harbour Boardln accordance with the resolution of tho Board of : September 27th, 1912, that a report should be furnished with respect. to ■ the harbour being utilised ai> a 6ub-nayal base, as suggested in the motion of Mr' Scollay, I have now the-honour to submit a plan, showing lines of improvement in the Lower Harbour which would, when carried out, give facilities for the docking, and berthing of vessels up to 10C0 feet m length, and render the-port- adequate for tho reception and refitting of any class of naval or mercantile vessel. The 'requirements to this end would include adequate width and depth of channel from the entrance to the berthage, a sufficiency of water at the berthage to allow free move-; ment of vessels at all states of the tide for vessels up to 1000 feet long, and provision for berthage and doekng such vessels.

Width and . Depth' of Channel. —It is satisfactory to! he able to report that the main channel from the entrance" to Deborah Bay, has now a minimum-depth of 31 feet at low water, with a navigable width of 700 feet at the bend south of Harrington Point. The depth in the entrance channel north of Taiaroa Head is 37 feet at low water, and the narrowest part 1 off the mole light .is 700 feet wide with a depth of 50 feet. From the bend at Harrington Point to Pulling Point the channel averages a depth of 40 feet with a general width of 1200 feet. Thence to Deborah Bay, where the wateT spreads out fan shape, the depth decreases gradually to 24 feet low water, deepening again until opposite Port Chalmers wharves, when t-he depth is 40 feet. With respect to the maintenance of the channel, one has 110 reason to doubt but that, provided. the tidal capacity of the harbour is channel depths and .widths will, with perhaps periodic fluctuations, bo maintained without resort to artificial deepening by dredging. There is evidence that the limit of improvement at the bend, due to tho construction of the training wall, has not yet been reached; the channel there is still increasing in width and depth. It is anticipated, however, that to maintain.' tho full depth of 30ft low water it will bo necessary from time to time to dredge the eastern end of the cross channel, where a tendency to shoal exists'; but such, up to . the present, has not been extensive or costly. It is estimated that the expenditure of £1000 yearly will meet the cost of maintenance dredging in the channel from the sea to Deborah Bav.

Training Walls, Deepening Channel (Deborah Bay to Port Chalmers), and Provision of Swinging Basins, etc.—The work necessary to deepen and widen the channel from Deborah Bay to Port Chalmers and provide the works necessary for the maintenance of the same as shown oil the plan would comprise the construction of a rubble wall extending 1600 ft in a curved direction from Acheron Head towards 'Rocky Point, a similar wall 2400 ft long along the edge of the bank opposite Kop.utai Bay, the removal of the sandbank opposite Deborah Bay to a. depth of 20ft low water, also the sandbank m Deborah Bay and the deepening of the bay itself to an average depth of 15ft low water. It would also comprise the deepening of the main channel opposite' Deborah Bay to 31ft low water, with a. width of 1000 ft, and the deepening to 36ft low water of an area of 98 acres in the vicinity of the proposed dock and wharves as shown on the plan. Exclamation, Wharves, and Docks.—lt is essential for the requirements of a refitting port and for shipping industries that areas of flat land along the water front be provided, and as there are no euch lands at Port Chalmers it be'comes necessary to consider the space that can be furnished by reclamation along the foreshore, and how far reclamation can be carried without prejudicially affecting the tidal.scour. After careful analysis I have concluded that the carrying out of the removal of banks and dredging at DeWah'Bay and vicinity will ■ balance the less of tidal capacity brought about by the reclamation of the area of 41 acres at Carey'6 Bay as shown'on plan. This,area is admirably situated with respect to the mam channel, and would make an excellent dock and slip site. The frontage will afford 2400 feet of deep water quayage, which from its position would not be liable to siltation. The reclamation of the area can be so arranged as to leave water spaces for a dock capable of taking vessels up to 1000 feet in length, and a slipway for vessels up to 700 feet. The portions shown in yellow on the harbour print at the entrance to Koputai Bay might, be reserved for storage and supply sites, while those along the north-west'foreshore of Carey's Bay could be availed of for workshops and factories. For the dredging operations entailed in the scheme it would i be necessary to provide dredging plant at an estimated cost of £40,000, but as 6uch plant would subsequently be useful, and ultimately required in other works in the upper harbour, it is calculated that one-fourth of the cost (viz., £10,000) need be charged to it. With respect to maintaining the depths of the portions dredged, it is anticipated that the works shown will ensure a self-cleansing velocity in the main cba.nricl. while the removal of 20 feet of the bank in the east side of the bend at Deborah Bay will furnish a settling ground for any material derived fran the channel. Those portions coloured black in the plan may be expected to *hoal slowly, but being outeide the slip channel nlroper it can be economically and quickly deepened without dredging being interrupted by the'general traffic. The estimated cost for such dredging, taken as a yearly charge', is £1500 per annum. With respect to the. proposal to reclaim 150 acres in the half-tide bank, I am of opinion that if the necessity arose for the reclamation of a larger area than embraced in the scheme outlined it would be better to reclaim the strip, of 44 acres coloured brown on plan, being the northern foreshore of Deborah Bay. The water front of this area would extend 3000 ft and cany from 30ft to 15ft alongside without being subject to undue siltation, wluch would be the case at the former sits. The estimated cost of walling and reclaiming 150 acres of the half-tide bank is £38,000, while that of the area-in Deborah Bav as described is estimated at £28,C00.

Estimated Cost—Tlie following statement gives the estimated cost of the various works .and operations as set forth; Training wall, Acheron Head, £4600; training wall alontj bank opposite Koputai Bay, £5300; walling ar.d reclamation of 41 awes for dockyards, shipyards, berthing, and storage sites, £64,000; dredging swinging and berthing area to 26ft low water (98 acres), £30,t>00; dredging channel Deborah Bay to swinging area to 31ft and 1000 ft wide (108 acrcs), £22,800; dredging approach to shipyard sites, Deborah Hay, to 16ft (21 acres), £5200; dredging portion of Deborah Bay reserved for defence purposes (74 acres), £15,700; dredging bank on cast side ot main channel opposite Deborah Bay to 20ft low water (86 acres), £34,800; one-fourth capital cost of dredging plant, £10,000;— total estimated expenditure, £192,900; if 44 acres additional . are reclaimed in Deborah Bay, £28,000, which gives a total cost of £220,900. Total annual cost of maintenance dredging, £2500. It is estimated that the works in the scheme a,s set jorth can be completed in six years.

Annual Charges of Item.—The cost of maintenance dredging can bu provided out of ordinary r«vcm:e. 'flic annual interest charges of 5 per tent, on -a total estimated expenditure of £192.900 would amount to £9645, a sum which' the board with its existing powers and in its present paction can only rai.se by an increase in tlie dues on goods and shipping. But. although the board may not deem it expedient to early proceed with works of sudi magnitude, yet I am strongly of opinion that a scheme of harbour improvement at Port Chalmers on the lines herein suggested or analogous thereto should be adopted by the board. Then all works, extensions of wharves, reclamations, and excavations. which may be undertaken Irom time to tune as circnmstanccs may demand will bo on definitely decided lines, and tihua largely prevent' the construction

of haphazard and temporary works, or works which, with time, may require to be undone.

Mr Soollay said this report embodied a nraetieal scheme for making Otago Harbour absolutely the leading _ port of the dominion, The point lie wished _to emphasise was this scheme, if carried out, would make Otago not only accessible at all states of the tide to. vessels up to 1000ftin length, but it would also provide attenuate deep-water berthage and first-class docking facilities for such vessels. A vessel with a draught of 30ft could, enter or leave the harbour at low water, and a vessel with a. draught of- 36ft could enter the harbour at high water, and could move about freely in the vicinity of bert.iE.ge and dock entrance at low water, kites would be available adjacent to the dock and slip at Carey's Bay for extensive and up-to-date repair shops of _ all classes, and shipyard sites of 44 acres in extent would be available at Deborah Bay, with a .iOOOtt water 'frontage, ranging in depth ironi 30ft to 15ft. He moved that the report, be received, aud referred to the favourable consideration, of the incoming board as a practical harbour improvement scheme which will, when completed, not only render Otago Harbour fully accessible to the largest vessels for,many years 10 coev', but easily make it the best harbour in s dominion. . ... Mr Dickson seoonded the_ motion, which was earned without discussion.