Harbour Commission

Hawke's Bay Tribune, Volume XVII, Issue 204, 12 August 1927, Page 5

Harbour Commission

$ To-day’i Proceedings. MB. D. HOLMES CONTINUES HIS EVIDENCE. CUBEENT IN THE CHANNEL. The Nzpier Harbour Commission resumed its sittings this morning. Continuing his evidence, Mr. Dudley Holmes, of Messrs. Holmes and Sons, consulting engineers to the Napier Harbour Board, stated that in regard to the boulders in the channel, it had been proved that a grab dredge had actually picked them up. In regard to Mr. Pengelly’s statement re the difficulty of mooring in the channel, witness said that the J.D.O. had been anchored there and dredged while the current was running. When the Public Works Department was using punts for pile driving at the new Westshore bridge, which was built across the main channel, the current being comparable with that of the channel in question, anchors of about h df a ton were used, which showed that the anchors used by Mr. Pengelly, which were of only 3 cwt., were too light. Witness had seen boring operations carried out near the Niagara Falls in a ten-mile current. The borings here were being done for the purpose of blasting the bottom of the canal where the material was picked up by a dipper dredge. He saw no reason for any difficulty in mooring in the Inner Harbour channel. Admiralty charts showed the velocity at Napier to be six or seven knots per hour, which was equal to a velocity of about 10 feet per second. If there was a current of 11 knots the bottom velocity would be 11 feet per second. Witness then quoted at length the velocities to move various materials. The power of water to move stones Ift. in diameter and 2ft. in diameter, was B}ft. per second in the former and ll}ft. per second in the latter. If there was a 11 knots current, which was lift, per second, it meant that boulders slightly under 2ft. could be moved. They had found from dredging that the average size of the boulders in the channel was much less than that. The question of the velocity of the current in this channel was very important when considering the effect of the silt brought down by the Tutaekuri, and any velocity over 2ft. per second would cause it to erode. The Tutaekuri was discharging sand and silt into the lagoon, and being lighter than gravel it was hardly to be expected that once the silt and sand had been deposited in the channel it would stay there. NO FEAR OF BLOCKAGE. There was no fear, said witness, that the channel would become choked, provided that the velocity never got below that above mentioned. Erosion had been going on in the jicinity of the Westshore bridge, and the material had been travelling down and through the entrance. This eroded material from near the embankment bridge was carried by the current over near the west quay, where the current was diverted toward the sea. A centrifugal motion was set, and the gravel was thrown across to the opposite side of the channel, where a shoaling took place, the soundings showing deep-water against the west quay while shallow water was shown further out. Cullen & Keele, in designing the Inner Harbour, provided for a training wall from the south end of the Westshore bridge in a northerly direction. The purpose of this wall was to maintain the tidal flow, and so keep the velocity up add prevent the deposit of the silt in the enclosed area by the embankment. There would be little fear of silt being carried into the Inner Harbour basin proper. LIMITED SHOALING. The shoaling that occurred opposite the Iron Pot was only to a j. limited extent, continued witness, the minimum depth there at present being approximately 14 feet on the line of the channel. Mr. Holmes then put in a number of samples of the borings taken by Mr. Pengelly. Mr. Lusk: Are samples of bores 39, 40 and 41 there?—We couldn't find them anywhere. Mr. Lusk: That is extraordinary. Mr. Gray: Have you got 51 and 52 there?—Yes, and 43 as well. The system of marking them is bad and identification wa sdifficult. Mr. Lusk : You said yesterday that you had identified them all?—Yes, six months ago. Mr. McKenzie then examined most thoroughly pieces of various samples produced. MISSING SAMPLES OF BORES. Continuing, Mr. Holmes said that there was also one sample, being either 85 or 86, which was described as being a cheek bore to No. 39, being put down only 30ft. to 40ft. distance. When he examined all the samples some six months ago be traced the results on the plans ot the borings, being satisfied at that time that he , had found a good idea of what Mr. Pengelly had considered that he found. Whether jar No. 42 was there he could not say. but he was satisfied that the samples of other bores close by gave a good idea of what Mr. Pengelly found. Last night all the samples were gone through when a number were missing. What had happened to them he could not say. Witness also produced a sample of the bottom as dredged in the vicinity of the area dredged by the Whakariri. It was similar material that was found all over the bottom, samples lieing collected m various places. This material was extremely fine and a velocity of two knots or even less should erode it. In regard to the shelter Afforded to the Inner Harbour during westerly and north-westerly winds, witness pointed out that in Wellington during a north-western Oriental Bay, though it was facing directly into the wind, was at asmospheric calm and he could not see why the same action that took place there should not take plpr-o at th e Inner Harbour. The rehe made yesterday to the the Breakwater was in rehe amount of shelter prov i.shipping between the inner an I outer harbours. This was necessniy when comparing the cost of the

two schemes. Schemes could not be compared unless the facilities and other conditions were comparable. In regard to the height of the San Pedro breakwater at Los Angeles, he wished to point out that this breakwater was only used to shelter vessels at anchor and it was not intended for them to lie at the wharf in close proximity to the breakwater. The Plymouth breakwater was very low, being about 4ft. and was for shelter only and not for a wharf harbour in close proximity. In Cullen and Keele’s report, said witness, it was stated that there was a gravel bar running from the mouth of the Tuki Tuki towards the Whakari bluff at Tangoio. The only explanation that he could give for the existence of such a bar was that it was an old sea beach that had gone down through earth movements. It was considered by geologists that what was known as “black faulting'’ had occurred in the neighbourhood of Napier. The ground all round Scinde Island was considered to have gone down bodily. Good evidence of this action was to be found at Nelson, where the boulder bank had evidently sunk bodily and another bank evidently built on top of it. BREAKWATER BREASTWORK. Witness referred to the present Breakwater harbour, producing a plan of it in 1925. showier the existing works and also that proposed The Glasgow wharf was shown and also the breastwork alongside the Breakwater. The latter received very severe treatment by the waves breaking across the Breakwater and striking the raised portion, the force being so heavy as to shatter the concrete from the top of the piles This breastwork should never have been placed in that position, he said. Sufficient should have been left between the Breakwater and that structure to enable the water coming across to pass into the harbour without affecting it. Should the Breakwater harbour be gone on with, an essential work was the reconstruction of Glasgow wharf, at a safe distance from the Breakwater, or otherwise it would not be safe to use it. even in moderately rough weather. He understood that two men were swept off the Breakwater near the boat davits during the gale in 1910. and drowned. In the first portion of the development of this scheme, Cullen and Keele proposed extending the main Breakwater 1500 feet, constructing a mole under the lee of tne Breakwater and leaving an entrance channel of a width of 600 feet, and constructing one wharf with sheds with necessary dredging. A certain amount of reclamation was also suggested. these making the chief features of the outer harbour design. In regard to a wharf at the Breakwater and the action of the wind, witness stated that at New Plymouth a wharf was constructed without sheds on it when it was found necessary to erect a high breakwater down the centre of the wharf. Cullen and Keele’s Inner Harbour scheme was outlined very clearly in their 1912 report. Briefly it was bounded on the south-w-est by the railway and road embankment, on the north of the training wall mentioned in connection with the currents, and on the east bv what is known as the West Quay extension The entrance was through the present entrance. Their suggestions as outlined in their 1912 report as to the widening had been desit with in their 1925 report. The suggestion now was to widen the channel from 400 ft to 500 ft bv moving the western pier 100 ft westwards. Mr Gray informed the Commission that this suggestion came from 'he board, being _ dealt with bv Cullen and Keele, in their 1925 report. WESTERN PIER. Witness, continuing, said he had suggested a slight modification to the western pier as suggested bv Cullen and Keere by swinging the outer portion slightly out of line, so as to form a wave trap on that side of the channel. By doing this a great benefit should be derived in the reduction of any wave that might come in the entrance. A number of harbours in New Zealand were fitted tn this way. among them being Patea, Westport, and Greymouth. Their suggestion as outlined in their 1925 report was to extend the West Quay a sufficient distance to accommodate four vessels, the length being 2600 feet. They also suggested dredging a channel 600 feet wide to 35 feet deep to the outer end of the mole, and also a sufficient area inside to allow for the handling of large vessels. Witness pointed out that there was a channel with 23 feet or water to within, roughly, nine chains of the entrance at the present time from the ocean. The line of this channel was one that could easily l.e used bv vessels approaching the entrance. allowing vessels of 23ft to get in at high tide with safety IMPORTANT PART. The presence of this channel, said witness, should play a very important part in the development of the Inner Harbour, because as soon as the entrance was deepened to 23ft and a basin dredged to approximately 21ft at low water, and rhe berths to 25ft. vessels drawing this depth could berth inside with ease. These vessels could not be brought closer to the West Quay than 30 feet. A vessel moored there would have to be worked by staging from the wharf. The proposal was to build deep water wharves higher up. In the estimates prepared they had allowed for the extension of the quay where a depth of water of 34 feet could be obtained. In the estimates they had allowed lor the dredging of a basm 1,000 feet wide opposite the quay, tapering to the proposed width of the entrance ohannel opposite the Iron Pot. COMPARISON OF COSTS. In comparing the Outer and Inner Harbour they had provided for sufficient wharfage accommodation for two overseas vessels. Besides this the West Quay in the Inner Harbour was about 1,200 feet, the Glasgow wharf being token to balance it when comparing the two harbours. Witness pointed out that in his firm’s opinion the Glasgow wharf was not really strong enough to moor large vesse's and to allow them to ride out heavy storms while alongside. For a reinforced concrete structure that wharf was too narrow to withstand the forces that would be applied fa it under the above conditions. >n comparing the two harbours allowance had been made for equal shed acoommodation at each place. Wit nesx stated that they had estimated on Cullen and Keele’s scheme. The statement of estimates that ho was making was under instructions from the Harbour Board for the Commission. To bring the two schemes on to a basis on which it would be fair to compare their cost they would have to include the raising of the Breakwater by ten feet throughout its length as recommended by Cullen ami K'-ele in +lu*ir 1(125 rono’-t r

that the Outer Harbour would ba comparable to that found in the Inner Harbour. He had a number of estimates of different depths at both places that could be compared. The cost of constructing the Breakwater Harbour, including one wharf, 22} acres of reclamation, and the filling in of the north and south ponds, reading the reclaimed areas and subtracting the estimated value of th? land that could be leased was a. nett cost of £1,170,060, this being based on a depth of 30 feet in the basin and 34 feet at the wharf. The cost of an Inner Harbour with a 30ft. basin of the size already described, a 34ft. channel in as far as the Iron Pot, and 34 feet at the berth, was £258.000 after taking into consideration the value of the reclaimed areas. A Breakwater harbour with a 26ft. basin and 30ft. berth was £1,140,000. An Inner Harbour dredged to 24 feet in the basin and 30 feet in the channel and berths, the nett cost was £220.000; when dredged to 30 feet in the basin. 30 feet in the channel and 31 feet at the berths the cost would be £223,000. The details of the estimates lor the Breakwater Harbour were: 24 feet in basin and 30 feet at berths. Breakwater extension six feet high above high water, 1550 feet, £386,800. The con. struction was estimated on similar lines to the present structure: the western mole £330,000: the wharf, 550 feet by 200 feet, plus the approach which makes it 66-1 Jeet in length, £161,000; the shed, 300 feet by 107 feet. £17,600; four cranes £4,000; a reclamation wall 2.900 feet in length. £12,000. This would enclose an area of 22} acres of reclamation; reclamation, approximately 300,000 cubic yards. £18.700. Sufficient time was not available to estimate the quantity of rock to be removed from the Auckland rock and Cullen and Keele’s estimates were accepted, being Auckland £3400. other rock £200; engineering and other contingencies making a total of £983.000. In estimating the rock, it was estimated at a cost to dispose of the stripping so no item was necessary for the work of actually reclaiming the areas, which would take in the reclamation ot tne 22} acres and both the north and south ponds. In calculating the leasable area available on the reclaimed lands 34 acres had been allowed at both pons for railway and Harbour Board pur. poses. The cost of reading the south pond war. estimated at £7,175. the north £5.100 and the extra cost of filling the south pond £7.500. being approximately a total of £20,00(1. The value of the reclaimed land was estimated as follow:—South pond £25.000 and the north pond £lB,OOO, making a total of £43.000. As a rough check to the cost of the Breakwata- extension it was interesting to compare the cost of the work to date with the estimated cost. The cost of the present Breakwater was £250.000. The cost of construction had gone up 75 per cent., making the present-day cost of the structure £437.000. The amount of material would be almost equal to the amount of materia] in the original Breakwater and he did not think it could lie said, that their estimate of £337, 000 was excessive. A contractor would require a large contingency for such a work and that was the'best check against estimates. COST OF MOLE. Witness then referred to Cullen and Steels report of 1925. where they showed the cost of tlie mole at £49,600. The unit cost was 4s 4d per cubic yard. He did not know of anywhere in New Zealand where it would be possible to construct a mole for 4s 4d per yard, let alone in this district, where so little stone was available. It. seemed that in adding up the details of the estimate those engineers must have missed a very large item. Witness considered that at the least the cost would lie 15s per yard, pointing out that the stone 'from Parke Island for the Eastern Pier was costing 34s Id per yard. The cost of raising the old breakwater by 10 feet was estimated at £115,00(1 constructing the extension 10ft higher. £97.000 contingencies for engineering £ll 000, making a total cost of £223,000. The extra dredging required to dredge the basin to 30ft and the berths to 34ft would cost £13,400. An extra sum was allowed for removing the Auckland rock of £7500, other rock £3OOO and contingencies £ll 000 making a total of £28,000.

[The report of yesterday afternoon’s procedings will be found on page B.]