HARBOUR INQUIRY

Hawke's Bay Tribune, Volume XVII, 31 August 1927, Page 8

HARBOUR INQUIRY

CROSS-EXAMINATION OF MR. J. D. HOLMES

COMMISSION’S QUESTIONS I During yesterday afternoon’s sit ting of the Harbour Commission. Mr Holmes, harbour engineer, was further cross-examined bv Mr A. C McKenzie. Mr. McKenzie.- Do you suggest that when Maxwell, Williams and Mason reported on this matter that they did not consider the use of this type of head to a dredge as this is not a new type of dredging apparatus?—l don’t think that they could have considered anything. What class of material was the Colon channel dredged through?—l could not say. They started dredging at nothing and ran to high water mark.

Are there no moles protecting it? — There is a high tide breakwater on one side but it did not extend to the outer end.

Do you know the harbour at Ade•laide ? —No.

Do you agree that prior to 1855 the shingle and sand travelled north in sufficitnt quantities across the entrance to the Inner Harbour to make up the erosion caused bv the tidal scour of the lagoon and the flood waters of the Tutaekuri river?-«No. I don’t agree.

Do you agree that the increase in the area of the pool between 1906 and 1927 is primarily due to the building of the Breakwater, the reason being that the Breakwater has diverted or reduced the normal flow of the shingle and sand, and that at the present time sufficient material is not available to replace that scoured out by the tidal flow?—1 do agree, with the exception that there has not been any diversion.

Do you agree that shingle and sand will ultimately resume their normal direction of travel in sufficient quantities to graduall- restore the contours existing in 1906. and the only method of preventing the same will be by extending the Breakwater or by maintenance dredging?—No. 1 don’t think that the shingle will ever resume its normal direction of travel so lone- as the first cant of the Breakwater is kept in repair. We have exactly the same difficulty with send on the Australian coast as gravel gives in New Zealand?—The main point is that only a certain amoun. of gravel arrives here. ft is ground into mud and carried out to sea. 1 agree that there is some coming around the end of the Break water. We have calculated that there was some 17,000 cubic -ards [Kir annum being deposited there. Mr Gray: Does that 17,000 - arils include what comes through the Breakwater ?—Yes Mr McKenzie: Assuming that the plans are correctly plotted from the soundings taken in 1906 and 1911. they would show that a silting from two feet to six feet had taken place?—lt would do. but I would want to know who took the soundings. and whether reliance could be placed on them. Does that not surest that the sea’ bottom is very unstable? —No; there has been a great erosion, as shown bv the Whakartri patch But there has been a tilling up?—l think from the soundings that more erosion than filling up will take place. Mr Marchant gives an estimate of £4OOO per annum to maintain the channel. You don’t agree with that?—No, I don’t. I think it will maintain itself. Do you think that in dredging the channel one should be guided bv the contours?—We worked it out on Cullen and Keele’s basis. Dredging the channel from 1 in 5 to 1 in 37 the dredging would be increased by 200,000 yards. At Is 3d per yard this would mean an extra cost of £12,500? —Is 3d is the outside price, and once the material is disturbed the scour would have a great effect, thus reducing the extra dredging considerably.

If flip material in the hoppers of the dredge is like a solid mass, how do they pump it through pipes?— With a water jet. What weight do you consider concrete blocks should be per cubic foot?—About 1451b5. "What should the crushing strength he?—l have simply taken into account a dense concrete that will not admit sea water.

What crushing strength would your mixture of 1. 21 and 5 stand in 28 days?—That I could not say. As long as there are no voids in the concrete you could not get if heavier. I would expect the concrete to have a crushing strength of 20001bs. and over in 28 days. What do you estimate the cost of concrete per yard in block?—l made it £2 9’-. but the contracts through New Zealand were £3 per yard For sand the hest piece I could get was 12/6 ner vard. and 6/6 for beach.run gravel. For the Wellington wall con tracts were called all over the world, and a tender was accepted for £2 18/per yard. Prominent firms tendered ns high as £4 14/-. Mr. Lusk: You know what the contractor made out of it.

Mr. Holmes: He did all right but drove the iob. The board recently accepted a tender for £2 18/- and higher per yard. It was intimated yesterday that it could be done for 30/- a yard

There are boards where a mixture of 1 to 8 is used?—No, I don’t think there are. Not one in the world has been built at such a strength. Well. I must, contradict you. You wil] find that out from tho result of the Warranhool Commission?—That wiis one in six.

Would there be a general tendency for the channel to depart from tin straight line, under the influence of the ebb tide toward the west?—Yes there is a general tendency for the whole of the sea bottom between the Breakwater harbour and the outtf channel to erode away.

Don’t you think that a radius of about half-a-mile rather a sharp turn for vessels entering the Inner Harbour?—lf it is you won’t get a ship into the Breakwater. 1 can't read into Cullen and Keele’s 1925 report that they don’t refer to the height of the Breakwater?—ln their 1912 report they recommended its Raising by 10 feet and seeing that they had not amplified it that recommendation has still to stand.

How could tho dredge work unless it was moored “—With the cutter t could work by steaming slowly ahead. You suggest that agitation might be given hv speeding up the propellers?—Yes. If you were an engineer on board those boats you would not like it“No. possibly not. Mr. Holmes then referred to n authority on the construction of artificial harbours, quoting references to Port Said and M-.drat. stating

that the Breakwater harbour oi Napier was quite as exposed as that of Madras.

Mr. Lusk: That last piece is your own comment.

Mr. Holmes:.Yes. If the contours shown on Mr. Kennedy’s plan of soundings are correct does it not show that the condition of the sea bottom is unstable. Mr. Holmes: I would like a little time to consider the question. The chairman intimated that Mr. Kennedy would be called to give evidence on that point, Mr. Lusk: I suppose his reputation is good enough?—lt is for most people. At this stage the Commission adjourned until 10 o’clock this morning.