THE OUTER HARBOR.

Gisborne Times, Volume XXVI, Issue 2331, 26 October 1908, Page 4

THE OUTER HARBOR.

MR. ftl ARCHANT’S SCHEME

REPORT OF

FINANCE COM

MITTEE

The report following, which has been kindly supplied by the chairman of the Board ' (Mr. J. . Townley), is that of the Finance Committee of the Harbor Board, which will bo presented to the Board on Tuesday, at their meeting. The report,. however, is not a unanimous one, and it- is understood that the minority may subsequently present an independent report of •their own. . Your committee have carefully considered the position both in regard to the proposed work and finances, and beg to report as follows: 1. AS TO THE HARBOR SCHEME. The scheme has been subjected to close inquiry and investigation by Messrs. Goode, Sons, and Matthews, and by Air. Leslie Reynolds, and your committee, while assured by all engineers that the Pah Hill site is the best, think it necessary to direct the Board’s attention to various matters in regard to which the several engineers differ, and about, which, if the scheme is to bo submitted to the ratepayers for adoption, they should have definite information placed before them. Notes on Mr. Marchant’s own report of February, 1907: —(a) As to harbor bottom, Mr. Merchant says: “Within the proposed harbor area the sea bottom is papa rock. It is baro and somewhat uneven from a lowwater depth of 24ft. shorewards. Seawards of that depth it is almost perfectly flat and overlaid with a covering of silt. One point bearing on the nature of the sea bottom lier© was raised during the progress of the survey, that was, whether the bottom would afford sufficiently good anchorage for largo vessels in the harbor. This is a, question for experienced nautical men to decide after probing the bottom. My opinion is, that while the anchorage cannot be said to. be first-class, it can be said to be sufficiently good. If, however, there should be a doubt about after trial, remedies can be applied at moderate cost to loosen the bottom within the harbor entrance- sufficiently to make the anchorage above suspicion.” The length of the proposed breakwater is 4700 ft. (b) The mound or rubble work: Air. Alarcbant proposes that the seaward slope shall be 2;| to 1. (c) The whole of the stone •required—both quality and quantity—he assures, can be got from Wailiirere, including blocks from 15 tons and over, but if experience shows that this cannot be realised then he suggests as follows:—“If, however, there should not bo a sufficiency of heavy natural blocks, then these must be supplemented by the addition of 30 ton concrete blocks laid on tlie surface of the breakwater, which will prooably be the cheapest method to •pursue. If, however, a very large quantity of such concrete blocks were required, then a composite breakwater, of set concrete blocks on a rubble foundation' with a concrete block breakwater would be more economical.” (d) As to tlie range or sccnd of waves in bad weather. No observation on this is made by Air. Alarcbant in his official report. . In his notes on Coode and Co.’s report he'refers to the subject as fellows:—“ln all these breakwater harbors the great- bugbear of shipping is “range,” that is, oscillation of the water which prevents vessels from lying quietly besides the wlnrvcs. Having experienced the great drawbacks of this motion at three breakwater harbors with which I have been or still am professionally connected, I consider that everything possible should be done to eliminate this undesirable factor. With this view I “hooked” the outer arm to give the swell running round! the end of the breakwater room to expand and consequently reduce itself in the sheltered, area I do not wish to unduly press the question of range, and admit that where a rubble breakwater exists, its effect is nothing like so strong and harmful as the reflections which take place from the lee-side of a solid concrete breakwater; but everyone who has had experience of the great disadvantage of a harbor subject to range would agree that everything possible should be done to reduce it.” (e) Ihe cost-of the No. 1. scheme is estimated by Mr. Alarchant at £331,000, plus £BOOO contingencies omitted by him, total £339,00Q.; but if concrete work be required as per above quotation in (c) then there is to be added £32,400 more. He, however, in his notes on Coode and Co.’s report says:—“l advise the Board to accept the consulting engineer’s estimate of £408,000 for loan purposes. With proper and experienced engineering, I believe the work can be carried out on my plan for much less than my estimate of £331,000, plus £BOOO contingency fund omitted.” (f) Generally in said notes he adds:—“The tact is that in many directions marine engineering is of necessity very experimental. One never ' really knows what he can or cannot do with breakwater work until he tries; there are too many unknown quantities and disturbing factors to allow of absolute certainty. It is, however, always safe anti permissible to argue from the results of similar works which have been built- under approximately similar conditions in the same country ”

With considerable reservations and •modifications- both as to work and cost, Messrs. Ooode and Co. adopt generally Mr. March ant’s sit e and soheme. (a) Breakwater: “There can be no question but that heavy seas from. the south-east are experienced at Gisborne. Mr. Merchant states, in lii.s report, that the sera bottom consists of bare papa rock up to a depth of 24 feet. This would indicate a considerable sea disturbance. Moreover, deep water is found in the immediate vicinity seaward of the proposed harbor. We should therefore anticipate that the breakwater mould would, in heavy south-easterly gales, experience' a very considerable wave stroke. For this reason we consider that it would - be advisable to provide lor a sea slope of 3 to 1, extending to a depth of 15 feet .below low-water of spring tides, ' Blocks from 15 to 25 tons should be used exclusively upon the top of the mould and upon the sea slope as shown upon the crosssection given upon drawing No. 3, accompanying this report. We should ■not advise filling in the intersicess between the stones forming the top With concrete, as advised by Mr, Mar-

chant.” (b) Anchorage in harbor: They say this is of prime importance, but they have not the information to form an opinion (paragraph 20). (c) They differ as to the mode of construction of works, and say that instead of using staging, a powerful travelling crane should bo used for depositing heavy' blocks (paragraph 26). (d) They consider that the enclosed' ground should be carefully “swept” so as to ascertain pinnacle rocks, in order to their removal as; dangerous to vessels (seo paragraphs 27 and *29). .(e) They consider (ho quarry plant proposed insufficient, and estimate the cost of the necessary plant at £48,000 (paragraph 32). (f) Their estimate for works (assuming as they do 3s per toil' for stone, as put by Mr. Merchant) totals £408,000, and should future extension bo required they estimate the additional cost at £127,000. 3. Mr Leslie Reynolds on the scheme of Mr. Merchant and Messrs. Goode and Co., largely differs from both, and remark© generally that the wave force being very heavy the breakwater must, be thoroughly substantial., and the alignment designed as far as' possible to eliminate range inside. • ‘lie teiideucv— of—w-n — t —-—-