THE OUTER HARBOR.

Gisborne Times, Volume XXVI, Issue 2288, 5 September 1908, Page 1

THE OUTER HARBOR.

A HALF-MILLION SCHEME

MR. LESLIE.REYNOLDS’ REPORT

Tho following report on nn outer harbor schemo for Gisborne has been received from Mr. Leslie .Koynoilus, C.E., and will bo considered at un adjourned meeting of tho Harbor Hoard next Monday afternoon: OTIRA, Aug. 27. The Chairman and Members, Gisborne Harbor Hoard, Gisborno. Gontleinon,—l have now tho honor to forward you’the following report upon tho proposed Outer Harbor Works for Gisborne. Tho question of an Outer Harbor for your Port is. ono of long standing; sovoral schemes 'hove been promulgated from time to time, tho latest boing that by Mr F. W. Marchant, M. Inst. 0.E., in 1907. Mr March ant’6 schemo and report woro submitted to Messrs Coodo, Son and Matthews, for tho purpose of obtaining their opinion upon his proposed works. Tips firm of engineers, in their criticism, endorse tho position choson by Mr Ala reliant, •and in many respects agreo with the main points of that gentleman’s scheme, but they suggest some modification In tho design .and alignment of the breakwater. They also estimate tho cost at some £77,000 in excess of the figure which Mr Marchant considers sufficient to execute tho work. Your Board have now referred the matter to me, with a view to obtaining my opinion as to whether tho schemo submitted by Mr Marchant, or tho suggested modification referred to, is bettor suited to tho physical conditions obtaining, and to tho general requirements of deep draught vessels, and as to whether tho respective estimated costs are sufficient to complete tho proposed works. My opinion is -also requested as to the best site for and alignment of an outer harbor, apart from tho above schemes.

To fulfil these requirements I have very carefully studied and analysed the reports and plans .referred to me, together with the Admiralty Chart of 1902, and various othordata, and now propose to deal in this report with the main points as they occur to mo. WIND, SEAS, AND SAND TRAVEL From observations made by the Board’s Harbormaster, Captain Cumniing, and from previous records, it is evident that the prevailing winds reach home from a. westerly direction, but the width and contour of the Bay, together with the protection afforded by Young Nick’s Head, does not offer sufficient fetch for those winds, unless from a direction south of south-west, to cause any considerable sea. and it has been noted that during such .winds, what little sea there may be is heaviest towards the westerly side o'f the Bay, and less towards the entrance of the present harbor and eastward thereof. Any winds from a direction north of west are directly off shore, and except as •affecting vessels lying at the wharves need hardly be considered. Southwesterly winds cause at times a considerable sea, but the heaviest and most dangerous to shipping are thoso from the south and south-east, mud as the latter are.at times severe, any works designed to meet their shock, require to be of a thoroughly substantial character, and the alignment designed to, as far as possible, eliminate wave scend or undulation within the enclosed area. The minimising of wave scend, in my opinion, is of vital importance in connection with any outer harbor schemo. With regard to sand travel, I behove, that before the present harbor works were constructed, .it . was generally acceptd that there was a dofinite and heavy sand travel eastward, but since then the works referred to have practically proved that the travel eastward is not continuous, nor of anything like the proportions previously assumed, and what really occurs is, so to speak, tho readjustment of the sand patches, depending upon the weather periods and currents, and it is now generally considered that if there be any eastward travel at all, such is practically nominal. Iu any case I am distinctly of opinion that sand travel need not be accounted a bar in any degree, to the success of harbor works, if constructed beyond liajf a mile eastward of the present harbor.

On my recent visit to Gisborne Captain Camming advised me tint upon occasions following heavy southerly seas, considerable masses of seaweed are driven inshore, which, upon the wind veering to the westward, drift towards the east, -and quantities of this weed would probably find its way into the proposed harbor. As this is merely an occasional occurrence, I do not look upon the circumstances as serious, and should the weed cause any inconvenience, doubtless some easy and simple method could be devised to overcome the trouble.

OUTER HARBOR SITE. The next point to determine is the locality best suited for the construction of a harbor, and this, .in connection with tho proposed works, is perhaps the most " important. After having thoroughly considered the question from information supplied by various plans and data, together with that obtained from personal observations during occasional visits extending over the last sixteen years, I have no hesitation in advising that the locality chosen by Mr Marchant is the best offering, although I may suggest amendments as regards the exact- position and area of enclosed harbor, which that gentleman has proposed to include in nis scheme. Irrespective of distance from Gisborne, the best harbor site in loverty Bay would, from the plans and charts, appear to bo under the protection of Young Nick’s Head, hut very-much fuller information as to nature of the bottom than is at piesent available would require to he procured before definitely deciding this point. Placing cost on one side, the bosharbor site in Gisborne Roads Ibetween the position marked “The Foul Ground” on the Admiralty Chart ana a point about half .a mile eastward ot ■the present breakwater. As, however, the construction of suitable worus at this site would entail the expenditure of somewhere in tlie neighborhood of £1,000,000, it must be put on one side.

MR At ARCH ANT’S PROPOSED SCHEME, AND AMEN DMEN IS SUGGESTED BY MESSRS COODE, SON AND MATTHEWS.

While approving of the position chosen by Mr Mnrcliant and the general outline of ids No. 1 scheme, I have grave objections to the area- ol deep water which his scheme would enclose.-and in terms of such area to the width of entrance, which wou-.u be exposed to westerly seas, rs also to the scend or undulation v l.icli would enter during southerly weather, and ground swell. One <A tne chief arguments'(igaiust the | roposed site lies in tlio fact that the bottom consists of bare pupil r° a,K * cannot be considered as good-anchorage for vessels entering during stress ot heavy weather. It is therefore, m my opinion, imperative fhay the enclosed area should have sufficient depth, ot binht, to admit of vessels entering dining such weather conditions to bring up and manoeuvre alongside their births, or to make fast-to moorbuovs. The necessity for ample depth of bight applies also to vessels leavin" the harbor, as. the physical conditions affecting the site will only admit of a line of fairway into or out from the harbor being practically at right angles to the direction of the heaviest seas, and it is tbereforo of utmost importance that there be. sufficient distance between the terminus of the breakwater and the berthages to permit ot vessels eu-

tor.ing maintaining, and thoso outgoin.' obtaining, sufficient speed to hod against the direction ot southerly seas, and to ensure their bate clearance of Toinoana Rock. A 1 though the harbor proposed by Mr •Marchant, which at tho time of mv visit was marked off by, buoys, may present an unquestionable area from a landsman’s point of view, tlie capacity, as also the entrance and approach thereto, should, I think, bo judged from the bridges pt tlie kir<rost class of vessels which might Fairly be cxpocted to enter or leave an outer harbor except during abnormally heavy seas. The .scend or range which would affect vessels when berthed, is .another all important point to. bo considered. Mr Marchant, in his notes on 'the report of Messrs Coodo* Son, and Matthews, refers thus to this factm - ■—“ln all these breakwater harbors the groat bug-bear of shipping is ‘range’, that is, oscillation- of water which present's vessels fioin tying quietly beside tho wharves. Tlavin or experienced tho ■ groat drawbacks of this moition at three breakwater hafbors with which I ■have -been, or: still am, profession ,ay connected, 1 consider that everything possible should bo done to eliminate this undesirable factor.” Mr ■ Marchant Is undoubtedly correct in terming harbor range “the great bug-bear of shipping”, and it is special.y important that in any scheme devised tins “bug-bear” should bo as far as possible minimised. I am satisfied that in terms of tho proposed width 0 f entrance, the area which would bo available ill tho ‘scheme submitted_ by Mr Marchant and Messrs Coode, Son and Malttliews’ amendment thereon, is insufficient to admit of large vessels entering or leaving during heavy weather without considerable risk, or of their lying at the berthages without inconvenience from range due to eoutli-westerly seas, as also those from any otlior quarter round to soutli°ain dealing with the entrance, 1 wish to be explicit in my views, and will therefore further explain that tlie width of entrance proposed by Mr Marchant would be ample, provided there , was sufficient distance from the foe of the breakwater to the bight of his proposed harbor to admit of vessels 'entering With sufficient speed to ensure fair steerageway, and their bringing up within tho distance, and also that there be ample room for tlie wave undulations to as far as possible become spent -before reaching the berthage accommodation. Bearing this object in mind, Mr Marchant has designed his scheme with a kant or elbow at the'seaward extremity of his proposed breakwater, and in this 1 entirely concur, and consider that the align--meat of breakwater submitted by him is preferable to the amendment suggested bv Messrs Coode, Son, and Matthews, but I do not consider that the Scheme submitted would afford the area necessary to meet the requirements above referred to, and 1 have therefore outlined upon accompanying plan the extent of works which iii iny opinion are calculated to fulfil the demands which may be reasonably expected from the construction of an outer harbor^ To my mind Sehenio No. 2 designed by Mr Marchant, does not compare at ail favorably with his No. 1 scheme, and while not affording the same protection against southerly and westerly weather, offers a smaller area for wave expansion, and the undulation or scend would consequently have .less room in, which to become spent. CONSTRUCTION OF BREAKWATER, ,

I. agree with. Mr Marclnint’s proposal that the breakwater should ho constructed entirely of , rubble, and that the only, suitable locality from which this class of material can bo obtained is AVaihirerc, but I am not at all sanguine that any quarry at the AVaihirerc Gorge will yield the quantity of •heavy blocks required, without a considerable proportion of the excavated material being outcast as useless for breakwater purposes. I have lmd occasion to carefully examine the shell limestone deposit at Waihirere, not .only for the purpose of harbor works,, but also ill connection with the water supply which at was proposed should ho obtained from that source, and I conclude that the uniformity of rock can nowhere bo gopended upon. I am satisfied that in whatever portion the deposit may be opened up, there will prove to be of the rock excavated ,a- very considerable percentage so soft and friable as to be useless for the work, juid that heavy blocks from 10 to 25 tons in weight, required for the seaward slope of tho breakwater, will be comparatively difficult to obtain. Holding this opinion, I prefer to materially increase my estimato of the cost of obtaining the rubble referred to, beyond tho figuro allowed by Mr Marchant. Mr Marchant, in reference to tho price of rubble upon which he has based his estimates, quotes that obtained at\Tiniaru and Now Plymouth, but the class of stono at either of these places is quite different to that at Waihirere., as the rock at cither place is of quite another texture, and withstands blasting without a material percentage being shattered to fragments, as will undoubtedly occur at Waihirere. It a comparison of probable cost bo instituted. I think 'that pertaining o tlie Grcymoutli Harbor Works may be cited as a more, analogous case, where the limestone, though of a very much more compact and uniform character than obtains at Waihirere, and quarried within practically a mile of the tiphead, cost 4s per ton. For estimate purposes in connection with the proposed worksv at Gisborne, I value the rubble deposited in the work at 4s per ton or 6s per cubic yard, including interstices, instead of os per ton as allowed by Mr Marchant. As regards a suitable section ot breakwater, I prefer that the sea slope should be at the rate of A to as advised by Messrs Coode, Son and Matthews, as against 2\ to 1 as proposed by Mr Marchant. In; the matter of executing the -work, -Mr Maiehant proposes to tip the nibble from a pile staging having a single track ot rails, but I consider it practically impossible that such method would succeed where the width of the breakwater, owing to the depth would he so -Teat, and where the bottom is papa rock, which makes pile driving, if not impossible, very expensive, consider that Messrs. Coode, Son, and Matthews’ suggestion, viz., that stone should he deposited by means of a powerful crane of wide gauge running along the top of the completed mound,” by far tho most suitable method, but I would advise a Titan having a radius of eighty leet- instead of 45 feet as mentioned by tins firm of engineers. A ‘‘Titan” would lie specially adapted for placing the heaviest stones upon the seaward slope of the breakwater, and although a machine of this description would cost, I estimate, some £16,000, I am satisfied that it would prove much less expensive than staging, and it would place or nest the blocks in ■ a manner

fclint cannot be accomplished by tipping, consequently, apart from the saving in prime cost and working expenses, less material would bo wasted in the construction of the break water. The major portions of tho harbor side of the breakwater and the hearting of tho work could be tipped directfroin. the top of the mound without staging.

RAILWAY TO QUARRY, AND CONNECTION WITH GOVERNMENT RAILWAY.

I entirely concur with Mr Marchwant’s proposal that tho Harbor Board should construct its own railway to tho quarry, instead of tapping tho Government line, as suggested by Messrs. Coode, Son, and Matthews. Although the construction of tho lino would be a considerable item, I feel certain that it. would prove the most satisfactory aiul economical course to pursue. For a work of this magnitude it appears to mo preferable for several reasons, that tho line to transport tho material should bo under tho direct control of the Board and independent of outsido jurisdiction.

I have not indicated upon file accompanying plan the line of railway from tho breakwater, either to the quarries or to connect with the Government station at Gisborne, as I consider this point immaterial at this juncture," but it sufficient amount has been allowed in the estimates to cover tlieso items. POSITION OF JETTY.

As already mentioned, tho prevailing winds aro westerly, but the heaviest gales occur, from u direction veering from south-westerly to southeasterly, and so far as possible, -ho wharves and jetties should bo constructed that vessels, may lie fore and aft to flic heaviest winds. Mr Marchant, as also Messrs Coode, Son and Matthews, have choson a direction more in keeping with that of tho westerly winds, .but I prefer to advise their alignment in a direction more in keeping with that of tho heavy gales. With regard to the construction of the jetty, Air Marchant provides two designs, one showing same to bo constructed entirely oi timber, and the .other of ferro-con-crete. Although I cannot approve of Mr Marehant’s designs, I would advise your Board to adopt a timber structure as shown upon -accompanying plan, in preference to owe of ferro-concretc, as I consider that fer-ro-concrete ,as applied to marine works, and especially to jetties subjected to tho bump and surging ot vessels lying alongside, has not been sufficiently tosted either lor stabiuty or durability, and moreover, the cost of >a fcrro-concrete wharf would be practically prohibitive, and I advise that the jetty be constructed of ironbark or turpentine piles, properly sheathed, and with suitable haruwooil stringers and decking.

PLANT. With regard to plant for expeditious and economical carrying out o tlie work, it is practically immateiial what scheme of outer-harbor, be considered as it may, 1 think, be accepted as a foregone conclusion, that die sea protective works would consis of a rubble mound involving a large expenditure. Plant, m tlie matte of an expensive undertaking, such as the. conditions demand for an outer harbor at Gisborne, is in the end comparatively a small item, though at first glance it may appear otherwise, and in this estimato, my figures, as will he shown later on, arc nearly double those of Air Marchant, including his staging, which, for comparison, should legitimately be classed as plant-, and some £lo,ooo less than tlie estimated cost of plant requirements by Alessrs Coode, Son, and Alatthews. As already explained, l prefer the method advised by Messrs. Oopdc, Son, , and Alatthews loi the construction of the breakwater, to that proposed by Air Marchant, and am quite satisfied that tlie sea staging suggested by him, if practical at all, could not possibly be carried out at anything tho figure ho has allowed for. it. My estimate of plant is based upon tho following:—For the quarries : One 25-ton locomotive crane, one 10-ton locomotive crane, and two 5-ton locomotive clinics. _ For tho breakwater :Oric 25-toil “Titan with 80ft. radius, and one 7-i-ton locomotive eraue. For transport of material: Two 25-ton shunting locomotives, and two 40-ton locomotives. The foregoing, together with stone trucks, rqck drilling machinery for sinking tlie jetty piles, pile driving appliances, machino shops, and quarry tools, brings the total practically up to £37,500, as shown hereafter in tho estimates.

SCHEMES AND ESTIMATES COAI- - It will be gathered from the foregoing pages, ot this report, that of the scheme already submitted, I prefer that outlined in Air Alarchant’s No. 1 scliomo to the amendment suggested by 1 Messrs. Coode, Son, and Alatthews, but I do not consider tho area which would bo included iu any of tho schemes sufficient lor navigation purposes during bad weather, nor for tho suitable reduction of scend or wave undulation due to heavy seas or swells, and I have therefore outlined a harbor of considerably larger capacity. I conclude that if the construction of an outer-liarbor be determined upon, it would be well adopt a Scliomo at this outset calculated to give satisfaction. In No. I schemo proposed by Air A 1 a reliant, that gentleman estimates the calm water area enclosed to be 156 acres at low water mark, and 77 acres of from 24ft and upwards at low water. The scheme I submit upon the plan herewith will afford a low water area of 265 acres, and an area of 160 acres, having a depth of 24ft. and upwards at low water, which’is more than double that of Air Marcliant’s scheme having the .same depth. Upon- the plan accompanying this report, I have shown in brown color No. 1 scheme advised by Air Afarchant, as also in rod the outline of a scheme which 1 propose your Board should adopt it an outerharbor scheme be determined upon. Although the cost of such scheme is considerably in excess of the other schemes recommended, 1 am satisfied that a harbor of smaller area would prove a disappointment, and in view of the large tract of country at tho back of your port, which I think may be fairly classed with the finest the Dominion can offer, I feel that if any outer-harbor works be proceeded with, such should be Satisfactory from a landsman’s as also from a shipmaster’s point of view, ami although the. scheme which I suggest may appear expensive, I can not do other than advise that if your Board are not prepared to undertake such work at tlie present juncture, tlie question of constructing an outer-harbor should be deferred until •such turns as the settlement of the district will admit of such works being undertaken bearing in view that in the construction of an outer harbor for Gisborne no half measures will satisfy the legitimate demands which your "Board, aud the public may ex-

peet Whatever suitable schemo may lie brought forward, must under any circumstances, involve a largo expenditure, and tho time occupied in completing same will he from lour to five years, dependant upon tlie class of material the quarries may tyrn In ordor to bring the different schemes to a common basis lor estimate purposes, I have allowed tho sea slope in each case to he at tho rate of 3 to 1 to a depth of 18ft. below low water, from that depth downward, as also on the harbor side, a slope li to ■l, which is that adopted by both Air Mai'chant and Alessrs. Coode, Son, and Alatthews, but in each case I have increased the price of rubble as already referred to, from 3s. to 4s. per ton. Any estimate of the quantities required includes the voids or insterstice.s between the stones, which I prefer for waste and sea risk, should not he taken into account. The estimates of other items are those which I consider necessary for the efficient carrying out of tlie work, and for the areas to he reclaimed upon the bench and at the foot of the breakwater as shown upon the accompanying plan, and the scheme which 1 propose’ includes cutting out to a depth of 38ft. at low water tho pinnacle shown upon plan to the North East of Toinoana Rock.

AIR MARCIIANT’S SCHEME, No. 1 Breakwater ... ...£308,300 Railway to quarry 23,-150 Connection to Government -railway station, Gisborm, imhiding swing . tir'd go aero, s present lmrbor cn. trance 8.000 Riant 37,470 Jetty ... 41,830 Reclamation on beach ... 7,000 Reclamation at root of jetty 9,260

. - . £435 330 Engineering and contingencies ...a 21,760

£457,090 MESSRS COODE, SON AND AIATTHEWS’ AAIENDAIENT, AS ESTIAIATED IN REPORT. Breakwater £282,930 Railway to quarry ... 23,450 Connection to Government railway station, Gisborne, including swing bridge across present harbor entrance • ... 8,000 Rli'et 37.470 Jetty 41,850 Reclamation on beach ... 7,000 Reclamation at root of jetty 9,260 £409,960 Engineering and contingencies 20,500 £430,460 SCHEME AS OUTLINED IN RED UPON ACCOMPANYING PLAN. Breakwater .£412,500 Removal of rock pinnacle referred to in report ... 4,000 Railway to quarry ... 23,450 Connection to Government way station, Gisborne, including swing bridge across present, harbor entrance ... 8,000 Plant 37,470 Jetty ... ... 41,850 Reclamation on beach ... 7,000 Reclamation at root of jetty 9,260 £543,530 Engineering and contingencies 27,200 £570,730 I would explain that the estimate and alignment of the scheme which I submit .herewith are based upon the data' offered by the most recent Admiralty chart and the soundings by Air. Ala reliant, and should your Board decide to proceed with same, slight modifications as to. alignment and saving in cost, could doubtless bo brought into practice, hut for present purposes, the alignment and estimate are in my opinion sufficient. In conclusion, I wish to thank your Board and tlie Harbormaster, Captain Gumming, for the assistance rendered me during my visit.

I have the honor to he Gentlemen, Your obedient servant, LESLIE H. REYNOLDS