HARBOR WORKS

Gisborne Times, Volume LXX, Issue 11123, 5 February 1930, Page 2

HARBOR WORKS

REPORT BY MR. LESLIE REYNOLDS.

WAVE TRAD WALL SHOULD BE EXPEDITED. OTHERWISE SHOALING WILL IN VOLv E HEA V i DREDGING. LEAKAGE THROUGH DIVERSION WALL. HOW IT AUGHT BE REAIEDIED. Responding to a request for a report on the harbor works, Air. Leslie Reynolds, consulting engineer, supplied the following information for consideration at Monday’s meeting.— “1 have at different tiroes inspected your Board’s works, sometimes in company with your Resident Engineer, sometimes with your. Chairman and- Engineer and the . last time with your Chairman and several members, the Engineer on that date being absent on annual holiday lioni which ho has not yet returned. As your Consulting Engineer, I desire" to furnish a few remarks !on the present progress of the work. WAVE TRAP WALL. “The Wave Trap Wall has been skeleton piled throughput tho designed length, but tho sheet piling has been completed only over a distance of some two hundred feel. Notwithstanding Lin’s, the effect, with only the bare assistance of skeleton piling is proving my contention that whom tho compliment of sheet piling be added the result will he the final clearing of the sand deposits which so handicap .the harbour entrance. Tins conclusion before expressed, lias’ample proof extant already, in that 1 lie. land laised .to suspension is duo to the wave swirl around tho piles alone and driven shoreward, has resulted in a seaward advance, of high eater mark within. I lie trap to the extent of some forty to lilty loot since ioioineiieeiuent ol Ihe wall construed ion. This bias its satisfactory points a.s regards proof of my contention viz. that with the river diverted tho sea rip along Ihe wave trap wall, will cut- deep" and drive tho sand of s-ieb cutting towards th'o Waikanac. .1 lie replacement of such quota- ol sand thus removed must be made good by replacement from file extensive sho.-iI at Ihe harbor entrance and in turn he driven westward by sea i iji along the. wall and as this /continues as if must so will the shoal decrease. This for the reason that the thrash of the seas along tiro wall will lie towards the west tor the simple reason that it can never be eastward. As that dissemination ol tho shoal sands will be gradual it must -ho expected that lor some period i thatthe reflex waves rounding the breakwater "ill drive some- portion of the shoal sands into tho present channel. With t-lio wave, trap wall completed this will be comparatively insignificant and short lived. As a result of tile wave trap wall being skeleton piled and the sheeting void over seme 700 feet now existent the seas ripping through drive the disturbed sand elite the beach and is causing rapid shoaling ol the trap basin and in their Mined strike in unison with the natural ileilex drive immense quantifies ol sand t-Inough the apertures ol the decadent grovne. These quantities through ihe' rip of t-lio seas along the groyne are re-distributed into the fairway. With such, facts in view, it should be obvious that some determined effort should be made to hasten the completion of the wall, firstly that portion of ICO lineal feet between the diversion and the commencement of Mr. Butler’s contract. “re proceeding further I wish to explain the why or whereiore tint such closure was not included in the wave trap contract. W hen your hoard invited mo to advise in PJ2S. Mr. Fulton was your board's resident engineer. He explained that there was an ample quantity of hollow or caisson blocks on hand, ivnowing that the t-lirash ol the seas along the wall must bo severe in tho corner where the trap wad junctions with that of the diversion cut. I threw tiie alignment seaward (vide my plans) and readily. agreed to concrete work for the ICQ feet closure ior engineering reasons if nought else, it was impressed upon me by your then engineer somewhat thus—seeing that the board have the blocks and the plant it- would be wise should the board’s staff undertake the closure and, that the designer of tho blocks. (Mr. Fulton) understood all about them, also the piant, etc. 1 thought then the suggestion a, wise one —lienee the nonmclusion in Air. Butler’s contract, this unfortunately was during the transition stage of your hoard’s staff, and the closure was not immedately put in hand. Indeed i. -.light rightly add, the importance of speedy closure was not grasped so early'as preferably might have been, 'fie' speedy completion of the wave trap wall is of significant importance. The root end of 100 ft. extent upon which tho contractor is- at present engaged, should he the luuiu item to speed up completion. The sheeting and filling of the skeleton should also he accelerated from the diversion wall towards t-lio groyne. No more sheeting than lias already been executed from the old groyne in the direction towards the diversion cut should be attempted.

“1 press these points for the reasons that if the completion of the wall be delayed the wave trap basin .aroa will through thrashing shoreward ol the shoal sands become somewhat akin to non existent and call for excessive dredging tor reinstatement. As shoaling of the ware basin since the skeleton piling has been driven shoreward is proving beneficial in the direction of coaxing Ibe seas to drive ashore the. disturbed (juota ol sands it would he incalculably' better were the wall completed- and sueJi disturbance and clearance of tile shoal sands many times multiplied and forced in the direction 'of the W aikanae Beach than at at present disseminated within the area of the basin. When inspecting the works- ,iu company with some of the members' of your hoard. I gathered that it has been suggested to the board to burry up tho purport of the, wait the seaward pile of sheeting only should be driven and till in a partial backing of filling m the meantime or until, the landward wall could be completed. Such an expedient I must frankly aver dictates to •mu' somewhat as dangerous. The wall facing would not stand tho sea thrusts and the wave overfalls ■ during . periods of heavy seas would, speedily cause such’filling of rubble to, scatter.

DIVERSION WALL. •

“Tho whole of the piling has been driven and the ,superstructure completed. There is, however, very considerable* leakage through the wall, not only at the recent work embodied in, closing the gap, hut in Nome of the old .work facing the floating basin where. tho. wall Ims not been .properly filled between the rows of piling. A considerable percentage -of leakage at what was . the gap is u.lup to t he spaces in the .pile heads whore they bnve been shattered-' im thei. operation of cutting over, length piles, to .receive the longitudinal, capping. These defects- the contractor is now making, good. The

leakage however, it not wholly due to top shattering,,, but.!, through spaces between, raapy of the piles throughout thieir lengths and I fool ooiiiidoiit that leakage will continue through the hearting which; is too coarse in, tho. aggregate to closely nest; tho smallest stones being of six inches diameter. Thlo intei-suees or voids in tilling such, as being .used, must be over 40 per cent., and it should be remembered that during Hood conditions there will be -&n;appreciable -pressure head oil the liver side. TlUe wall may take up due to silt and river wrack but 1 leer jn. any case it will take considerable, time, if ever. I would the re tore advise hearting of general debris such as is available at fir-niotii island taken, as it p bo shot or excavated, i.e. the fine with the coarse to be utilised for the b‘ilatice of the hearting. “It has been suggested by the Harbormaster, Captain Carson, to obtain tilling lrom the papa, re» 1 abreast f the breakwater viaduct whi :li he avers has been blasted, therefore it could be dlodged Filling iTOin’ either source • above suggested or from e.sewheie could ce ! loaded into ships or truck tops. Which ate available, and-dumped- j or crane from a punt. I have been led to unde 'M.aiid that about one seventh 'art of the stein: vcquiied has already Ivin .supplied, but in’ v’ew of the ne.-eteuy of having the "Ml. lor practical purposes watertight, a. more suitable class of hearting tor the balance js very well worth considering. “There is a method which suggests itself, viz., rich mortar loosely bagged in tiie form of what might lie tertned cartridges and kneaded into.the open joints after the hearting of wall has boe-n ( .completed. This would require the, services of a diver and a lowering -platform. 1.1 would be a tedious- undertaking which' might be. hastened wore-(br-ed speaking communication obtained whereby the diver could advise, from time to time the size of the cartridges required, etc. The right angle laiulffig or lap ,on the edge ifit tht; pile wings would make tho cartridge tilling sate against falling out. This is the only method which occurs to me to advise your Board to try. 11 will boa, tedious and delicate undertaking necessitating handling by those who have intui- | ion or grasp of tuo work and the import combined. it may appear somewhat of a ease ui puMyiug, but when all be considered it is surely somewhat akin to the plastering up of the spaces n tho precast slab su pci’s true tore. mi any case J. ro. commend a trial of closing the s-pac-i- n It v moans- I this method. No other th i.t 1 can .think of is appjie. ah!.' where any porno.i ol the 1 :i |- 1 - ing is in posit on. As. to <o-t, •it i t i;j v |m> £./;! N. i ;lU,' 11 Il!<> I must. }*:r force be a crude at tempt • hut for piv"‘-,.v purpose* allow that accepting the pn-MOole joints ilk th-; had," throe jf i.it- or ati .*q"iveL coi to say seven and one halt rur.u mg feet, of wall should to trcaivd pc. i?ay. 1 • p.re coiK-mduig my remarks upon the diver.-; on" wall, may i be | v,; mittoil in -.-spies.-, my i.punc:. \l/ , that the „ dcs as lies ..pied rev not coincident with e-.nso ranted sheeting a-ud should, not. have been exploit'd to fulfil Midi requ.ii-ments in the strata into '■yb’eh- they have been driven yspe< buly, here rciliivcu after through flood mishaps 1 >>’- fore completion they hud to he nitlidrawn anu mlriven. A here such occurrences pertained the class oi hearting might have been more studiously considered- In any case v hen or where erratic behaviour in the. piles unavoidably occurred it would have been well to alter the class oi material used, in the hearting, and extended such above die longitml. mat cap by some two 'or three feet, j tried to impress this ; dint upo' vour recent resident engineer, but evidently it has been 'overlook'd. ! have for the purposes of this rei ort made a fairly extensive inspection of the diversion wall and the works in progress in connection with the wave trap, also Tuamotu Bland, which has enabled me to express my views as before written concerning each.”

ADDENDUM

“As there may he some misunderstanding as to what 1 proposed in the term “debris” available at Tuamotu Island, etc. I wn-ii if ’•’> be gathered that l was net reLr. mg to. the general face of the Island, where soluble clays - obtain, but to that pertaimug almost immediately to the light- ot the root id the jetty as one approaches the island. In that vicinity, say a chain or so from the jetty, then is material admirably suited dor the diversion wall hearting, using the line with tim coarse. I may add that tiie hearting .should he carried iff) some two or three leet above the pile string ocurc; aid finally pro. tented •.gainst- wave wash and pa os. sure uplift by layer (-1 itaiiu paci - c-d boulders. E\en wnere the na st suitable of hearting ;he employed gaps (of any material consequence between the piles should be made (Airly watertight ■ for , a- depth of three feet below the pile can course, The above remarks Tefor to :iie bend in the wait where Hood (iisli will impinge and tend.-to scour deep. .! have tested Trinidad bitumen in ffuxeil form and (oncluile swell wJptdd prove suitable Jilling for spaces where the use ol (emenl. earlridges may be impracticable.

RESIDENT ENGINEER'S REJOINDER. M IST USE HIS OWN JEDOM E NT. I n a rejoinder, Air. U. !. .Marshall Smith, the resident engineer, said—“As regards .Mr. Reynolds' report, when it is all boiled down, it contains very little .information that has not previously, been given to the Bjuard either, by Mr. . Reynolds or myself. The history ol the wall and its oll'ect on the harbor entrance is very interesting, but, at The present stage, quite, irrelevant. I lie wall was designed and; its site.- lixod bv Air. Rovnolds for, just .fliat purpose, and, when completed, will undoubtedly (Jo what was ; expected) .The time taken to complete, the wall, has unfortunately, created other difficulties in the way .of sand accumulation which no method of working- cot# have diminaLeii. J.n .fact Mr. .Reynolds lumsef, in his original estimai'o, allowed a sum to cover .the cost-.-ot remov-ing-any such accumulation c-i‘ sand.. Even at the-present, time, the accumulation -of saud has not readied such proportions that any- special dredging will be necessary, though tho channel nia-y take a little longer to become stabilised. No onemore than myself sees the necessity ol oomplethm the wall, as soon as . possiblo£, ancF every.. oll'o.rb will he made' to do so, .tukiiig .Into.■ consideration the natural' and other difficulties that have, been encountered. As. to the method of carrying out tho work, no two men are .cwf fully agreed as to method or order of , work though- oventually,., arriving- at the same rofiulty' A.VJi'ilo agreeing therefore with Mr. Reynolds that the result to IK.K-aiiuc.dv aUds -dho. completion (of the wall, as soon as possible, I do not agree with his rriti icjsm of the. methods, being used; to achieve the same result.- I am not in my position a pupil of 1 Mr. •'Key-

• • ■ - i- ■> nolds and', while grateful to him for Hi's suggestions; emusb ,be allowed to use. my own. .judgment aiid discretion jri earryiiig ouUV tlio work under my, cliargeA'-A .; --, IhU diversion wall tlierp:;sXSy‘abs(>lutely -i xiothifig to;, oceasiopt'anya Uneusines’s". '-it is' xiot ,a’ job liiat (.-an'-'hh 'i.'ibiiipleted in a week (irvtiv.oj iii'Kj" vv licii .completed, can it ho ■ expected- to- bo perteet witliout a'casonablc” 'niaiiitenatice.', ", Be’ycrai, xoaliageK 'iu tiie Kaiti Basini portion of the wall come m the latter category and are being attended to as {opportunity offers. As for the later part of the wall, it is far from complete and comprehensive criticism of. thiisi portion is distinctly premature. Not long ago Air. Reynolds was adversely criticising the actual design of -the wall and its stability. He is 'apparently more satisfied now. in this connection, but, nevertheless, continues his criticism by making other premature statements. “I think I have satisfied tine board by. this time that expense with me is ; not a secondary but where equally good results can be obtained by a cheaper method I have not' hesitated tp recommend it. In this case, as the stone filling is a lengthy process extending. over a period of a good many months, it will be some time before the ultimate benefit is obtained, hut it will be progressive, especially as the lower layers of stone are becoming more and more compacted with mud. ft is hoped that by this means the wall will become practically impervious, but .if not and it is found that some of the worst openings persist then will be the time to carry out any plugging required. At the mostonly a small proportion of the joints would then need treating. “As regards the size of live hearting, a small proportion of smaller stones would doubtless- hasten the compacting with mud, but extra expense would be incurred in handling the smaller material for very little ultimate advantage. I am not prepared to relax - materially the specification regarding the size and quality of the stem's, and this would create-a difficulty in maintaining I li'e quality of stone in the sea wall contract. Botin .jobs are being supplied simultaneously and it is not possible to separate tho stuff, delivery being given to whichever vessel is there. ]. can assure the board that everything possible will be done 1.0 ensure the success of the work both oil the training wall and ebe. 'whore.”