THE HARBOUR SCHEMES.

Wanganui Chronicle, Volume L, Issue 12765, 17 June 1911, Page 8

THE HARBOUR SCHEMES.

, REPORT BY-MR. REYNOLDS.

DREDGE

£ THE UPPER SCHEME CONi DEMNED.

■VA PRACTICAL IMPOSSIBILITY."

SOME INTERESTING READING,

The report from Mr. Leslie Reynolds, C.E., regarding the '• upper <and "lower" harbour schemes ■. was Considered at a special meeting of the Harbour Board last evening. The members expressed satisfaction at the .estimates, which confirm those of the SesSent Engineer, but as will be seen from the report below, extension of ■the moles and increased floating basin iave been allowed • for. Following is fthe report: —

Wellington, . 9th June, 1911. "/The Chairman and Members of the Wanganui Harbour Board, *»Gentlemeii,— . In response.to your Boards request of the Bth ultimo, that 1-should make an inspection, and report on the Harbour extension scheme as outlined by Mr. Howorth and also to report on making a deep sea harbour at the town, 1 visited Wanganui on the 17th of May and remained until the 24tn -of the same month. The weather, during portion of that visit, was exceptionally boisterous, but I had .ample opportunity to inspect the works generally, and especially the quarry and the' entrance to the -estuary, extending seawards to well -•over 20 feet at l.w.s.t. Upon completion of my investigations, I returned to Wellington, in «order to refer to my original plans and * data and for the purpose of arriving -at an independent estimate to that submitted by Mr. Howorth: your "Board will therefore understand that rSn the figures hereafter given, the 'items although grouped as far as pos- ■ sible under the same headings as those submited by your Resident Engineer, have been' separately arrived ,at, and from totally independent sour- * ces of investigation. WORKS AT THE ENTRANCE. The' works at. the entrance conaiprising the" n6rth-east and south-west "moles have been extended to a mean distance of some 11700 feet beyond ihe short 'length of breakwater on the north-west side, which existed in 1894, and I am pleased to be in the position to report that I find no. shoaling seaward of the.work has occurred' ,•. since my investigations and soundings *of that year; but that the depth at the entrance of the present work has * considerably improved, being on the - date of my last, observations from 18 to 19 feet at h.V.s.t., or a general .increase on what was formerly the Bar -of from 6 to 7 feet. It is now proposed by.your Resident Engineer, Mr. Howorth, to extend the moles to the distance shown ."in green upon the plan acepmpauying my report of 15th January, 1895. ~This addition involves tlie construction of 2,100 feet to the North-west mole, and 1,800 feet to the south-east mole; and I might here remark that _ the termini of the moles to obtain the T>est results, both from scour and protection from sea run, should, upon be practically abreast, with, if anything, a lead on the northwest mole. When dealing with fu/ture extension, in my report of 1895, I expressed the opinion that when the moles were completed to the points your Board now contemplates, they -should be raised to nearly full tide . level, and that the extensions should give a depth of 20 feet at 1.w.5.t., and -.28 feet at h.w.s.t; and in view of the improvements obtained from the works so far constructed, I have no hesitation in stating^that such" depth "•will be' fully realised and maintained foy acour, but to obtain 'jk deptiL-qf.-jJ,1?1 feet at Idw water it%ill be necessary -, to\ extend' the moles to the 25 - feet «ontoar: line, which means an addj-r tlonal 500 feet to the north-west mole -.and 400 feet to the south-west mole -to that which Mr. Howorth has re^ -■commended. I am satisfied that with the propos : %6d extensions and the raising o£.the moles to 1 foot above, the level r of h.w.B.t. the depth which will be maintained by scourjwillbe from 24 to 25 feet at 1.w.5.t., or Equivalent to 32 or .~33 feet at high water during tfre same .. ' . \'.Z: V-V - ■■■■ '(•;. It might be found an advantage to -■-flecrease the width between the moles

which are now being constructed at 600 feet apart, to 550 feet, as originally estimated, but this is a point which can be decided later, and acted upon should experience, as the works progress, prove such course advisable. 1 am also satisfied that if constructed to the height just referred to the foreshore will not make to such an extent as to decrease the depth seaward of the work, and that there will be scour sufficient past the end of the moles to prevent any lodgment of littoral drift, which will be swept clear and driven by the action of the sea on to the South Spit. I might here remark, that it is evident from Mr. Howorth s recent survey, that no denudation has occurred on the. seaward face of the spit, except over a distance of some 2 000 feet from the south-east mole, and such alteration only occurs in the line iof low water mark. Beyond this, the low water mark has advanced seaward on an average about 150 feet, and the width of the spit at high water mark increased .throughout by jiiiout the same distance; while on the north-west side of the moles the advance of both high and low water lines is practically immaterial from that "which obtained in 1894. INTERNAL" WORKS. Floating" Basin.—ln my original scheme I outlined a floating basin at Castlecliff, when, as will be seen from the plan then submitted, 1 assumed the Board might acquire some 300 feet width of property fronting the floating basin". The -vested interests have since that date-increased to such magnitude that such suggestion appears now out of the question; and after^cohferring with Mr. Howorth in the matter, I have decided to obtain the swinging room required by large vessels, by amending the original line of the channel wall of the basin, as per plan herewith, some 250 feet towards the South spit, which will give the same results as the original line, and the width of the basin required. Mr. Howorth,'" in his, estimate, allowed ifor dredging some 15 acres of the floating basin to a depth of 3,0 feet at low water; whereas I think it necessary to increase the?area to 25 acres to the same.depth; and have made allowance for; same in the estimate hereafter, given. Ifind this imperative, as 15 acres would not" give swinging room for the larger vessels. It might also, be In conjunction with the scheme" your Board npw.-.,Cjontempilates,» to extend the South spit training wall some 1,300 feet in advance of: the work shown.! dotted in black upon accompanying plan, and no^ed "in course of construction," but this is a matter which, in my opinion, can be left in abeyance at present, and until the works so far recommended and shown^m_red upon accompanying plan have been com-" pleted. The dredging which I now propose to shortly refer to should demonstrate the necessity for extension or otherwise. I have.estimated the channel wall of ]the floating basin as consisting of a hearting of the best clay pbtaiakbie. fTpm Landguard Bluff which, apart from attrition, is insoluble "in water, covered where the current is not material "by lignite and shinglel co^glonlerlate' from the same? locality1/ Initf protected'where the wall enters the •^stream by rubble from .the quarffesr "^ jtin; tliatl Landguaiird* Bluff v holds* more -than ttinple material suitaWe.^r.; the work, and I woiild have advise^ its us© for the present South spit^ttainlng-wall except that I Judged in dredging ~ the chaWei' ip ioMs. '•$&&& b«s;sufn-; cierit<snibgM'which:-Woiildvnot p^ss theTdred'g<§vJiuMp 'a'nef c&uld be utilis 1 ed far* the;«ons|ruc£iQßjOf the, wall. tl&l|sES£ I^^|^.;l^SSELS, ;].:, It ■'■.fic^ni my prej vioual^einarks i^ipdtt a ; jdejei> .sea harbour at {Jastlecliff, that 4, have i.,ostjU mated that? the continuation of the moleg.^ill maintain; by igovtrsi <161>t% -of 'irp^:;^-^t«r'-;2'5-''feefe:-iait ldwfrateiv -which wiitild be equivalent t<» 3"^ tP S3 ieejt at hrw.S-1-. and thafc:!the floating iliasin aX Castlecliff should; haw a dredged: "< area of 2 5 acres,', most Of which should be excavated to 30 feet at J.w.s.t, ... The largest boats within j our. vision, which are likely to visit Wanganui, "will, when loaded draw from 25 tP 27 fee,t, as, I do not con-, sider it' probable that Wanganui will | be the last port of call before leaying j the Colony. Referring now to 'the channel to town, l] have gone very, j jthpTOiighly into tlie question of the depth to .be obtained and maintained, throughout excessive dredging, and the conclusion I have arrived at is, that at mos,t,l.2.fejßtat•l.w.s.t, or, say, 17 feet at h.w.Tn.t., with a bottom width of 200 feet is the limit obtainable. The flow in terms of the tidal volumei -and normal river discharge I'atxo.ve-the town would, during the second and third quarters; of the ebb tide, be^say; 15,300 cubic feet per second, which would maintain during such period a velocity in a, channel of the. dimensions above given, of, :say,3 1 feet;per'second; or, approximately 2, ■miles per^hour,. which is the least velocity permissible for the purpose of keeping the channel clear without excessive and continuous dredging. DEEP SEA HARBOUR AT TOWN.

The construction of a deep s6a harbour in the vicinity of the town of Wanganui is, in my opinion, a practical impossibility, without recourse to heavy and continuous, dredging. In this, I am referring to deep draught vessels of from 25 to 26 feeL My, reason for arriving at this conclusion is that the total tidal arid river compartments, as affecting the outflow, extends for a distance of 23 miles from the Heads, and taking the whole volume or capacity of the estuary as a unit of scouring energy, practically only one-half of that unit is contained in the river reaches above the town, the balance being due to the wide expanse of the estuary between the town and the Heads. It should, therefore, be manifest that if one unit of volume is required to maintain a depth for deep draught vessels, onehalf the unit cannot do so; and it should be plain that no deep sea harbour can be maintained in the vicinity of the town without heavy annual upkeep in dredging. What the annual expenditure in dredging would be is problematical, and would depend.upon the rainfall during the year, and the suddenness of heavy floods. It might be objected that the same reasoning pertains to my calculated depth obtainable at the Heads in connection, with the entrance, and deep water berths, at Castlecliff; but my observations tend to convince me that the whole unit of volume will, unless extraordinary conditions occur, maintain by scour the depth before given. I am aware from my investigations of 1895 that from the town, and extending up-stream for some 14 miles, deep water exists, sufficient to float a fair sized vessel, but the depth is hedged by such narrow confines that no deep sea vessel would attempt to navigate the track. It will be gauged from my previous remarks that a deep sea harbour at or near the town, apart from continuous and heavy dredging, can only be an assumption, but as your Board have asked me to give an estimate for the construction of such harbour. I propose to roughly outline the works that would be necessary in connection therewith, leaving alone the annual cost of dredging. And I wish.it to be.understood that I have weighed the ques-

tion from the point of obtaining the best effects from scour and when the river might be in flood, and consequently minimising so far as possible continuous dredging. It might be argued that were the training walls constructed to the level of the river banks above the town, the depths required for deep draugnt vessels might be acquired; but I am satisfied such could'not be obtained, or maintained; and moreover a heavy flood would be throttled to such an extent as to cause most serious damage. It is the wide expanse of estuary below the town that is to be accredited to the flood escape; and I maintain that the training walls over the flats should never be constructed to a height of more than one foot above half-tide, and to this height only when the channel has been excavated to a depth of, 12 feet below low water, as previously referred to. I can only look upon the deep sea harbour question at town as a theoretical problem, and I find my conclusions on such basis. -It is on the face of it impossible to berth large vessels at the town wharf, as there is not sufficient swinging room. Moreover the present wall and breastwork would fail if the depth were ob* tamed to accommodate berthage, as would also the piers' of the town bridge. Mr. Howorth, I understand, in his estimate to your Board, assumed a site for a floating besin on the Gonville side of the north wall, abreast of the green light. Accepting such, site for a floating basin, the only navigable entrance would be one frortv the present channel at a point abreast of the middle red light, as no vessel would attempt to deviate' from its course at a sharper angle where there is the existence of a river current. Tn the estimate which I shall presently give, I have assumed that the training walls -be constructed to full tide level, and continued to the 'leads, aiid that the channel from there to the suggested floating basin oe dredged to a depth of 25 feet below l.w s.'i.,. with a bottom width of 300 feet.

It will be necessary, in connection with any proposed extension of the harbour scheme to obtain an up-to-date dredge of a type corcil-niin? a bucket ladder and centrifugal pinup to discharge into the dredgy hopper, pump direct ashore, as would best suit, the condition? of the locality where the dredge at^he moment may be operating; for in excavating thf floating? basin, about onethird of which I estimate to be sand, and. two- thirds soft clay, which cou Id be whoiJy iveratediibn by the cenc.ifugal pump with cutter appliances; and I would suggest the possible ad /.Usability of driving al| the material irom tbe floating basin ashore with a view the • extensive *nea of r lc>--ly>ng;swainp in the proximity o* the Soap Works. In .deepening tue "entrance, the material to be dealt with will prove to be principally sand and; gravel which the pump would 'U +it while the dredge was in motion,'and deliver into the dredge hopper and • dump at sea. "The bucket ladder would be necessary for increasing the depth over the flats, as the papa ridges aod "incrustated— shingle could not be otherwise satisfactorily attacked.

QUARRY,

I made, during my visit,, a thorough examination of the quarry, and also of the outcrops showing oh the flanks of the gully adjoining. These outcropsv whichMr.vHo^orth proposes- to investigate, did not appeal to me as a freliable: source for either quantity or of stone, but I think that his suggestion of running a cut or. more tp_ prove them;. Should: be followed i biiti in anticipation of: this, source . proyirig fruitless, "and bearing in mind .the paramount advantages to be gained in rapid-(supply- of- stone, and execution; jof. thft works which;1, with thet present face cannot be materially,increased, I . have, as will be seen in my estimates, included sufficient for another line .of track to attack the stone deposit at the up-river end- of the bluff. The maximum gradient on -this line would be, say, 1 foot in "1 % feet which, although steep, offers, in my opinion, n6 bar against perfect safety and^ecpnoiny in working, which hinges entirely on the adequacy of the brake gear. I feel convinced that for speedy exeeiitioii.'Tof the' proposed extension t>f the works, and failing the outcrops in the gully previously referred to proving satisfactory,., that a second line will be of considerable advantage. There would be-less stripping and more speedy delivery of stone, and therefore more continuous progress in the formation of the works than at present, and, I judge there, would be a saving effected of .at least 20 per cent, upon the-present cost of rubble.

ADDITIONAL PLANT.

I might explain that in the matter of additional plant, I have allowed for three cranes, and the other items the same as Mr. Howorth. It appears , that the 7-ton 'crane at the head of the ..quarry incline is proving rather light for the work ifc.is called upon to perform,, especially in dragging heavy of stone from the face; and I propose that its-place be taken by one of heavier design, and that it be removed to the south-west mole, where the crane now performing the work there is of obsolete design and well worn. The proposed new incline would have a heavy crane at the top, and derrick-crane similar to that which how loads the stone on to the barges from the present incline, and which has proved to be in every way satisfactory., ESTIMATES. For the sake of comparison, I have grouped the following estimates as nearly as possible under the headings as those supplied to your Board by ,Mr. Howorth, and I am satisfied that the amount to each item is sufficient, with fair and proper management during construction.

Extension of harbour works, with floating basin at Castlecliff, and 500 feet of new wharf. Entrance depth,

25 feet at low water. Basin depth, 3 0 feet at low water:— Wharf at Castlecliff: -, £ 500 feet 6,500 Alterations, and strength^ ening present wharf ... 2,000 Dredging: 25 acres of basin mostly to 3 0 feet below low water 18,720 Dredging between bar and basin to 25ft. below low Water . . 8,750 Wall to Basin: Length 2,800 feet . .. . . . 10,700 Extension of Moles: North mole, 2,600 feet .. 46,140 South mole, 2,200 feet . . . 39,050 Quarry Extension: Second incline, including 2 new cranes, wharf and plant -. 5,690 Tug, Crane and Barges: Tug, crane and 4 punts.'. . .4,550 Dredge: Combined suction and bucket ladder dredge .. 36,000 Engineering and- Contingencies ..........f....... 10,000 \"■ .' Total ...... £188,100

FUTURE DEVELOPMENT OF FLOATING BASIN; I estimate the cost of future developments of the floating basin as follows: — (a) With area as recommended at present. 25 acres, and additional wharfage age accommodation of 800 feet, exclusive of 500 allowed for in the preceding estimate, and including two goods sheds £13,600 (b) For fully developing the basin to 36 acres with a depth of 24 feet at low water over the area beyond the 25 acres already referred to, including 1,500 additional feet of wharfage, and necessary goods sheds .... £33,850 IMPROVING DRAUGHT OF CHAN-. • " NEL TO TOWN.. ;■■ V I estimate the cost of dredging the* channel to town to a depth of" 12 feet below 1.w.5.t., With a bottom width' of .2,00 feet, or, say, 17 feet at. h.w.ni.t., which depth should be mainr tamed by scour, with little, i£ any, dredging upkeep, and, including the raising of the present-training1 walls j to full half-tide level throughput, and extending the north wall to: the* floating basin, and the south wall from Landguard Bluff to Spit training wall: - • ■ -£ ' Dredging . . . . 10,700 Additional wall '. , 26,800 Raising present wall ,»-. - 3,300> • ' £40,800 DEEP SEA HARBOUR NEAR TOWN. I estimate the approximate cost of jsl dep sea harbour near town in terms of my previous remarks as follows: — £ Training walls from Landguard Bluff to floating : basin at Castlecliff 39,000 Raising present training walls to full tide lejrel 27,720 Dredging 71,150 Castlecliff basin wall 10,700 Dredging 36 acres on same '-'basis as basin'^at "Castlecliff ' 26,720 Wharfage 21,t>00' Channel wall of basin . .'. .*. .- 42,000 Training walls..at entrance, to floating basin to high water , v . level 15,000 £253,290 - Additional works at entrance (other than pertaining to floating basin), also qtoarry extension and^plant: -* . -■ I : * £ £ , Predglng between " ' " " bar and basin . . 8,750 Extension of moles &5.190 - „ Quarry extension ~. 5,690 Tag, craire and punts 4,55,0 , Dredge '• 36,000 140,180 .3-83,47<) Engineering and Contingen- _ cies ... . 24,000 - . ' £417,470 In conclußipn, I can only express tny satisfaction./with the resufts obtained from the works: so far executed, and I desire to tender my. sincere appreciation of the -courtesy always extended to me by the members of the .Board during my many visits, and to ■Mr f Howorth and Mr. RodVell and othfer officers of the Board for their willing assistance rendered to me in obtaining data necessary for formulating my various reports. I have the honotrrto be, Gentlemen^ • Your obedient Servant, LESLIE H. REYNOLDS.