HARBOUR BOARD.

Otago Daily Times, Issue 4436, 8 May 1876, Page 6

HARBOUR BOARD.

A special meeting of the Harbour JBoard was held on Tuesday, 11th ult. Present: — His Honour <the Superintendent (in the chair), and Messrs M'Kinnon, Reeves, Reid, Ritchie, Turnbull, Tewsley, ana the Secretary

MAJOR GORDON'S REPORT. _ The Secretary said that, according to instructions, he had only ten copies of Major Gordon's report printed, one for each mamber of the Board and one for the Engineer. It was resolved that the following report be taken as read —

Dunedln, 22nd March. 1876

To tho Chairman of the Otago Harbour Board. Sir -1. In compliance with your request, I have the honour to,.give my opinion ami suggestions oa tho scheme of harbour improvements now before you. I havo read the reports furnished me by.the Secretary, and Mr Simpson has kindly put at my disposal all the information he has on the subject. The subject seems to divide itjelf into the following main paits, :— 1. The improvement of tho access to the Port,; 2. The reclamation, including tho quay walls, the mode of disposing of the excavated material, and provid ng Btuff for the reclamation; 3. Tho cost and time.occupiod in execution, into which, however, I can only enter in a general way. No more, however, seems necessary, as the estimates of your Engineer of the proposed works, modified (if it seems to you desirable) by tho observations 1 huve to make, can be checked by calling for tenders for the works. I.—ACCESS; TO. TUB. PORT. 2. The harbour of Dunodin Is a tidal inlet with&wo channels in tha lower part, and tho natural tendency of the tidal .water would appear to be to follow the: south channel, as it affords the more uninterrupted couras, tho shorter channel on the aorth Bide being b'ock'ed oy.sandbanka a little above Burko's. Above i this thero con only bo said to be ono channel, and th it ia gradually spread out into abroad expanse ol shallow*, .water at the head of the harbour. 3 In order to improve either of these, channols so as to admit of large .vessels going up to Dunedin, either of two plans may, in my opinion, be adopted ; but these are essentially dijferont, and cannot be cow-: bined, and Ui this particular I am obliged to dissent; from the, views both of Mr Balfour and Mr Simpson, whose plans are to a certain extent similir. 4. .One plan would be to .confine the channel by an otnbinkment to one sido or the other, so as to cause tho tide to pass up one channel, round in front of Duncdln, and up the other channel in a. reverse direction—the latter being closed at the north-east end. 'this would change'the Harbour,from a wide tidal inlet with two channels to a narrower one of greater length, with ono channel, and its head would then be where the embankment joined tho main land at the north-east end,, instead of at Dunodin, where it now is, tho flood and ebb strovms passing along the front of , the proposed reclamation. 6 The other plan would bo to deepen one or both channels, and maintain the depth by dredging and by stopping up the channels through the sandbanks ,n ar Burke s. . 0 Thero will bo always a tendency to shoaling m the up or part of tho Harbour. This is tho .cure In ali .similar waters, and it is proved in this case by tho advancement of the six-foot contour-lino outwards from tho shore-line sinco tho time of Captain Stokes's aur.vey. In the first of the ahove modos of treatment this tendency to silt would bo partially counteracted ,by tho tidal Btroam in the part ot the channel leading from deep water to Dunedin, or some distance beyond it • while the tendency to shoal would be greater then than it now Is at tho new head of tho Harbour. By tho second mode of treatment, tho tidal action would bo little more than it ,is at present, and dredging .would be .required to niatutaiu the depth, aided by training walls iv certain places. In either case tho dicp water channel would havo .to bo first formed by .dredging, the effect of the walls would only bo to assist in maintaining it. . .. »,» 7. Although I agree with the greater part of Mr Bilfuur's report, I have the following objections to his plan:—First, ho would partially obstruct one .of tho passages for the tide at tho Half way Islands, whore the sewiona.l area is already too limited; secondly, by leaving oponings ,in the training wall at that end to would admit tho tidoand so neutralise to agieatcxt«nt the action of the training wall, which would havo Ithe effect of entirely confining the tidal water to one channel. If the principle of tho dividing embankment were adopted, it shou d bo mode up to about one foot abavo ordinary high water, and should in my opinion bo continued across the " Cros3 Channel in its shallowest part, and then curved round to Grassy Point;" access being given, if desired, to the south ■channel by a louked entranco provided with double gates. The reason ior tak njr it across tne " Cross Channel" is to avoid the deep water where that channol and the Portobello Channel meet, and it would also givo a bettor form of entrance to the north ,8. I do not approve of Mr Simpson's half-tide training' wall, because it would not, in my opinion, materially assist in confining the stream to the north channel, unless it were continued on to tho east shore and were also made up to hiich-water level, so as to Bhut up the south channel. Ihe wall, if made, should be considerably more to the south than shown on the plan, in order, flrat, that the channel might follow more nearly the natural set of tho stream as indicated by the depths; and, secondly, that the space to the north of the wall should ba more oxtensive, for it is, as designed, out of proportion to the spaco on the sou'b side which it would have to fill with tidal 9. I think tho quostion of a dividing wall extending tha whole way may be deferrod at present, as I understand it is the wish of the Board to undertake first such works only as will enable large vessels to come up and be berthtd at Dunedin as soon as possible ; and with that object in view, and considering that in auy cose the most important part of the work is the dredging, tho first thing to be considered and determined is the best course for tho channtl. 10. The tiortli channel is the deeper as far as Burkes. From that point upward* it may be said hardly to exist, and tho deep water is in the corresponding pirt of the south channel from Macandrew's 'upward. The south channel is longer by one-seventh 'than thoDroposedchanne1, but owing to the greater average depth, the quantity to be dredged would be less by about 207,000 cubic yards than in the north channel, supposing each to be 100 ft. wide. If we examine the plan which bas boen prepireJ, evidently with groat care, by Mr Simpson, we shall find, by the aid of the contour lines which I have drawn on it, that the natural tendency of the str< am passing up tho north channel to seek a southerly course is shown by the Bteep slope of the channel on that side in tho deep part of it, and by tho line of deepest water md cited by several pools of greater depth above the point where the sandbanks opposite Uurke's first interfere with tho flood stream. There is not a continuous depth of 6ft. even on the north side. These characteristics indicate, in my opium, that tho proper direction for the channel, as well as the line of least excavation, would bo nearly th .t shown on tho accompanying plan by a red line. On this line,««., following Mr Simpsun's channel from Kilgour's Point up tho north channel to near tiurke's and then trending southwards in tha lino of deep water, I find that the amount of dredging for a lOCft. channel will be about 913,500 cubic jards, as against 1.3GG.000 cubic yard 3 bythu proposed plan (although it is 10 chains lunger), showing a reduction of nearly one-third and representing a saving of £10-720 at Mr Simpson's rates—which, however, I think are too low-and a correspondingly greater difference if the channol is made wider. Whether the north, the south, or this middle channel be constructed, about the same length—l9Bo yards—of high water training-wall at the sandbanks will be needed to regulate the current and assist in keeping the channel open; and it it is hereafter found advisable, as a matter of economy, to construct a training wall or dividing embankment from Grassy Point to Dunedin, that principle may be adopted as well with the middle as the north channel. Tho south channel is not so well adapted to the plan described in paragraph 4 above, as it would bo very expensivo to close the north channel, owing to its depth. It would a'so be well, though not absolutely necessary, to construct about 1400 lineal yards of Mr Simpson's training-wall at its east end on the south sWe of the channel. I would remirk that at this part, and wherever else the borings show the bottom to be soft mud, the banks should bo constructed with fascines in the manner in us 3in Holland, viz., by sinking large areas of fascine work. In paragraph i of his report of 16th August, 1875, Mr Simpson has, I believe, attached undue importance to one item in the results of his tidal observations, inasmuch as he assumes that, because the tide now falls more rapidly at Burkes than it rises, while the converse takes place at Macandrow's, therefore the scouring action would be greater on the ebb if the new channel were constructed on the north rather than on the south side. The construction of the proposed training-wall and the deepening of either channel wouid alter to some extent the tidal economy of the harbour ; and, be-Bid-8, It should not be assumed that the scouring action must bo greater in one case than in the other, merely because the tide falls more rapidly, unless the relative quantities of water passing up and down, and i ho sectional area of each stream te also known.

lI.—RECLAMATION.

11. Although it U nearly always undesirable to reduce the tidal area of a harbour, I do not think that the more necessary portions of the proposed reclamation would be likely to injuriously affect the inner Bar. I am informed that it is now nearly the same as when Captain Stokes surveyed it; and the tidal area has been much encroached on since then. The improved depth will increase the tidal action, but only to a small extent, as it is checked by the narrows at the Halfway Islands. I would, however, recommend that Pelichet Bay and the portion on the opposite side of the Water of Leith should be left open until they are absolutely needed for building or other purposes. 12. The question of timber or concrete for the wharves is an important oae, and ha-i received my best attention. There can be no doubt that the latter is the most desirable form of construction, and judging by the results of tha borings and from the fact stated by Mr Simpson that the piles cannot be driven to a greater depth than that shown on his drawings, I believe it can be Buccessf ully carried out. There might possibly be some advantage, in the way of quickness of execution, in favour of timber wharves, but on this point I cannot speak with certainty. If it is so, some parts of the wharves might be constructed of timber simi'ltsnoously with the concrete walls, each mode of construction being pushed on at its greatest possible rate of progress. 13. Timber Wharves.—-Tho tenders received for these show, I think, that £48 may be tiken as the average price per lineal yard, to which has to be added thi rocky fllinsr proposed by Mr Simpson, and, I believe necassary, bringing the cost up to £(53. I think that Mr Simpson should lengthen his anchor piles and I lace them further back, and that the she-;t pil ng should be carried down to the more solid stratum under the mud. This would add to the cost, but, on iho other hand, a considerable saving could be effected by omitting one of the rows of 15in. piles, wh:ch are closer than necessary. The upper walii.go should, I think, be 12in. by (Sin. I would have recoiumcndud the front raking pile to be driven deeper, but Air Simpson informs me it cannot be done. The rubtil-j which Mr Simpson proposes to tip in between the piles, would, I think, be objectionable there, as it would interfere with the driving of new piles when that became necessary, and it should rather be placed in front of the anchor piles and walings couueciitg them. In my opinion the addition to the eros^ jetty or wharf shuuld be widened Hit., as the piks will not have guflicit-nt hold when the ground is excavated and it will probably be ncx-s^iry to tip i" n.liMi! to hold up tho slope-see sketch on the contract drawing No. 2.

11. Concrete Walla onre constructed would last f r all titm- and require no rc;i:Jrs; 1 would rccoii.nivini timber only if this u^e of it would s.ive time T-o plans have been pr.-prsed fur construct^!.' tho.se run ore to wharves, both of which ar« cxpoeied t'i U-li-.-spef. th ill coffer-dams, viz , the onicr. te •vl.i di-r----i.f .Mr irOrcuor, and the com-rete wall buia 1-y the "id fMr Xai-iiT'* pmtuon. Mr M'(Jrt#>r's limner I'm !iijfo. 1 pi-'ll amounts to £71 15s per lineal yard, aid tv tins Ims U) l>oad(J«'i for compai won witli Iho limber

construction £6 per yard for making up the width of tho roadway, nuking tho total Co3t £16 Ifis per lineal yard. As the tenderers were not furnl.-hed with the register of the borings, It is not certain that Mr M'Gregor has reckoned for the proper depth of cylinders. Further, as his tender ia only given in a lump sum it is impossible for me to, judge whether sufficient allowance has been made for much pumping, which I think would be necessary with concrete only 2ft. thick. The first difficulty applies equally to his No. 3 design, in which the wall could be founded by means of Mr Napi-r's pontoon, and which is, with the same addition of £5, estimated to cost £82 18s per lineal yard. I should say that I have never seen the latter system employed, although I have used a similar one on a much smaller scale, but I think it would answer well in stiff clay, in which the cylinders are apt to hang, while they would bo preferable in soft mud. The average cost of these modes of construction would, according to the tenders, be £79 18s per lineal yaTd but I think the Board requires more aSsuranoe that eitherplancar.be carried out for the sum tendered fur, and also more information as to what additional cost would be incurred if tha design had to bo a'tered as provided for in Mr M'Gregor's tendor. In short, plans and spo ideations of both modes according to the ascertained nature of the ground are required, and tenders for the work should be based on these.

15 As to the material for forming the reclamation, a rough estimate (which should be verified) induces me to believe that the quantity of stuff to be dredged from the docks and basins and tho deopened approach to them, together with 310,000 cubic yards from Dowling street, would amount to 2,281,479 cubic yards (sco Hr Simpson's report), and to reclaim the ground shown on the plan between the proposed steamer basin near Jetty street and Albany street, and to raise it Bft above high water would, allowing 25 per cent, for settlement, require 2,831,6C1 cubic yards of material, -showing a dene eney of 050,182 cubic yards, to bo brought from the uuper end of the channej, and leaving 337,Cba cubic yards to be dredged and otherwise, disposod oi. I think tho cheapest way of filling in the above portion of the reclamation would be by sending the mud ashore in shoots direct from the dredgers, so iong as the dredging is in close neighbourhood. 1 have not seen in practice any plans similar to those of Mr Simpson and Sir Jenkins, and I fear there would-be a. great deal of trouble ciused by the softness of the deposited material, which will take s me timo to consolidate sufficiently to carry a rail or tramway. It has been proved that it is possible to send mud a considerable distance in shoots, assisting its motion when necessary by water pumped up with it. At thejßame time, lam not prepared to say that by the plans proposed by these 'gentlemen, the additional quantity required fr..m the channel could not be deposited more expeditiou9ly than by hoisting or harrowing from bargos. I do not consider it safe to estimate ,it at a lower rate than Is 3d per cubic yard. The excavation from Dowling street should all be expended in filling in behind tho walls and between the sheet piling and anchor piles of the timber wharves. I think it would cost 2s (id per cubic yard.

111. COST AND TIME FOB EXECUTION.

10. It is always well to check estimates by the ascer-: tamed cost of completed works of similar character, and taking those on the Clyde as a standard of comparison, as beiiiy those the cost of which is the most carefully recorded I know of, I am bound to say that I think Mr Simpson has very much under estimated the cost of the works and the time required for completing them. The cost of dredging on the Ciydo in 1870-1872 was 3 86d per cubic yard. The cost ol towing and depositing on shore was 9.78 d, and that of carrying and , depositing in Loch Long 5.29 d. The total cose per cubic yard varied from 7.94 dto 38.27 d, and the average wiis lu.uad per cubic yard. Ido not think au average of less than Is 8d can be reckoned on for Buncdin Harbour. 17. Tho time of oxecutjon depends mainly on the plant omploj ed as regards the dredging. From an examination of the Clyde records, I find—ls>t. The average quantity dredged per hour per horse-power of dredger was 1J cubic yard. 2nd. Kach machine worked on on average 0J hours per day for 312 days in the ycitr, or two-thirds of full time. 3rd. That with an aggregate horse-power of dredging machines of 239 horao-power, tho quantity dredged in a year was 092,351 cubic yards, or 4162 cubic yards per horsepjwor per annum. The quantity to be dredged here being as above throe million cubic yards, tho time required by the above data would be (3,000,000 by 95 by 4152) seven years and seven monthij, the new dredger being taken at 05 horae-power, and the present ono at '30 horse-power. The time required for tho total quantity proposed—viz , eight mill., adding as a Dove 10 per cent, fur rcdredginjj—would in the samo way be 20 years. It is evident, therefore, I think, that tho dredging power must be increased in order that the wharves and dredging operations should be completed ab ,ut the same time. To complete in three years it would seem to be necessary to employ 240 horse-power, or, taking the most favourable example en the Clyde, the now dredger ought to lift 307,600 cubic yard*, 0.----1177 cubic yards per day, supposing she worked on the average nine hours a-day for 312 days—i.e., double shifts in summer. At the very least, therefore, the plant ought to bo doubled if it be desired to complete tho improvement in three years, to the extent suggested abovo—i.e., a channel 100 ieet wide, and the reclamation Dct.weon the coal basin and Albany street Jetty. „ , 18. I submit, for the consideration of the Board, the following rough estimate of the sum which I think oufeht to be provided for the completion at tho work so far, and 1 would suggest that the channel be first dredged to a depth of 13 or 14ft. at low water, and afterwards increased in depth, working from below upwards : — ESTIMATE. Dredging and depositing material from the 100 ft. channel, 18ft. deep; the Import, and Export Docks, 22ft.; the Steamer Basin. 17it: and approach, 15ft.—equal to 2,831,661 cubic yards, landed at ls,Bd £235,072 322,660 cubic yards, deposited at Is 4d 20,166 .Reclamation— 6,500 lineal yards concrete walls at £80 620,000 Say, 1,000 lineal yards concrete walls of less depth,'at £65 65,000 310,000 cubic yards excavation from Dowling street, at 2a Cd , 33,750 Training Wall at the Fork, say 10,000 Ditto at east end, 1,400 yards 2,000 Contingencies 48,11Depreciation of plant in three years 30 per cent 25,000 £905,000 The substitution of timber wharves for concrete would probably effect a saving at first of £112,500, but against this is to be placed the annual repairs, probably equal to £11,800. RECATITULATIOZf. ' 19. Tha suggestions and recommendations iii this report are as follow :—That, if it be determined to cary out this scheme, the whole of in should not be entered on at once, but that a channel, on the line proposed by Sir Simpson, with a deviation near " the Fork" and upward, should bo dredged to a depth of 13ft. at low water. That a training bank, one foot above high-water evel and 19S0 yards long, should be constructed where it is shown on tho plan. Tnat the wharves should be of concrete, 'lhat the reclamation should be not less than eight feet above high water, and should at first exte d from the proposed stenmer basin to the Albany street Jetty. Tnat the work could • be done in three or four years, and would probably coat nearly one million sterling. 20. I have not referred to the other reports furnished me by the Secretary, as, excepting Mr Thomson's, they are more or less modifications of, or remarks on, Mr Balfour's; and, with respect to Mr ThemseviV., the points on which I differ or hjcree with him are sufficiently indicated above. I would take the liberty of suggesting that a more complete s>et of continuous observations of the tide 3at tho Port, Burkes, Macandrew's, and Dunedin, should be taken for at least six months. I have not been able to make much use of those attached to Mr Simpson's report, from the fact that only three-fourths of a tide seems to be given daily, anil also, there is apparently no complete record of the direction of the stream and its chanco new high and low water, the term "slack water" being applied to the time when the level of the water was stationary. The distinction is important in discussing the tide-i of a port, 'flic observations would be of great value when the question of a central training-wall his to bo tiken up. I shall be happy to give further information, if on any point I have failed to make my meaning quite clear.—l have, &c.,

3. Gordox, M. Inst. C E.

The Chaibman said he had received many letters, which he had not yet opened, as he had been engaged at an. Executive meeting during the last two hours and a half. He sent for the documents, amongst which waa the following report of Mr Simpson upon Major Gordon's report: — Harbour Engineer's Office, Dunedin, 10th April, 187 G. The Chairman Ofcago Harbour Board. Sir—l have the honour to acknowledge receipt from the Secretary of a printed copy of Mr Gordon's report upon the projected harbour improvements. With your Honour's permission, I make the following comments upon the same in the order ol the several clauses therein contained:— Nos. 1 and 2 need no comment. 3. This will be more intelligible when subsequent clauses are under consideration. In the meantime, I may say that there exists the greatest dissimilarity between the late Mr Balfour's proposed mode of improvement and my own. i. This is almost precisely Mr Balfour's plan, the only difference being that Grassy Point would be the head of the navigation instead of Portobello. 5. This plan is suggested, but not supported by Hr Gordon. 6. The information contained in the first part of the clause is self-evident; the remaining part does not call for comment.

7. Is a criticism upon Mr Balfour's plan of Harbour improvement. 8. Contain* a difference of opinion as to the efficiency of the half-tide wall. To make the wall successful in Mr Gordon's estimation, it should be brought up to above the level of high water, and it should be made to connect! with the Peninsula—presumably about " Grant's Braes."

I should be sorry to see such a proposition carried out. As a lilbli tide wail, severing the north from the south channel, would in my opinion have the effect of interfering with, If not absolutely rendering fu ilo, the effective tidal working of the Upper, if not also the Lower, Harbour.

As to the wall being placed more centrally in the Bay to suit the " natural set" of the stream, Mr Gordon must surely be aware that the natural sec of the uorth stream would more or less loilow the coast line, were it not that a necessity existed for its departure therefrom, as fully indicated in clause 8 vt my report of date the 16th August, 1875, to which I wonld refer.

Were the sandbanks cut through as recommended in my plan, it would be found that the direction I propose for the clunne! would be very nearly the natural set of the stream; the course recommended by Mr Gordon would, on the contrary, give a forced set. In reference to tho remark respecting the disproportion of the water area north and south of tho wall I propose, such inequality or disproportion could only exist were Mr Gordon's' suggestion of a high tide wall carried out.

9. My opinion is that the erection of a training wall the c' tire lef-gth, is as neoea-ary a work as the drcdjfinjr of tho channel itself. First cost should not exclusively ir.onoijulise the attention of the Koird; future maintenance is one item which, if not carefully provided against, will assuredly have the effect of rendering the efforts of the Board tv keep open the communication a very expensive contingency; if cot altogether abortive.

10. Mr Gordon says that the south channel is about one seventh longer th-ui the north. In this he is nearly correct, but he is in error in stating that the former would necessitate less dredging than the latter by 207,000 cubic yards. An accurate computation civeslhc south cbaunel an excess over I lie north of 26,000 yards. Assuming, as vr Gordon does, the width at 100 ft. and depth, lSft. This error docs not alf ct the question of choice of permanent channel, but it is well at all times, in arriving at conclusion-, i-> approach more clotely tlie true contents th n the f,gun.-s of Mr Gordon's do m this instance.

Jt is ;usume 1 th.it because the southern slope of the north . haiui.-i is sti.cp, as-d si-vciul dei-p penis .-ho"'in the souiMlnus at the s-iidlnnks, itis;Ui iiiiiiuitiou tli.u th>: proper direction for t!ie eh umel i-> pointed <mt by the lino of proposed devotion. Suiiposiii- that an obiiructiou to the pr-'p'.":'-'.! !!■>«• of the strain, such is -in embatikr/,ent, were th'owti out f'<m ilurl;«'s .Icti.i, in mi li v ni ii.<-r us to tontruet tho pie cut, width of the clmnn. 1, whit would l>e the result .' Simi'ly this—that the process of attrition on the

opposite sandbank ot southern slope would go on more , rapidly than at present, until tho uniform width of the channel below was attained. Exactly the same holds good with the obstructbn above. Kemove it by cutting through the sandbanks in tho direction I propose, and the result will show that the southern slope alluded to will not bo further encroached upon, but will act as a guide in determining the proper direction of tho channel to be that running at an averaga uniform distance from the cca^t line. Mr Gordon again erra in his figures when he .gives, tho cubical contents of his proposed deviation as 422,500 yards less than the one I recommend. The' actual difference is. 243,600, or a trifle more than onehalf his estimate. The sum, consequently, represented as a saving will be proportionately less; but then , comes a.compensating item in the exira cost of wa\Hng entailed by the greater depth of Mr Gordon's line, which should not have been lost sight of. I think, however, the question of choice of channel is not one that ought to bo decided upon purely on the ground of s vying some two or three thousmd pounds. My prices are considered low. I will refer to this matter in a subsequent clause. ll' Gordon tturifcs that whether the north, south or middle channel be adopted, 19iO yards of high water training wall will be needed to regulate the current and assist in keeping the channel open; to this will be added extensions at each end as shown on his plan. Thi means, that a high water training wall or embankment ij to do taken all the way from " Grassy Point," to Dunedin, thus effectually closing up the cross channel, in fact severing tho north from the south channel and confining all tho traffic to the former, \vhi<;b is to be cut to the width of only 100 feet. Mr Gordon says in clause 2 of his report, that "the natural tendency of the tidal water would appear to follow the south channel as it affords the most uninterrupted course." Again in clause 10, now under comment, he says that y' the south channel is not so well adapted to tho plan described in paragraph 4 absve as it>would ba very expensive to close the north channel owing to its depth." .If careful attention is bestowed on tho plan, Mr Gordon will find that the cost of closing the north channel would not be much in excess, if at all, of the cost of shutting up the Cross and Portobello channels, as embraced in his scheme. Such being tho case, and finding as he did, in tho former part of this clause, that there would be less dredging in the south than in the north channel, the following question naturally arisea:—Why not adopt the south channel as the permanent one, seeing that no further reason to that expressed above is given for not adopting it in preference to.the other It is said tint I have attached undue importance to the result of tidal observations at Burkes andMacandrew's. Perhaps Mr Gordon may not be aware that the sectional areas of the relative streams were duly considered in arriving at the conclusions indicated in 11. A recommendation is made to the effect that Pelichet Bay and the portion on the opposite side of i he Water of Lcith, shoul i be left opon until they are absolutely needed tor building or other purposes. As these areas are the very last proposed to be reclaimed, they ate not likely .to be interfered with for a few years. 12. Referred to hereafter. . 13 The lowest tender received for timber wharves shows at the rate of £46 per lineal yard, to which must be added £5 10s, the cost arrived at from actual experience of rock filling behind, giving a total of £51 10s per lineal yard, which affords an available width of 63 feet over ill. Mr Gordon gives £63 as the cost per yard, or one-iourth more than the correct rate. The question of removal of the anchor piles of the timber wharves farther back is one that depends greatly upon the nature of the material to be driven through. While in some plac s it may bo advisable to adopt Mr Gordon's suggestion, in others io may be superfluous. The sheet piles, when the material is soft below the depth to which it is intended they shall he driven, I propose to dispense with and fill in between the main piles with rock. The angle of the slope in the event of the latter course being desirable, will not exceed 45 The distance between the piles is regulated by the compression is is intended each pile will require to The upper wrings are 12in. by 6:n., and aro shown as such distinctly upon the drawings. The objection of filling in loose rock between u>e piles, where soft material is met with, because it would interfere with tho driving of new piles, when that became necessary, seems to me an objection that need not iiave been entertained, as it is unreisonablo to anticipate that replacements of any parts of the substructure will be necessaryThe Crosa Wharf additional width of 6ft. is provided for under the contract for which tenders have been already recoived. Mr Gordon appears to have overlooked this. li. Mr M'Gregor's tendors were tho lowest for concrete—his No. 2 one being at the rate, as shown by Mr Gordon, of £71 15a per lineal yard, to which must be added £10 per yard to give the same width of roadway as provided for in tlie limber wharves. The total cost per yard will, therefore, be represented by a sum of £8115s, being about £30 per yard in excess of the timber wharves. Mr Gordon's remark as to the absence ol detailed information in the concrete tenders to test their reliability coincides with those expressed by me in my report upon the tenders. 15. Mr Gordon assumes Bft. as the proper level of reclamation above high water. This height is certainly excessive, five feet is the level I propose, being 3ft. below the roadway of the timber wharves. Of course Mr Gordon's quantities and estimates are based upon thU datum, rendering them unreliable It is suggested that the mud "oe " snooted" on to the reclamation areas. Such is my intention when tho dredges "re in close proximity to the wharves, the height of discharge being regulated to suit this conjointly with that of affording facilities for filling the trucks on the barges. An admission is made to the effect that the mode of procedure in depositing the dredged material on the reclamation areas is not familiar to Mr Goidon. Moreover, ho is not prepared to say that by tho plan proposed by me the deposit couli uot be more expeditiously ana consequently more economically effected than by hoisting or barrowing from barges. Then, is it not reasonable to ask, how does he arrive at the conclusion that it cannot be done at a lower rate than Is 3d per yard? 10. For comparison purposes, Mr Gordon introduces the cost of dredging m the Clyde, and also that of the deposit of the material in Loch Long and on shore. He assumes that the works on the Clyde and those contemplate I here are parallel cases, and draws his inference from results which he must know to be as misleading as they are uncalled for. Supposing the circumstances to be similar, Mr Gordon does not furnish the distance towed on the Clyde, the elevation of the shore reclamation, the obstruction met with by the heavy and incessant water traffic, the modus opermuU generally, and such collateral information as is unquestionably necessary to aid one in arriving at a fair compirisan of tho cost there and here. Dredging operations have been carried on by the Harbour Board here for over 15 months, and the exitct cost per yard, including towage and deposit in tho bay by the rude appliances at present in use, does not exceed, according to last month's return, 9d per cubic yard. It must be borne in mind that the dredge New Era has an end discharge, and entails great loss of time in regulating the punts so as to place them for filling, and remove thorn whan filled for towaze. A statement (No. 2) was appended to my report upon harbour improvements, givinn the details ot cost upon which the price per ya'd for dredging and deposit was baa^d. This statement was very carefully prepared, and, in order to Bhow that the price per yard was not under-estimated, the aciual cost of working the dredges, steam barges, stationary engine for incline haulage, locomotive and trucks for land haulage, repairs, contingencies, &c., was tabulated, and the result showed that tho cost would only ba 6120 d per yard. In order to provide for every possible contingency, 50 per cent, was added to this, nuking the price 9d per cubic yard. Mr Gordon appears not to have observed tnis statement; if he had, then it would have been competent for him to have challenged any ono of the items to show that it w«s wrong, or based upon imperfect data. This was not done, but reference, for comparison, was made to tho Clyde rates, which are arrived at under widely different circumstances from those which we may fully expect to meet with in the Dunedin harbour. 17. The time f>f execution is likewise founded upon Ciydo returns. Mr Gordon bases his calculations upon the hor e-powcr of dredge engines, without regard to the modj of discharge, nature of the material t) be dredged, and, in general, the circumstinees attending the working of the dredges. Instead of proceeding in the manner he has resorted to, it might have been advisable, indeed it was absolutely necessary, for him to have inspected the drawings already prepared, and ascertained, from examination and calculations, the velocity and capacity of the bucke's, mode of reception of the mverial, &c, and not tike returns for granted which have nothing further to recommend them than that they answer the requirements of the Clyde, without special reference to any place other th m that which may be similarly circumstanced. 18. The recommendation in this clause is similar to that I made in my supplementary report of date the 2Gtb August, 1875, with this exception, that I suggested 12ft. as the depth at low water and 300 ft. as the width of channel. In the estimate given by Mr Gordon, he states that the price ot Is Si par yard is necessary for dredging and deposit, yet he doe* not furnish the diti which enabled him to arrive at this rata; probably a Clyde compiri=on has influenced him. The rate of Is 4d mentioned is intended, I think, as the cost of dredging and discharge by " shoots " This Uan increase of 7d per yard over and above our present rate, with deposit by punts and towage. I cannot understand where it is intended that the 32 2,650 cubic yards is to be deposited, as the quantity of 2,831,660 nearly corresponds with my estimate of tho cubical contents, in providing a 100 ft. channel, with docks, steamers'basm, and approach. Probably it is cilculated to accommodate Mr Gordon' fixed height of Bft. above high water level for reclamation. Under the heading " BeeUmation," thera are 6500 lineal yards concrete walls provided for, at £80 per yard; and as, in accordance with the foregoing linii: of reclamation, such can only include walling for tlu steamers' basin, docks, and frontage to 15(t. and 18ft. channels, I am at a loss to know how the length of walling is arrived at, as tho entire extent of wharfage comprised in my scheme, embracing- a much greater distance than that abovo indicated, does not exceed 4900 lineal yards. To show the unreliability of the estimate furnished by Mr Gordon under this beading alone • let the walling of the docks, which is represented by the 6500 lineal yards, be reduced to the accurate length-2200 yards-and let the difference be calculated at his rate of £80 per yard (whuh I behevo to he too low), the result will Bhow the modest sum of The next item of lOOOlineal yards cf concrete walling of less depth swells the excess already reached by the previous item. The remaining items have been given at random, ard are evidently not based upon an acquaintance with either the harbour or the mode of carrying out the works. . In the substitution of timber wharves for concrete, Mr Gordon anticipates a probable siving of £112,500. How can this amount be possibly arrived at when the concrete walling by his own estimate amounts to £535,000 a.% against £336,250, which represents tho cost of the same length of timber wharves calculated at tho lowest tender rate received, viz., £51 10j per yard ? but this difference of £30,000 or £90,000 is a trifle compared with the last item of £344,000. Again, £11,800 is set down for anuuil repairs to timber wharves, an amount so egregiously excessive as to bo beyond crticism. 19. This clause has been already commented upon. 20. Mr Gordon thinks that the tidal records have not been so numerous as they ought to have been. I agree with him so far, in this way, tint had the observations extended over a term of years, the result to suiouce might have been of great value indeed ; but the subject of harbour improvement had to be dealt with in a practical way, and tho observations, so far as they were carried on, answered the purpose for which they were instituted. Mr Gordon's recommendations may be thus summed up : His h tide wall is virtually Mr Balfour's, the alurattun in the lower part being, in my opinion, no improvement upon tho formei's plan. I content! that the severance of the north and south channels, and the mode of improvement suggested, will prejudicially interfere with the effective tidal working of the harbour to an event that cannot a', present be foiv.-.eoii. Wiiiie under, this lidding I may rcm irk tli >t Mr Gunion has notyiven a decided expression hi opinion j as t) the width the channel should bo; he only assumes it (is 1.0 ft., but dues not explain wlietlitr or not he considers this width to v.o a workable one, or one s.ife for navigation purposes under the tiu'Uinstunees in which tho harbour would be placeil were li's plan carried out. llie ilevkrtion proposed in tho channel above l'.nr'.ii-'s uriM-.-i from a HiUUkt'ii conception of tile jolianiicl current there.

As to concrete in preference to timber for wharfage, this is simply a question of finance. The matter may be put in ihis thape-Is the Board willing that a sum of about £200,000 should be expended upon concrete walling in excess of that required for timber wharves, serin? that the latter may safely bs estimated to last for over 30 years, with an annual expenditure upon maintenance of a sum not exceeding £1000? In conclusion, the Board i 3 asked to undertake certain important works upon the recommendation of Mr Gordon, whose sole experience of the Otago Harlwnr consists in that of his having undertaken a four hours trip in the steam launch Vire to and from tho Otago Heads, and effecting a survey of the harbour entirely from the steamer's deck, with the exception el his having, upon one occasion, landed on ono of the upper sandbanks, and probed tho sand in two or threa places with a small pointed stick to the depth of two or throe inches.—l have, &c, D. h. Simpsos, Engineer. iilt was resolved that Mr Simpson's report be printed, and that consideration of the proposed harbour improvements be deferred till next meeting.