THE HARBOR IMPROVEMENTS.

Evening Star, Issue 4098, 15 April 1876, Page 1 (Supplement)

THE HARBOR IMPROVEMENTS.

The report of Mr Gordon on Mr Simpson’s plans for improving Dunedin Harbor deals with the following subjects :—(1.) The improvement of the access to the port. (2.) The reclamation, including the quay walls, the mode of disposing of the excavated material, and providing stuff for the reclamation. (3.) The cost and time occupied in excavation. The document Is written in paragraph form ; and for the better understanding of the matters touched upon we give first Mr Gordon’s opinion, followed immediately by Mr Simpson’s comments under paragraph 4.

Gordon: One plan would be to confine the channel by an embankment to one side or the other, so as to cause the tide to pass up one channel, round in front of Dunedin, and up the other channel in a reverse direction —the latter being closed at the north-east end. This would change the harbor from a wide tidal inlet with two channels to a naruotfer one of greater length with one channel, and its head would then be where the embankment joined the main land at the northcast end, instead of at Dunedin, where it now is, the flood and ebb streams passing along the front of the proposed reclamation. Simpson : 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,

The second plan, which Mr Simpson points out, is suggested but not supported by Mr Gordon, is to deepen one or both channels by dredging and by stopping up the channels through the said banks near Burke’s. Mr Gordon then observes:—

6. There will always be a tendency to shoaling in the upper part of the Harbor. This is the case in all similar waters, and it is proved in this case by the advancement of the six-foot contour-line outwards from the shore-line since the time of Captain Stokes’s survey. In the first of the above modes of treatment this tendency to silt would be partially counteracted bv the tidal stream in the part of the channel leading from deep water to Dunedin, or some distance beynnd It; while the tendency to shoal would be greater then than it is now at the new head of the Harbor. By the second mode of treatment, the tidal action would be little more than it is at present, and dredging would be required to maintain the depth, aided by training walls in certain places. In either case the deep water channel would have to be first formed by dredging, the effect of the walls would only be to assist in maintaining it. 7. Although I agree with the greater part of Mr Balfour’s report, I have the following objections to his plan :—First, he would partially. obstruct one of the passages for the tide at the Halfway Islands, where the sectional area is already too limited ; secondly, by leaving openings in the training w r all at that end he would admit the tide and so neutralise to a great extent the action of the training wall, which would have the effect of entirely confining the tidal w'ater to ®ne channel. If the principle of the dividing embankment were adopted, it should be made up to about one foot above ordinary high water, and should in my opinion be continued across the ‘ Cross Channel” in its shallowest part, and then curved round to “ Greasy Point,” access being given, if desired, to the south channel by a locked entrance provided with double gates. The reason for taking it across the “ Cross Channel ” is to avoid the deep water where that channel and the Portobello Channel meet, and it would also give a better form of entrance to the north channel.

The last-mentioned paragraph merely evokes from Mr Simpson the remark that it is a criticism on Mr Balfour’s plan. Under paragraph 8—

Mr Gordon : 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 the east shore and were also made up to high-waiter level, so as to shut up the south channel. The wall, if made, should be considerably, more to the south than shown on the plan, in order, first, that the channel might follow more nearly the natural set of the stream as indicated by tbe depths ; and, secondly, that the space to the north of the wall should be more extensive, for it is, as designed, out of proportion to the space on the south side, which it would have to fill with tidal water.

Mr Simpson: This contains a difference of opinion as to the efficiency of the half-tide walk 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 high-tide wall, severing the north from the south channel, would in my opinion have the effect of interfering with, if not absolutely rendering futile, the effective tidal working of the Upper, if not also the Lower, Harbor. 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 set of the north stream would more or less follow the coast line, were it not that a necessity existed for its departure therefrom, as fully indicated in clause 8 of my rerrt of date the 16th August, 1875, to which would refer. Were the sandbanks cut through as recommen/led in my plan, it would be found that the direction I propose for the channel would be yery nearly the natural set of the stream; the course recommended by Mr Gordon would, on the contrary, give a forced set. In reference to the remark respecting the disproportion of the water area north and south of the wall I Sse such inequality or disproportion only exist were Mr Gordon's suggestion of a high tide wall carried out.

Paragraph 9 deals with the proposed dividing wall—

Mr Gordon : I think the ] question of a dividing wall extending the whole way may be deferred 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 he berthed at Dunedin as soon as possible; and with that object in view, ana considering that in any case the most important part of the work is the dredging, the first thing to be considered and determindd is the best course for the channel.

Mr Simpson : My opinion ia that the erection of a training wall the entire length, is as necessary a work as the dredging of the channel itself. First cost should not exciu sively monopolise the attention of the Board; Suture maintenance is one item which, if not carefully provided against, will assuredly ■have the .effect of rendering the efforts of the Board to keep open the communication a very expensive contingency; if not altogether abortive. __ , Paragraph, ftkiEf reference to the “whole question of (judging, its cost, &c.

Mr (Jordon; The north channel is the deeper as (ar as Burke’s, from that point op words, it pay be

said hardly to exist, and the deep water is in the corresponding part of the south channel from Macandrew’s upward. The south channel is longer by one-seventh than the proposed channel, hut owing to the greater average depth, the quantity to be dredged would be less by about 207,000 cubic yards thau in the north channel, supposing each to 100 ft. *vide. If we examine the plan which has been prepared, evideuily with great care, by Mr Simpson, we shall find, by the aid of tne contour lines which I have drawn on it, that the natural tendency of the stream passing np the north channel to seek a southerly com ae is shown by the steep slope of the channel on t hat side in the deep part of it, and by the line of deepest water indicated by several pools of greater depth above the point where the sandbanks opposite Burke’s first interfere with the flood stream. There is not a continuous depth of Oft even on the north side. These characteristics indicate, in my opinion, that the proper direction for the channel, as well as the line of least excavation, would he nearly that shown on the accompanying plan by a red line. On this line, i.e., following Mr Simpson’s channel from Kilgour’s | Point up the north channel to near Burke’s and then tending southwards in the line of deep water, I find that the amount of dredging for a lOaft channel will be about 943,500 cubic yards, as against 1,366,000 cubic yards by the proposed plan (although it is 16 chains longer), showing a rduction of nearly onethird and representing a saving of L16.72U at Mr Simpson’s rates —which, however, I think are too low—and a correspondingly greater difference if the channel is made wider. Whether the north, the south, or this middle channel be constructed, about the same length—l,9Bo yards—of h'.gh water training-wall at the sandbanks will be needed to regulate the current and assist in keeping the channel open; and if 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. The south channel is not so well adapted to the plan described in paragraph 4 above, as it would be very expensive to close the north channel, owing to its depth. It would also be well, though not absolutely necessary to construct about 1,400 lineal yards of Mr Simpson’s training wall at its east end on the south side of the channel. I would remark that at this part, and wherever else the borings show the bottom to be soft mud, the banks should be constructed with fascines in the manner in use in Holland, viz., by I sinking large areas of fascim work. In paragraph • 4 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 Burke’s than it rises, while the converse takes place at Macandrew’s, therefore the scouring action would be greater on the ebb if the new channel were constructed en the north rather than on the south side. The construction of the proposed training-wall and the deepening of either channel would alter to some extent the tidal economy of the harbour; and, besides, it should not be assumed that the scouring action must be 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 the sectional area of each stream be also known.

Mr Simpson: Mr Gordon says the south channel is one seventh longer than the north. In this he is nearly correct, but he is in error in stating that the former wr.uld necessitate less dredging than the latter by 207,000 cubic yards. An accurate cotnputatii n gives the south channel an excess over the north oil 26,000 yards. Assuming, as Mr Gordon does, the width at 100 ft, and depth, 18ft. This error does not affect the question of choice of permanent channel, bub it is well at all times, in arriving at conclusions, to approach more closely the true contents than th« figu es of Mr Gordon’s do in this instance. It is assumed that because the southern slope of the north channel is steep, a id several deep pools show in the soundings at the sandbanks, it is an indication that the proper direction for the channel is pointed out by the line of proposed deviation. Supposing that an obstruction to the proposed flow of the stream, such as an embankment, were thrown out from Burke’s Jetty, in such a manner as to contract the present width of the channel, what would be the result ? Simply this—-that the process of attrition on the opposite sandbank or soutln ru slope would go on more rapidly th u at present, until the uniform width of the channel below was attained. Exactly the same holds good with the obstruction above. Remove it by cutting through the sandbanks ;n the direction I propose, and the result will show that the southern slope alluded to will not be further encroached upon, but will act ns a guide iu determining the proper direction of the channel to be that ruimine at an average uniform distance from the coast line Mr Gordon again errs in his figures when he gives the cubical contents of his proposed deviation as 422,500 yards less than the one I recommend. The actu 1 difference is 243,500, or a trifle more than one-half his estimate. The sum, consequently, represented as a saving will be proportionately less ; but then comes a compensating item iu the extra cost of walling 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 be decided upon purely on the ground of saving some .wo or three thousand pounds. Mr Gordon thinks that whether the north, south or middle channel be adopted. 1980 yards of High water t aimug wall will be needed to regulate the current and assist iu keeping the channel open; to this will he added exteusicus at each end as shown in his plan. This means, that a highwater training wall or embankment is to he taken all the way from “ Grassy Point ” to Bum din, thus effectually closing up the cross channel, iu fact severing the north from the south channel and confining all the traffic to the former, which is to be cut to the widt • of only 100 feet. Mr Gordon says in clause 2of his report, that “ the natural tendency of the tidal water would appeal to follow the south channel as it affords tne most uninterrupted course." Again iu clause 10, now under comment, he says that “the south channel is not so well adapted to the plan described iu paragraph 4 above, ns it would be very expensive to close the north channel owing to its depth.” If careful attention is bestowed on the plan, Mr Gordon will find that the cost of closing the north chnueel would noi.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 the case, and flndii g as he did, iu the former part of this clause, that there would be less dredging in the south than the north channel, the following question naturally arises Why not adopt the south channel ns the permanent one, seeing that no other reason to that expressed above is given for not adopting it iu preference to the other. It is said that I have attached undue importance to the result of tidal observations at Burke’s aud Macandrew’s. P. rhaps Mr Gordon may not be aware that the sectional areas of tho relative streams were duly considered iu arriving at the conclusions indicated in my report. Reclarpation is next discussed.

Mr Gordon : Although it is nearly always undesirable to reduce the tidal area of a harbor, I do not think that the more necessary portions of the proposed reclamation would he likely to injuriously affect the inner Bar. lam 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 he left open until they are absolutely needed for building or other purposes.

Mr Simpson : A recommendation is mad® to the effect that Pelichet Bay and the portion on the opposite side of the Water of Leith, should he left open until they are absolutely needed for building or other purposes. As these areas are the very last proposed to he reclaimed, they are not likely to he interfered with for a few years. lie timber or concrete wharves.

Mr Gordon: 'This question has rceeived my best attention. There can he no doubt that the latter is the most desirable form of construction, and judging by the results of the 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 successfully carried out. There might possibly be some advantage, in the way of quickness of execution, in favor 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 simultaneously with the concrete walls, each mode of construction being pushed ou at its greatest possible, rate of progress. The tenders received for the timber wharves show, I think, that £4B may be taken as the average price per lineal yard, to wh : ch Las to be added the rocky filling proposed by Mr Simpson, and, I believe necessary, briu iug the cost up to £63. I ’Link that Mr Simpson should lengthen his anchor piles and place them further back, and that the sheet oiling should be carried down to the more solid stratum under the mud. This would mid to the cost, but, ou the other hand, a considerable saving could be effected by omitting ouo of the rows of 15iu. piles, which nre closer than necessary. The upper wallings should, I tin k bo 12iu. by Cin. I would have recommended the front rakiug pile to bo driven deeper, but Mr Simpson informs me it cannot be done. The rubble which Mr Simpson proposes to tip m 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 bo placed in trout of the anchor piles and waliugs connecting them. In my opinion the addition to the cross jetty or wharf should bo widened 6ft., as the piles will not have sufficient hold when the ground is excavate!, and it will probably bo necessary to tip in rubble to hold up the slope—see sketch on the contract drawing No. 2. Concrete walls once constructed would last for all time and require no repairs; I would recommend timber only if the use of it would save time. Two plans have.beeri prepared for constructing those concrete

wharves, both of which are expected to be cheaper j j than coffer-dams, viz., the concrete cylinders of Mr 1 M’Gregor, and the concrete-wall built by the aid of 1 Mr Napier’s pontoon. Mr M’Gregor’s tender tor his No. 1 plan amounts to L7l • 5s per lineal yard, and to this has to be Mrldod for comparison with the timber construction L 5 per yard for malting up the width of the roadway, making the total cost L 76 Ins per lineal yard. As the tenderers wore not furnished with the register of the borings, it is not certain that Mr M'Gregor has reckoned for the proper depth of cylinders. Fur’her, as his tender is oily I given in a lump sum it is impossible for me to judge I whether sufficient allowance has been made for mu hj 1 pumping, which I think would bo 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 Napier's pontoon, and which is, with the same addition of L 5 estimated to cost LB2 18a per liueal yard. I should say that I have never seen the latter system employed, although I have used a similar one ou a much smaller scale, but I think it would answer well in stiif clay, in which the cylinders art; apt to hang, while they would be prefers' le in soft mud. The average cost of these modes of construction would, according to the tenders, be L 79 18s per lineal yaid, but I think the Board requires more assurance that either plan can be carried out for the sum tendered for, and also more information as to what additional cost would be incurred if the design had to be alteied as provided for in Mr M'Grego's tender. In short, plans and specifications of both modes according to

the ascertained nature of the ground are required, and tenders for the work should be based on these. Mr Simpson: The lowest tender received for timber wharves shows at the rate of L 46 per lineal yard, to which must be added L 5 10s, the cost arrived at from actual experience of rock filling behind, giving a total of Lsl 10s per lineal yard, which affords an available width of 63 feet overall. Mr i Gordon gives L 63 as the cost per yard, or one fourth more than the correct rate. The question of removal of the anchor piles of the timber wharves farther back is one that depends great ly upon the nature of the material to be driven through. While in some places it may be advisable to adopt Mr Gordon’s suggestion, in others it may be superfluous. The sheet piles, when the material is soft below the depth to which it is intended they shall be 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 degrees. The distance between the piles is leguiated by the compression it is intended each pile will require to sustain. The upper wallings are 12in, by 6iu., and fire shown as such distinctly upon the drawings. The objection of filling in hj ose rock between the piles, where soft material is met with, because it would interfere with the driving of ne -v piles when that became necessary, seems to me an objection that need not have been entertained, as it is unreasonable to anticipate that replacements of any parts of the substructure will be necessary. The Cross Wharf additional width of 6ft- is provided for under the contract for which tenders have been received. Mr Gordon appears to have overlooked this. Mr M’Gregor’s tenders were the lowest for concrete—his No. 2 one being at the rate, as shown by Mr Gordon, of L7l 15s per lineal yard, to which must be added LlO per yard to give the same width of roadway as provided for :n the timber wharves. The total cost pr yard will, therefore, be represented by a sum of LSI 15s, being about L3O per yard in excess of the timber wharves. Mr Gordon’s remark as to the absence of detailed information in the concrete tenders to test their reliability coincides with those expressed by me in my report upon the tenders.

As to the material for forming the reclamation— Mr Gordon : 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 bases and the deepened approach to them, together with 310,000 cubic yards from Dowling street, would amount to 2,281,479 cubic yards (see Mr 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,(J1jl cubic yards of material, showing a deficiency of 050,182 cubic yards, to be brought from the upper end of the channel, and leaving 387,008 cubic yards to be dredged and otherwise disposed of. I think the 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 long as the dredging is in close neighborhood. I have not seen in practice any plans similar to those of Mr Simpson and Mr Jenkins, and I fear there would be a great deal of trouble caused by the softness of the deposited material, which will take some time 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 with it. At the same time, I am not prepared to say that by the plans proposed by these gentlemen, the additional quantity required from the channel could not be deposited more expeditiously than by hoi.-ting or barrowing from barges. I do not consider it safe to estimate it at a lower rate than Is 3d per cubic yard. The excavation from Dowding street should all be expended in filling in behind the walls and between the sheet-piling and anchor piles of the new wharves. I think it would cost 2s 6d per cubic yard.

Mr Simpson ; 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 this datum, rendering them unreliable. It is suggested that the mud be “ shooted ” onto the x’eclamation areas. Such is my intention when the dredges are 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 Gordon. Moreover, he is not prepared to say that by the plan proposed by me the deposit could not be more expeditiously and 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 ? The cost of the works is next discussed.

Mr Gordon ; It is always well to check estimates by the ascertained cost of completed works of similar character, and taking those on the Clyde as a standard of comparison, as being 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 Clyde in 1870-1872 was 3.BGd per cubic yard. The cost of towing and depositing on shore was 9.78 d, and that of carrying and depositing in Loch Long 5.29 d. The total cost per cubic yard varied from 7.94 d to 38.27 d, and the average was 10.69 d per cubic yard. Ido not think an average of less than Is 8d can be reckoned on for Dunedin harbor.

Mr Simpson: For comparison purposes, Mr Gordon introduces the cost of dredging on 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 contemplated 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 ou the Clyde, the elevation of the shore reclamation, the obstruction met with by the heavy and incessant water traffic, the modun opera di generally, and such collateral information as is unquestionably necessary to aid one in arriving at a fair comparison of the cost there and here. Dredging operations have been carried ou by the Harbor Board here for over fifteen months, and the exact cost per yard, including towage and deposit in the bay by the rude appliances at present in use, docs 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 j the punts so as to place them for filling, {

and remove them when filled for towage. A statement (No. 2) was appended to my report upon harbor improvements, giving the details of cost upon which the price per yard for dredging and deposit was based. This statement was very carefully prepared, and in order to show that the price per yard was not under-estimated, the actual cost of working the dredges, steam barges, stationary engine for incline haulage, repairs, contingencies, etc., was tabulated, and the result showed that the cost would only be 6.120 d per yard. In order to provide for every possible contingency, 50 per cent, was added to this, making the price 9d per cubic yard. Mr Gordon appears not to have observed this statement; if he had, then it would have been competent for him to have challenged any one of the items to show that it was wrong, or based upon imperfect data. This was not done, but reference for comparison was made to the Clyde rates, which are arrived at under widely different circumstances from those which we may fully expect to meet with in the Dunedin Harbor. And as to the time that will be occupied in carrying out the proposed im prove ments—

Mr Gordon: The time of execution depends mainly on the plant employed as regards the dredging. From an examination of the Clyde records, I find —lst. The average quantity dredged per hour per horsepower of dredger was 1£ cubic yard. 2nd. Fach machine worked on an average hours per day for 312 days in the year, or twothirds of full time. 3rd. That with an aggregate horse-power of dredging machines of 239 horse-power, the quantity dredged in a year was 992,354 cubic yards, or 4,152 cubic yards per horse-power per annum. The quantity to be dredged here being as above three million cubic yaads, the time required by the above data would be (0,000,000 by 95 by 4,152) seven years and seven months, the new dredger being taken at 65 horse-power, and the present one at 30 horse-power. The time required for the total quantity proposed viz., eight mill., adding as above 10 per cent, for redredging —would in the same way be 20 years. It is evident, therefore, I think, that the dredging power must be increased in order that the wharves and dredging operations should be completed about the same time. To complete in three years, it would seem to be necessary to employ 240 horse-power, or, taking the most favorable example on the Clyde, the new dredger ought to lift 367,500 cubic yards, or 1,177 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 be doubled if it be desired to complete the improvement in three years, to the extent suggested above i.c. f a channel 100 ft wide, and the reclamation between the coal basin and Albany street jetty.

Mr Simpson : The time of execution is likewise founded upon Clyde returns. Mr Gordon based his calculations upon the horse-power of dredge engines, without regard to the mode of discharge, nature of the material to be dredged, and, in general, the circumstances attending the working of the dredges. Instead of proceeding in the maunoi 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 buckets, mode of reception of the material, &c., and not take 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 than that which may be similarly circumstanced.

Mr Gordon next; suggests that the channel should he first dredged to a depth of 13 or 14ft at low water, and afterwards increased in depth, workin of from below upwards, and he makes the following rough estimate of the sum which he thinks ought to be provided for the completion of the work so far : Dredging and depositing material from the 100 ft channel, ISftdeep; the importand export docks, 22ft; the steamer basin, 17ft; and approach, 15ft—equal to 2,831,661 cubic yards, landed at Is 8d ...L235,972 322,650 cubic yards, deposited at Is U Reclamation—--6,500 lineal yards concrete walls at o L 80 | iinn L 520.000 oay, 1,000 lineal yards concrete walls of less depth, at L 65 ... 65,000 310,000 cubic yards excavation from Dowling street, at 2s 6d 38,750 Training wall at the Fork, say ... 10,000 Ditto at east end, 1,400 yards . 2 000 Contingencies ... 4^ Depreciation of plant in three years, 30 per cent ‘ ... 25,000 L 965,000 The substitution of timber-wharves for concrete would probably effect a saving at first of L 112,500, but against this is to be placed the annual repairs, probably equal to

Mr Simpson : The recommendation in t.Tn'g clause is similar to that I made in my supplementary report of date the 26th August, lb/5, with this exception, that I suggested 12ft as the depth of low water and 300 ft as the width of channel. In the estimate given by Mr Gordon, he states that the pricejof Is 8d per yard is necessary for dredging and deposit; yet he does not furnish the data which enabled him to arrive at this rate; probably a Clyde comparison has influenced’ hnn. The rate of Is 4d mentioned is intended, 1 think, as the cost of dredging and discharge by “shoots.” This is an 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 32,650 cubic yards is to be deposited, as the quantity of 2,831,660near1y corresponds with my estimate of the cubical contents in providing 100 ft channel with docks, steamers 1 basin, and approach. Probably it is calculated to accommodate Mr Gordon’s fixed height of Bft above high water level for reclamation. Under the heading “ Kcclamaiion ” there are 6,500 lineal yards concrete walls provided for, at LSO per yard ; and as, in accordance with the foregoing limit of reclamation, such can only include wailing for the steamers’ basin, docks, and frontage to 15ft, and 18ft. channels, I am at a less to know how the length of walling is arrived at, as the entire extent of wharfage comprised in my scheme, embracing a much greater distance than that above indicated, does not exceed 4,000 lineal yards. To show the unreliability of the estimate furnished by Mr Gordon under this heading alone : let the walling of the docks which is represented by the 6,500 lineal yards, be reduced to the accurate length—--2,200 yards and let the difference be calculated at his rate of LBO per yard (which I believe to be too low), the result will show the modest sum of L 344,000. Tue next item of 1,000 lineal yards of concrete wallinoof less depth swells the excess already leached by the previous item. Tae remaining items have been given at random, and aie evidently not based upon an acquaintance with either the harbor or the mode of carrying out the works. In the substitution of timber wharves for concrete Mr Gordon anticipates a probable saving of L 112,500. How can this amount be po&sibly

arrived at when the concrete walling, by his own estimate, amounts to L 555,000 as against L 386,250, which represents the cost of the same length of timber wharves calculated at the lowest tender rate received— viz., LSI 10s per yard ? but this difference of LBO,OOO or LOO,OOO is a trifle compared with the last item of L 344.000. Again, LI 1,800 is set down for annual repairs to timber wharves, an amount so egregiously excessive as to be beyond criticism. 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, that had the observations extended over a term of years, the result to science might have been of great value indeed ; but the subject of harbor improvement had to be dealt with in a practical way, and the observations, so tar as j they were carried on, answered the purpose for which they were instituted.

CONCLUDING HE AKKS. Mr Gordon: My suggestions and recommendations are ns follow: —That, if it be determined to carry out tins scheme, the whole of it should not be entered on at once, but that a channel, on the line proposed by Mr Simpson, with a deviation near “ the Fork” and upward, should be dredged to a depth of 13ft at low water. That a training bank, one foot above high-water level and 1,980 yards long, should be constructed where it is shown on the plan. That the wharves should be of concrete. That the reclamation should be not less than eight feet above high water, and should at first extend from the proposed steamer basin to the Albany street jetty. That the work could be done in three or four years, and would probably cost nearly one million sterling. I have not refen ed 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 Thomson’s, the points on which I differ or agree with him are sufficiently indicated above. I would take (he liberty of suggesting that a more complete set of continuous observations of the tides at the Port, Burke’s, Macaudrew’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, and also, there is apparently no complete record of the direction of the stream and irs change near high and low water, the term “slack water” being applied to the ti-re when the levi lof the water was stationary. The distinction is important in discussing the tides of a port. The observations would be of great value when the question of a central training-wall has to be taken up.

Mr dm,.son: Mr Gordon’s recommendations may be summed up : His high tide wall is virtually Mr Balfour’s, the alteration in the lower part being, in my opinion, no improvement upon the former’s plans. I contend 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 harbor to an extent that cannot at present be foreseen. While under this heading I may remark that Mr Gordon has not given n decided expression of opinion as to the width the chauuel should ne; he only assumes it ns 100 ft., but does not explain whether or not he considers this width to be a workable one, or one safe for navigation purposes under the circumstances in which the Harbor would be placed were his plan carried out. The deviation proposed in the channel above Burke’s arises from a mistaken conception of the channel current there. As to concrete in preference to timber for wharfage, this is simply a question of Ann nee. The matter may be put in this shape—ls the Board willing that a sum of about L 200.000 should be expended upon concrete walling in excess of that required for timber wharves, seeing that the latter may safely be estimated to last for over thirty years, with an annual ex enditure upon maintenance of a sum not exceeding LI,OOO. In conclusion the Board is asked to undertake certa u important works upon the recommendation of Mr Gordon, whose sole experience of the Otago Harbor consists in that of his having undertaken a four hours’ trip in the steam launch Yiro to and from the Otago Heads, and effecting a survey of the harbor entirely from the steamer’s deck, with the exception of his having, upon one occasion, landed on one of the uppe*' saudb inks, and probed the sand in two • r three places with a small pointed stick to the dspth of two or three inches.—l have, &c..