OAMARU HARBOUR

Otago Daily Times, Issue 22057, 13 September 1933, Page 4

OAMARU HARBOUR

BREAKWATER EXTENSION AND DREDGING MR F. W. FURKERT’S REPORT (Special to Daily Times.) OAMARU, September 12. The following is the test of a report submitted' by Mr P. W, Furkert (late chief engineer to the Public Works Department) to the Oamaru Harbour Board, and considered at the monthly meeting of the. board to-day:— “In accordance with arrangements made between your secretary and myself, I have visited Oamaru and closely investigated the problem Confronting your board. When I say ‘the problem confronting your board ’ I do not mean the ordinary problem of whether any extension of your facilities is necessary or not, as I understood from discussions with yourself and also with the former chairman of the board (Mr Milligan), that this question has been definitely settled by the board in the affirmative, and therefore from my point of view the question now becomes one of how best your port can be modified to enable it to receive and accommodate vessels drawing approximately four feet more than is now practicable.

“Experience both on the spot and at other ports similarly situated has shown that it is hardly practicable to dredge a channel from the sheltered -water within the • harbour to a point where the sea naturally has a sufficient depth, I say hardly practicable; this does not mean impossible. However, to render it possible would involve the provision of dredging plant of a very special type, the exSenditure on which would not be justified y the amount of business which could be reasonably looked forward to at your port for very many years to come. We, therefore, are faced with the definite necessity for extending the breakwater to such a point as will give adequate shelter, under the protection of which an ordinary dredge could, operate. “Unfortunately, when the breakwater was first conceived, the class of vessel which now trades between New Zealand and ouc principal markets was not foreseen, and ‘consequently it was laid out on an alignment, which, while providing facilities for vessels of much greater draft than any then trading on your coast, does not allow for providing increased depth by means of further extension on the present alignment. As it is what one might term a pioneering enterprise, and one for which in this country at any rate there is no precedent, I am inclined to think that the present alignment was chosen in order to avoid presenting to the prevailing storm waves too abrupt an obstruction, the idea, being rather to deflect the waves than directly to oppose them. ' /'

“Although with the aid of your secretary I made a very extensive search, I was unfortunately unable to find the original report or reports made by the late Mr John M'Gregor, when the whole question of a port for Oamaru was being considered. Apparently the first idea was to make a small dock of the type known as a “ wet dock" in the Oamaru Creek, but before more than tlie smallest of beginnings had been made Mr M'Gregor evidently was able to convince the Dock Trust that such a dock would have been unworkable without the protection of a breakwater, and I found letters of his strongly urging that work which had already been contracted for in connection with the dock should be abandoned and the money diverted to breakwater construction. “ In the construction of breakwaters at that time, there were practically only two alternatives as regards material —one being concrete and the other stone, and I was particularly anxious to see how Mr M'Gregor argued the relative merits and on which grounds he finally decided that the breakwater should be constructed of solid concrete. The fact, however, that the'works were originally built almost entirely of concrete and that the „ use of the small amount of stone which was incorporated in the earlier part of the breakwater, thereby unfortunately weakening it, was soon abandoned, indicated that in the opinion of those then in charge of the works suitable stone could not be obtained on the spot. “We have to-day to face the same question whether any extensions now recommended are to be built of concrete or stone. Secondly, if of concrete, whether this should be in the form of a pell-mell mound of precast blocks, or whether the blocks are to be laid somewhat as was the case in the seventies of last century. I gay ‘ somewhat 5 because, unfortunately, in at least two very important directions the existing breakwater is not well designed. First, blocks of the slice work are of the same size, and consequently do not ‘break joint’ as they should do; and, secondly, they are entirely plainr instead of being cast in such a shape that one interlocks with its neighbour—a vanation which would have made the structure greatly superior at practically no additional cost. . . , , “ Then, if stone is to be adopted, from what source is it to be obtained* When I saw your quarry being cleaned down some weeks ago I hoped that the lower portion, then considerably obscured by overburden which had fallen down m the last 40 years, would have been fairly solid, and that a proportion _ of large blocks might have been obtained. In fact I was advised by some members of the staff that already quite a number of very large stones had been placed on the apron of the breakwater. At that time the sea was so rough that it was quite impossible to examine the breakwater, or even walk upon it. Last week, however, I was able both from the breakwater and from the sea at dead low water to examine the stone which had already been taken out. 1 doubt i. saw 20 stones which approached the size it will be necessary to use in a random rock mound type of breakwater, and the toe of the quarry which has since been exposed and m which a few shots have been fired, leaves one very doubtful as to the possibility of obtaining blocks of sufficient size. In considering a matter of this kind, one requires to visualise stones of the size and proportion of a full-sized billiard table, say, 12ft x 6ft x 4ft, or its equivalent. All the stones which have yet been obtained from your quarry are far too nearly spherical. Perhaps ‘spherical 5 is not the right word, as they are in no sense like waterworn boulders, ’but their dimensions in all three directions, length, breadth, and thickness, are all too nearly alike. t€ 1 approached the problem with a predisposition towards the use of local rock, particularly on account of the laboiu conditions existing at the present time, knowing that it was highly desirable in the interests of the working men of your town that the major part of the work should be of such a class as could be executed bv unskilled or semi-skilled labour, without the use of any great amount of plant and material. “In searching through the old records, I found that in the construction of the north mole, which was almost entirely built of stone from your quarry, great difficulty was encountered in obtaining sufficient blocks of adequate size; and when we realise that the size then aimed at was only three tons as a maximum, and that tTie work was frequently held up owing to the fact that not sufficient of even such small stones could be collected to face the outer part of the core of smaller stones, one is not encouraged to -feel optimistic with respect to the finding of many thousands of stones ranging from five to 20 tons. I noticed in some of the old documents that when half a crown was being paid

for waste materia] run to reclamation, 30s was being paid for rubble suitable for protective work. Such prices should have prompted a contractor to concentrate on the production of large stone. At one time Mr M'Gregor was so worried about the difficulty of getting suitable stone that he cast a few small concrete blocks to ascertain their cost, and he then tried to arrange with the contractor to change over to concrete blocks. However, the contractor, probably thinking that he had the board in a corner, made what Mr M'Gregor considered exorbitant demands, and the decision was made to struggle on with the quarry. “Frequent reports and discussion's of the board show their worry at the continual piling up of reclamation which they really at that time did not want, while simultaneously the extension of the mole languished for want of proper material. I have been advised that it is a tradition in the town that the contractors, while not making any great profit out of their rock work, were doiug very well at the price which the board paid them for the rubbish and spoil from the quarry which was used for reclamation purposes. While such a state of things would fully account for their disinclination to change over to concrete blocks, I think it very hard to believe

that a man of the evident strength of character and knowledge of work of Mr M'Gregor would have countenanced any methods of quarry working calculated intentionally to produce undue quantities of rubbish and spoil, and simultaneously less than the total possible of heavy stone. “ Reports by Mr La Roche, for a great many years your harbour engineer, indicate that he is of the opinion that the quarry would not yield stone suitable for protective works, even for maintenance of the existing breakwater.

“ Dr J. Alan Thompson, who apparently went very fully into the question of stone for your harbour works, was quite definite as to the unsuitability of the present quarries, though inclining to the belief that suitable stone could be obtained further round the Cape. Mr P. G. Morgan, who made a further report, concurred in the condemnation of the present quarries, and also considered that the rock known as the ‘ pillow lava ’ beyond the boat harbour was also unsuitable. Dr Marwick, of the Geological Survey, a few years later, while not agreeing with all the suggestions of previous investigators, agreed as to the improbability of your quarry furnishing the necessary stone. Professor James Park also spoke in no uncertain terms ns to the necessity for looking elsewhere for a supply of stone. Mr Cyrus Williams, who reported on the breakwater extension in 1914, uses the words: ‘But at the best this quarry will only yield material suitable for the bottom of the work, and the larger stone must be obtained elsewhere.’- He further mentioned that your engineer advised him that when the mole was being constructed 75 per cent, of the material was unsuitable, even for that light and_ protected structure. With the best will in the world to use the local material, it cannot be denied that the indications are all against the practicability of constructing a breakwater at Oamaru with'stone from the local quarry. If there were large areas of land adjacent which required reclamation, or if there were a closely adjacent point at which waste could be safely tipped into the sea, it might’ be reasonable when considering the large amount of labour which is available practically without cost to your board to persevere with the quarry even if only 10 to 15 per cent, of the material, as suggested by Professor Park, was suitable. But unfortunately there is no land worth mentioning on which spoil .could be tipped cheaply or advantageously. Your area of water is already too small for adequate stilling of the waves which enter through the unduly wide entrance, and conditions in the harbour in storm time would be better than they are today if a considerable part of the reclamation which was carried out in the early eighties had not been done. The spoil from the quarry is now being taken away by the County Council, the Borough Council, and the Railways Department, but the small quantities now being dealt with do not in any way indicate that the vast quantity of small material which would be produced in an endeavour to extend the breakwater from the present quarry would find purchasers even at the cost of simply taking away; in fact, the board would be faced with the expense of loading the waste on to railway trucks, railing it for ’ some distance to an area which might have to be purchased, and there throwing it to spoil. With seven yards to throw away ior every one that was used, the cost of the work would inevitably be high, even if all the advantages due to practically free labour are allowed for.

“A point which makes the stone question more difficult than it was in the past is that any useful extension of the breakwater must be on an alignment which will cause it to be struck by the prevailing weather, and also the worst storm waves, more heavily than has been the case with the present breakwater, and therefore stones or concrete' blocks which were adequate on the present work would not necessarily be adequate on the new work, and there is evidence that the present work is barely strong enough. Undoubtedly the breakwater is in a much more secure position than it was in 1886, vlien it badly breached in two places, because on the inside it is now supported by approximately 15 feet of sand which has been swept over in heavy weather; the breakwater therefore on the inside now stands in sft of water instead of 20ft. It may be appropriate at this point to sound a note of warning against this deposit ever, being dredged away in an endeavour to obtain more swinging room in the harbour. I understated from your harbour master that dredging is never earned nearer to the breakwater than the black buoy, and in the meantime I would say that this is a policy not to be departed from. “In such a question as the suitability of a quarry for harbour works there is always room for differences of opinion, but in your case there seems to have been no difference of opinion from the earliest times; thus in 1870, May 7, we find Mr M'Gregor stating that he proposes to construct the breakwater of 20-ton concrete blocks, utilising broken rock from your quarry as displacers to lessen the cost of the concrete. Ten years later we find him bemoaning the difficulties of completing the mole from the quarry, and again suggesting even for this light work the use of concrete. Your own engineer, after a long period of years, considers the quarry unsuitable. In 1014 Mr Cyrus Williams considered nothing but foundation small stone could be got. In 1915 Dr Thompson and Mr P. G. Morgan practically condemned the quarry, and in 1921 both Professor Park and Dr Marwick also condemned it. “It is hardly reasonable to suppose that all of these observers were mistaken. However, there is no proof like that of putting it to the test of public compete tion. When the work is to proceed, tenderers should be asked to quote alternatives, the first being the construction of the breakwater using only local stone, and the other alternative the construction of the breakwater by other means. "If the contractor considers that he can produce the breakwater from material obtainable on the spot, even allowing for all the waste, at a figure more favourable than that in which any other source of material is to be tapped, then he should be allowed to try, provided his tender is in other respects satisfactory. But if the board itself were thinking of carrying on by day work I would not be inclined to advise the spending of . any huge amount of money in preparation for the use of this quarry.

“Perhaps I should qualify this. I mean the use of the quarry for obtaining large blocks; undoubtedly some material suitable for the lower part of the breakwater can be obtained locally. “It is not possible to come to a definite conclusion on this matter, because of the peculiar labour conditions existing at present. If the Unemployment Board will continue to give assistance on the lines

that it now does, but declines if the work is let by contract and the material obtained elsewhere, then in spite of other difficulties it may pay the board to continue obtaining stone from the present quarry, but in that case the board should make such financial arrangements with its workers as would justify it in dismissing any man who showed any tendency to slackness. At the present time, with men only getting two or three days a week relief pay, it is unavoidable that those in charge would be more lenient towards idling, and that the men themselves would not have the heart to work as they would if they were being better paid, and, therefore, had something substantial to lose by dismissal. Undoubtedly, however, from the board’s point of view, payment by results would be more satisfactory, through a contractor preferably, because the board would nob then have to deal individually with the men; but failing a straight-out contract, then the cooperative piece work basis should be aimed at. This latter might take a little arranging, and should be subject to close study and the taking into consideration of all the local circumstances by an engineer constantly on the work, who is used to handling men. “ My examination of the board’s quarry reserve at Bushy does not cause me to view it in the favourable light in which previous investigators have done. At the present time there is no proof that the stone ‘ lives ’ into the hill. I note one geologist sounding a note of warning on stone near Ngapara, and stating that in effect the stone available is that which can be seen. Should the same conditions obtain at Bushy .-the expense involved in running the railway to the site would not be justified. The suitability and extent of the stone can only be proved by the sinking of shafts or driving of tunnels, or both, through the deposit, so that its character and location can be ascertained with certainty for a good distance below the surface. “Reading the reports that have been made in the past it does not seem that the observers or the board carried the investigations to a definite conclusion. However, again I do not consider that the merits and extent of any quarry can he told from simple observation of the surface, hut boring or shafts or tunnels, or a combination of all three should always he utilised. “ One observer mentions that Alexander M'Kay, at one time Government Geologist, reported the existence of suitable breakwater stone in the Kakanui Valley. This should be investigated: in fact, all possible sources should be investigated. It is always possible to throw such a responsibility upon the person tendering to carry out the works, but I think it would be more satisfactory if the board satisfied itself as to possibly two or three sources from which it would accept stone, and from which it definitely could bo obtained, and then left the rest to the contractor, “I notice a statement in the report of one of the investigators, to the effect that 12 ton was the lai’gest weight that can be carried on the railway. If such a i

limitation exists at present, then steps must either be taken to have this modi-

fied (by strengthening up existing railway trucks, or by your board obtaining suitable rolling stock such as is available at Westport or Titparu), or the board must use large concrete blocks to protect the outer and upper portions of the breakwater, the core and foundation of which would be of smaller material. Unfortunately the prices which applied in 1914, as quoted by Mr Cyrus Williams, no longer apply. As you are aware, Timaru recently had to carry out restoration work on its mole, due to storm damage, and I am informed by the secretary that the stone in position on the mole cost just slightly under 7s per ton. The favourable railway rate, i.e., three-eighths of clause Q, which applied in those days, no longer applies, it having been an unpayable rate to the department. It might be possible to make arrangements whereby special rolling stock was run in special trains by or for the board or its contractor at hours which would suit the Railways Department’s other traffic. I am inclined to think that arrangements could be made in this way which would be cheaper than ordinary standard rates and methods. When considering the alternatives of stone and concrete, it will be well to remember that Oamaru is particularly well suited for the manufacture of concrete. Cement can .be cheaply brought from Dunedin by rail or ship, or can be obtained by direct steamer from England by ships which would otherwise come out in ballast, and would therefore quote a very cheap rate. I have heard of some cargoes having been brought out within the last year at 7s 6d per ton. Shingle is available in considerable quantities even on the board's own property, while sand can be delivered to the site of the works at under 5s per cubic yard. “ The very extensive and systematic soundings taken by your harbour master indicate that the slight deepening effect referred to by Mr Cyrus Williams since 1886 is still maintained, but, speaking in a general way, I think it can be said that the sea bottom is reasonably stable. "Coming now to the details of the actual work to be executed. It would appear that a channel run seaward almost at right angles to the breakwater would reach water 22ft deep at low water in a minimum of distance. The turns which are navigated by vessels entering Timaru appear to present no difficulties, and the alignment which 1 have shown docs not involve any sharper turn than that of your neighbouring port. Instead of carrying on the extension from the end of the breakwater, which would give the least amount of new work, the extension should commence at a point .‘!ooft landward of the. present end, and instead of removing tiiis 30011 should be left as a wave trap, which would have a very beneficial effect in preventing range from entering the inner basin. The alignment selected allows of most economical extension in the future should the trade of the port warrant the trading there of vessels of deepen draft. lurther, it would act as one of the walls giving entrance to a much larger port should it be necessary in the future to increase your harbour to two or more times its present area. The second line of beacons indicated would connect the sheltered water of the channel with the deep water of the ocean by the most direct route, even though depths several feet deeper than are now under consideration were required and worked in the future.

“ 1 have previously remarked that the extension will be subject to heavier seas than those which have in (he past beaten upon the breakwater. Undoubtedly the more the breakwater is swung to the cast the greater will be the wave stroke, but the difference between (he effect of the waves on the alignment I propose and on one with a more northerly inclination, such as has been considered previously, would not be sullicient to neutralise the benefit which would come from the shortening of the whole structure, and from its suitability for future extension into deeper water. “There has always in the _ past been a tendency for the material drifting from the south to travel along the breakwater and to be deposited as a shoal encroaching on your navigable channel just under the lee of the breakwater. Such an effect was unavoidable with the alignment of the past, but the alignment I now propose would present, a much greater obstacle to the passage of drifting material,

and there is quite a possibility that nothing appreciable will find its way round the end of the new breakwater, at any rate for a great many years. The great success in this particular instance of the Napier breakwater has been due to the alignment of the first kant or section from the shore outwards, where the sea impinging upon it in rough weather tends to run in towards the shore, and thereby beats back_ the stream of sand and shingle which is travelling up the beach. For 50 years it can be said that no quantity, certainly of coarse material, has travelled along the breakwater. It is beaten into fine material, which mostly drifts out to sea. Such a condition.at Oamaru is one devoutly to be wished. It may be, however, that your port altogether is situated in water so shallow that in spite of a breakwater, even of the length now under consideration, material will pass outside in heavy weather, but the quantity will be small —smaller than at present, and the material finer.

"I understand that such stone as you have obtained from Port Chalmers in the past has been brought in railway trucks down to the port, and then has been transferred to your own rolling stock for final transport down the breakwater for tipping. This is an extra handling for which there does not appear to me to be any justification. A curve on which the railway wmgon can be utilised can easily be'made to connect the railway with the breakwater, so that the same wagons, assuming them to be bringing stone from other parts, can be run direct to the point at which the stone is to be deposited. “ I propose that the extension should be constructed of random blocks, whether these be stone or concrete or a combination, rather than a solid wall such ns was utilised originally. This structure cannot be built at the low level of the present works. In fact the present works are too low, as has been proved by the immense amount of material which has been driven annually over the breakwater, thus involving the board in a considerable recurring expenditure for dredging. (Still, in spite of this, it cannot be denied that the breakwater has been a highly satisfactory work, despite some earlier vicissitudes.) But to build a random wall practically at right angles to the prevailing seas, either the top of the stone work (if end tipping is adopted) or a deck to the trestle (if the trestle method is adopted) must be 18 or 20 feet above sea level. Otherwise the interruptions due to bad weather would be too frequent, and the possibility of the loss of the trestle would arise. If the end tipping method is adopted the cost of the trestle is saved, but on the other hand as good a job cannot be made, for the various grades of material coming from the quarry cannot be kept separate and placed where they will be most useful. Also, the breakwater itself must be kept up to, say, 18 feet above sea level, an unnecessary height for its future use, and only required by the need for keeping the work space out of the reach of the ordinary rough sea. (Naturally, wdien there was a violent storm, work could not be carried out whatever method was adopted.) Further, the liability of scour round the end increases the theoretical quantities in tjie case of the end tipping wall, while the trestle enables the lower course of cheap stone to be placed with facility in advance of the heavier and higher work, and thus obviates a great deal of scour and sinkage. “ But it is no use making the extension of this height unless arrangements are made whereby the trucks of stone can get to the extension trestle without running the gauntlet of the waves at present over-topping the breakwater. There are at least two ways in which this can be done. One is by means of a trestle inside the breakwater, grading from the level of the lines at present near the quarry to the predetermined height of the extension trestle.

“ The other method is by raising the present breakwater or carrying the trestle upon it. It would be most difficult to secure the trestle on top of the present structure, and this trestle would be practically valueless on the completion of the work, while if the work were strung out over many years it might have to he renewed from time to time. If, on the other hand, the breakwater is raised, this can be done very largely with material now being obtained from your own quarry, which can be placed very simply and without the aid of much more plant than you now have. To which must be added the value which the raised breakwater would have over the present low structure. “ f have already said that the breakwater is too low', but if the extension wore made a« I suggest, its effect would be to cause the waves to rise higher in the angle between the two works, and thus to cause more water to pass over the old portion, and also would cause waves to pass over which now do not do so. “ From the foregoing you will sec that whether the breakwater at present requires raising or not, the construction of the extension will bo very likely to force the raising of it. The raising should be done in such a way as not to require any material —certainly any small size material—to run over the seaward side. lu other words, the inner lino should be so fixed that the seaward slope is supported entirely on the present concrete. I have indicated on one cross section a method ot raising the present breakwater with solid concrete which would he little, if any, more expensive, and would permit of the future running out of cranes for repairs. If raising is done with stone as on the other cross section, then the work must be done backwards from the seaward end, and future maintenance would bo difficult. The large amount of spoil in small stones which will inevitably be produced in obtaining the large stone for raising the existing breakwater (if this method is adopted) can with advantage bo placed along the inner side of the

present solid breakwater. As remarked elsewhere, the breakwater is now well supported on the inside by sand which has ucumulated over a long period of years. This sand comes in the waves which dash over the breakwater in rough weather. When the breakwater is raised very much less sand, and possibly none at all, will come over. The tendency then will be for the sand now lying between the black buoy and the breakwater to drift away into the swinging basin or the navigable channel and to be dredged therefrom, and consequently for the sandbank to become lower in

height, and eventually almost to disappear. The latter possibility is many years in the future, but as a place must

be found for the small material from the quarry it should be placed as I have indicated, and will then act as a backing for the breakwater even after the greater part of the present sand backing has gone. “ The necessity for raising the old portion would be greater at the junction of the new than at the shore end, and this characteristic will suit well the grading of the line from the trestle level clown to the level existing near the root of the breakwater.

“ In the last point under discussion, the connection of the extension trestle and the' land, various expedients (as with the stone supply) can be left to the successful contractor, the board deciding what amount of raising is imperative on the existing structure, and then leaving it to the contractor as to what he would do to get access for the stone from its source on to the extension; but an examination of the probable cost leads me to think that the most economical course would be to raise the present breakwater with selected stones from your own quarry, or by concrete blocks, utilising the present old 20-ton crane, and to construct a trestle running from the end of the Macamlrew wharf to a point about 150 feet west of the breakwater, 700 feet seaward at the end of the Macandrew wharf, and then curving round at a radius of chains or thereabouts, so that when the line of this curve intersects the breakwater 300 feet from its outer end it is then tangent to the line of the breakwater extension which inclines from the present breakwater line 65 degrees (approximately E.N.E.). The extension would then carry on at this angle for approximately 750 feet and then curve on a radius of seven chains and a-half until the total length of 880 feet, at which point, water 22 feet deep is encountered. Isy continuing this curve a slight distance further a bearing is arrived at almost at right angles to the present breakwater, and parallel to the sailing course which gives most direct access to deep water — which is the line I would recommend for any future extension. However, we are not called upon at _ the present time to make a definite decision as to the alignment of work so far in the future, and it is better to keep a matter like this still open, so that the experience gained by the first extension may be utilised in making the final decision as to the alignment of any further extension. “The end of the breakwater should be made particularly heavy, higher than the average, and containing few stones less than the maximum size on the work generally, and if at any time the works are to be suspended for lengthy or indefinite periods, then the end ns then existing should be similarly strengthened. Otherwise there is a danger of the end being broken down progressively and the material being driven into the navigable channel. It is surprising how far heavy seas can remove rocks under such circumstances, and such rocks are not easy , to find afterwards, and might easily have a disastrous effect on a vessel. *' Provision would also have to be made for the temporary lighting of the end of the trestle, and for a permanent light on the new breakwater end at the completion of the work. The question of access to this light has to bo considered; I am of the opinion, however, that it would not be necessary to retain in perpetuity a walking access to tire light. It could be tendered by the pilot staff with a boat, particularly if acetylene were used and bottles of gas of proper capacity were installed. “ I have indicated (lie extent of the dredging which I consider necessary, and although this appears to extend considerably the area which you now find it necessary to dredge, 1 am inclined to think that the actual total tonnage to bo removed yearly will be less than is now the case for the smaller area. “A vessel, from the time its bow comes within the shelter of the breakwater, in southerly weather, will have more than three lengths in which to reduce speed before making the turn on to the line of the inner beacons, but should this be considered insufficient, 1 have indicated a further area which, at very moderate expense, could bo dredged, and which would give ample length in which to arrest the vessel's progress. “Your present berths, being amply deep enough, call for no further work, but the swinging basins should all be reduced to a depth of 22 feet. “You have asked me to express an opinion as to the effect of the further harbour works upon coastal erosion from Oamaru northwards, I am of the opinion that the erosion which has taken place in tile last 50 years would have taken place whether your harbour had been built or not, though possibly it would not have been quite so extensive in certain parts. The effect of the harbour is to create a semi-protected zone up to about Ribble street. This has accentuated the difficulty further up the beach—perhaps for half a mile. Beyond this point its effect would greatly diminish, and has been limited to the lessened protection due to the loss of such portion of the shingle on the bench as has been trapped in the area ,jnst north of the mole. The natural protection of any sea cliff is (ho beach deposit, at its base. When shingle, etc., is denuded, the seas attack the foot of the cliff and erode it. When there

is ample shingle the erosion is diminshed. Insofar as the amount of shingle is reduced so the amount of erosion is increased. The effect of your harbour in creating the more protected zone mentioned above has been to cause a certain amount of the shingle, etc., on the beach to lodge there when it has been driven south by the comparatively infrequent northerly rough weather. When the weather changes round to the prevailing south or south-east the waves which reach the shore within the semi-protected areas have, when they strike the beach, practically no northerly travel, and therefore any shingle which lies there remains. Extending the breakwater will lengthen the protected area, making this protection better, and both these effects will tend to the lodging therein of more shingle. It can thus be seen that there will be less shingle drifting northwards to protect the cliff against the wave stroke. As the protected area will, on completion of the breakwater extension, reach somewhat north of the railway yards, the railway property will receive benefit, but the property immediately northward of that will have its condition made worse. It is very difficult to say how far this effect will extend, but I would not expect it to be felt for more than a quarter of a milue or half a mile at the outside. Beyond this point I do not consider that your works have had in the past, nor will have in the future, any appreciable effect.

“Reports by Government engineers 50 to 60 years ago mention the extensive erosion then being carried out by the sea' north-ward of Oamaru, thus it can be seen that the erosion is no new matter being brought about by the harbour works. The wall as at present does not, as previously mentioned, prevent the material from passing the outer end, so that what limited amount of material comes round the Cape still travels on, but I consider that an extension on the lines I_ recommend would prevent any appreciable drift passing and thereby improve the dredging position; but it cannot be denied that the stoppage of the material from the south must have some effect upon the erosion position to the north. However,! do not consider that it would be sufficient to be noticeable. “ The estimated cost of the work is as follows, assuming that at least half of the stone will have to be brought from as far as Sawyers’ Bay, or that concrete blocks are used:— Inside staging, 800 ft, at £4 ~ £3,200 Outside staging, 880 ft, at £l2 .. 10,560 Stone in Mole, 60,000 tons, at 14s 42,000 Stone in Mole, 60,000 tons, at 7s 6d 22,500 Dredging 4,000 Raising old breakwater 5,600 £87,860 Contingencies—Plant, etc., 10 per cent., say 8,640 £96,500

“The estimates which I have made .are based upon a random rock wall raised Oft above high water-mark, with a slope of 2 —l on the outer side and 1J —1 on the inner side; the base and a considerable portion of the core being composed of stones from 2cwt up to a few tons ns may be most economical from the quarrying point of view, but the outer face, from 10ft below low water to the top, and the top, to be composed of blocks ranging from 5-12 tons, not less than 15 per cent, of the latter, and the whole to be covered by approximately 10 per cent, of 20-tou blocks. The inner face need not have any 20-ton blocks except at the entrance end.

“ In drawing up the specification, however, the contractor should be given the option of carrying out the whole or anydesired portion of the work in concrete, provided that blocks are not, in general, smaller than the sizes specified for stone; in fact, as the difference in cost by increased size of producing and placing the large concrete blocks is practically negligible, the use throughout, or extensively, of concrete would enable largei units to be employed, with consequently improved stability. “ The trestle from the end of Macandrew wharf need only bo a light and cheap structure and with a single track upon it. The extension trestle previously mentioned would require to carry three lines and to be strong enough to stand the wave strokes duo to its exposed position. Australian hardwood piles, 60ft in length and not less than 12 inches at the point, would be required. In addition to the wave strokes, a trestle of this kind is always liable to damage by the tipping of large blocks. Though in general

the y-estle should be made of medium spans, thus enabling each track to be carried on two stringers, it may be found difficult to drive piles through (he existing protective apron where the extension will strike off from the existing breakwater, and it may therefore be found necessary to adopt a fairly long spall carrying the track to a point at which piles can be easily driven into the sea bed. Where actually crossing the existing breakwater, it may be found advisable to build up in solid concrete, which would act as abutments to the spans free from each direction, and would also give operating room for the man working (ho points leading from the single (o the treble track.

“Even if concrete should prove cheaper than stone for the main work it would be wiser to incorporate in the core n good deal of small stone in order to prevent the travelling through the breakwater of sand which would afterwards have to be dredged away. In fact, after the breakwater is completed, it may bo found that a certain amount of sand is still accumulating under its Ice, being driven over the top or through the interstices in heavy weather. The only way to avoid this is by increasing the cross section of the breakwater, but whether the _ considerable expense of this would be justified can only be judged after experience has shown to what extent this dredging is necessary, thus giving a line on the amount of capital which could justifiably be spent in obviating it. “The dredging that I have indicated only carries the channel into 22ft of water. It might be possible in very favourable weather to go out to the 23ft contour, hut I am doubtful ns to the necessity for this work. To carry the breakwater into 23ft. of water it would require an extension of 100 ft at an additional cost of probably £11,700, and to increase the dredging depths to 23ft it would cost another £2500,

“ I have to acknowledge the very great assistance which I have received from your staff, the harbour master furnishing me with his records and a viva voce full account of the weather conditions; and, particularly, I would like to refer to the ungrudging efforts of your secretary, who spared neither time nor trouble in placing me in possession of all the information ol which he was possessed or of which he was able to extract particulars from the past records of the board. DISCUSSION BY HARBOUR BOARD REPORT REFERRED TO STANDING COMMITTEE (From Our Special Reporter.) OAMARU, September 12. At the Oamaru Harbour Board meeting this morning, the chairman (Mr R. K. Ireland) moved that the report be sent to the Standing Committee for report to a special meeting at a later date. He thought it better to leave the matter open instead of making a hasty deceision in such an important matter. Their object in obtaining the report was to deepen the entrance to the harbour to 22 or ‘23 feet, and it was impossible to dredge to this depth without further protection to the harbour. Already this season they had suffered some loss through three boats allotted to Oamaru having to go past the harbour owing to their draught. Those three boats would have come to Oamaru if they had the depth aimed at. The report indicated that that depth was attainable at a cost of £IOO,OOO, which, taking into account the cost of harbour works and dredging, was a reasonable cost, and the report also showed that the plan could be developed further if required. It would now be necessary to decide if the board could finance the scheme at £96,000, or part of the scheme for future development as finance became available. Mr Ireland referred to the silt coming over the ■ breakwater. Mr Furkert reported that the raising of the breakwater, could be done at a cost of £SOOO. The inside depth at the breakwater when built was 20 feet, but now the depth was from two to seven feet. Mr Furkert explained that that strengthened the breakwater, but the heavy seas carried silt over even right down on Macandrew wharf. Further protection along the breakwater would considerably reduce dredging inside the harbour. The questions regarding the use of concrete, quarries, and also the trestle or end-tipping methods were matters for further consideration, and would require careful thought before a decision was reached. The question of finance was the first thing on which to concentrate, and if they decided to go on with the scheme they would have to decide on the method. Mr Hayes seconded the motion, and after a brief discussion it was agreed to refer the report to the Standing Committee for report to a special meeting of the board.