PORT OF GREYMOUTH

Hokitika Guardian, 6 February 1930, Page 7

PORT OF GREYMOUTH

NEW IMPROVEMENT SCHEME

BY FOREMOST SCOTTISH ENGINEER. PROVISION FOR. BREAKWATER HARBOUR, I What may be destined to mark a new era in the history of the port of Greymouth was the report which the ! Chairman of the Harbour Board Mr Joseph McLean, on Tuesday submitted to the Board at the ordinary meeting. The report outlines a schemo quite new to the local Board, in the form of a construction of two curved breakwaters, roughly each of a length of between three and four thousand feet, from the foreshore, at either side of the existing harbour entrance. These structures would, rough- ( ly speaking, be for their entire length ' a distance from the present walls of say between thirteen and sixteen chain. The object of their erection is suceintly explained by the Engineer responsible for tlie scheme, Mr R. Gordon Nichol, 0.8. E., M.lnst.C.E. M.I. Mech.E.. J.P., Harbour Engineer of: Aberdeen ,and Consulting Engineer to the Fishery Board for Scotland, who is regarded as perhaps the leading harbour engineer in Britain to-day.

THE REPORT. The following is the text of the report received by Mr McLean from Mr Gordon Nichol, 0.8. E., M.lnst.C.E., M.l.Mech.E., J.P., Harbour Engineer Aberdeen, and Consulting Engineer to the Fishery Board for Scotland:— Harbour Engineer’s Office, Aberdeen, 18th November, 1929: Dear Mr McLean, —Improvement of Greymouth Harbour, New Zealand :—Referring to our interview in August and again during the last few days regarding the improvement of Greymouth fiar- J hour 1 have given the matter careful consideration and I beg to submit the following observations: — In considering the question of the

improvement of Greymouth Harbour New Zealand, it is impossible, without full local information and a personal study of the conditions, to .put forward a detailed scheme for improving the harbour. 1 have, however, care-

fully studied the information... which you have placed at my disposal, and the engineers’ report and plans which you loaned me.

The problem is complicated by the existence of the Grey River, which is a stream subject at times to intense floods carrying large quantities of detritus and also .by the littoral drift of sand and shingle from south to north along the sea coast.

The existing breakwaters are designed as training Walls for the river and these have been extended from

time to time with a view to reaching deeper water,-as the combined action of river and sea has caused the deposit of material in the channel of the river, which forms the entrance channel to the harbour.

The most- probable effect of a further extension of the existing breakwaters

is the reproduction of the existing state of affairs at a point further seaward that at present, and it is doubtful whether sufficient scouring effect can be obtained under normal conditions from the outrush and lagoons to provide for an increased depth of water in the entrance channel. The littoral drift of sea, sand and shingle will tend to produce shallow water about the extended pierheads, and to cause an accretion of material principally outside the South Breakwater, and the river will continue to bring down detritus which it will deposit m the form of shoals iu the entrance channel to the harbour. These conditions may be improved to some extent by controlling the flow of water in the entrance channel from the lagoons, but I am doubtful whether such betterment will be sufficient to improve the harbour entrance permanently. As the size of ships frequenting the port increases, requiring an increased depth of water in the entrance channel, these difficulties will become more acute. It appears to me that the harbour of Greymouth has now reached a stage in its development when further improvement is difficult along the present lines and when it is advisable to supplement the existing training works by the construction of sea works designed to secure the entry of large vessels into the harbour in all weathers. I would recommend a policy of providing the harbour with an entrance which would afford easy access to shipping and of maintaining the required depth of wafer .in the entrance channel principally by means of dredging. ' I . ' \.

To provide for the' requirements of navigation it is necessary that the entrance to the harbour should be in deep water, that the entrance should' face the direction of the worst seas, tliat it should be sufficiently wide to admifc\of the entrance of vessels of the largest size likely to use the harbour and sufficiently narrow to exclude storm waves as far as possible, and that immediately inside the entrance an expanse of protected water should be provided to reduce the storm waves passing through the entrance. Keeping these principles in view I would put forward the following outlines of a scheme\of seaworks for Greymouth Harbour. The scheme would provide for the construction of two long curved breakwaters extending from the foreshore, one on each side of ‘ the existing har hour entrance.

The breakwaters would leave an entrance of about 800 feet in width at low water level, the width of the entrance being reduced at the sea bottom by the slopes of the breakwaters. They might be formed of heavy rubble mound construction, and I understand that there is an abundance of stone in the neighbourhood, suitable for this purpose. I' consider that the South Breakwater is the* more important of the two and that construction might be carried out To' v advance df the North Breakwater. The two breakwaters would enclose a large additional water area outside the present piers, and this area lyould form an effective stilling basin so that vessels entering the harbour would have no difficulty in passing between the existing pierheads.

I have prepared a sketch plan, on • which I have indicated suggested lines for the two breakwaters, and I send you duplicate copies of this. The problem of maintaining the depth in the entrance channel would be met by dredging material deposited by the river, probably by means of a suction dredger. The depth in which these breakwaters are constructed would be sufficient to prevent silting at the entrance due to the action of the sea. The littoral drift along this coast would tend to an accretion of 6and and shingle outside the South Breakwater, but I do not anticipate that the deposit would encroach on the entrance channel to the harbour to any appreciable extent. A study of the problem on general lines and with the information which I have does not seem at present any more satisfactory solution than the one I have outlined. The plan which I have prepared is in the nature of an outline plan and before estimates or working drawings could be prepared it would be necessary to have careful surveys made of the harbour entrance and a study of local prices and conditions. If it is considered that such a scheme is unwarranted by the prospects of • the trade of Greymouth and it is necessary to consider alternative proposals,l do not consider it advisable in the interests of navigation to reduce the existing width of the entrance between the pierheads. The improvement of the lagoons by dredging and the utilisation of the water flowing out of the river and lagoons with the ebb tide will help to scour the entrance channel, but lam of opinion that the channel will always require a considerable amount of dredging to maintain its depth. I have not dealt with the internal development of the harbour. I understand that the existing wharfage is sufficient to deal with the present trade of the harbour. It appears to me that future extension of wharfage when required might be provided by converting a portion of the lagoon area south of the harbour into a dock with an improved entrance from the river on the site of the present outlet from the lagoons into the river.—l am vour sincerely: (Signed) R. Gordon Nichol, Harbour Engineer.