CAUSE FOR ANXIETY

Nelson Evening Mail, Volume LXIV, 2 April 1930, Page 2

CAUSE FOR ANXIETY

CONDITIONS AT MOTUEKA HARBOUR

THE MENACE OP THE SANDS ENGINEERS' REPORTS Two independent reports were received at the last meeting of the Motueka Harbour Board in respect to Motueka harbour conditions, (a) from Mr F. W. Kurkerl, Etigineer-in-Chief Public Works Department, and (b) from Messrs Vickcrnian and Lancaster, tho board's consulting engineers. The first, dated 17th March, was from .Mr F. W, Furkert, Engineer-in-Chief, Public Works Department, and read as follows:

"Last year Mr Vickerman and myself made investigations of the conditions at the mouth of your harbour, and since that have had a further survey made to show the latest, developments, and it cannot bo denied that the northern spit is advancing in a way which gives cause for anxiety. "After considering the matter from all points of view I cannot see that any stops can be taken to improve the position, unless your board is in a position to spend a very considerable amount of money in training walls. "Mr Vickerman has shown me a copy of his report, and I am in general agreement therewith. A certain amount of sand could be stopped by means of planting the spit, but even if all the sand travelling above high water mark were arrested by some such means, you would still have to cope with the sand travelling on the actual beach and in shallow water offshore. I know of no way in which this could be arrested at a cost which would be justified by the apparent business offering. I understand that so far you have not lost any trade, but simply that the vessels trading to Motueka have been forced to give-inore attention to the tide, and have had a little tricky navigation to perform. "It cannot be overlooked that the day nay tome when the spit will have ex"i !o such an extent that it will not be possible for vessels to navigate the tortuous and shallower channel, and before that day arrives it may be necessary for your board to consider, bringing in shipping by the other entrance to the Moulere Lagoon, and providing a dredged channel from there to the present wharf, or alternately, training wall or walls will have to be constructed to straighten up the present entrance, and dredging done to accelerate the,na-tural-forces which, though sufficient after construction of the training walls to keep the mouth open, may not for some time scour out an adequate channel. "In the meantime, all that I can suggest is that your dues be fixed at such a figure as will enable you to accumulate a reserve fund, and the increase should be as great as it is possible to impose without adversely affecting the business ; endeavour by planting to arrest movement along the northern spit, and continue to make periodical surveys to keep a record of the changes which take place both above and below water."

CONSULTING ENGINEERS On 26th March, Messrs Vickerman .and Lancaster, Consulting Engineers, Wellington, wrote as follows: "We have yours of the 18tli'inst. and are glad to learn that you have received a report from Mr Furkert, who, we know, was deterred by stress of business from attending to the matter earlier.

"We refrained from discussing ~the„ question with him, beyond what was said before and during the. visit of ini spection, in order that his report'lnight?' be quite unbiassed by ourselves, arid"' would for that reason be glad to have a copy of his recommendations when these become available.

"Wo are forwarding herewith a supplementary report containing our present views, but would, as you suggest, be very pleased to go over the ground and discuss the matter further at some future date when the writer happens to be in Nelson, or, if the board wishes, to make a special visit. Our present report may however assist the board in considering that given by Mr Fnr : kert. > •

"We have to thank you very cordially for the information you have sent us from time to time. We realise that it must now be increasingly difficult for siiip masters to enter the port, particularly if the weather is bad. It remains to be seen whether a distinct channel will be maintained naturally, or whether the entrance will spread. If the former happens conditions would not be much worse than they are now, but if the latter, they will become increasingly bad. "One thing that does strike an.outsider is the comparatively low charges you make. Would it not be feasible to' increase these to provide a fund which would enable works, which must ultimately be faced, to be carried out. We are probably out of order in referring to this aspect, but do so with the best intentions."

SUPPLEMENTARY REPORT The supplementary report of the consulting engineers stated:— "With reference to Port Motueka harbour entrance on which we reported fully on the 23rd July, 1928, we now have the honour to make.the following, supplementary report, as a result of the inspection made with Mr Furkert on the 23rd May, 1929, and the information you have from time to time very kindly furnished since that date: — "I.—Sandspit: The same trouble exists as at the time of our previous report, viz., the steady growth of the sandspit across the mouth of the harbour. "We then reported as follows: 'A study of the rate of growth and change in shape of the sandspit is possible by reason of the existance of a series of old plans of the harbour, dating, from 1881, and the very complete records kept since 1916 by Mr* P. G. Moffatt, Harbourmaster. These records show clearly that in the 47 years which have elapsed since 1881, the high water mark at the end of the spit has advanced southwards some 34 chains, or .725 chains per year, whilst in the' same time the low water mark has advanced some 40 chains. The rate of advance has been fairly uniform except that there appears to have been a slight check about 1915, when the then "existing channel made the outflow from the Moutere impings directly on the end of the sandspit. However, once the advancing sand, assisted probably by the alteration made in alignment •when the channel was dredged, succeeded in turning the stream, the general average rate of advance was again fully resumed and recently appears to have increased.' "At that time the low water mark at the end of the sandspit was 5 chains southward of the 1916 entrance line. In February, 1929, it was 25 chains southward ; in October, 1929, when the Publi- Works Department survey was made, it" was 32J,- chains and from your letter of the 17th March, 1930. it is now about 40 chains, and in addition the seaward

bank, to which we made reference, has now moved forward till it is almost up to the 1916 entrance line. "The rate of.gnnvth has thus increased in a most alarming manner, due, at any rate to a large extent, we consider, to the sand bank having succeeded in turning the stream emerging from the harbour so that this, is no longer effective in checking the onward, advance of the sand. This success has certainly been aided to some extent by the change made in direction when the harbour entrance was dredged. We are, however, as we have already stated,, of the opinion that even. had the old line been maintained, you would ultimately have been in trouble, as nothing apart from extensive and expensive walls could be expected to meet such an attack. "2.—Remedial Measures: We can offer no further -suggestions than those contained in our old report. In this connection, however, the recent occurrences only strengthen our doubts as to the ultimate effectiveness of • walls unless the board is prepared to face the expense of continually pushing these seawards, which in the course of time would certainly absorb a very large amount of money. "In the face of this we jtill consider that the most economical method of dealing with the problem, when interference with shipping demands this, will be to utilise the southern Moutere entrance in order to provide a passage to the present wharf. "We also consider that means should be adopted for trapping the sand and believe, in this connection, that, if you cannot face tjie costs of the old proposals, the position might be most cheaply met by starting planting Marram grass, lupin, etc., near the mouth of the Motueka and allowing the seed and plants to spread from these southward, which, with some attention, they might reasonably be expected to do, even though somewhat slowly. We would stress this because even if the south entrance is used, the sand bank must continue to grow and may, in the course of time, if unchecked, threaten you even at the South Moutere.

"We have to again place on record our indebtedness to yourself for the very illuminating information and sketches you have periodically furnished."

BOARD'S ACTION After full consideration of both reports it was resolved (Messrs Harvey and Haining) that Mr Furkert and Messrs Vickerman and Lancaster be thanked for their reports; and that Mr Vickerman be invited to pay a special visit to Port Motueka, with.a view to his making further personal investigation of the present condition of the sandspit and the south entrance to Moutere Lagoon, at all stages of tides; and that subsequently a special meeting of the board be called to discuss the matter witli Mr Vickerman in order to arrive at a. solution.