SILTING IN BAY

Timaru Herald, Volume CXXXVII, Issue 19523, 24 June 1933, Page 19

SILTING IN BAY

POLICY OF DREDGING. HARBOUR BOARD DISCUSSION. Considerable discussion ensued at the monthly meeting' of the Timaru Harbour Board yesterday on the following motion, moved by Mr R. S. Goodman:—“That arrangements be made for the annual docking and inspection of Dredge 350 to take place immediately or to be completed by the end of September 1933, so that dredging operations may be commenced e.t the beginning of the financial year.” The motion was seconded by Mr I. J. Bradley.

In speaking to his motion, Mr Goodman said that a good many people were somewhat concerned regarding silting of the area surrounding the inner harbour and the channel. He viewed the situation very seriously, and considered that it was the most important problem facing the Board to-day. For the last six months he had watched the action of the sea, not only during a heavy sea, but during a oalm sea, and it was most notices'ole, more especially during the last two months, how much the low water mark had gone back along the Bay from the North Mole, round to the Waimataitai Beach. In one report by the engineer it was stated that over the sea bed of Caroline Bay, that was the area from the outer end of the North Mole to Waimataitai Beach, there was deposited 80,000 tons of silt annually (another report put the figure down at 95,000 tons) and the same report further stated that the lift in the bed was about 3 inches annually. If they took the annual reports for 1930 and 1931, it would be seen that 357,000 tons of silt was taken or dredged from the Bay cuts. This seemed a very large amount, but it igd to be remembered that it would contain a certain amount of stiff clay. They had been told that the trap had almost filled up, and if they were to make a simple calculation over two years, they would see that the bed of the ocean would have been lifted at least another foot. That was, if the 6ilt had been allowed to spread over, and it would have done this if it had not gone into the trap. There could be no doubt that silting was going on at a faster rate than previously. The silt could be noticed banking up along the North Mole, and if the position was not watched, it would percolate through into the harbour, and this would be a serious matter. In a few months the sand would be giving a good deal of trouble, and he contended that they would not have to wait 50 years, as had been stated, for trouble to arise. It would come in a few months’ time. To his mind the laying up of the dredge was false economy, and, he believed, the decision to lay the dredge up was on the score of economy, as it was considered that the shoaling was not causing any trouble. If that was the policy of the Board, he did not like it, and there was only one thing the Board could do, unless it was going to build moles, and that was to dredge, and continue dredging. The channel should be maintained to a depth of at least 30 feet, and the cut should be maintained. If members were to read the report of the Royal Commission of 1926, they would see that in dealing with the improvement schemes, the Commission stated “that it did not matter what was done, any attempt to curtail dredging will lead to increased silting in Caroline Bay.” It would appear that the engineers at that time were alarmed at the progress the sand

was making, and in view of the Commission’s statement, he considered that the low water mark should be maintained at the same mark as in 1926. During the lay up of the dredge between 1917 and 1919, the channel silted up from 26 feet to only 21 or 22 feet, the result being that the area between the extension and the old breakwater silted up extensively. It was the chairman, he thought, who had stated that the cost of making the Bay cut was prohibitive, namely £15,000, but a fair amount of this work was new, and in clay. For his part, he did not think the cost was prohibitive, because it was new work, and he had to fcongratulate the Board on having made the cut. He was disappointed in the fact that the Board had not maintained the cut up to the present time. He contended that it should be maintained to its original depth. Mr Goodman said that the first duty of the Board was to maintain the harbour so as to make it efficient and safe for shipping at all times. Dredging should be re-commenced almost immediately, or not later than tl.r end of October. If the silting was allowed to go on, they would find themselves maintaining two dredges instead of one.

Mr Bradley said that he thought the people of South Canterbury should be proud of the harbour they possessed. During the last few days the biggest ships coming to New Zealand had been accommodated, and the harbour was a credit to all concerned. However, he was very dubious regarding the avalanche of sand which was slowly creeping seawards. The toe of it was out to the Bell Buoy, and the further it went out, the deeper it got inshore. It was all very well to say that nothing should be done. Lots of things had happened that no-one had dreamt of. No-one had greater respect for the Board’s engineer than the speaker, but no-one could estimate what was going to happen fifty years from now. The further the sand crept out, :ne more likely was it that the channel would become blocked. Even though the dredge was working, the sand was gaining, so they should dredge continuously. It had been said that they were saving money by laying the dredge up, but he wondered if they were. They might just be passing the burden on to a future generation. They should make every endeavour to keep the port in its present efficient state.

Mr A. R. Guild said that members knew that he had been against the laying up of the dredge, but they had decided to lay the vessel up till the end of the financial year, and they might as well leave it at that in the meantime.

Mr W. H. Orbell asked if it was not a fact that the sand which had gone into the Bay cut, had come off the Bay.

The chairman (Mr G. T. Dawson) reported that this was so. He added that at the present time the channel was deeper than the ocean outside the extension. Until this was deepened, it was no use deepening the channel. In reply to a question the chairman said that the Harbourmaster had stated only a few days ago that the Bay cut made a difference to the harbour. Had it not been for the cut, he did not believe the Coptic could have been held in port. No-one would deny that silting was going on, but he contended that dredging was the wrong method. It was costly, and would not be effective. Referring to Mr Goodman’s statement that the sand was piling up on the North Mole, and would percolate into the harbour, he had asked the Harbourmaster when the inside of the harbour had last been cleaned out, and he had replied that it had not been done during the 16 years he had been in Timaru. There was only a small depth of water on the inside, u v.t a great depth was not required, and this showed that a rubble wall w: an effective barrier.

Mr A. F. Campbell said that he could see no reason for altering the Board's policy. The chairman said that Mr Good-

man had quoted him as having said that the position would be safe for 50 years, but he had said 20 years. By laying up the dredge they were saving £SOOO a year, which in 20 years would amount to £IOO,OOO, and that would be sufficient to meet the situation. There was an impression that the bed of the ocean might rush into the channel m a heavy storm, but there was only a few inches on the surface which was loose sand, the walls of the channel being practically solid. When the suction dredge had come down from Lyttelton it had been able to remove very little sand. The channel silted up at the rate of 3 feet per year, but it was only between 18 inches and two feet now, and that was after eight months’ inactivity on the part of the dredge.

On being called in to the meeting, the Harbourmaster (Capt. D. McDougall) said that as far as the channel was concerned, the position was quite all right, but the Bay was the big problem. There was a chance that the channel might become blocked in a heavy and prolonged storm, but that was one of the risks that had to be taken.

Mr Goodman: “Do you think the Bay cut is an effective trap for silt?”

Captain McDougall: “There can be no question but that it is, seeing that it has filled up. If the trap had not been made, the sand would have built up along the North Mole, and would have found its way into the channel.”

Mr Goodman said that if soundings were taken to-day, it would be found that there was a big difference in (tie cut, even since the February report. The motion, on being put to the meeting, was lost, only mover and seconder voting for it. The chairman congratulated Mr Goodman on having brought the matter forward, stating that it showed he

had the interests of the harbour at heart. He also agreed to have soundings made in the cut when the next channel soundings were Tarried cut.