BAR AT TAIAROA HEADS.

Otago Witness, Issue 3774, 13 July 1926, Page 5

BAR AT TAIAROA HEADS.

A MENACE TO THE POET. CAPTAIN M'DONALD’S WABNING. The bar at the Taiaroa Heads and the menace to the harbour entrance that exists at the Heads formed the subject of a long statement made by Captain O. M‘Donald at the special meeting of the Harbour Board on Wednesday last. He commenced by urging the board to procure as large a dredge as possible; because the largest that could work with advantage in the harbour would be required to clear the bar outside the Heads. He said that on September 4 he made a statement regarding the bar at the Heads and its surroundings. He then asked the board to prove or disprove fche statement made. So far little or nothing had ijeen done. True, the engineer had spent a week or more surveying in the offing, but with unsatisfactory results.- for when asked to table his report he said he preferred to leave it until after his return from the (..-Id Country. He had said that he w.»s satisfied, however, that no engineer had given fche question the necessary consideration. Or words to that effect. The speaker said, very sorrowfully, that any tew idea or suggestion was at first laughed at, because there was a conservatism among people that made people stick fast to the policy of not giving a prophet honour in nis own country. The speaker referred individually to a number of men with new ideas who had been scoffed at during their lifetimes only to have their inventions later become ol world-wide use. He was, therefore, not surprised at the small effort made by the board to either prove or disprove all that he had already said regarding .the entrance to Dunedin Estuary. Before a large sum of money was spent on throwing out the western mole, a complete survey of the approaches to the Heads should be made, and a large dredge for clearing the bar obtained. Knowing that it was difficult for those not conversant with this important matter to understand his remarks, he had made out a plan, which showed and proved to anyone the change brought about for the last 36 years by running out the western mole. 'Die question of the ocean pressure had far too often been overlooked by those recommending breakwaters where there .vas much tidal current, as had the fact that the tidal wave in the open sea did not exceed 3ft at any time. , , . m . For example, at che bar at Taiaroa Heads there was a fair average of about 40ft in mid-channel irom Harrington Point to about 3000 ft outside the Mole. At this point the effect of the scour from the estuary commenced to lose its effect, and a serious shoaling had taken place or a new bar was forming. In other words, there was now 35ft where there had been about 65ft 40 years ago, due to the fact that the scour from the harbour was meeting a greater pressure, and in consequence joined the ordinary tidal wave in the open. On September 4 last, he had said that owing to the rotation of the earth on its axis all loose material in the Southern Hemisphere travelled to the north, but why did such loose material move faster along the shore or beaches ? Because the sea pressure was continually pushing the loose material in-shore, and the current or drift to the north - was, stronger on the surface. In the case of the Ninety-mile Beach there were five large rivers—the Rakaia, Ashburton, Rangitata, Temuka, and the Waitaki —besides many smaller streams, carrying large amounts of sand, shingle, etc., ,to sea, arc yet the depth along the wtioV length was not affected except for a few yards, at the mouths of the larger rivers. Why did all the West Coast Sounds have bars at their entrances? Because there was a great depth of water outside and inside the sounds, and the sand that ?. d been travelling for ages was held at the entrance by the great sea pressure from outside and .nside. “In conclusion, le» me say,” he continued, “that I am not going to keep harping on this important matter. I have said enough before and now to prove the necessity of a large and up-to-date dredge to keep the port open for large" ships m all weather. I might also say that it is up to those who would throw cold water on my remarks and suggestions to give this, important matter as much thought and consideration as I have done, not only at Taiaroa Heads, but all over the world.”