ST. CLAIR BEACH

Otago Daily Times, Issue 18293, 9 July 1921, Page 7

ST. CLAIR BEACH

AN EXPERT’S VIEWS. The subject of ocean currents and erosion at St. Clair is one that has interested many experts from time to time, and many divergent views are held. Among those who have given considerable thought to the problem is Professor R. S. C. Brown, of Dunodin. now principal of Poona College of Engineering in India. In a recent informal letter, from which we have been permitted to make extracts, hft expresses some of fits views on the matter.

“I seo the Ocean Beach is likely to disappear at the present rate of erosion.” he writes, ‘‘and tho more rapidly for the kind of precautions which tho authorities are contemplating. If they try to fight the Pacific Ocean with stores and brushwood they will make no end of a mess of things. The type of groin “like a picket fence" is not much bettor. The kind of groin which they had there when I was out is the best for the purpose, but, when neglected, is worse than useless. It wants n man on the spot to bo continually altering and adjusting them to make a success of them. Water in quantity and in motion will not bo driven, but it may bo coaxed. ’That is true of the sea and also of the big rivers such as wo have in Indio.' Before Graham Smith came hero, tic was erecting a bridge jot a railway over a tributary of tho Ganges; a big affair of 20 spans of steel girders; when tho bridge was finished tiio river had changed its mind end taken another route live miles away from the bridge, and tho next job was to coax it back again, which was done in tho course of a year. Its departure was rather a relief than otherwise, as it left the old river bed dry to work in. Before the coaxing methods were used on Indian rivers they wore a source of groat danger and expense to all tho railway works in the neighbourhood. The groins which were used at the bench defeat, their own ends unless they are continually watched. Tho boards must not project more than a foot above the sand, and when the latter accumulates almost level with the top of them, they must be raised by another 6-inch board, and so on. If a gale removes some sand, leaving the boards more than a foot above ground the surplus ones must bo removed, otherwise the high projection causes' scour, and the sand is rapidly lowered. So that there is good deal of give and take, gain and loss, but in the long run tho beach will bo raised n groat deal, provided it is someone's duty to pay a daily visit of inspection and adjust the boards whenever necessary. Many of the beaches on the ,English coast, which had been rapidly disappearing, have been built up greatly by this process, and a wide stretch of sand now exists where a few years ago tho existence of the town was threatened. Someone hag had the right idea at St. Clair, and put in the groins, but they, have been neglected, and in some cases the boards were standing high and isolated, so that one could walk under them, and wore thus a great cause of increased scour. Anything which tends to increase the speed of the water, or its eddying, to a marked degree, promotes scour, and this is why stones and sea walls are likely to cause harm. What is wanted-is something which, without causing scour will catch the blown sand, and the sand which is carried along by the water on the bottom, and cause it to bank up. The effect of a low obstruction on a beach is seen in tho way the sand hanks up round a log of wood or bunch of seaweek; while tho scouring effect round a boulder is always seen in the pobl produced. So there’s the tin! I believe the right place to begin to tackle the danger now is not at the break. Until yon have a small margin of beach to work on such methods are difficult to work. The place to begin is east of the bad bit; if the bench is built up there it will build itself on further west, tho effect extending gradually along. On that, const scour nlwnvs tends to occur at the south and west end of tho beaches, as raw lie seen from the onenings of all tho inlets, along the const. Where there is ft headland it builds iro immedintelv to the south of it; that is, at the north or east end of the bea , ’h B”ild un to the norih and east and the sand w : b bank up against the proicctjnn so formed.