DENUDATION AT ST. CLAIR.

Otago Daily Times, Issue 17871, 28 February 1920, Page 10

DENUDATION AT ST. CLAIR.

TO THE EDITOR. Sir,—ln your issue of yesterday there ;s a very sensible letter signed by "Lover of Nature," dealing with the denudation of the foreshore at St . Clair. Anyone familiar with our ocean currents and prevailing winds will agree with every word he says. Ho is evidently a close observer, ann tne writer, who lias been a. irequuntcr of the beach at St. Clair since childhood's days, and knew tho state and contour • f the beach iut the St. Clair end before the first seawall was built, has noted at woric tho same factors which have made such a sad of that boautiiul and healthful adjunct to the city. As far as the groins proposed are concerned they will have as great a utilitarian effect as a wall ot butterflies' wings would have in stopping the denudation. Indeed, as your correspondent states, tho groins would be worse than •useless, for they step the return of the sand during northerly weather. The denudation is caused by the trend of tho northerly ocean current and south-west weather, aided by the basalt shore platform and reef extending seawards from the small promontory below which tho baths are cut. Pressure of heaped up waters extending from the Green Island beach along the sandstone cliffs and obstructed by Curgill's promontory, the baths' platform and its reefs, cause the lash to scour round tho reef and platform into St. Clair, and tho tendency of that lash is to make an opening at or near the St. Clair end. Anyone having a slight acquaintance with physiography knows that in all the small bights or bays up the East Coast, the openings are always at the south end of the beaches or sand spits. After the big Clutha flood in the "seventies," the southern <r Port Molyneaux mouth of the Clutha. was blocked, and the liver broke through at tho northern end; but again, the lash of the seas caused by the sou'-westers round the promontory and reefs of the Nuggets has reopened by denudation the outlet *t the southern ezid of the estuarine sandspit of tho Clutha. Groins will under the circumstances tend to make the conditions worse. Putting a mo]e near the weather end or north-west end of the spit at the Heads helped to deepen the entrance to our harbour, and a similar result will follow if groins axe erected opposite the sandhills on the middle beach. Timaru affords an example—no disputable experiment, which tells us what should be done. A mole should be built far enough out from tho baths to stop the lash or scour round the reefs, and then the sand coming in with the northerly weather would rest permanently, as sand does in Caroline Bay, at Timaru. Thus a beautiful beach has been formed by the breakwater interrupting the waves and tho east shore current. A boach_ perfectly safe for bathing and even boating could be made at St. Clair by putting a mole out from the rocks. If that is not done, given a cycle of sou'westers for five or six years, and the whole of tho sandhills between St. Clair esplanade and St. Kilda will disappear. That, from the enormous inroads the sea has already made, is a certainty. What may happen to the residents on the low-lying ground adjacent may be left to the imagination. -writer has seen a wave top the road leading round the corner near the baths. Somebody must get busy.—<l am, etc., Moxe. Dunedin, Febuaary 25. Sir,—lf "Lover of Nature," who writes on the subject of foreshore protection, wero to study Nature he would see that there are more important factors to be considered than he has stated. He is quite right, I believe, in expecting that the erection of groins will be a waste of money. Tho only reason tho sand is moving from opposite the esplanade is that it forms a and on the coast you never find a 6and beach at a bluff and sand in a bay where the sea deposits it when it has spent its force. Tho winds have not much direct action in ih© i sand coming and going, but when there is very Utile wind from any direction, and the sea becomes calm, tho sand in suspense is deposited on tho shore. At Tnnn.ru, behind the breakwater, Caroline Bay is a concrete example—once a shingle beach, now a sand ono. A wall might stop tho erosion of the shore, bat at a loss of the sand beach.—l am, etox, St. Cl&ib.