OUR DEFACED BEACH

Evening Star, Issue 17367, 1 June 1920, Page 3

OUR DEFACED BEACH

■LOWERING AT THE ST. CLAIR, END [By Old Ideutitx.] The lowering of the beach at St. Clair Is the result of the south-east drift or current setting inshore during the prevalence of south-east winds or gales. There are two main factors which produce the scour which removes the sand. No. 1 ia the "lash" Tound the small shore platform, out of which the baths have been cut. No. 2 is the overflow at the north . end of the baths. ' The cause of the "lash," -which scours out the sand, is the pressure of the winddriven waters against the reef or shore platform on the south side. When the pressure is released by escape round the end of the reef,, the relieved waters' take the line of least resistance, which is on the north side of the reef, and the rush along that side of the relieved water is aided by the waves that have been tripped by the reef and swung parallel to the shore. One would be inclined to think that when a period of north-east winds sets in, and creates a drift from the north-east, that the drift, would strike, in at St. Clair and scour out the sand. The reverse is the effect. Observation over a long period of years enables one to speak definitely upon the subject, and the conclusion come to'-is that north-east winds raise the St. Clair end of the beach, and a series of strong south-east gales lower it. An individually expressed opinion of the causes and effects connected with the phenomenon ,of the periodic raising and lowering of the St. Clair end of the beach may be questioned, and viewed with a . certain amount of contempt if the individual is not a harbor expert or a skilled hydrographer; but no expert opinion is necessary when the fact about the lash and scour is demonstrated , for us by Nature all along our. coast. Wherever there is a lagoon or harbor open to the sea along the east coast of the South Island, the scour and opening will be found at the nearest end *>f the entrance to the south-east drift. If one examines a good map of the coast from the Bluff to Cape Campbell and notes the openings into coastal lagoons, the theory laid out by the writer will be found proved by the experiments of Nature. Numbers of instances of the work of the south-west drift can be found around. Dunedin. The channel of our own bar harbor is on the side nearest to the lash of the drift. The same is the case at Hooper's Inlet, Purakanui, Waitati, and Waikouaiti. The butt end of all shingle and sandy bars is always at the north or -.vest end of the harbors and lagoons. Two rivers, the Taieri and Clutha, are at times exceptions., but the tendency to open at the south end is always there. When these rivers break through at the north end the effect is due to floods or the prevalence of a period of north-east winds. On iur Ocean Beach front the thick end of what was once a sandy bar is at the Lawyer Head end of the beach, and in an age long past a river flowed out at the St. Clair end. When the land sank and the ocean waters flowed in, they formed what, is now the Otago Harbor, the Flat formed a ledge which caught the sand brought in by the south-west drift, and the tidal effect of the water entering at the Heads drove up silt, and these two effects combined with the sub-aerial denudation of the hills round St. Clair, Caversham, and Dunedin generally, gradually built up the Flat above sea level and overcame the tendency of tho lash of the south-east drift to maintain un opening at the St. Clair end. Still, though beaten by the various conditions, the tendency of the sea to scour out an opening is always there. Now, at Timaru a sandy beach has been formed where once there was deep water. That beach is an accidental result of the Timaru harbor works cutting of the scour of the south-east drift, the effects of which are seen in the piling up of the river shingle against the break-water and the accumulation of sand forming what is now tho Caroline Bay beach. The same tendency to form a sandy beach may be seen at 'Oamaru, where there is a small sandy beach on the north side of the mole. The cause of the accumulation of sand is the destruction of the lash of the south-east drift and the reduction of the thrashing effect of the waves by construction of harbor works. Now, the problem is how to produce • the same effect at the St. Clair end of the beach, and thereby to make that end a perfectly safe and ideal place for bathing.' All that is wanted is an obstruction to the lash and the wave effects, which are there great because the lash of the drift or current gives deep water along the north side of the Teef or shore "platform " that runs out from tho north end of the second beach. To break the wave effect and thereby stop the scouring, all that is wanted is some obstruction that will break the scour and trip the waver, as they swing round the point of the reeL_ That can best be done by either building a mole running out in a northeasterly direction from the reef, or bv the cheaper*and rougher method of building concrete pillars and tumbling them into the sea from the edge of the reef It was by means of a ferro-concrete pillar that the waters at the top of the Niagara Falls were- cheaply and effectivelytrapped for the purpose of making a dam on tne Canadian side for hvdro-electric purposes Tho, pillar was built on a wooden base, which was fired or blown out on tne side to which it was required that the piha-r should form an obstruction. A gradually shelving beach would b° formed without dangerous holes in it and would be perfectly safe for children' Those wnopreierred heavy snr f coll]d find it further north. By making the mole long enough a boat harbor, safe in south-west weather, could bo formed. ' THE DANGER-REMOVE IT. TO THE EDITOR. Sir,—lt is usually considered sounder business when confronted with a danger to, if possible, discover the cause, the-, remove it. In your issue of July 3, 1919 you published a communicated article of a most interesting and informative character which was practically unacknowledged by the army of amateur marine engineers, and, indeed, by the professionals. It bore the impress of an expert's judgment, and was worthy of better treatment. My reason for drawing attention lo it now is not only that it bore out my own observations, extending' over the pa«t oO years, but is confirmed in your "last evening's issue in the report of the inter view with Mr Slinger. Quoting your correspondent of 1919: "It i 3 evident from a study of the physiography of the coast line and the natural conditions rivalling that the greater part, if not "the whole, of the trouble caused by encroachment of the sea at St. Clair has been generated by the injudicious interference of man with the processes of Nature, and an utter disregard of the well-known axiom that he who obeys Nature will be assisted by her, but he. who opposes her will surely meet with disaster. The natural tendency of the sea is to fill up the coastline with material eroded from the land by its own action and the streams which flow into it. On this coastline . y 1 ?. 1 ; 6 ls a general trend of the littoral drut up the coast to the northward, caused by a combination of the off-shore current which sweeps up the coast from the Southern Ocean, the tidal flow, and the on-shore winds. The Admiralty chart shows a one-knot current setting up the coast off White Island, but close *in shore toe. effect of this current, as also that of «be tidal set is evidently at times mo-e than counterbalanced by the effect of the shore currents caused by wind action and such abnormal storms as we are just experiencing, as may be seen by the manner in which the St, Clair end of the beach is eroded and the St. Kilda end , made up during periods of on-shore winds, particularly those from north to east. The a accretion of the St. Clair beach during > ofi-shore winds is no doubt accounted fox to a certain extent-'by the \vell-knowu action oi the sea, by which, generally speaking, on-shore winds cause erosion and off-shore winds; cause accretion of the beaches." Mr Slipger's verdict is pracMcally the same, aa follows i—" Interfering • with wave aciion begin with the eieo"

tion of the esplanade'. It was continued with the construction of the short-lived road towards St. Kilda along the front "'J: 16 sandhills." Again Mr Slinger says: Wherever there is an opening between rocky promontories and the waves have scope to spend their force, they will warp or build up beaches, and the wind will blow the sand up into dunes behind the beaches." There is plenty of evidence in support of this along the coasts of our own Dominion. I was a close observer, while resident in Timaru, of the action of the sea along its foreshore before they started to put down the first caisson for the breakwater, and the subsequent difficulties with the accumulating shingle south .of the breakwater, and have followed its history right along, and am in perfect agreement with both " Communicated" and Mr Slinger in denouncing the breakwater suggestion, for the obvious reason, to those who have studied the history of similar efforts elsewhere, that sand will only travel freely in a certain depth of water, and, as "Communicated" points out, on this coast the limit of depth at which it will travel in any quantity in ordinary weather is probably between four and six fathoms, so it would be difficult to calculate the period which would elapse before'the sand would shoal up sufficiently round the end of the suggested breakwater., without which there would be no possible hope of the beach making in the St. Clair corner. Meanwhile, as has already been emphasised by the experts, before that desirable consummation was reached the effect on the beach further along in the direction of Lawyer Head would be likely to prove, disastrous, and if such a work was ever commenced it would be time for the residents of St Kilda ft tako to the hills. The rabble apron idea is against all expert advice. I noticed this morning that—for appearance sake, presumably to pacify public clamor for something to be done—a gang of men were placing rubble over the embankment, and there was a load or two of scrub to bind it together, and everyone seemed hopelessly helpless in face of the mighty onslaught of the Waves, as well they might. The general opinjpn is with the experts in this. We might just as well put a few hundred bags of sugar there for all the good it will do. In fact, better, as it would not be likely to do the same injury. The bags of sand at St. Kilda end were effective. When our engineers tell us " a rigid defence there would be the undoing of the natural defence in the shape of warped-up sand," and as our own common sense tells us if we think it out, why persist in such foolishness? These gentlemen nave pointed out the cause of the trouble. Why not face it at once—jettison the cargo to save the ship I In plain language, the esplanade is the cause of the trouble. It is a chain beyond high-water mark. Remove it, and let the beach recreate its old natural batter, as,_in view of all the evidence, it will do, ' : if the waves have scope to spend their force." A batter on the wall would be no help. It must be shelving sand and nothing else for a sandy beach. This can only be secured by "removing the dead wall, which, whenever the sea reaches it, gives the sand no resting place—simply churns it up, and carries it along the coast to where it can rest in peace. The first blunder was made by the old Provincial Council when it sold the sections along the sandhills, and it should be evident, however unpopular the suggestion, that even at this late date it would be cheaper in the, long run to make the first loss the greatest. It would mean a general average as far as the ratepayers are concerned. It has become a Government duty to take the' matter in hand, resume possession of all private properties between Bedford street and :he ocean, and reconstruct the esplanade above high-water mark, converting the rest of the land into an attractive reserve. As a boy I was able to walk beyond the baths on the sand, and there .was a line of dunes right up to Beach street. Meantime, if Mr Stringer's groynes do no good, they are not likely to do any harm, and it will pacify the public to know that something definite is beinrr attempted; and there is always the possibility that they may aid the elements when the off-shore winds are working with the waves to warp up the sand, and bo restore our once beautiful but now for-lorn-looking beach. I think, eir ; the " communicated" article, if republished to-day, would be more : fully appreciated. In conclusion, to anticipate those who may wish to slate me for my temerity in proffering a solution to the problem, I have already been advised not to place my fingers in a hornet's nest, but I'm risking it. If ■it contributes to centring attention on the cause of the menace, probably the correct solution may be the ultimate outcome. It is to !e regretted that the public memory should be so short-lived as it was proved to be in the case of the Domain Board, whose chairman has done surh splendid service right along, and can in no sense be held responsible for the present situation, he haying acted on the best adivice at his disposal.—l am. etc., C. J. Wattsox. May 51.