EROSION ALONG THE SHORE

Auckland Star, Volume LXVII, Issue 114, 15 May 1936, Page 6

EROSION ALONG THE SHORE

Tito great damage by erosion along the coastline of the gulf is a reminder of the persistent work of the sea and its continual encroachment upon the solid land. The gentle lapping of the tide, as it does its double duty day by day, may signify to us little else than a universal agent providing a healthy clean-up of jetsam of the teeming ocean. And without these tides how offensive would be the stench of decaying organisms. But here conies the storm, with its great waves lashed into uncontrollable fury. Suddenly there is created a mighty engine charged with compressed air and armed with the battering ram of tons of sand, stone and shingle. Thus the cliff faces are undermined, the fallen blocks are broken into smaller fragments and all passing from shingle to sand is carried far out to sea. There is less knowledge of the effects of erosion on New Zealand shores than on those of England because of the longer human history and the early, maps of England. But the results in both countries arc much the same, although from the effects of earthquake in Wellington and Napier groat reclamations were effected by cataclysmic shakes. It has been estimated that the English coast retreats at the rate of one foot a year. This rate is much exceeded where the rocks arc soft and without intercalated bands of harder material, the latter by gentle folding often forming protective headlands or points, as we may see in many places round Port Phillip. Such English coastal regions as East Anglia, Thanet in Kent with the Goodwin Sands, and the shallows and limestone stacks off Selsey in Sussex, are areas where excessive denudation has gone 011 in the past. There the rock cliffs, clays, marls and sands have been unable to withstand for long the fury of the storms. The histories of these localities are full of interest and even fascination. At Selsey, for example, in Saxon times (080 A.IX) St. Wilfrid built a cathedral on a site now one mile out at sea, where formerly there was a great wood stocked with deer, and known as Selsey Park. The fishermen now anchoring on this great waste of waters still call it "The Park,'' and it is so marked on the ordnance maps of Sussex. Chichester Cathedral, some miles inland from Selsey Bill, shelters certain of the memorials, windows and other relics of the ancient Selsey Cathedral. Even the stones from the Mixcn rocks that are now far out at sea are to be seen built into the walls of the present churchyard of Chichester.

Occasional encroachments l>v the sea have been caused through a subsidence of the land, or, as some have it, by a rise in the tide level. -"V notable instance of subsidence of a land surface in the British Isles occurs at Barry Dock, 011 the coast of Wales, near Cardiff. Here the old land surface is found at (iO feet below the present sea level, and upon it have been discovered stone implements and bone needles of the Neolithic period. Jt has long been the practice in England to assist Nature in its protective work of forming bulwarks of shingle and gravel, by setting piera or . groins (sometimes spelled groyne) at an oblique angle to the set of tl\e tide. The shingle against the tide tends to fill lip the angle- to the top of the groin and to pour over the other side. Material forming the shingle generally consists of the hard limestones or ironstones of the tumbled beds. It is true that during heavy storms such protective shingle benches may be bodily shifted, but the bar is soon restored. An instance of such is mentioned by Sir Chas. Lyell in his "Principles of Geology," where, near Lymington, in Hants, the shingle thus temporarily disturbed continued to preserve the same coastal outline; and that it had done so for many centuries was proved by the old maps. Tlie expedient of a sea wall is a very expensive one, and liot always efficient, as was proved at Milford during the March gale. This is due to the fact that the waves in their action of creating an undertow during the outgoing tide exercise a tremendous suction. Thus there may be a continuous process of foundation weakening, with a disastrous termination sooner or later.