THE ORIGIN AND STABILITY OF BEACHES

J. W. Hoyle, G. T. King

Abstract


One should not lose sight of the fact that the origin of beaches goes back into antiquity. The story "begins with the origin of matter and continues through the aeons with the evolution of the solar system and the appearance of the Earth as a fiery ball gyrating in space. As one's focus narrows there is to be seen the cooling of that ball, the formation of dense clouds of water vapour in the atmosphere, the torrential rains and the beginnings of the seas. Perhaps it is at this point that the introduction is completed and the real story of the beaches begins, for with the rains came erosion of the land masses, and the transportation of the eroded material by river and rivulet towards the sea. At the brink of the ocean a brief halt is called in its journey, for here a portion of this eroded material takes position as beaches around die coast, before ultimately joining the remainder in the depths of the sea. For many thousands of years the sediment so formed and transported collected on the sea bed, consolidated and hardened and was transformed into the sedimentary rocks which, by adjustments in the Earth's crust, were later lifted above the surface of the sea to form new islands and continents. Still the rains fall, although perhaps not so heavily as before; still the processes of erosion continue upon the land masses, old and new, still a part of the products of this erosion remain for a while at the coastal fringe before they pass on to the ocean depths - the raw material of what may be, by completion of the cycle, the continents of tomorrow. Such is the sequence of events over a period of millions of years and, as the process continues during the millions of years which the future holds, the existing land masses will no doubt be eroded away and the materials of which they are composed will finally rest again on the bed of the sea. For so long as the seas have washed the shores, and the rains have fallen and reduced the mountains and high places, there have been beaches. Those beaches, which are found today may have existed from time immemorial in some form or other, perhaps since before life appeared on the surface of the Earth. Due to their position in the pattern of Nature they will have changed as the coastline changed, and as the eroded ingredients of the land which formed them changed. They will have grown when the new material supply exceeded the wastage, and they will have diminished when the wastage was more rapid than the replenishment. The changes which are taking place today and which are engaging the attention of the Civil Engineer, form an infinitesimally small incident in the history of the beaches; and in the considerations of the Engineer they should be related to the whole, of which they form a part.

Keywords


sediment characteristics; equilibrium slope; beach stability

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