Abstract
A natural beach system is in equilibrium when there is a balance between sand supply and erosion such that the volumes of material entering and leaving the system are just equal. If the erosion rate exceeds the supply rate, a beach retrogrades; if the erosion rate is less than the supply rate, a beach progrades. Unfortunately, coastal engineering works, which are meant to improve the shore for commerce or recreation, often upset this delicate balance with very deleterious results: great accretions of sand and high dredging costs, accelerated beach erosion and much property damage. It is the task of the geologist to determine the secular equilibrium conditions of a beach system and to supply the coastal engineer with the information he needs to control the natural forces acting on the shore in such a way that this equilibrium is maintained. In order to accomplish this task, the geologist needs to make a thorough study of the source, transportation, and deposition of beach sediment. He must determine the stable position of the shore line and the profile of equilibrium of the beaches through detailed physiographic investigations. The geological report can and should close with the prediction of just what will happen to a natural beach system if man introduces a disturbing element.
Highlights
A natural beach system is in equilibrium when there is a balance between sand supply and erosion such that the volumes of material entering and leaving the system are just equal
There is an increase in the heavy mineral content of many beach sands as the sediment is transported away from the source areas (Handin, 1951). Still another use of the petrographic study is to determine the characteristics of the beach sediment which is in equilibrium in its natural environment
Foreshore slopes in turn depend upon grain size among other things, so that it is well for the geologist to make a study of prevailing wave heights
Summary
A natural beach system is in equilibrium when there is a balance between sand supply and erosion such that the volumes of material entering and leaving the system are just equal. Coastal engineering works, whlch are meant to improve the shore for commerce or recreation, often upset this delicate balance with very deleterious results: great accretions of sand and high dredging costs, accelerated beach erosion and much property damage. It is the task of the geologist to determine the secular equilibrium conditions of a beach system and to supply the coastal engineer with the information he needs to control the natural forces acting on the shore in such a way that this equilibrium is maintained. The geological report can and should close with the predlction of just what will happen to a natural beach system if man introduces a disturbing element
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