Mechanism of Sand Movement on Coastal Dunes

Sand supplied to a coast by streams, cliff erosion, and other sources generally is moved in one direction along the shoreline as littoral drift under the action of the prevailing wave conditions in the area. When this drift encounters a partial obstruction, such as a prominent natural headland or a major engineering structure, a condition is realized that is conducive to sediment deposition. Such a littoral compartment eventually becomes filled and some sand is carried past the obstruction. If the topography back of the area of deposition is relatively low and the prevailing winds are onshore, a considerable volume of sand may be moved inland to create a dune system. This loss of material from the coast may affect the stability of the down-coast shoreline. Therefore, knowledge of the annual loss (or supply) of sand from a particular section of coast by wind action is necessary in many instances. A method for estimating the rate of supply or loss of sand involves the use of a suitable transport equation. Numerous laboratory investigations on sand movement by wind have been made over the last 2-5 years. In the last 4 years these various studies were critically reviewed and the need for a method based on a better understanding of the mechanism of the bottom became apparent. The problem now is to determine a suitable method to describe the over-all mechanism of sand movement by wind. Each phase of the phenomenon will be explained herein and the desired relationships will be developed.