A Class of Probability Models for Littoral Drift

William R. James

Abstract


The major goal in the development of sediment tracer technology is to produce an accurate method for the field measurement of short term volume littoral rate Many of the technical difficulties involved in tagging, injecting, and sensing the movement of radioisotope sand tracers in the littoral zone have been overcome by the RIST project However, quantitative determination of volume drift rate requires more than knowledge of tracer position in time and space A mathematical model is required to relate the flux of tracer material to the sediment flux A linear (or average) rate of tracer transport along the coastline can be measured to a fair degree of accuracy with tracers These measurements, when determined from tracers injected along a line source which span the transport zone, can be used to provide an estimate of an areal transport rate However, it is not obvious how to measure the third dimension, depth of transport This, of course, is needed to provide the desired estimate of volume transport rate This problem arises, even if the relation of tracer concentration to burial depth is everywhere known without error Sediment transport does not occur as a sheet of constant thickness moving at a constant rate If this were so tracer concentration would rapidly attain a uniform concentration over a fixed depth and no tracers would appear below that depth In fact no observations of the relation between tracer concentration and burial depth support this model as even a first approximation Studies such as those of Courtois and Monaco (1969) and Hubble and Sayre (1964) suggest that the concentration of tracers is related to burial depth in a complex fashion The concentration on the surface is finite, but not maximal The concentration increases with depth to some point where a maximum is reached and diminishes in a "long tailed" fashion.

Keywords


littoral drift; probability; probability model

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