Use of SEM/EDS and X-ray diffraction analyses for sand transport studies, Lake Erie, Ohio

Natural tracers offer advantages over artificial tracers because larger vol umes can be studied over longer time intervals. However, natural tracers pr esent their own set of problems, including non-uniform starting conditions due to variation within the tracer population, dilution by mixing, and abra sional destruction of the grain characteristic. A beach nourishment project in Lake Erie used about 7000 m(3) of sand that was found to have a distinctive iron-rich clay coating on quartz sand grain s. The sand was uniquely introduced, because it came from a quarry 15 km in land and had not been used for other beach nourishment projects in the regi on. Experiments were undertaken to identify the coating, assess the hydraul ic equivalence of the tracer sand to native beach sand, and to determine th e resistance of the grain coating to abrasion. Results indicate the sand behaved as a natural tracer that was detectable f or approximately 2.5 years after introduction. Plume centroid migration rat es averaged 2.45 mday(-1) westward during the first 20 months of the study. Eventual dissipation of the tracer plume (due to mixing and abrasional los s of the coating) resulted in an apparent reversal of the plume migration d irection.