LABORATORY APPLICATIONS OF RADIOISOTOPIC TRACERS TO FOLLOW BEACH SEDIMENTS

Abstract

For many years coastal scientists and engineers have attempted to label sedimentary particles in order that their movement paths might be determined. Several attempts have been made at the Beach Erosion Board, none of which met with any measure of success. Furthermore, inherent in this system is an extensive sampling program and arduous identification of the labeled particles. Recently, however, the labeling of natural sediments or simulated sediments with radioisotopes as tracers has proved successful and a long sought goal has been achieved. The utilization of radioactive material as sediment tracers has increased during the approximately 10 years since its inception. Since the initial test in the Thames River^1' in England, the utilization of this technique has spread until it is practically worldwide!2""8^ In the main, the objectives of these tests have been qualitative, the determination of movement path and of sedimentation areas of the tracer material, and thus of the sediments, which are being followed. Labeling techniques have varied widely and involve plating or precipitating a thin film of radioactive material on the natural sediments, the utilization of glass containing a radioactive tracer to simulate the natural sediments, the incorporation of radioactive material within the natural sediments or within simulated sediments, and ion exchange between the natural sediments and tracer material. The means of detection have also varied broadly: Geiger-Mueller systems with one or several GM tubes in gangs, scintillation systems making use of pulse-height spectrometry, and autoradiographic techniques have all been used. The monitoring has varied also as sediment and tracer materials have been monitored in situ or samples have been taken and the monitoring accomplished in the laboratory. The staff of the Beach Erosion Board has been interested in this new application of radioisotopes since 1955. A literature survey was initiated at that time and is continuing at present. A feasibility study was completed in 1958 which indicated that radioisotopic tracers presented a new technique with which to study sediment transport. The report strongly recommended that studies be planned and executed utilizing this technique. In the Annual Bulletin of the Beach Erosion Board, 1960,^9'several test objectives and procedures were outlined.