Application of radioactive tracers in the study of sediment movement

Abstract

Radioactive tracer techniques were employed in order to investigate the dispersion and transport of bed material in a test reach of the North Loup River near Purdum, Nebraska. Sand particles, labelled with Iridium-192, were used as tracers to enable observation of the natural dispersion and transport processes. The amount of radioactivity and the number of tracer particles required for the experiment was determined by considering the sensitivity of the radiation-detection system, the characteristics of the test reach, and radiological safety considerations. In the experiment, the tracer particles were released from a line source which extended across the bed of the stream. As the tracer particles were transported and dispersed downstream, their longitudinal and lateral distributions in the bed were observed by periodic surveys with a sled-mounted scintillation detector, and their vertical distribution in the bed was observed by monitoring core samples. Information obtained from a laboratory calibration of the radiation-detection system under simulated field conditions was used to reduce the field data to a set of tracer-particle concentration-distribution curves. The results of the field study indicate a potential for the wide application of radioactive tracer in sediment studies.