USE OF A RADIO-ACTIVE TRACER FOR THE MEASUREMENT OF SEDIMENT TRANSPORT IN THE NETHERLANDS

Abstract

The "Rijkswaterstaat" has developed a method based on the use of radio-active tracers for the evaluation of sediment transport due to the combined action of waves and currents. The results of preparatory studies and a laboratory test were published in a previous report by J.J. Arlman, P. Santema and J.N. Svasek [1]. The main principles of the method were 1. Detection by a sledge-mounted unit towed by a survey vessel and continuous registration on board of the radio-activity measured on the sea bottom. 2. Employment of low specific radio-activity of tracer material and a large quantity thereof. 5> Use of a long-life isotope and high radio-activity. k. Measurement of the vertical distribution of radioactivity in core samples or if possible by discrimination. In March 1958 the first lot of tracer material was placed on the sea bed. The tracer material consisted of the radio-active isotope Scandium^" emitting 2 curies incorporated in 100 kg "greensand". Scandium^" has a half-life of 8^ days and emits strong gramma radiations with energies of 0.89 and 1.12 MeV. Afterwards, in 1959, two series of measurements were taken near the entrance to the Rotterdam Waterway. Four droppings formed one series; they were generally carried out in the following manner: 50 kg greensand labeled with 2 Curies Scandium was dropped in k places at a safe distance from each other. 2 of the 8 portions consisted of smaller quantities of both radio-activity and greensand. In the following paragraphs the preparation, dropping and detection of the tracer, the working out of the registrations and the interpretation of the results of the 1959 measurements are discussed.