New enrichment and multiple sampling procedures to investigate radioactive tracer mixing in a small river

Abstract

Recent work in the measurement of flow in rivers and canals with radioactive tracers has stressed the importance of the use of many sampling points. A thorough investigation of the lateral distribution of the tracer at sampling stations is necessary. Invariably, it is the distance required for complete lateral dispersion of tracer which determines the mixing distance in natural streams. The use of floating samplers was found to be most satisfactory in an investigation of lateral mixing in a small stream. The small size of the samplers, 1000 ml, ensured that comprehensive investigations using many sampling points were undertaken without difficulties of handling after the experiment. A new method of concentration of radioisotopes using paper evaporation of the samples ensured that the tracer was counted with high detection sensitivity despite the small volume of samples. Accurate measurement of the tracer concentration as a function of time at two stations allowed the tracer passage curves to be reliably determined. Use of this data enabled the longitudinal dispersion coefficient to be calculated by two methods.