Dispersion in natural streams

Eleven tests were conducted to study the dispersion patterns of a radiotracer in five natural stream channels and in one canal. The radiotracer was injected as a line source. The patterns of dispersion that were observed in these channels were compared with patterns predicted by the theoretical models for one-dimensional flow developed by Taylor and other investigators. Analysis of the relation between time and concentration of the tracer at several sections in each of the six reaches shows that the available theoretical models are not adequate to describe the dispersion patterns actually observed. Dispersion coefficients determined from the test data are from 2 to 30 times greater than those predicted by the theoretical models. It is apparent that a better understanding of the dispersal phenomenon is needed in order to predict dispersion patterns in natural streams.