Pollutant transport in rivers : estimating dispersion coefficients from tracer experiments

Abstract

To better understand the dispersion characteristics of small streams which are sparsely represented in published work, eleven successful tracer experiments were carried out on the same reach of a small stream (Murray Burn) in Scotland over various flow and seasonal conditions. Four different analysis methods (Reduction of Peak, Method of Moments, Routing Procedure, Analytical Solution) were used to determine dispersion coefficients and flow velocities from observed temporal concentration profiles. A new weighted average approach for the Analytical Solution method produced improved velocity and dispersion results, i.e. ones that were more consistent with the results from the other methods. One aim was to investigate the influence of long tails (on the concentration profiles) on the results by truncating the profiles at the 1% peak concentration level, repeating the data analysis and comparing the truncated results with the original analysis. It is concluded that truncation of concentration profiles is beneficial for the methods used in the thesis. The dispersion coefficients obtained for the Murray Burn (0.15 – 1.0 m2/s) augment our knowledge of dispersion in small streams by complementing the few previously published data for stream flow rates less than 1000 l/s.