Longitudinal and transverse dispersion coefficients in braided rivers.

ABSTRACT

The dispersion characteristics of braided rivers are presently unclear. The comprehensive flow structure in a physical braided river model was measured and was used to estimate its dispersion coefficient tensor. The largest values of the longitudinal and transverse dispersion coefficients occurred in the separation zone in two anabranches. The separation zone disappeared in a small diversion angle model of braided rivers where the coefficients were smaller. As for the sectional transverse distribution, the two coefficients varied markedly and an interesting negative correlation between them appeared in several sections. The dispersion coefficients increased with upstream flow rates. Comparison between the coefficients for different anabranch widths revealed higher values in wider sections. Finally, the values of the laboratory tests were compared with those in a real braided river, and relatively larger coefficients were found in natural rivers. The findings of this paper could be helpful in understanding the dispersion characteristics and in estimating pollutant concentration in braided rivers.