Transverse Mixing in an Unregulated Northern River

Abstract

Transverse mixing in an unregulated northern river in Canada was studied in different discharge conditions with and without ice cover. The distribution of cumulative discharge was constructed on the basis of river cross-sectional shapes, and a modified streamtube method was proposed to describe transverse mixing. The modified method only uses raw field data to calibrate the modeled concentration profiles and thus, can produce a reliable mixing coefficient even with relatively low-quality field data. The effects of river discharge and ice cover on the transverse mixing coefficient were examined in a fixed study reach. It was found that the transverse mixing coefficient increased approximately linearly with river discharge (from 84 to 960 m3/s). The dimensionless transverse mixing coefficient, scaled with river shear velocity and river depth, appeared unaffected (within 14%) by the river discharge in both open-water and ice-covered conditions, and its value was 21% smaller in the ice-covered condition than in the open-water condition.