Computation of Transverse Mixing in Streams

Abstract

The problem of solute-mass transport in natural streams is tackled via a governing equation that employs the cumulative discharge, instead of the transverse distance, as an independent variable thus eleminating the need to know the transverse-velocity field. The problem is solved by a numerical scheme, which utilizes exponential interpolation between adjacent nodes. The scheme can regress to a linear-interpolation scheme for Peclet number equal to zero or to an upwind scheme for very large values of the Peclet number. Comparison with field data showed that the problem can be solved satisfactorily based on the knowledge of cross-sectional-geometric data and total-river discharge only, provided that the riverine cross sections are not highly irregular. The computed transverse-dispersion coefficients agree well with values reported in the literature. An independent verification of the transverse-dispersion-coefficient values was obtained by application of a modified method of moments on the same field data.