Scalar Dispersion in the Salado River Through Tracers Test and Two-Dimensional Model

A field tracer test and two-dimensional numerical modeling were used to analyze the scalars transport in an 8.0-km reach of the Salado River (Santa Fe) where urban and industrial pollutants are released. Rhodamine WT was injected as tracer, and its concentration was recorded in three sections located at 1000, 3000, and 4500 m. SisBaHiA numerical model was used to represent the hydrodynamics and the scalar transport. The transverse and longitudinal dispersion coefficients obtained from fitting the observed concentration curves were in the range of 0.0078–0.037 m2/s and 0.25–1.46 m2/s, respectively. The best fit was achieved with the classical ratios: KL/u∗H=5.93\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${K}_{L}/{u}_{*}H=5.93$$\end{document} and KT/u∗H=0.15\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${K}_{T}/{u}_{*}H=0.15$$\end{document}. Both measurements and simulation showed the presence of the tracer in the banks at 1000 m from the injection point, but the particle transport model revealed the heterogeneous distribution of the tracer at the section width in the whole study reach. The maximum concentration curves were located near of the banks, which could be due to the fact that the concentration was maximized when the particle cloud reaches these shallower zones. The complex flow pattern caused by bathymetric irregularities and sharps bends largely explains the deformation of the concentration curves. The large spatial variations of the line of maximum velocity caused the particles to evolve with increasing relative displacements to each other. While that in S1 zone, the particles and concentration curves showed typical pattern with relatively concentric concentration isolines towards the middle of the section, the S2 and S3 zones showed a large particles dispersion with long tails, mainly on the left bank.