JFET_V8_N1_RP3 Marilena Pannone Journal on Future Engineering and Technology 2230 – 7184 8 1 25 31 Backwater Flows, Solutes Dispersion, Lagrangian Stochastic Approach, Particle-Tracking Techniques The article focuses on the analytical/numerical modelling of the solute transport taking place within large rivers flowing through wide alluvial plains, and characterized by a weak bed slope, near the confluence into large reservoirs collecting water for potable or agricultural destinations. The aim of the study is represented by the analysis of the effect that the macroscopic morphological features of the channel induce on the hydrodynamic dispersion of effluents accidentally injected along its course, when a downstream obstacle can critically slow down the flow, preventing the dilution of the solutes. A recent work (Yudianto & Yuebo, 2008) has dealt with the problem resorting to a Eulerian numerical approach, and coming to the conclusion that, in the most part of the gradually varying steady flows, the adoption of a single velocity value (i.e. the corresponding uniform-flow section average) is sufficient to represent them even in terms of pollutants dispersion. Present work analyzes the dispersive properties of non uniform fluvial streams by an analytical-numerical stochastic Lagrangian approach and identifies the existence of a characteristic travel time, which is function of bed slope and width to depth ratio, beyond which the longitudinal hydrodynamic dispersion undergoes a clear and potentially dangerous regress. August - October 2012 Copyright © 2012 i-manager publications. All rights reserved. i-manager Publications http://www.imanagerpublications.com/Article.aspx?ArticleId=1976