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• The three-scale perturbation model is built to study dispersivity in wetland flows. • Extended analytical solution for two-dimensional concentration distribution is given. • Effects of vegetation and bed absorption on environmental dispersion are discussed. Bed absorption and vegetation in natural wetlands exert considerable influence on contaminant transport. A three-scale perturbation method is extended in this work to present an exact analytical solution for the spatial concentration distributions affected by vegetation distribution and bed absorption. Compared with concentration moments-based analytical methods that were adopted previously to solve vertical concentration distribution in wetland flows, the multi-scale method used in this study is more concise without complicate integrated operations. The analytical solution is explicit and applicable without complicated integral form. Moreover, by comparing with the analytical solution obtained by the moments method, the analytical solution given in this work is accurate particularly after the initial stage. This study focuses on a large time scale in investigating spatial concentration distribution. Results show that concentration distribution is not uniform in the vertical direction. Hence, this study recommends the accurate two-dimensional spatial distribution rather than the cross-section averaged concentration distribution to achieve accurate concentration predictions. [ABSTRACT FROM AUTHOR]

• The spatial concentration distribution with FVI is illustrated. • The removal process of FVI is studied. • The effect of damping factor on contaminant transport is discussed. • The temporal contaminant residue mass is studied. The fate of the contaminant transport process within wetland flows considering contaminant depletion via a floating vegetation island (FVI) is the focus of this work. To identify the feature of contaminant cloud expansion under an FVI, multiscale theory is extended to obtain a two-dimensional spatial concentration distribution analytical solution. The characteristics of two-dimensional concentration distributions under upper FVI absorption and damping factor within wetland flows are illustrated. The performance of the contaminant depletion process via an FVI is also examined in this work, with discussions on removal efficiency, the absorption ratio, and the nonuniformity of contaminant mass. As FVI removal intensity changes along the stream direction, the analytical solution of removal efficiency is obtained to illustrate the longitudinal variation in the FVI removal intensity. Furthermore, the effects of removal intensity and damping factor on FVI removal efficiency are expressed separately. In addition, the removal intensity variance in the vertical direction is discussed using the defined absorption ratio. Moreover, as residual mass is a fatal issue in the contaminant removal process, temporal residual mass is discussed, and the residual mass proportion within different layers is depicted. Finally, the difference of the mass proportion between layers is employed to explain the transformation of the contaminant cloud. [ABSTRACT FROM AUTHOR]

• A SSC distribution model is established in canopy flow based on gravitational theory. • A new formula is proposed to estimate Reynolds stress in vegetation layer. • Transition of SSC distribution types relates with the ratio of gravity to turbulence. Vegetation plays a significant role in river ecosystem, which has a great influence on hydraulic structures and sediment transport. Understanding the vertical distribution of suspended sediment concentration (SSC) in canopy flow is helpful to study the process of riverbed erosion and deposition in vegetated channels. Aiming at the sediment-laden flow in open channel covered with submerged vegetation, this study divides the water depth into two layers along the vertical direction with the vegetation height as the boundary and then proposes a new SSC distribution model based on gravitational theory to estimate the vertical distribution of relative SSC in the free water layer and vegetation layer respectively. In the meanwhile, a new formula is also proposed to evaluate the Reynolds shear stress below the submerged vegetation height, which has been successfully applied in the derivation of the new SSC distribution model. The validation results of the simplified velocity model, the new Reynolds shear stress formula and the new SSC model compare well with the collected experimental data series. On top of that, it is found that the uniformity of SSC distribution profile progressively decreases with the increasing sediment particles diameters. Besides, according to the validation results and discussion, it is believed that the controversy point about gravitational theory would not have obvious influence on the estimation of SSC distribution so that the gravitational theory can be adopted to investigate suspended sediment transport in vegetation flow. That would be benefit for river ecological restoration and better management. [ABSTRACT FROM AUTHOR]