Abstract
Suspended sediment concentration is a key aspect in the forecasting of river evolution dynamics, as well as in water quality assessment, evaluation of reservoir impacts, and management of water resources. The estimation of suspended load often relies on empirical models, of which efficiency is limited by their analytic structure or by the need for calibration parameters. The present work deals with a simplified fully-analytical formulation of the so-called entropic model in order to reproduce the vertical distribution of sediment concentration. The simplification consists in the leading order expansion of the generalized spatial coordinate of the entropic velocity profile that, strictly speaking, applies to the near-bed region, but that provides acceptable results also near the free surface. The proposed closed-form solution, which highlights the interplay among channel morphology, stream power, secondary flows, and suspended transport features, allows reducing the needed number of field measurements and, therefore, the time of field activities. Its accuracy and robustness were successfully tested based on the comparison with laboratory data reported in literature.
Highlights
IntroductionThe study of suspended load in open channels has a central role in the analysis of river dynamics, in which suspended particles affect both the flow field and the interaction between flow and river-bed
The study of suspended load in open channels has a central role in the analysis of river dynamics, in which suspended particles affect both the flow field and the interaction between flow and river-bed.Humans can alter fine sediment supply to river networks and solid transport processes within them via activities, such as agriculture, mining, forestry operations, and the construction of dams.a dam creates an upstream area with low water velocity, which affects solute/sediment dynamics and river morphology and induces sedimentation in reservoirs that gradually lose their useful capacity [1,2,3,4,5,6,7,8]
The present study proposes a simplification of this model that allows for analytically solving Equation (3) while consistently incorporating the effect of velocity dip position (e.g., [31])
Summary
The study of suspended load in open channels has a central role in the analysis of river dynamics, in which suspended particles affect both the flow field and the interaction between flow and river-bed. The experimental studies by Righetti and Romano focused on the characteristics of suspended heavy particles and their turbulence modulation effects in open as well as in confined channel flows [22] They observed that, in particle-laden flows, the vertical profiles of stream-wise mean velocity for both fluid and solid phases and turbulence intensity were reduced in the outer layer and increased in the viscous sublayer as compared to the clear-water case, which led to an apparent slip kinematic boundary condition near the wall. Analytical solutions of the transient advection-dispersion equation for dissolved chemicals and fine sediments in open channels were given by the authors in the case of deterministic depth-averaged velocity distributions and different initial conditions by the method of moments (e.g., [34]); in the case of randomly uniform flows in the presence of morphologic heterogeneity by a stochastic Lagrangian approach (e.g., [35,36]); and in terms of second-order concentration statistics based on a stochastic Eulerian approach (e.g., [37]). ADE in the case of non-uniform transverse mixing, highlighting the occurrence of concentration boundary side-pockets (e.g., [38])
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