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The one-dimensional numerical model presented in the present paper divides the flow in two fully coupled layers, a water layer and a water-sediment transport layer. Initially, this model was used to depict dam-break flows, which do not require a specific treatment of boundary conditions. The aim of the present research is to extend the model to fluvial flows requiring an appropriate boundary condition treatment. This treatment commonly relies on characteristics. However, in the frame of a two-layer model with five equations, those characteristics are not obvious to determine. This paper shows, how to extend numerically the common eigenstructure analysis to address the problem. Examples are presented and the boundary conditions treatment is illustrated on the particular case of a hydraulic jump over a mobile bed. Results of the numerical model including the adequate boundary conditions are favourably compared to experimental results.

Impulsive waves impinging over steep slopes of dams or embankments may produce erosion with intense sediment transport and relevant morphological changes during fast geomorphic transients. In order to be employed as valuable tools for risk assessment and hazard mitigation, the performance of current morphodynamic models in reproducing the physical evolution of such processes has to be carefully assessed. However, despite the inherent interest of the topic, the availability of suitable experimental data is relatively scarce. For this reason, additional tests, carried out under controlled conditions, may furnish the basis for an improvement in the knowledge of the bed evolution. The obtained experimental results constitute also an important resource to evaluate the numerical models performance. To this aim, a set of laboratory experiments, in which the impact of a dam break wave on an erodible slope is reproduced, has been designed and conducted. In the paper some preliminary results are presented and discussed.

The adoption of the Diffusive Wave (DW) instead of the Full Dynamic (FD) model in the analysis of mud flood routing within the shallow-water framework may provide a significant reduction of the computational effort, and the knowledge of the conditions in which this approximation may be employed is therefore important. In this paper, the applicability of the DW approximation of a depth-integrated Herschel–Bulkley model is investigated through linear analysis. Assuming as the initial condition a steady hypocritical decelerated flow, induced by downstream backwater, the propagation characteristics of a small perturbation predicted by the DW and FD models are compared. The results show that the spatial variation on the initial profile may preclude the application of DW model with a prescribed accuracy. Whenever the method is applicable, the rising time of the mud flood must satisfy additional constraints, whose dependence on the flow depth, along with the Froude number and the rheological parameters, is deeply analyzed and discussed.

Climate change is exposing more and more frequently flood prone areas to potential casualties and damages. The capability of the flow to carry relevant quantities of sediments interacts with the presence of obstacles in flood-inundated areas and contributes to the increase the related hazard, constituting a relevant concern in the framework of risk analysis. Unfortunately, existing literature on this topic is rather scarce, especially for the features of sediment transport and the forces acting on rigid obstacles. In the paper, a recent two-phase shallow-water morphodynamical model, particularly suited to the analysis of fast geomorphic transients, is applied to the numerical simulation of the propagation of a dam-break wave over an erodible floodplain in presence of a rigid obstacle. The geometry of the test-case is inspired to a recent fixed-bed study reported in the literature, for which extensive experimental and numerical data concerning the flow field and the dynamic loading against the obstacle are available. Results of the numerical simulations contribute to highlight the effect of the obstacle on the changes in the bottom topography, along with the subsequent change on the loading condition on it. * Corresponding author Engineering EPiC SeriesinEngineering Volume3,2018,Pages564571 HIC 2018.13thInternational Conference onHydroinformatics G.

Dikes and levees are encountered very often along rivers. They are crucial as defence structures for flow channelization, protecting population and properties from floods as well as against lateral riverbed migration. However, the combination of their aging and increased exposition to extreme hydrological events may cause these structures to breach, and subsequently to fail. Understanding the dynamics of breaching is very important for developing adequate countermeasures, for civil protection initiatives and for land use planning. Recent literature shows many studies concerning, both from experimental and numerical point of views, frontal dike breaching. Based on several evidences, it is well assessed that depth-integrated numerical models can successfully reproduce this kind of phenomenon (e.g. Greco et al., 2012). Recently, Rifai et al. (2017) investigated a different setup in which the embankment is parallel to the main channel flow and thus a lateral breaching occurs. It is worth noting this scheme resembles real-world situation of levees breaching along a river. In present paper, the capability of depth-integrated approaches in reproducing such tests is investigated. Numerical results obtained with different models are compared against experiments from both the qualitative and quantitative point of views. Considerations about the applicability of depth-integrated models in real world situation of lateral breaching of dikes and levees are also drawn.

Simplified wave models - such as kinematic, diffusion and quasi-steady - are widely employed as a convenient replacement of the full dynamic one in the analysis of unsteady open-channel flows, and especially for flood routing. While their use may guarantee a significant reduction of the computational effort, it is mandatory to define the conditions in which they may be confidently applied. The present paper investigates the applicability conditions of the kinematic, diffusion and quasisteady dynamic shallow wave models for mud flows of power-law fluids. The power-law model describes in an adequate and convenient way fluids that at low shear rates fluids do not posses yield stress, such as clay or kaolin suspensions, which are frequently encountered in Chinese rivers. In the framework of a linear analysis, the propagation characteristics of a periodic perturbation of an initial steady uniform flow predicted by the simplified models are compared with those of the full dynamic one. Based on this comparison, applicability criteria for the different wave approximations for mud flood of power-law fluids are derived. The presented results provide guidelines for selecting the appropriate approximation for a given flow problem, and therefore they may represent a useful tool for engineering predictions.

"The occurrence of roll-waves in mud-flows is commonly investi-gated starting from the formulation of the marginal stability threshold of a linearized one-dimensional viscoplastic (shear-thinning) flow model. Since for this non-newtonian rheological model such a threshold may oc-cur in hypocritical flow, the downstream boundary condition may have a non-negligible effect on the spatial growth\/decay of the perturbation. The paper presents the solution of the 1D linearized flow of a Herschel & Bulkley fluid in a channel of finite length, in the neighbourhood of a hypocritical base uniform flow. Both linearly stable and unstable condi-tions are considered. The analytical solution is found applying the Laplace transform method and obtaining the first-order analytical expressions of the upstream and downstream channel response functions in the time domain. The effects of both the yield stress and the rheological law exponent are discussed, recovering as particular cases both power-law and Bingham fluids. The theoretical achievements may be used to extend semi-empirical criteria commonly employed for predicting roll waves occurrence in clear-water even to mud-flows."

Unsteady shallow-layer flows may be described through full dynamic models or using simplified momentum equations, based on kinematic, diffusion, and quasi-steady approximations, which guarantee a reduction of the computational effort. This paper aims to investigate through linear analysis the applicability range of simplified shallow-wave models with special concern to unsteady flows of mud. Considering a three-equation depth-integrated Herschel-Bulkley model, the applicability of the approximated wave models is discussed comparing the propagation characteristics of a small perturbation of an initial steady uniform flow as predicted by the simplified models with those of the full dynamic model. Based on this comparison, applicability criteria for the different wave approximations for mud flows of Herschel-Bulkley fluids, which account for the effects of the rheological parameters, are derived. The results show that accounting for the fluid rheology is mandatory for the choice of an appropriate simplified model. DOI: 10.1061/(ASCE)HE.1943-5584.0000881. © 2014 American Society of Civil Engineers.