A regularization strategy for modeling mixed-sediment river morphodynamics

A notable drawback in mixed-size sediment morphodynamic modeling is the fact that the most commonly used mathematical model in this field (i.e., the active layer model Hirano, 1971) can be ill-posed under certain circumstances. Under these conditions the model loses its predictive capabilities, as negligible perturbations in the initial or...

A Well-posed Model for Mixed-Sediment River Morphodynamics

The mixed-size character of sediment is a necessary property to ex- plain physical phenomena such as downstream fining or the presence of armor layers. The active layer model was developed to model mixed-size sediment in river morphodynamics. This model assumes that the topmost part of the bed, the active layer, has no vertical stratification...

Ill-posedness in modeling mixed sediment river morphodynamics

In this paper we analyze the Hirano active layer model used in mixed sediment river morphodynamics concerning its ill-posedness. Ill-posedness causes the solution to be unstable to short-wave perturbations. This implies that the solution presents spurious oscillations, the amplitude of which depends on the domain discretization. Ill-posedness...

An accurate numerical solution to the Saint-Venant-Hirano model for mixed-sediment morphodynamics in rivers

We present an accurate numerical approximation to the Saint-Venant-Hirano model for mixed-sediment morphodynamics in one space dimension. Our solution procedure originates from the fully-unsteady matrix-vector formulation developed in [54]. The principal part of the problem is solved by an explicit Finite Volume upwind method of the path...

A new technique for measuring the bed surface texture during flow and application to a degradational sand-gravel laboratory experiment

We present a new image analysis technique for measuring the grain size distribution (texture) of the bed surface during flow in a laboratory experiment. A camera and a floating device are connected to a carriage used to take images of the bed surface over the entire flume length. The image analysis technique, which is based on color segmentation...

A laboratory experiment on the evolution of a sand gravel reach under a lack of sediment supply

A flume experiment was conducted to examine the evolution of a sand-gravel reach under a lack of sediment supply. A bed composed of a bimodal sediment mixture was installed with a uniform slope and an gradual fining pattern. At the upstream end of the flume the initial bed consisted of 100% gravel, which decreased stepwise (10% steps) in...

Mathematical analysis of the Saint-Venant-Hirano model for mixed-sediment morphodynamics

Sediment of different size are transported in rivers under the action of flow. The first and still most popular sediment continuity model able to deal with mixed sediment is the so-called active layer model proposed by Hirano (1971, 1972). In this paper, we consider the one-dimensional hydromorphodynamic model given by the Saint-Venant equations...

Mathematical analysis of the Saint-Venant-Hirano model and numerical solution by path-conservative methods

A coupled numerical solution to the shallow water-Hirano model (abstract)

Modelling the morphodynamic evolution of rivers due to flow-driven sediment transport requires the adoption of a flow model, such as the shallow water equations, and a conservation equation for sediment mass (the Exner equation). When dealing with mixtures of grain sizes, one can account for the interaction among sediment transport, bed level...