A Depth-Integrated Morphodynamical Model for River Flows with a Wide Range of Shields Parameter

Proceedings of 2013 IAHR World Congress ABSTRACT : Fast geomorphic transients may involve complex scenarios of sediment transport, occurring as bed - load (i.e. saltating, sliding and rolling) in the region close t o the bottom, or as suspended load in the upper region of the flow . These two modalities of sediment transport may even coexist or alternate each - other during the same event, owing to the variability of the shear stress. T he modeling of similar processes i s therefore a really challenging task, for which usual representation of the flow as a mixture may result unsatisfactorily. In the present paper, we propose a two - phase depth - averaged model which is able to deal with both bed - load and suspended sediment tr ansport. T he mathematical model is derived from the expression of mass and momentum conservation equations , separately for liquid and sediment phase. The equations for the solid phase are written separately for bed - load and suspended load region. The bed - l oad layer thickness is assumed variable with the actual shear stress, while the solid concentration is describe d by the differential equations. The ent rainment/deposition of sediment from the bed towards the bed - load layer is evaluated by a formula based o n a modified van Rijn mobility parameter, while for the suspended sediment a first - order kinetic law is considered . The behavior of the resulting model under uniform conditions of flow complies with some of the proposed empirical formulations for bed - load thickness, average particle velocity and solid discharge. A numerical method based on a finite - volume approach is employed for the simulation of experiments in which both bed load and sediment transport are present . Even without any detailed calibration, s imulated and experimental results show reasonable agreement