Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 10 5 2010 10.5194/nhess-10-1051-2010 http://www.nat-hazards-earth-syst-sci.net/10/1051/2010/ http://www.nat-hazards-earth-syst-sci.net/10/1051/2010/nhess-10-1051-2010.html http://www.nat-hazards-earth-syst-sci.net/10/1051/2010/nhess-10-1051-2010.pdf 1051 1059 2010-05-28 An expression for the water-sediment moving layer in unsteady flows valid for open channels and embankments A. M. Berta anna.berta@polito.it G. Bianco Dipartimento di Idraulica Trasposti ed Infrastrutture Civili, Politecnico di Torino, Torino, Italy During the floods, the effects of sediment transport in river beds are particulary significant and can be studied through the evolution of the water-sediment layer which moves in the lower part of a flow, named "moving layer". Moving layer variations along rivers lead to depositions and erosions and are typically unsteady, but are often tackled with expressions developed for steady (equilibrium) conditions. In this paper, we develop an expression for the moving layer in unsteady conditions and calibrate it with experimental data. During laboratory tests, we have in fact reproduced a rapidly changing unsteady flow by the erosion of a granular steep slope. Results have shown a clear tendency of the moving layer, for fixed discharges, toward equilibrium conditions. Knowing the equilibrium achievement has presented many difficulties, being influenced by the choice of the equilibrium expression and moreover by the estimation of the parameters involved (for example friction angle). 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