1D morphodynamic modelling using a simplified grain size description

ABSTRACT This paper introduces an 1D numerical code RubarBE for hydraulic and mobile-bed simulations. The code's ability to reproduce the downstream fining of a gravel–sand mixture in response to bed aggradation is tested against laboratory experiments. Unlike in most numerical models, grain size distribution in each sediment layer is not represented using a multi-class model, but using the median diameter and a sorting coefficient σ. The comparison of numerical results with experimental data shows that the adaptation length , classically used for non-equilibrium sediment transport, is an essential parameter of the model to accurately reproduce the evolution of the deposit front. Empirical laws for adjustments of and σ are proposed to reproduce sediment sorting through two grain-size related adaptation lengths (, ). They are scaled by the length of the reach in morphological equilibrium, which is a useful result for field applications.

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