Abstract. A new particle-based reduced-complexity model, CAST, to simulate sediment transport and channel morphology in steep streams is presented. CAST contains phenomenological parameterizations, deterministic or stochastic, of sediment supply, bed load transport, particle entrainment and deposition in a cellular-automaton space with uniform grain size. The model can reproduce a realistic bed morphology and typical fluctuations in transport rates observed in steep channels. Particle hop distances, from entrainment to deposition, are well-fitted by exponential distributions, in agreement with field data. The effect of stochasticity both in the entrainment and in the input rate is shown. A stochastic parameterization of the entrainment is essential to create and maintain a realistic channel morphology, while sediment transport in CAST shreds the input signal and its stochastic variability. A jamming routine has been added to CAST to simulate the grain-grain and grain-bed interactions that lead to particle jamming and step formation in a step-pool stream. The results show that jamming is effective in generating steps in unsteady conditions. Steps are created during high- flow periods and they survive during low flows only in sediment- starved conditions, in agreement with the jammed-state hypothesis of Church and Zimmermann (2007). Reduced-complexity models such as CAST can give new insight into the dynamics of complex phenomena (such as sediment transport and bedform stability) and be useful to test research hypotheses, being an effective complement to fully physically-based models.
Sediment transport at the network scale and its link to channel morphology in the braided Vjosa River system
