For a gravel bed river and a sand bed river with coarse and fine sediment with different geometric standard deviations morphological computations have been made with an uniform and a graded 1-dimensional numerical model. For the gravel bed river the reiver bed river the river bed development is calcualted for a period of 15 years with both models. The computations with the uniform model show severe erosion along the river reach, while the computed erosion with the pgraded model is less severe. Along the river reach the differences between the bed levels computed with both models vary between -0.2 and 3.0 metre. For the sand bed river these differences are much smaller and vary between -0.40 and 0.40 metre. The erosion and the sedimentation computed by the graded model show a more gentile behaviour with less extreme values. Further two series of computations are carried out for the gravel bed river with varying sediment mixtures. In the first series the sediment mixture is varied from very coarse gravel to very coarse sand and in the second series the geoemtric standard deviation of the sediment mixtures is varied between 1.0 and 2.73. The resutls of these computations show a large influence of the grain size and a small influence of the geometric standard variation on the bed levels computed by the uniform and the graded model.
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