Downstream fining by abrasion and sorting in context of a bedload management in the Danube River east of Vienna

In gravel-bed rivers there is a strong influence of abrasion and sorting on grain-size distribution and bedload transport. To assess the relevance of these processes for the regulated but free-flowing Danube River east of Vienna, characteristic parameters such as sorting coefficients and downstream fining coefficients are determined based on bed material samples taken in this reach. The obtained results are discussed in the context of literature data with special reference to the problem of superposition of abrasion and sorting. These processes and controls are not only important for an improved understanding of the river behaviour, but also for the necessary bedload management in this river reach. This becomes even more important if the current management practice will be extended in the future via an increase of bedload recirculation operations. To evaluate the effect of such recirculations quantitatively the concept of a “surplus material-equivalent” was developed which allows to take the effects of downstream fining due to abrasion and sorting into account.