The extent of partial transport in a disturbed gravel-bed braided river (Piave River, North-Eastern Italy).

Sediment transport is one of the most important factors affecting the physical habitat of a riverine ecosystem and it is essential to understand the morphological changes occurring in rivers. Unfortunately, it is extremely difficult to measure it directly using sediment traps, especially in gravel bed rivers. Here we present an attempt of assessing sediment mobility in a gravel bed braided river (Piave River, northeast Italy). The analyses were carried out on different cross sections where 65 areas were painted and the size and travel distance of the mobilized particles were measured after flood events. The results show that the phenomenon of partial transport occurs with dimensionless shear stress ranging between 0.015 and 0.045 while with stresses > 0.040 the bed experiences full mobility. The analysis of the particle displacements revealed that the travel distance of a certain size increases with the shear stress, and that a certain threshold between equal-mobility and size-selectivity conditions can be identified. Finally, the values of deposition or erosion detected in the sample areas were analysed, observing a rising trend of these values with the higher dimensionless shear stresses.