Sediment Transport on Block Ramp: Filling and Energy Recovery

The effect of sediment transport on both morphology and energy dissipation in presence of non conventional stream rehabilitation structures, such as block ramps or rock chutes, is a not well explored topic on hydraulic engineering. Namely, in normal functioning conditions, these types of structures are generally located in mountain rivers, which are characterized by an elevated sediment transport which can be deposited and trapped between the rocks constituting the ramp. This causes a change in the bed roughness and in the energy dissipation process that is present on a block ramp. This occurrence was experimentally investigated at the Hydraulic Laboratory of the University of Pisa. Different experimental conditions were tested and the main hydraulic and geometric parameters controlling the filling phenomenon and its effects were highlighted. Namely, it was experimentally proved that both the median diameters of the filling material and of the ramp blocks, the ramp slope and the discharge are the most relevant parameters governing the ramp filling. Thus, experimental formulae were derived to foresee the ramp morphological changes and the interaction between the filling process and the geometric and hydraulic parameters. Moreover a comparison of the energy dissipation on block ramp was conducted and the energy recovery in presence and absence of filling material was compared.