Hydraulic jump classification downstream of block ramps for non-uniform channel bed material

Generally downstream of block ramps, hydraulic jump takes place. Tests showed that two types of hydraulic jump can occur: FMB and SMB types. The first type FMB (Free Jump in Mobile Bed) appears similar to a traditional free jump; a succession of waves is present starting from the toe of the ramp and proceeding downstream of it. The second type SMB (Submerged jump in Mobile Bed) occurs when the jump tends to submerge the toe of the ramp. In this case, the flow at the entrance of the ramp toe is directed with the same inclination of the ramp itself. Normally, the final configuration of the jump is reached after an alternation of two different configurations. Initially, the jump presents a roller and tends to submerge the toe of the ramp. The scour produced by the hydraulic jump, in this phase, is short and deep. The downstream face of the scour is steep and the material moves downstream of this face and the flow coming from the ramp at its toe is directed with the same inclination of the ramp. After a certain period, the jump passes to the second configuration resulting in a flatter and longer scour as sediments are moved downstream and the ridge becomes flatter. The flow direction tends to be horizontal and the roller changes sense of rotation. For uniform mixtures of sediments (<1.2), experimental tests allowed to define the range of values of the parameters Fd50 and S0, dense-metric Froude number and ramp slope, respectively, for which different jumps and different bed profiles occur. A jump classification in function of Fd50 and S0 was proposed, in this case by Pagliara et al. (2006). The aim of this paper is to extend the jump classification valid for uniform channel bed material to the non-uniform case. Moreover, the effect of non-uniformity of channel bed material on scour process and jump classification has been discussed.