Morphological effects of bed sills in degrading rivers

Effect of sill spacing and sediment size grading on scouring at grade‐control structures

“…Unless the toe of the structure is protected, the plunging jet has the potential to erode the bed locally, generating a scourhole. The predictive formulae for the depth of scour that can be found in the literature are all based on experimental tests based on scale models (Mason and Arumugam, 1985;Bormann and Julien, 1991;D'Agostino, 1994;Martin Vide and Del Agua Razquin, 1995;Rice and Kadavy, 1998;Gaudio et al, 2000;Chen and Hong, 2001;Ghodsian and Faradonbeh, 2001;Gaudio and Marion, 2003;Lenzi et al, 2002). Many approaches are fully empirical, being based on curve fitting of experimental data.…”

“…He obtained a formula where the step height implicitly accounted for the sill spacing. Gaudio et al (2000) also included the sill spacing in their approach to scouring at sills on mild slopes. They also obtained a formula for the scour length and they found that the scour shapes are affine, i.e.…”

“…Many approaches are fully empirical, being based on curve fitting of experimental data. In the most recent attempts, a semi-empirical approach has been followed (Gaudio et al, 2000), based on the identification of appropriate dimensionless groups using dimensional analysis before employing best-fitting procedures. No theoretical models can be found to date, due to the extreme complexity of the flow field generated within the scour hole.…”

Channel degradation and slope adjustment in steep streams controlled through bed sills

“…Moreover, the slope difference (i − i′), called slope reduction, is such that the longer the distance, the less the slope reduction; the higher the initial slope, the greater the slope reduction; and finally the higher the ratio q/q s of the disturbance, the greater the slope reduction. A relationship by best fit of the experiments is (Whittaker, 1987;Gaudio et al, 2000). It is assumed that, given enough spacing between structures, the final slope would be the same as that produced in an undisturbed bed.…”

“…Starting from isolated structures (see, e.g., Bormann and Julien, 1991;Martín-Vide 1994), the length and depth of the scourhole scaled with the specific energy have been related to the morphological jump in clearwater experiments of sill groups (Gaudio et al, 2000;Lenzi et al, 2002), even in the case of interference due to short sill distances . The formulas obtained have also been compared with field data and with live-bed experiments (Marion et al, 2006).…”