Clear-Water Scour at Comparatively Large Cylindrical Piers

New long-duration clear-water scour data were collected at single cylindrical piers with the objective of investigating the effect of sediment coarseness, $D_p/D_{50}$ ($D_p$ = pier diameter; $D_{50}$ = median grain size) on the equilibrium scour depth and improving the scour depth time evolution modeling by making use of the exponential function suggested in the literature. Experiments were carried out for the flow intensity close to the threshold condition of initiation of sediment motion, imposing wide changes of sediment coarseness and flow shallowness, $d/D_p$ ($d$ = approach flow depth). The effect of sediment coarseness on the equilibrium scour depth was identified; existing predictors were modified to incorporate this effect for $U/U_c\approx 1.0$; $D_p/D_{50}>\approx 60$ and $d/D_p\ge 0.5$; the complete characterization of a known scour depth time evolution model was achieved for $U/U_c\approx 1.0$, $60<D_p/D_{50}<500$ and $0.5\le d/D_p\le 5.0$.