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 $0.5\le d/D_p\le 5.0$ .

Groups of piles are frequently used as bridge foundations. Different group configurations, characterized by different pile spacing, skew-angle, number, and arrangement of pile group columns interact differently with the flow field and lead to different scour patterns and equilibrium scour depth. There have been a number of past studies on the characterization of scouring at pile groups, but most of them report short duration scour experiments. A priori, such short durations may be postulated to inherently carry important uncertainties into existing scour predictors. In this study, 75 long-duration laboratory tests were run under steady, clear-water flow close to the threshold for initiation of sediment motion, to address the effect of time, pile spacing, skew-angle and number of pile group columns on the equilibrium scour depth. Pile groups consisted of matrical arrangements of one, two, or three columns of four rows, with spacings of 1, 2, 3, 4.5, and 6 pile diameters; the tested skew-angles were...

This paper describes the application of four Large Eddy Simulations (LES) to an open-channel confluence flow, making use of a frictionless rigid-lid to treat the free-surface. Three simulations are conducted with a flat rigid-lid, at different elevations. A fourth simulation is carried out with a curved rigid-lid which is a closer approximation to the real free-surface of the flow. The curved rigid-lid is obtained from the time-averaged pressure field on the flat rigid-lid from one of the initial three simulations. The aim is to investigate the limitations of the free-surface treatment by means of a rigid-lid in the simulation of an asymmetric confluence, showing the differences that both approaches produce in terms of mean flow, secondary flow and turbulence. After validation with experimental data, the predictions are used to understand the differences between adopting a flat and a curved rigid-lid onto the confluence hydrodynamics. For the present flow case, although it was characterized by a moderately low downstream Froude number (Fr ≈ 0.37), it was found that an oversimplification of the numerical treatment of the free-surface leads to a decreased accuracy of the predictions of the secondary flow and turbulent kinetic energy.