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Scour at uniform cylindrical piers has received considerable attention in the past. However, bridge foundations can be subjected to the flow due to single or combined effects of long-term riverbed degradation, lateral shifting of the stream, contraction scour, local scour or other factors. This paper focuses on bed morphology changes due to local scour at piers founded on piles or caissons when the foundation is located at the initial bed level. Experiments were carried out in a 1 m wide 20 m long rectangular channel under clear-water and steady flow conditions. The majority of runs were of long duration in order to guarantee sufficient interaction between the flow and pier foundation and to approach the equilibrium phase. Two nearly uniform bed sediments were considered to assess grain size effects. The experimental data obtained provided new information on the temporal variation of scour depth, the areal extent of the scour hole and the scour volume, which are useful for validation of advanced numerical models. In this paper, scour depths are compared with the HEC-18 approach and agreements appear suitable only at the equilibrium phase. Moreover, scour progress is compared to that of uniform cylindrical piers and foundation effects are emphasised. A generalised scour equation is proposed, accounting for such effects.

Sediment transport at river contractions is an important process of engineering concern which might occur when a river encounters a reduction in flow area because of either natural or artificial constraints. This paper focuses on the morphological patterns that are prone to form at and around the constriction of watercourses based on experimental investigations at laboratory scale. Experiments were carried out at the University of Basilicata, Italy, in a 1 m wide and 20 m long rectangular channel. The length of the working section extended up to 16 m, according to the length of the contraction model. Two nearly-uniform sediments were used as mobile bed, sand with median grain size d50 = 1.7 mm and gravel with d50 = 9.0 mm. The contraction length was either 0.5, 1.0, 2.0 or 3.0 m. Runs were carried out under steady flow and clear-water approach flow conditions. Typically, they were of long duration (up to 15 days) also to achieve an equilibrium state. New predictive equations are given on the temporal progress of: the maximum scour depth, the scour hole length, and the axial bed profile with emphasis on the processes of bed aggradation or degradation beyond the contracted region.