15 / 2025-04-24 11:27:17

Analysis of Scour at Bridge Piers during Floods: Unsteady Modelling of General and Local Scour and Sedimentation

The total scour depth at bridge piers is produced by the superposition of different scour mechanisms. During extreme floods, the main mechanisms are the short-term general scour, the local scour and the sediment deposition. Perhaps the adequate estimation of the design scour depth is crucial for bridge safety, previous efforts focused on the estimation of equilibrium local scour depth only. Especially, a lack of research is detected for the time dependent short-term general scour. In this line of research, Wang (1999) proposed a formula based on laboratory-scale experiments, Lu et al. (2008) developed a model to determine the temporal variation of channel depth under unsteady flow conditions, using Wang (1999) approach for modeling the evolution of short-term general scour, and Martín-Vide et al. (2019) solved the non-convective term of the Exner equation for transient erosion and deposition.

In this paper, a novel model for the computation of the time-dependent total scour, considering the short-term general scour, the local scour and the sediment deposition is proposed, based on the work by Link et al. (2020). Following the methodology by Rifo et al. (2022) the proposed model is applied to a study case to analyze the scour dynamics at a bridge pier during floods. The study case consists in a Railway bridge over the Biobío River (basin area of 24300 km2, river width of 2000 m) located at the city of Concepción, in Chile. The river sediments are composed by homogeneous quartz sand (d_50=0.9 mm).

Obtained results show that the different possible hydrological and sedimentological conditions during floods can cause a wide range of different scour depths. The relative contribution of the short-term general scour and the local scour to the total scour and to the risk of collapse of the bridge is analyzed.