Local scour in rivers due to bridges and natural features. A case study from Rönne river, Sweden
Bridges are important components in many transportation networks often spanning rivers and other water bodies. The failure of a bridge will cause significant direct and indirect economic losses to society. Scouring of the river bed around bridges is a principal mode of bridge failure typically associated with large floods. The risk of such scour may become higher with the emerging climate change that can induce large floods in a short period of time, significantly changing the river hydraulics. The objective of the present study is to review the significance of different types of riverbed scour with a focus on the funda- mental mechanisms and governing parameters controlling bridge scour. The study was conducted in the Rönne River at Ängelholm Municipality because many scour holes were discovered along the river bottom during a high-resolution bathymetric survey. The bathymetric analysis identified 14 major scour holes of between 1.3 and 3.5 m depth from the existing, undisturbed river bed. The investigation revealed that the scour holes originate from bridge, bend, and hard bottom scour. A special analysis of bridge scour was performed using river hydraulic properties obtained through simulations with the one-dimensional hydraulic model HEC RAS. According to these scour simulations, the studied bridges show more poten- tial risk for abutment scour and pier scour than for contraction scour. The bridge Flygarebron shows the highest potential risk for abutment and pier scour, whereas the Kristian II bridge has the highest risk for contraction scour.