**Scour at Bridge Foundations in Supercritical Flows: An Analysis of Knowledge Gaps**

#### **Oscar Link 1, Emmanuel Mignot 2,\*, Sebastien Roux 3, Benoit Camenen 4, Cristián Escauriaza 5, Julien Chauchat 6, Wernher Brevis 7 and Salvatore Manfreda 8**


Received: 17 June 2019; Accepted: 8 August 2019; Published: 10 August 2019

**Abstract:** The scour at bridge foundations caused by supercritical flows is reviewed and knowledge gaps are analyzed focusing on the flow and scour patterns, available measuring techniques for the laboratory and field, and physical and advanced numerical modeling techniques. Evidence suggests that the scour depth caused by supercritical flows is much smaller than expected, by an order of magnitude compared to that found in subcritical flows, although the reasons for this behavior remain still unclear. Important questions on the interaction of the horseshoe vortex with the detached hydraulic-jump and the wall-jet flow observed in supercritical flows arise, e.g., does the interaction between the flow structures enhance or debilitate the bed shear stresses caused by the horseshoe vortex? What is the effect of the Froude number of the incoming flow on the flow structures around the foundation and on the scour process? Recommendations are provided to develop and adapt research methods used in the subcritical flow regime for the study of more challenging supercritical flow cases.

**Keywords:** bridge foundations; scour; supercritical flows; sediment hydraulics
