The development of scour holes in lowland rivers: a review on the hydrodynamic and geotechnical conditions

Scour holes are common features in lowland rivers. They can have significant depths and steep slopes which may threaten the stability of infrastructure. Therefore, understand-ing the dominant conditions that control the development of scour holes is essential. Previous studies mainly focused on the hydrodynamic conditions (i.e., flood events, channel geometry, and presence of a structure) that induce the formation of a scour hole. However, more recent research illustrated that the formation of a large group of scour holes cannot be explained by hydrodynamic conditions solely. The geotechnical conditions (i.e., the subsurface composition) significantly in-fluence the location of a scour hole, as it reflects the local susceptibility of the bed to erosion. Yet, the hydrodynamic and geotechnical conditions are mainly isolated in scour hole analysis. This review provides an overview of the drivers of the formation and migration of scour holes focusing on the interplay of hydrodynamic and geotechnical conditions.