Modified Einstein sediment transport method to simulate the local scour evolution downstream of a rigid bed

The present study consists of a new mathematical-numerical modeling formulation to simulate the spatial and temporal scourdevelopment downstream of a rigid bed for both a noncohesive sediment bed and a cohesive sediment mixture with relatively smallpercentage of cohesive material. Laboratory tests were conducted in a rectangular tilting flume having a recessed box filled with the selectedbed sediments and placed downstream of a rigid rough bed. The scour pattern was accurately acquired with a three-dimensional laser scannerat various time instants. The numerical code was calibrated through the scour profile data obtained under steady-state flow condition and thenvalidated on the basis of scour patterns acquired under both steady and unsteady flow conditions (symmetric and asymmetric hydrographs).Contrary to most previous studies conducted with an issuing jet, the present study’s experiments were performed under non–strictly uniformflow conditions. The numerical model utilized information concerning the erosive turbulent flow characteristics as well as physicaland mechanical properties of the movable-bed materials. The mathematical framework of the numerical model was a second-order partialdifferential parabolic equation in which the form of the scoured bed was assumed as an unknown parameter. Instantaneous near-bed velocitydata, acquired with an acoustic Doppler velocimeter, was used to modify the Einstein sediment transport method, leading to a significantimprovement of the simulated longitudinal scour profiles. Simulated temporal evolution of the scour profiles was in good agreement with themeasured ones for both cohesive and noncohesive bed materials under steady and unsteady flow conditions.