Local scour around bridge piers is a significant problem in the design and maintenance of bridges. Knowledge of the rate at which scour occurs can help engineers in the areas of design, monitoring, and scheduling of repairs. The temporal variation of clear water local scour around a single circular cylinder is examined. Physical experiments are conducted using erodible bed and fixed bed models of a single scour event. The erodible bed experiments include a near equilibrium scour experiment and two experiments that are stopped at intermediate times during the scouring process. The fixed bed experiments model the holes created during the erodible bed experiments as well as an initial flat bed condition. The velocities of the flow around the cylinder for these four cases are measured using an Acoustic Doppler Velocimeter (ADV). Numerical simulations of the flow through the scour holes are conducted using the commercially available three dimensional Navier-Stokes equation solver FLOW3D{dollar}spcircler.{dollar} The results of the simulations and the measurements from the physical experiments are compared to justify the use of the software for further numerical experiments. The software is used to produce numerous simulations of the scour event at intermediate depths. These simulations are used to develop a method for predicting the depth of scour time history. This method is based on the competing mechanisms of the erosive and resistive actions of the hydrodynamics and the scour hole geometry. The method relates the volumetric rate of sediment leaving the hole to the kinetic energy at some fixed distance above the surface of the scour hole and the potential energy associated with removing sediment from the bottom of the scour hole. This method is validated through the analysis of a second scour event that has entirely different flow, sediment, and structure properties.
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