Time-dependent scour processes on granular beds at large scale

A theoretical framework, based on the phenomenological theory of turbulence applied to scour-related processes due to plunging jets on cohesionless beds, is considered in this paper. More specifically, its predictive capability is assessed herein for large-scale domains, after it was developed for small scales elsewhere. The analysis focuses on both the time-evolution process and the equilibrium configuration for a wide range of hydraulic structures. After revisiting the theory for the temporal evolution of the scour processes, the scour for large-scale tests is investigated using unpublished experiments performed at Colorado State University by the last author. These tests confirm the existence of two stages in the scour hole development, namely the developing and developed phases. Thus, the scour dynamics at large scales is shown to be consistent with that at smaller scales. Then, the theory recently introduced by the first three authors is used to predict the time evolution of scour, corroborating that the very same equations, together with the same coefficients, provide successful predictions, regardless of scale and granulometric distribution. Finally, the theory is again verified against laboratory data on PK weirs obtained at the University of Pisa. Overall, the work described in the paper offers a tool with general validity.