Effect of Stilling Basin Geometry on the Dissipative Process in the Presence of Block Ramps

Abstract

The dissipative process that occurs in the presence of a hydraulic structure is a major topic in river engineering. The energy dissipation has to be correctly evaluated to prevent structural stability risks and to optimize the hydraulic performance of the structure itself. Moreover, the analysis of the dissipative process cannot be limited only to the dissipation that occurs with the structure, but it must also take into account the amount of energy dissipated in the stilling basin. The analysis was conducted considering a block ramp, which is a peculiar stream restoration structure. Experiments were performed in clear water conditions for a fixed ramp slope and different stilling basin geometries. The basin geometry was both symmetrically and asymmetrically enlarged, and mobile bed conditions were also tested. The global energy dissipation was shown to increase for enlarged stilling basins. A simple empirical relationship was derived to evaluate the energy dissipation for both prismatic and enlarged configurations. For asymmetrically enlarged configurations, the flow pattern was analyzed and two hydraulic jump typologies (the repelled asymmetric and the repelled asymmetric oscillating) were distinguished and classified.