Block ramps are hydraulic structures generally used in mountains rivers. In the last decades they have become more common in river restoration as they minimize the environmental impact. Anyway, as other hydraulic structures, a scour hole forms at their toe which has to be foreseen and eventually controlled in order to avoid structural risks. The scour downstream of a block ramp in a stilling basin having the same width of the ramp was studied by many researchers who proposed relationships in order to evaluate the main geometrical parameters of the scour hole and ridge, but no studies are known in literature which analyze the scour mechanism downstream of a block ramp in an asymmetrically enlarged stilling basin. The aim of this study is to deepen the hydrodynamic behavior and the scour process in presence of two different asymmetrically enlarged stilling basin configurations. Tests were performed for block ramp slope 1V:8H and uniform stilling basin material. It was observed that a three dimensional scour hole forms downstream of the ramp toe when the channel bed has not the same ramp width. The maximum scour depth at equilibrium was compared to the respective ones that occurred in the same geometrical and hydrodynamic conditions in presence of stilling basin with the same ramp width. The scour depth was found much more prominent in the former case (asymmetric enlarged stilling basin) as the scour mechanism completely changes. A new useful relationship, taking into account also the effect of the downstream water level, is proposed in order to evaluate the maximum scour depth.
|Titolo:||Scour downstream of a block ramp in asymmetric stilling basins|
|Anno del prodotto:||2008|
|Appare nelle tipologie:||4.1 Contributo in Atti di convegno|