THE TEMPORAL SCOUR PROGRESS DOWNSTREAM OF LOW-HEAD STILLING BASINS UNDER UNSTEADY FLOW
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This paper deals with the temporal evolution of local scour downstream of low-head stilling basins. In comparison to previous companion papers the most real conditions of unsteady approach flow are considered here. In this aim, experiments were carried out in a 1 m wide and 20 m long rectangular channel. Free overfall jets plunging into a horizontal apron were caused by an ogee-crested spillway. A nearly-uniform sediment with median grain size d50=9 mm was used as mobile bed. The temporal effect of six different hydrographs on local scour depth was investigated under clear-water scour condition. Based on the data collected and the previous results for steady flow conditions a predictive model is proposed to simulate the temporal progress of the scour depth along the channel axis as function of tailwater densimetric Froude number, relative submergence, and dimensionless time.
local scour, sediment transport, stilling basin, unsteady flow