SCOUR BELOW UNSUBMERGED FULL-FLOWING CULVERT OUTLETS

This paper presents the results of an experimental study of local scou r below circular culvert outlets, The culvert considered was the wall jet type, and experiments were conducted under full-flowing conditions with the jet outlet unsubmerged by the tailwater, The main aim is to study the geometry of scour hole below the culvert at the equilibrium scour conditions with respect to the erosive strength of the jet and d ownstream channel width, Dimensional analysis was used to delineate th e characteristic scouring parameters of the phenomenon, and the study has shown that the scouring process is a function mainly of the densim etric Froude number F-0. The lateral development of the scour hole was affected by the downstream channel when it became too narrow and rest ricted for the normal diffusion of the three-dimensional jet how, Exce pt for the width of the scour hole, the effect of the channel width on the maximum length, depth and volume of the scour hole was not signif icant when data for wide and narrow channels were compared, Based on t he present data, empirical equations were established to reflect the r elationships between the maximum scour width W-se, length L(se), and v olume V-se with the maximum depth d(se) of the scour hole, The latter has been used as the representative length scale for the three-dimensi onal scour hole. The study also compared and highlighted the Limitatio ns of two scour depth formulae by Abt et al, (1984) and Breusers and R audkivi (1991), with data from the present study and relevant data fro m past studies, To this end, a database of 150 maximum scour depth dat a points has been compiled. A new scour depth prediction formula has b een proposed (equation 14), and its uses and limitations are discussed .