Difference between 3D jet and culvert scour in terms of relative tailwater depth

This study investigates the tailwater depth effect on scour formed by circular jets in a cohesionless uniform sand bed. The variables studied are tailwater depth, H and mean flow velocity, Uo. The relative tailwater depths, H/d0(do =diameter of jet) were varied from 0 to 16.4 to cover from unsubmerged to fully submerged condition. Another set of experiment with selected H/do were conducted at higher Uo. The higher Uo indicates a higher densimetric Froude number, Fo because other variables were kept constant. The values of Uo were set such that the scour is formed within the width of flume. Each run of experiment were left to run for 48 hours for the equilibrium scour state to be achieved. A depth gauge was used to measure the scour hole. The centreline and contour of the scour profile were recorded at 2cm interval. The results showed that Fo is the main parameter to describe the scour characteristic dimensions which are the maximum scour depth, dse, maximum scour length, Lse, maximum scour width, Wse and scour volume, Vse. In general, tailwater depth, H/do affects these dimensions. The effect is different at different Uo. The trends of the effects of H/do on scour geometry at lower Uo are not as obvious as that of higher Uo . Multiple regression analysis was conducted and empirical equations were obtained to correlate with scour dimensionless characteristic scour dimensions (dse/do , Lse/do , Wse/do , Vse/do3 ). The empirical equations were also used to study the relations between dimensionless parameters in order to better understand their effect. Based on the empirical equations, one can note that Fo is the most influential parameter, followe by σg, H/do and lastly d50 /do .Bachelor of Engineering (Civil