Effect of bed roughness on velocity profile and water entrainment in a sedimentary density current

In this study, the effect of bed roughness on velocity profile and water entrainment in a sedimentary density current for Richardson numbers of 1.2-7 (subcritical flow conditions) was investigated. Experiments were carried out in a tilting flume with four different bed slopes, four roughness heights, and two fluid densities of sedimentary density currents. The results showed that bed roughness significantly affects the general shapes of velocity profiles, especially in the wall region. Two empirical equations were developed as the functions of the relative roughness for the wall and jet regions of velocity profile using the measured velocities of density currents. Water entrainment was also affected by bed roughness and an empirical equation was developed describing the relationship of this phenomenon with the Richardson number and relative roughness. Sensitivity analysis of this equation by using elasticity coefficient method showed that the effectiveness of the Richardson number is 3.9 times more than the effect of relative roughness on water entrainment.