Document Type : Research Paper
Sedimentation in dam reservoirs is the most important phenomenon in reducing their useful life. One of the most important phenomenon affecting sediment movement in dam reservoirs is density current. Therefore, understanding of density or gravity current can be helpful in controlling this phenomenon and increasing the useful life of dam reservoirs. In this research the effect of the roughness and bed slope on the head and of body density current velocity has been studied. Experiments were performed in a flume with a length of 780 cm, width of 35 cm and height of 70 cm with 4 height roughness (0, 0.5, 1 and 1.5 cm), 4 bed slopes (0%, 1.5%, 2.5% and 3.5%) and with two sediment concentrations including 10 g/lit ( ) and 20 g/lit ( ), in total 32 experiments were carried out. The results showed that the head and body velocities decreased with increasing roughness height and increased with increasing bed slope. The Keulegan coefficient for estimating head velocity results decreased about 40% in comparison with the conditions without roughness, with its mean value being obtained about 0.4. However, increasing the bed slope reduces the effect of roughness in decreasing of head and body velocity. Finally, two equations were developed using Datafit software to estimate the head and body velocities of density current as the functions of roughness and bed slopes with the determination coefficients (R2) being calculated 0.85 and 0.73, respectively.