Experimental Investigation of the Effect of Height and Distance of Successive Obstacles on Head and Body Velocities in Sedimentary and salty Density Current

Density current is one of the most important phenomenon in reduction the useful life of dams, that it is the main cause of the sediment movement in the dam reservoirs. Therefore, Study of density or gravity current hydrodynamics plays an important role in increasing the economic life of dams though reduction in sediment accumulation. In this research the effect of the height and distance of successive obstacles and bed slope on the head and body velocity of density current has been studied. In the experiments, four types of height models and 3 types of distance model were used for obstacles. Also, the experiments were carried out in 3 slope and 2 concentration and in two sedimentary and salty types. In total 117 experiments were carried out. The results showed that the head and body velocities decreased with increasing height and distance of obstacles and increased with increasing bed slope. Also, the results showed that using of 3 rows of obstacles can reduce the head and body velocity of salty density current about 31 and 20% respectively, in comparison with the conditions without obstacles. In sedimentary density current numerical values of this reduction was 33 and 19.5 respectively for the head and body velocity. The Keulegan coefficient for estimating head velocity results decreased about 27% in comparison with the conditions without obstacles, with its mean value being obtained about 0.48. However, increasing the bed slope reduces the effect of obstacles in decreasing of head and body velocity. Finally, two equations were developed using Spss software to estimate the head and body velocities of density current based on height of each three obstacles, distance of obstacles and bed slopes.