Experimental Investigation Effect of the Porosity and Angle of Permeable Obstacles on Density Current Sedimentation

Flood flow in rivers is often of density current type. Hence, recognizing and exploring these currents can solve some problems of sedimentation. In this study, the effect of porosity and the angle of permeable obstacles on the control and trapping of density current have been investigated in the laboratory. For this purpose, an expanded polystyrene (EPS) polymer was used with 1.135 g/L density and average diameter of 1.15 mm. The experiments were carried out with two concentrations (10 and 20%) and 5 porosity and 4 angles. The obstacles were made of palsy glass plates and two types of groove and cavity with 8.2 mm width of the groove and the diameter of the cavity. The results showed that, with an increase in porosity ratio, the amount of trapping to optimum porosity decreases and then increases. The optimal porosity of the cavity and groove is 22 % and 19%, respectively. In experiments, the cavity trapping was observed more than the groove, in the concentrations of 10.20% it was 0.13 and 0.14%, respectively. In addition, with the increase of the angle, the amount of trapping has reduced and its value was observed in the groove more than the cavity. The correlation coefficient in the grooves and cavities was 0.996 and 0.937, respectively. The major effect of obstacles, reducing velocity and slowing flow were identified as the average velocity in the cavity was 62.3% higher than the groove. Accordingly, in the same conditions, the cavity obstacles have better performance than the groove obstacles.