mahmood kashefipour

Obstacle usually blocks the current and it has been found by other researchers an obstacle with a height more than two times of body height of flow is necessary to fully block the density current. The construction of an obstacle with this elevation creates problems in terms of performance and sustainability as well as the accumulation of sediments behind it.Rottman et al. (1985) solved the analytical solution of the two-phase current in a horizontal slope with an obstacle in the steady and unsteady flow and concluded that if the height of the obstacle is twice the body height of the density current so the density current is completely blocked. Prinos (1999) conducted studies on the effect of the shape of the obstacle on the current control. In his experiments, he used two semi-circular and triangular obstacles with the same height and concluded that the shape does not have a significant effect on the control of high current. Also, in the range of densimetric Froude number, 0.7 < Frd < 0.8 if the height of the obstacle is twice the height of the body of the density current, the current will be fully restrained. As it has been stated, for a complete block of density current, based on the results of previous investigators, the height of the obstacle should be at least twice the height of the body.The purpose of this study is to use successive obstacles with lower height, with greater sustainability and lower cost, in controlling density current. For this purpose, in different conditions, in terms of slope and concentration, three rows of obstacles with different heights and also different distances were used to control 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.

The purpose of this study is to compare the scouring hole geometric dimensions for three kinds of spur-dike: permeable, impermeable and bandal-like for submerged conditions by conducting a set of experimental tests. Bandal-like is made by combining permeable and impermeable spur-dikes.Experimental tests were carried out in a straight flume at a constant structure height equal to 12cm and three angels equal to 60, 90, 120 degrees at a constant flow condition (Fr=0.24 , y=16cm). Results were presented as bed topography, depth, length and width of scour hole. It was found that the ratio of maximum scour to flow depth occurs at 90, 120, 120 degrees for impermeable, permeable and bandal-like spur dike, respectively. Permeable part of bandal-like was found to be effective in decreasing the ratio of maximum scour depth to flow depth and the ratio of scour width to flow depth. The ratio of maximum and minimum scour width to flow depth occurs at 60 and 90 degrees, respectively for three kinds of spur-dikes. The ratio of maximum scour length to flow depth in impermeable, permeable and bandal-like occurs at 90, 60 and 60 degrees, respectively. Impermeable part of bandal-like was found to be effective in increasing the ratio of maximum scour length to flow depth.

Today, flood management is one of the most important topics in river engineering due to reducing the fatality and damages caused by it. Several hydrodynamic models including 1D, 2D, 3D and couple hydraulic models have been developed in the world. One dimensional models have a short computation time and only compute the hydraulic parameters of main river channel. They provide no details about inflow or overbank flow and flow changing between river and floodplainds. Dez river in Khuzestan province (Case study) is surrounded by wide low elevation plains. Since the elevation of floodplains is lower than the main channel, when overbank flow occurs, two flows with different velocities and depths should be considered in the main channel and floodplains. In the present study three different modeling including: 1D simulation using existing cross sections, quasi 2D simulation using LINK CHANNELS, 1D-2D modeling with MIKE FLOOD, were investigated. The results indicate the quasi 2D model, despite of the limited computational time than 1D-2D model, has an acceptable accuracy in predicting discharge, water level, inflow and overbank flow simulation and reduction in inundation volume, which is compatible with the fact of inundation volume storing in the floodplains and it can separately compute hydraulic parameters of main river and floodplains. In contrast, there is no possibility for 1D model with the original cross sections to simulate overbank flow, discharge and flood volume reduction. It provides the average of hydraulic parameters throughout the whole cross setions. Moreover, flood routing is imposibe to be investigated in this model.