Abstract

Background and objectives: Local Scour phenomenon in downstream of hydraulic structures such as spillway, gate, stilling basin is one of the most important issue. Scour around the structures in addition to an important impact on the stability of the structure, may change the flow characteristics and the result of changes in the structural design parameters. Reveals the importance of scouring time that the scour depth is considerable, so that the depth of the river is the foundation structures and stability of these structures are at risk. If the maximum scour depth is not anticipated, it creates a serious problem in design. Hydraulic structure designers aren't able to provide the necessary measures to reduce damage caused by scour. Careful examination of the claim requires more tests and more accurate. The aim of this study is to investigate the effect of Bentonite clay in the form of the bed scouring. Materials and Methods: For this purpose, 87 tests were conducted in different laboratory conditions on flume of Hydraulic laboratory which Situated in Research Institute of Soil Conservation and Watershed Management. Studies were conducted on 29 tests of non cohesive materials with average of 0.2 mm diameter as an evidence and 58tests on materials with a viscosity of 2%, 5%, 8% and 20%. three crescent gate with 5,7.45,10.82 cm diameters, with the different tail water within 5 cm to 21 cm and four gate openings of 1,2,3 and 4 centimeters, three discharges about 1 to 5 liters per second. To measure tail water depth and measure flow discharge used a standard sharp edge triangular weir with 90 degrees. Results: By examining the longitudinal profile of scouring was found dimensionless scour hole profiles and hills created with three curve edge sluice gates diameters 5, 7.45, 10.82 cm and a simple slider, That retains its shape over time and They almost overlap and the curves are similar and stylish. It is worth mentioning scour profiles that were created after curve edge sluice gates was observed secondary hill in the ratio of tail water to opening of gate size 3, 5, 9 but the ratio of more than 10 in its impact will be low enough. As a result of scour profiles behind the slide gate is simple and there was no secondary hill. With using point gage took hole dimensions and the diagram of the scour hole was presented with software surfer. The results showed that the addition of Bentonite clay minerals is reduced scouring hole size. It was also observed an increase of 5% Bentonite clay is reduced 80percent and about 8 percent rise is reduced 84percent scour depth. Dimensionless relationship was presented for effective parameters. Logarithmic line fitted with the interpretation is fairly good correlation with a correlation coefficient of 0.76. Conclusion: Studies in this research showed that the crescent gate has impact on the scour hole, and in the majority of cases examined scour profiles after the crescent gate can be seen secondary hills