Some facility for the prevention of piping, reducing exit gradient and seepage amount under hydraulic structures, is construction of cutoff wall and drain. Therefore, this study compares the efficiency of cutoff wall on some design parameters in an assumed diversion dam cross-section. For this purpose, different placements of cutoff wall with various angle of inclination were used in the dam foundation. Results of this study showed that minimum uplift pressure happens when cut off wall is in the heel (upstream) of the dam. With fixing of longitudinal cut off wall placement, inclination of cutoff wall respect to the vertical position, results in reducing of uplift pressure. Effect of inclination of cutoff wall in upstream of the dam; respect to vertical position, in reducing of uplift pressure is very high.

Water hammer is a transient flow in pipes that was created by sudden changes of velocity in pipe lines. This phenomenon can cause strong positive and negative pressures in water conveyance pipes and usually it poses pipeline to danger. Overall, water hammer creates by rapidly closing valves, shutting off or suddenly restarting pumps. It has destructive hydrodynamic effects in pressurized pipelines. In this study, governing equations of water hammer is numerically simulated using MATLAB software. Then, the sensitivity analysis in negative and positive pressures by changing some variables such as pipe diameter, pipe length and also wave velocity in pipe was investigated. Numerical simulation is based on characteristic method. Sensitivity analysis help designers to have well understand of water hammer phenomenon.