Sediment desilting of dam reservoirs is done by different methods such as hydrosuction. In order to precisely design of hydrosuction systems resulting in higher efficiency and avoiding water loss of the reservoir, it is necessary to experimentally study the process of sediment desilting. The main parameters which influence on the efficiency of such systems include: the suction pipe diameter, the angle of suction pipe relative to the bed surface, and the effective head (head difference between reservoir water level and system outlet). To study the impact of those parameters on outflow density, a physical model of reservoir has been designed, constructed and investigated. Experiments have been conducted on each parameter at three levels and three replications for each run. Results show that the outflow gets denser by increasing amount of these parameters. For example by increasing effective head from 50 cm to 65 cm and then 80 cm, the outflow density increases 9.4% and 20.9%, respectively.