Bottom outlets are a set of structures used to transfer water from the dam reservoir to the downstream. Therefore, due to the importance of this part of the dam, the study of the cavitation phenomenon is particularly sensitive. In the downstream bottom outlets, the flow is transferred at high speed, and due to the separation of the flow and its sudden transformation from a pressurized state to a free state, a sharp drop in the pressure values downstream of the valve occurs. The flow passing under the valve creates a swirling flow downstream of it, the main characteristic of which is a sharp pressure drop. The drop created is a function of the valve opening, the water head behind the valve, and the geometry of the channel. On the other hand, severe pressure fluctuations cause a decrease in local pressure in that area, and due to the high flow velocity, the potential for cavitation increases. How to minimize the negative pressures created downstream of the valve is one of the important issues that are raised in the case of valves. The negative pressures created will ultimately lead to damage to the downstream structure and the valve itself. Cavitation is one of the most unpleasant hydrodynamic phenomena that occurs as a result of such negative pressures created downstream of the valve. In this paper, the governing equations of flow in the two-dimensional case in the physical model of the bottom outlet of the Narmashir dam were solved using appropriate turbulence models to calculate the flow and turbulence pattern. The pressure values were obtained from the numerical solution and then the pressure values on the bottom outlet and the surface in front of the bottom outlets were investigated for 30, 50, and 80 percent opening. The results show that the pressure values obtained from the numerical model follow a similar pattern as the results of physical model. With greater opening, the pressures on the bottom and top of the bottom outlet decrease. In this study, by installing a reverse slope transition after the valves and a larger diameter pipe after the transition, the negative pressure at the end of the pipe after the valve can be reduced. By opening the valve up to 50%, this negative pressure is reduced and the possibility of wastewater returning to the pipe is reduced. Also, the risk of cavitation due to direct impact of the jet with the seabed is reduced. A very strong jet may cause: sediment erosion, local mud, pollution, bed erosion and damage to benthic habitats near the seabed. Therefore, installing a reverse slope transition and an end pipe with a larger diameter than the transfer pipe can be a good idea to reduce the risk of the jet impacting the seabed.