In this paper an experimental study is presented for the problem of the thermal power stations, which is discharging the hot water into relatively deep rivers. The receiving water of the river is said to be deep when the jet is free to mix due to entrainment and buoyancy and is not constrained by neither the river bed nor the water surface (6), which increases the temperature dilution. The water depth (H) is constant during the experiments. The main objective of this paper is to develop a new general equation which can be used in designing the multi-ports diffuser of the thermal power plant discharging hot water into relatively deep rivers. Also, the rapid dilution and minimizing of the mixing zone length of the hot water 10 reduce the environmental effects are considered. In this paper, the effects of the different parameters related to both the out-fall structure and the river characteristics on the rapid dilution of the hot water concentration (Cm/Co) are considered. These parameters are, the effluent/ambient velocity ratio (V/U), the number of ports (n), the spacing between the ports with respect to its diameter (s/D). the vertical angle of ports in combination with the ratio of its height to the flow depth (θh/H), and the horizontal angle between the diffuser line and the flow direction (β). The analysis of the experimental results shows that the relative thermal concentration (
Cm/Co ) is directly proportional to V/U, n, θh/Hand β. while it is inversely proportional to SD. Also, it is found that the maximum value of Cm/Co occurs when the diffuser is aligned parallel to the direction of flow. A general equation between the relative thermal concentration (Cm/Co) and the aforementioned parameters is developed. The comparative study between the experimental results, which is carried out by Mowed [7], and the corresponding results by applying the developed equation, illustrates that there is a good compatibility between the two results.