Abstarct: Countries are now looking for environment-friendly ways of producing electricity. For many years hydro-power plants have been used for producing electricity. During the operation of plant, water is taken from reservoir to turbines via the intakes. It is normally likely that the entering flow create vortex at the entrance, causing the air and floating trash to enter the power plant. The intake of plant should be designed so that no vortex forms near the entrance. During the recent years, many investigations have been performed with the aim of controlling this phenomenon. A trashrack structure is normally used at the intakes entrance to prevent the trashes of entering the plant. This structure reduces the net intake area and causes extra head loss for entering flow. Because of the complexity of the vortex phenomena and wide range of results from previous investigation, further studies are necessary. In this study, a 1:25 scale model of Gotvand dam’s hydro-electric power plant was used and the effect of various parameters on vortex formation and energy loss was investigated. The model concluded four similar intakes with rectangular cross-section. Tests were carried out in different reservoir water levels and discharges, during which the effects of different parameters such as the existence of trashrack at the entrance, various combinations of operations and variations of submergence depth were investigated. By measuring dynamic pressure using a transducer, the head loss caused by installing the trashrack was calculated for different blockage percentage. The results showed that a suitable combination of intakes operation with symmetrical and uniform streamlines could reduce the power of vortices to one lower degree. In these experiments, the above conditions were achieved by choosing the intake entrance direction in the some direction of flow in approaching channel. The results of present study along with those of other researchers were analyzed and a new relationship for the prediction of critical submergence depth for different Froude numbers of the horizontal intakes was introduced. The result for measuring the head loss due to the existance of trashrack at the entrance was also employed and a new empirical equation for prediction of head loss at different blockage percentage was suggested.