The most important practical and critical problem related to the performance of reservoirs is the estimation of storage capacity loss due to sedimentation process. Sedimentation triggers several important issues such as operation and maintenance of engineering infrastructures, economical feasibility of the project, environmental problems with social aspects upstream and downstream, increasing evaporation from the surface of the reservoir and reduced flood attenuation and changes in water quality. Palmieri et al. (2001) reports, that the loss in volume capacity requires an annual replacement cost of US$ 13 billion dollars. Although suspended sediment load can be predicted using numerous developed methods including remote sensing, hydrographic survey, hydrologicy and mathematical and computer models their results often differ from each other and Every of these equations are gained based on climate or laboratory conditions in different places in the world and they have different factors for determining transporting sediment amount. These methods are cumbersome, time consuming and expensive. There is a need for developing simple methods, which require less time and are cost. In the present study, six different hydrology models were tested using measured data based on effective factor of sediment transfer such as time of measurement for determining suspended sediment load on the reservoirs of Karaj and Torogh on the Karaj and Torogh Rivers catchments area, which are located in Iran between 1961-2007 and 1978-2009 respectively. At the end, the results of developed models were compared together and with actual amount of sediment obtained from primary and secondary area �volume height- curves. The Mean Squared Error (MSE), Root Mean Squared Error (RMSE), are used as error evaluation criteria to verify, and compare the results of developed models and select the best model. The results of this research demonstrated that the model B, based on a monthly data analysis, had the least root mean squares errors for the inlet hydrometrical stations of Karaj and Torogh Dams and was selected as the best model. The volume of annually sedimentation in Karaj dam between the years 1961-2007 was 4810000m3 while the annual sedimentation by means of hydrograph was estimated 510000m3, which confirms the high accuracy of the model. The model A based on total data analysis and without separation of data had the highest root mean squares errors in Karaj hydrometrical station and was the most undesirable model.

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