Sedimentation is a very complex process of entrainment, transport and deposition of soil particles in the reservoir basin. Silting of reservoirs is influenced by many parameters, amongst which the reservoir shape is one of the most important. Till now, different empirical and semi empirical methods based on reservoir shape parameters have been presented to predict sediment distribution pattern. In an extended investigation over hydrographic maps of some Iranian dams, a strong relationship between the reservoir shape and sediment distribution pattern was found. So a new method for predicting sediment distribution through reservoirs was introduced. In this method, based on special definitions a new parameter which determines the reservoir shape was presented. It is suggested that this new technique, which accounts for distribution of sediment in a wide variety of reservoir configurations, can be used for preliminary design purposes.