This research was developed for the evaluation of the thickness of turbidity currents coming into the reservoir of the Dez dam. In recent years, for the simulation of turbidity currents two types of mathematical models have been employed: (1) the extended shallow water model (ESWM), and (2) the suspension balance model. In this study, we used the ESWM to estimate the thickness of turbidity currents. A random study was carried out from January 2002 to July 2003 in the Dez dam reservoir. Dez dam in Iran is facing a serious sedimentation problem, and its dead volume will be quite full in the next 10 years, and now the inflow water in the hydro-power conduit system is becoming turbid. Based on the values of friction dimensionless number (Nf) and dimensionless number of entrainment (NE), the regime of the turbidity currents is Negligible Friction and Negligible Entrainment in the Dez dam reservoir, and the thickness of the turbid layer is assessed as a function of concentration, settling velocity of particles and entrainment. A positive correlation between measurement and model values has shown that this model is the profitable option for estimating the thickness of turbidity currents in dam reservoirs. © IWA Publishing 2014.