This paper presents development and an example of application of turbid density current module for RESSASS, a one-dimensional quasi-steady reservoir sedimentation model suitable for long term simulations. The module determines plunging point of density current based on the criterion of densimetric Froude number. Following plunging simulation continues in a supercritical regime as long as the energy of the density flow and slope of bed are sufficient to support the transport in this mode, or until the dam is reached. A muddy lake is then formed. An adapted version of the theory of Toniolo et al (2007) is used to compute water and sediment balance in a muddy pond. If the level of muddy pond exceeds the lowest level outlet, sediment is vented from the reservoir. The model was applied to one of the largest reservoirs in the world, the Nurek reservoir in Tajikistan. Historical data on bed levels and sediment inflow as well as a recent survey from 2015 were used to calibrate and validate the model. The model showed good results both in terms of modelled bed levels and composition of deposited sediment.