Evaluation of variation of useful storage of reservoir in stream dams by GSTARS3 software

Stream dams are small dams. If the conditions of site are not suitable for construction of reservoir dams, stream dams will be constructed. These dams have small reservoirs. These dams are without gate or these are controlled by gates. The major problem of stream dams is sedimentation special in rivers with high sediment load. In gated stream dams, flushing is accomplished by opening of the gates in flood condition. Construction of physical model is very difficult for evaluation of efficiency of flushing in removal sediment from reservoir of stream dam. Also the cost of construction of physical model is very high. Development of mathematical models is essential for modeling of successive processes of sedimentation and flushing in useful lifetime of stream dams. Because of variation of boundary conditions in successive processes of sedimentation and flushing of gated stream dams, Available mathematical models can not model continuously these processes at total of yield period. In this research, the long term sedimentation and flushing process will be simulated by development of a mathematical model. Modified mathematical model can simulate successive processes of sedimentation and flushing in useful lifetime of stream dams for different conditions of use of reservoir. The time and cost of simulation by modified mathematical model is very low. Also accuracy of this model is acceptable for simulation. In this research, the case study is successive stream dams on the Dez River in Iran (Dez1 Dam, Dez2 Dam and Dez3 dam) for evaluation of efficiency of modified mathematical model.   Key words: The Dez river, stream dam, GSTARS3, flushing, sedimentation.