Development of a non-coupled algorithm for simulating long-term sedimentation in the Zonouz dam reservoir, Iran

摘要

Purpose This paper reports the development of a non-coupled algorithm and its application in a real case study. The main objective was to provide 2D/3D, long-term simulation of dam reservoir sedimentation by removing the part of calculations which did not significantly affect the results. The model was used to simulate sedimentation in the Zonouz dam reservoir, Iran, over a 30-year period. Method The non-coupled algorithm couples the flow, sediment transport, and bed modules, solving the depth-averaged Navier-Stokes equations for the flow module, the 3D equation of sediment mass conservation for the sediment module, and the Exner equation to calculate the bed deformations. This algorithm minimizes the computational costs by optimizing the frequency of interactions between the modules, based on the validity of the quasi-steady-state approximation for the flow and sediment modules. The algorithm is developed using the continuity correction to account for the impacts of time and space lags, and adjust the flow parameters after small changes in the bed level. Due to the highly varying water surface elevations and sloping bed in the reservoir, flooding and drying phenomena may occur. Therefore, some artificial resistance was introduced. Results and discussion The Zonouz dam, located on the Zonouzchay River, supplies water to 950 ha of agricultural land, and has other environmental purposes. The predominant sediment type was suspended sediment. The reservoir surface was discretized by a 91 x 80 grid. The number of layers in thez-direction was eight, with different thicknesses. The reservoir was hydrographically surveyed in 2012 and 2016, and the numerical results were verified accordingly. The "quasi-steady time step" and the "updating time step" were equal to 1 day and 8 h, respectively. For flood days, a 3-h updating time step was used. The criterion for determining the steady-state condition was 2%. The simulation indicated that the sediment deposition in the reservoir area was mostly accumulated at the inlet of the reservoir. The predicted value of the total cumulative volume of the deposited sediment in 2042 was approximately about 1.0 Mm(3). Conclusions The present study demonstrated the appreciable accuracy and efficiency of the non-coupled algorithm. This algorithm shortened the simulation time and proved that the 3D sediment model is applicable in long-term modeling.