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 × 80 grid. The number of layers in the z-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 Mm³.

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.

中文翻译：

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开发用于模拟伊朗Zonouz大坝水库长期沉积的非耦合算法

目的

本文报告了非耦合算法的发展及其在实际案例中的应用。主要目的是通过删除对计算结果没有显着影响的部分来提供2D / 3D长期模拟坝水库沉降。该模型用于模拟伊朗Zonouz大坝水库30年的沉积。

方法

非耦合算法将水流，泥沙输送和床模块耦合，求解水流模块的深度平均Navier-Stokes方程，泥沙模块的3D泥沙质量守恒方程和Exner方程以计算床变形。该算法基于流和沉积物模块的准稳态近似的有效性，通过优化模块之间的交互频率来最小化计算成本。该算法是使用连续性校正来开发的，以解决时间和空间滞后的影响，并在床位发生微小变化后调整流量参数。由于水库中水面高度和坡度的高度变化，可能会发生洪水和干燥现象。因此，引入了一些人工抵抗。

结果和讨论

Zonouzchay河上的Zonouz大坝为950公顷的农业用地供水，并具有其他环保目的。主要的泥沙类型是悬浮泥沙。储层表面由91×80网格离散化。z中的层数方向是八个，厚度不同。在2012年和2016年对水库进行了水文调查，并对数值结果进行了验证。“准稳定时间步长”和“更新时间步长”分别等于1天和8小时。对于洪水日，使用3小时更新时间步骤。确定稳态条件的标准为2％。模拟表明，沉积物在库区的沉积大部分聚集在库区的入口处。2042年沉积沉积物总累积体积的预测值约为1.0 Mm ³。

结论

本研究表明了非耦合算法的可观的准确性和效率。该算法缩短了仿真时间，证明了3D泥沙模型可用于长期建模。