| Summary: | 碩士 === 淡江大學 === 水資源及環境工程學系碩士班 === 103 === In Taiwan, landslide frequently triggered by typhoon events can generate large quantities of sediment into a river. When the river flow enters a reservoir, the turbidity current plunge along the bottom of reservoirs as a submerged current driven by the velocity and density differences between the sediment-laden inflow and the stagnant deep clear reservoir water, called a density current. The density current reaches the dam to form a submerged muddy lake and the level of muddy lake would rise if the outlets are close. Therefore, estimating suspended sediment concentration in upstream river and near dam wall is one of important issues for reservoir management.
This study applies the NARX and R-NARX models for estimating suspended sediment concentration at Lo-Fu gauging station of Shimen Reservoir upstream and at S07 gauging station of near dam wall. Before analyzing sediment concentration near dam wall, the necessary condition of density current reaching dam wall needs to be identified. According to statistical analysis of data of several typhoon events, the threshold is the reservoir inflow > 1500 cms.
The results show that NARX model is successfully applied to construct estimation model at Lo-Fu gauging station to predict hourly suspended sediment concentration. If the observed sediment concentration cannot be obtained from Lo-Fu gauging station, then the R-NARX model can be instead of the NARX model for proceeding on prediction. By taking various input variables into account at S07, the results demonstrate that precipitation does not affect the prediction of sediment concentration. The performance of NARX is still nice, even though the training data is few. The R-NARX model can provide the trend of sediment concentration near the dam wall.
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