Study on Sediment Flushing Using a Reverse-Flow System

バイパストンネルによる貯水池流入土砂の排除法を比較的大規模な流域に適用するには, 貯水池の上流端付近に副ダムを設置して, 洪水時に流入する土砂を一旦この上流域に貯留し, 流入流量が減少してきた時点で排出する方法が考えられる。この時, 副ダムに設けたゲートから上流向きに貯水池内の水を逆流させれば, 堆砂の再侵食を促進できると考えられる。本研究ではこの「貯水池逆流システム」の機能を明らかにするために, 副ダム上流域における堆砂の進行過程, 並びに堆砂の再侵食過程を再現し得る2次元河床変動モデルを提案し, トンネルの容量やゲートからの放流の有無といった条件を変化させて数値シミュレーションを行っている。We propose a new flushing system that is a combination of a by-pass tunnel and a sub-dam in order to control reservoir sedimentation. The sub-dam is a small dam constructed at a little downstream of the upstream end of reservoir and equipped with a gate and an introductory channel.During a flood, sediment is deposited upstream of the sub-dam forming a delta. After the flood, water stored upstream of the sub-dam is drained away through the by-pass tunnel. Then, the delta is eroded by the flow introduced from the gate of the sub-dam and the river flow. The eroded sediment is transported into the by-pass tunnel. The deposition process and erosion process are investigated by two-dimensional numerical simulation.The simulated rainfall fields will be used to evaluate the uncertainty of real-time river discharge predictions on a Monte Calro simulation framework.The investigaton of statistical characteristics of real-time rainfall prediction error by a translation model shows that a relative prediction error is modeled as lognormal random field.Then a method to generate rainfall fields with the characteristics of the random field is developed based on a matrix factrization technique of a covariance matrix decomposition into its squre root matrix approximately by using the Chebyshev polynomials.バイパストンネルによる貯水池流入土砂の排除法を比較的大規模な流域に適用するには,貯水池の上流端付近に副ダムを設置して,洪水時に流入する土砂を一旦この上流域に貯留し,流入流量が減少してきた時点で排出する方法が考えられる。この時,副ダムに設けたゲートから上流向きに貯水池内の水を逆流させれば,堆砂の再侵食を促進できると考えられる。本研究ではこの「貯水池逆流システム」の機能を明らかにするために,副ダム上流域における堆砂の進行過程,並びに堆砂の再侵食過程を再現し得る2次元河床変動モデルを提案し,トンネルの容量やゲートからの放流の有無といった条件を変化させて数値シミュレーションを行っている。We propose a new flushing system that is a combination of a by-pass tunnel and a sub-dam in order to control reservoir sedimentation. The sub-dam is a small dam constructed at a little downstream of the upstream end of reservoir and equipped with a gate and an introductory channel.During a flood, sediment is deposited upstream of the sub-dam forming a delta. After the flood, water stored upstream of the sub-dam is drained away through the by-pass tunnel. Then, the delta is eroded by the flow introduced from the gate of the sub-dam and the river flow. The eroded sediment is transported into the by-pass tunnel. The deposition process and erosion process are investigated by two-dimensional numerical simulation.The simulated rainfall fields will be used to evaluate the uncertainty of real-time river discharge predictions on a Monte Calro simulation framework.The investigaton of statistical characteristics of real-time rainfall prediction error by a translation model shows that a relative prediction error is modeled as lognormal random field.Then a method to generate rainfall fields with the characteristics of the random field is developed based on a matrix factrization technique of a covariance matrix decomposition into its squre root matrix approximately by using the Chebyshev polynomials