考虑干支流倒回灌的小浪底水库异重流模拟

Modeling Turbidity Currents in the Xiaolangdi Reservoir with the Effect of Flow Exchanges with Tributaries

小浪底水库支流众多,支流库容占总库容的41.3%,干支流倒回灌对干流洪水演进和库区淤积过程有重大影响,为此作者提出了考虑干支流倒回灌影响的水库1维明流及异重流耦合模型。推导了不同类型倒回灌引起的水沙控制方程附加项,并提出了相应的水沙耦合形式的浑水明流与异重流控制方程。针对不同的倒回灌形式提出相应的倒回灌流量计算方法:对于干流水位涨落引起的干支流倒回灌,提出了零维水库法在使用有限体积法的数学模型中的实现方法;对于异重流向支流的倒灌,采用考虑支流底坡影响的异重流倒灌流量公式加以计算。将这两种方法与已建立的水库1维明流与异重流耦合模型结合,模拟了2006年小浪底水库调水调沙实验的完整过程,对库区内水位下降、上游段冲刷及人工异重流形成与发展均做出了较为准确的模拟。模拟结果显示,干支流倒回灌过程对于异重流厚度变化过程和调水调沙出库沙量有显著影响,对于汛前泄水阶段库区水位下降速度也有一定影响,支流淤积在一次异重流过程淤积总量中可达43.5%。相对于简化干支流倒回灌过程的计算方法,该模型对异重流排沙比的预测效果更好,证明其有助于实现更加科学合理的调水调沙方案设计。

The Xiaolangdi Reservoir is characterized by its many tributaries.The storage capacity of tributaries accounts for 41.3% of the total capacity of the reservoir,and the flow exchanges between the main channel and tributaries have a great impact on the flood routing and sedimentation distribution.Therefore,a one-dimensional model for open channel flows and turbidity currents with the effect of flow exchanges with tributaries was proposed in this study.A composite method to calculate the flow exchanges between the main channel and tributaries was presented.For flow exchange caused by the water level variation of the main channel,the storage cell algorithm was implemented in the numerical model based on the finite volume method.For turbidity current intrusion into tributaries,an improved formula to estimate the intrusion discharge was introduced,with the effect of bed slope of the tributary being considered.These two methods were integrated with an existing coupled model of open channel flow and turbidity current to simulate the whole process of flow-sediment regulation in the Xiaolangdi reservoir in 2006.Successful predictions were obtained,including the processes of water level falling,bed erosion in the upstream reach,and formation and development of the artificially created turbidity current.The simulations indicate that the flow exchange processes have great impacts on the amount of released sediment during an event of water-sediment regulation.As compared to the simulation methods neglecting or oversimplifying the flow exchanges,the proposed model produces a better prediction to the sediment delivery ratio,which demonstrates its potential to help design the scheduling scheme for water-sediment regulation.