利用水库泄空冲刷形成高含沙水流的机理

利用黄河干支流水库运用的实测资料，对高含沙水流的产生条件进行了研究。结果表明，水库水位的迅速下降并泄空，可使水库的淤泥流动并产生高含沙水流。水库淤土抗剪强度参数(C和Φ)依排水条件而异，抗剪强度一般不排水不固结的最小。水库淤积物在水下处于饱和状态，库水位迅速降低时，淤土中的孔隙水来不及排出，摩擦角值低，Φ=0，只要下滑的剪力大于黏着力淤泥便开始流动。当库区淤积物抗冲性较强时，溯源冲刷纵剖面调整又具有自动调整的特性，使冲刷以“局部跌坎”的形式向上游发展，使水流能量集中，加强冲刷能力，随着主槽冲深，滩槽差增大，促使淤土向主槽内滑塌，为高含沙水流形成创造了有利条件。

Formation mechanism of hyper-concentrated sediment flow caused by scouring of reservoir emptying

The formation condition of hyper-concentrated sediment flow is investigated based on the operation practice of reservoirs in Yellow River. Generally, the sedimentation in reservoir is always saturated and unconsolidated. The pore water will not be drained when the water level is rapidly dropped. Under this condition, the interior friction angle of the sediment is approximately equal to zero, so that the shear strength of soil is approximately only dependent on the bounding coefficient of the soil. If the sliding force due to water level dropping is higher than the shear strength the movement of sediment will occur. In case the erosion resistance of the sedimentation is high the retrogressive erosion of the river may concentrated to the main stream and forming a deep channel. The elevation difference between the floodplain and deep channel results in the sliding of the sediment towards the main channel and forms the high-concentrated sediment flow.