山区河流河床形态与水沙变化下的水位响应机理研究

山区流域暴雨山洪、滑坡、泥石流等灾害频发，大量泥沙以不同方式进入河道，河床形态在极短时间内迅速调整。在宽窄相间河段水流输沙能力差异较大，展宽段常因挟沙能力的降低而淤高河床，致使水位陡增，引发洪水灾害。为探讨山区河流宽窄相间河段与泥沙补给变化下的水位变化致灾机理，以室内物理模型系列试验结果为依据，分析不同流量定床清水时河床形态参数与各水力参数的变化关系，以及泥沙补给变化对河床形态及水流参数的影响。试验表明：上游泥沙补给量及河床形态是影响水流流态、水位变化的重要因素；定床清水条件下，河宽与比降的局部急剧调整影响水流参数变化，水流对河床变化的响应具有滞后性；当上游有泥沙补给时，水深变化较清水来流明显；随着来沙量的增大，大量泥沙淤堵河道且呈现溯源淤积的趋势，并淤高河床；在淤积段顶端，水流发生水跃现象，水位陡增，甚至出现漫滩致灾。由此可见，上游来沙及水流挟沙能力的降低将引起河床不同程度的落淤，造成河床形态改变，特别是在宽窄相间河段泥沙易落淤，水位增幅较大，为洪灾泛滥区，应作为水沙灾害的重点防治区域。

Study on Water Level Response to River Morphology and Sediment Supply in Mountain Rivers

Due to the frequent occurrence of heavy rainfalls,landslides and debris flows in mountain regions,a large amount of sediments enter into rivers in different ways,silt up riverbed and change the river pattern,especially in wide-narrow reaches which cause water level to increase sharply and induce flood disasters.In order to study the mechanism of water level change under different river morphology and sediment supply changes in mountain rivers,the experiment was conducted.The correlation between the hydraulic parameters,the river morphology and the sediment supply was discussed.The experimental results showed that the hydraulic parameters were affected by river width and riverbed gradient under clear-water condition and the response of water flow to riverbed change was delayed.The sediment supply affected river morphology and further affected the flow parameters.The water depth changed more obviously compared to the clear-water condition.With the sediment supply being increased,more sediments silted in the riverbed,raised the riverbed towards the upstream.At the top of the siltation,a hydraulic jump was found to occur accompanied with a sharp increase of water level,leading the water up to the floodplain.Thus,the upstream sediment supply exacerbated the riverbed elevation,especially in the wide-narrow regions,where sediment was easily silted and water level increased steeply causing flood to occur.The flow-sediment disasters prevention should be the focus of these areas.