非恒定流条件下宽级配推移质输沙机理试验研究

Response mechanism of bed load transport with a wide size distribution under unsteady flow condition is a key scientific issue for the understanding of mountain river bed load transport mechanism. Several experimental methods are adopted in this study, including simulation of the floods in mountain rivers, artificial flood peaks released from hydro-junction, and clear water scouring under unsteady flow. This research takes bed load transport with a wide size distribution as the subject, measures the dynamic changes of hydrodynamic parameters, and response process of bed load transport with different sizes and of grain-size distribution adjustment of bed sediment under unsteady flow and bed load transport experiments, and analyzes the change law of near-bed flow velocity and bed shear stress under unsteady flow, and the effect of unsteady flow on movement of coarse and fine sediment and coarsening of bed sediment. The study, through the construction of armor layer under steady flow, measures bed load transport rate variation in unsteady clear water, and reveals the dynamic response of sediment movement in armor layer against rising and falling process of unsteady flow. Response mechanism of bed load transport with a wide size distribution under unsteady flow condition is illustrated according to the response process of unsteady flow and coarse and fine sediment movement, which promotes the development of bed load transport theories and provides scientific evidence for predicting downstream channel evolution of mountain rivers below the hydro-junction.

宽级配推移质运动在非恒定流条件下的响应机制研究是认识山区河流推移质输沙机理的关键科学问题。本研究采用模拟山区河流洪水波及水利枢纽下泄"人造洪峰"和非恒定流清水冲刷等试验手段，以宽级配推移质为研究对象，量测非恒定流及推移质输沙试验中水动力参数的动态变化过程以及不同粒径大小推移质输移和床沙级配调整的响应过程，分析非恒定流作用下近底流速及床面切应力的变化规律，非恒定流对宽级配推移质中粗细泥沙颗粒运动及床沙粗化的影响；通过恒定流条件下构建的粗化层，量测非恒定清水作用下输沙率变化，揭示粗化层内泥沙颗粒运动对非恒定流涨落过程的动力响应。从非恒定流及粗细颗粒运动的响应过程阐明非恒定流条件下宽级配推移质输沙机理，以推动推移质泥沙运动理论的发展，为预测山区河流枢纽下游河道演变趋势提供科学依据。

当前我国大部分山区河流已相继梯级化，水利枢纽对河流的人为调节，使得河道内水流在洪中枯水期均呈现显著的非恒定性，引起山区河流宽级配床沙复杂的输移过程，研究宽级配推移质运动在非恒定流条件下的响应机制是认识山区河流推移质输沙机理的关键。本项目采用理论分析结合水槽试验的手段，研究了非恒定流作用下近底流速及床面切应力的变化规律，宽级配推移质输移及床沙粗化对非恒定流的响应机理以及粗化层泥沙运动在非恒定流条件下的动力响应。主要成果如下：（1）非恒定流条件下近底流速、床面切应力随来流涨落而变化，且先于水深达到峰值，同水深条件下，涨水期近底流速、床面切应力大于落水期，涨水期水流对床面切应力的累积作用（冲量）强于落水期，涨落水期冲量之比随非恒定强度的加大而线性增加。（2）下泄径流量相同的泄水波，水流非恒定强度愈强，冲刷他移级配愈粗于初始床沙级配，输沙量也越大，宽级配床面愈难趋于粗化稳定，提出了非恒定泄水波作用下宽级配推移质输移量的经验公式。（3）非恒定流强度越强，已形成的稳定粗化层越容易发生破坏；床面粗化程度越高，在非恒定流作用下的输沙量越小。.研究成果对于推动推移质泥沙运动理论的发展具有重要意义，同时对预测山区河流枢纽下游河道演变趋势，指导受枢纽泄流影响下的河道治理等具有重要的生产实用价值。