山区河流推移质运动的野外试验研究

山区河流推移质运动与河床结构发育程度之间紧密联系,认识这种联系有助于揭示山区河流的推移质输沙规律。通过专门设计制作的推移质运动观测-视频采集系统和河床结构发育程度测量装置,对河床结构发育良好、部分发育及无河床结构(平整床面)三种典型床面条件的山区河流推移质颗粒运动进行了观测分析,并初步研究了推移质运动和河床结构发育程度的制约关系。试验发现,河床结构发育良好时,推移质输沙率很低,推移质输沙主要通过跃移运动实现;河床结构部分发育时,颗粒跃移强度上升,并逐渐有颗粒突破结构束缚,在床面滚动(间或滑动);无河床结构条件下,滚动(间或滑动)和跃移输沙均为推移质输沙的重要方式;如果水沙浓度达到一定值,可能发生层移质运动,滚动(滑动)输沙超越跃移输沙成为推移质输沙的主要方式。宏观上看,山区河流推移质输沙和河床结构发育程度之间相互制约。对同一河段,当水流功率不变时,推移质输沙率和河床结构发育程度之间在对数坐标下基本呈线性负相关关系。

Field experimental study on bed load particle movement in a mountain stream

Bed load transport in mountain streams is very difficult to be determined since it strongly correlates to streambed structure ( roughness structure ) . Based on a specially designed underwater observation and video-capturing system , experiments on bed load movement under three streambed structure development scenarios , i.e. , well developed , partially developed , and no streambed structures ( plane bed ), was conducted in a mountain stream in southwest China. Dynamic features of bed load transport ( starting mode , trajectory , velocity , and acceleration velocity ) under these three typical streambed conditions were observed and analyzed. The streambed structure development degree was measured by a specially manufactured instru ment to analyze correlation between bed load transport and streambed structure development. Bed load movement strongly depends on streambed conditions of mountain streams. For channels with well-developed streambed structures , bed load mainly move in intermittent saltation , and almost no other motion form occur , bed load transport rate is often very low under this condition. For channels with partially-developed streambed structure , saltation motion is still the main motion form , and contact motion also occurs. When no streambed structure develops ( plane bed ), both saltation and contact motion occur , contact motion gradually become the main motion form , and if flow intensity and incoming sediment reach the critical high values , laminated load motion occur and will be the main part of bed load transport. In essence , bed load transport and streambed structures both form flow resistance ( dissipate flow energy ) and are inter-restricted. For a specific stream power , the bed load transport rate is inversely proportional to the development degree of streambed structures in a logarithmic coordinate system for the same stream reach.