【作者】 余国安；

【导师】 王兆印；

【作者基本信息】 清华大学 ， 水利工程， 2009， 博士

【摘要】 本文以我国西南山区小江支流吊嘎河为对象,通过野外观测和试验研究了山区河流推移质运动规律和河床结构对推移质运动的影响;以人工阶梯-深潭系统作为典型河床结构,研究了其对下切河流微地貌、水力特性及生态的影响。采用子-母槽坑测法测量推移质输沙率。设计制作推移质运动观测和视频采集装置研究河床结构不同发育条件下山区河流推移质运动规律。设计制作床面结构测量装置,实现河床结构发育程度参数SP的测量和量化,为分析河床结构发育程度与推移质运动之间的关系提供了基础。山区河流推移质输沙率在相同水流条件下可能相差数百到上千倍,一般汛前比第一次洪水后大,在输沙率-水流强度关系图上呈顺时针“绳套型”,其主要原因是汛前和汛期第一次洪水后来沙条件明显不同。来沙条件的不同也会使输沙量呈现显著的年际差异。山区河流推移质运动与河床结构的发育程度有密切关系,河床结构发育良好时,推移质输沙强度低,跃移运动是推移质输沙的主体;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主要方式;如果水流和来沙强度达到一定限值,可能发生层移质运动,此时滚动(滑动)输沙超越跃移输沙成为主要推移质输沙方式。推移质输沙和河床结构均消耗水流能量,两者相互制约,是一对矛盾统一体。对同一河段,在同等水流条件下,推移质输沙率和河床结构发育程度系数在对数坐标系下成线性负相关关系。野外试验表明,人工阶梯-深潭系统在稳定河床,改善河流生态上作用显著。人工阶梯-深潭系统布置后,吊嘎河试验段河床结构发育程度明显上升,推移质泥沙起动受到抑制,同时蓄积部分上游来沙,因而河床下切趋势得到有效控制。不同底质、流速和水深环境交替出现,在空间层次上塑造了多样性的水生环境,栖息地多样性指数从试验前的11上升到九个月后的42。随着水生栖息地环境提升,底栖生物密度和物种丰度分别从61.5个/m2、17种上升到5217个/m2、22种,水生生态明显改善。吊嘎河野外试验的已有结果表明,人工阶梯-深潭系统是一个值得继续探索的方法,对我国山区下切河流的治理具有参考作用。更多还原

【Abstract】 The dissertation studies the impacts of streambed structures on the bed load transport and effects of an artificial streambed structure on channel incision control and ecological restoration through two field experiments in the Diaoga River, a tributatry mountain stream of Xiaojiang River in Southwest China.One experiment was conducted to investigate the bed load transport under unsteady flow conditions. The bed load transport rate was measured with a double-box pit trap sampler and the motion of bed load particles were observed by using a video-capturing instrument in a flume buried within the channel bed. The streambed structure was quantified by using a parameter SP, which was measured with a specially-designed instrument.The flow discharge and sediment transport respond well to the rainfall process in mountain stream, showing the feature of“drastic increase and dramatic fall”. Bed load transport rate may be thousands times less after the first flood of the year than before under the same flow conditions, and the bed load transport rate versus stream power diagram shows a clockwise looped curve. The difference of incoming sediment also causes distinct discrepancy of total annual bed load between years.The bed load transport and the development degree of streambed structures in mountain streams is closely interrelated with each other. For streams with well-developed streambed structures, bed load transport rate is low, and particles moves mainly in saltation. For streams without streambed structures, both contact load motion and saltation load motion occur; and if the flow intensity and incoming sediment reach a critical high value, laminated load motion may occur and be the main part of bed load transport. Both the bed load transport and streambed structures consume flow energy; they act as resistance to the flow and are inter-restricted. Given a 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. Step-pool system is the strongest bed structure in mountain streams on flow energy dissipation and bed incision control. In case of no naturally developed step-pool system, artificial step-pool system may be used. The second experiment was conducted by constructing an artificial step-pool system to study its effects on streambed incision control and aquatic ecology restoration. The experiment has been showing marked positive effects on these aspects. Initiation of bed particles have been controlled and bed load from upstream is partly stored in the experiment sections, therefore the stream bed incision in the experimental reach is effectively controlled, and consequently improves stream bed and bank slope stability. Different substrate, flow velocity and water depth environment alternating upstream steps and in pools creates spatially diversified stream habitats which enhances the development of the aquatic creatures. The habitat diversity index increases from 11 for natural channel to 42 nine months after the artificial step-pool system. The number density of individual benthic invertebrate and taxa richness (number of benthic invertebrate species) increased from 61.5/m2 and 17 to 5217/m2 and 22 respectively, indicating the stream ecology is obviously improved. The results of the field experiment show that, artificial step-pool system is worthwhile for further research, and is positive on restoration of incised mountain streams in China.更多还原