刚性植被区域床面泥沙起动特性

为研究植被环境中床面泥沙起动特性，以天然河道中的植被及沙床为原型，对刚性植被环境中床面形态变化及泥沙起动规律进行了试验研究，并采用单位床面空间平均流速表述植被环境中泥沙的起动流速。研究结果表明，淹没植被条件下动床床面泥沙运动可分为3个阶段，即静止、部分起动及全部起动阶段，定义第3个阶段为刚性植被环境中泥沙起动的标准；推导的淹没刚性植被环境中的泥沙起动流速半经验函数关系式可以表述植被环境中泥沙起动特性，其中植被因子F_v对泥沙起动的影响最明显；植被密度一定时，植株周围冲坑深与空间平均流速成线性关系。研究认为采用植被环境中单位床面空间平均流速表述泥沙起动特性的方法是可行的。

Sediment incipient motion on movable bed in rigid vegetation environment

Vegetation in open channels has a significant influence on the characteristics of bed load movement. To date, studies of incipient motion of sediment in open channels with submerged vegetation have been restricted by limitations in statistical approaches and measuring equipment. Researchers have also neglected incipient motion of sediment in the presence of vegetation when deriving semi-empirical equations for the rates of bed load transport, and have generally considered it the same as that without vegetation, which is clearly inconsistent with, and does not represent, the actual conditions. In this study, we therefore studied the vegetation and sandy bed in a natural river to determine the characteristics of incipient motion of sediment within rigid vegetation on a movable bed. From the spatially averaged velocity, we then described the incipient motion of sediment under the water-vegetation interface. We found that there were three phases of incipient motion of sediment, namely static, partially in motion, and entirely in motion. We defined the incipient motion of sediment from the conditions for the third process. We derived a semi-empirical equation for the sediment incipient velocity in the presence of submerged vegetation from our experimental results, and found that, of the factors explored, the vegetation factor F_v had most influence on the incipient motion velocity of sediment with vegetation. For a given vegetation density, the average depth of the scour holes around the vegetation elements were linearly related with the spatially averaged velocity of the flow under the water-vegetation interface. These results demonstrate that our method gave reasonable estimates of the spatially averaged velocity for incipient motion of sediment.