山区河流植被洲滩河段水沙运动特性试验研究

Experimental Study on Characteristics of Water and Sediment Movement in Vegetated Beach of Mountainous Rivers

山区河流受水沙条件和河流形态影响,植被洲滩发育丰富,显著改变局部河段的水沙运动及其演变特征。基于室内洲滩模型自然生长植被的水沙试验,探讨了植被与泥沙补给对洲滩河段水流结构及冲淤变形的影响。试验结果表明:植被茎叶加大了对水流的扰动,减缓水流流速,上游补给泥沙在植被周围形成小型沙丘,以波状输移为主;大量来沙条件下,泥沙多落淤洲头及洲尾,促使洲滩快速发育;淹没植被枯萎,茎叶凋落,加剧洲头及洲滩两侧冲刷;植被与上游来沙显著影响洲滩汊道分流特性,加沙和植被茎叶促使左汊分流比降低。因此,山区河流植被与上游泥沙补给调整洲滩汊道过流能力及发育过程,对植被洲滩河段的水沙运动产生较大影响。

The complex water and sediment conditions and river form in mountainous rivers result in abundant vegetation covering the beach,which significantly changes the water and sediment movement and bed deformation characteristics.The experiments were conducted in a physical model with natural vegetation for studying the effects of vegetation and sediment supply on the river deformation and flow structure in the channel.According to the experimental results,it can be concluded that vegetation leaves increase the disturbance of water flow and reduce the flow velocity.When the upstream supply sediment occurs,the sediment is wavily transport in the vegetated beach,and form some small sand dunes around the vegetation zone,and most of the sediment is deposited at the head and tail of the beach.When the submerged vegetation withered,the stems and leaves are washed away,the flow washes the foot bases of the beach more intensely.Vegetation and sediment supply can adjust the flow division ratio of the branch.Sediment supply and vegetation reduce the diversion ratio of left branch.As a summary,vegetation and sediment supply significantly reduce velocity and thus have an important influence on the water-sediment movement,which accelerates the beach development and adjusts the flow division of branch.