Effect of riparian vegetation roots on development of meander bends in Tarim River, Northwest China

摘要

Meandering channel with distorted bends develops along the Tarim River, the longest dryland river in China. The river bank and bed is majorly composed of coarse silt and fine sand and almost none clay content, making the bank strength very low. The development of meander bend in such environment hence is somehow irrational. We preliminarily investigate the effects of riparian vegetation root on bend development in this region through examining the root cohesion and its enhancement on bank stability. In-situ measurements and sampling of roots from local typical riparian vegetation (i.e., populous, Tamarix, and Phragmites Australis) were conducted to obtain root parameters like diameter and root area ratio. Local bend curvature corresponding to sampling sites are also obtained. BSTEM model is used to quantitatively estimate the effects of different root conditions on improving channel bank strength. Four vegetation root scenarios were modelled, i.e., tree (populous), shrub (Tamarix), grass (Phragmites Australis) and no root. The results show that root supplies effective cohesive reinforcement for the channel bank and enhances the bank safety factors (F_s). Riparian vegetation should be a necessary condition for development of meandering channel in Tarim River.