Riparian vegetation's effects on the evolution of an experimental meandering channel driven by an upper vortex flow

Abstract

AbstractFew investigations of river evolution have incorporated the series of upper vortex flow disturbances induced by quasi‐knickpoints, and it is unclear whether the regulating ability of riparian vegetation in maintaining meandering channel patterns is valid. In this study, we therefore conducted meander evolution experiments to confirm the effects of vegetation species and vegetation strength on this complex system. Two nonleguminous plants with salinity and alkalinity resistance had non‐uniform degrees of normal seedling growth and different root network lengths. Our findings show that braided swales formed between the upstream developing zone of the vortex flow and the nearest bend and the riparian vegetation generally consolidated the single‐thread channel planform without branching outward under the conditions of flooding flow. Transverse point bars on inner banks were replaced by downstream scroll bars in the overall channel for long time, unless riparian vegetation and flood scour were coupled. Shallow‐rooted plants were inadequate to withstand the inner‐banks being cut by the upper vortex flow. Deep‐rooted plants can significantly stabilize bank lines and thalwegs but are vulnerable to locally low vegetation coverage. Using evolutionary spectral analysis based on thalwegs, we found that the streamwise high‐frequency distribution of bed topography was primarily concentrated downstream of the bifurcation interface when a flood was present in the unvegetated scenario, shrank to the isolated turning interface of the upper reach and the large‐scale spiral swale of the lower reach in the shallow‐rooted scenario and stood out along the area disturbed by bare roots in the deep‐rooted scenario. This experimental study broadens our understanding of vegetation effects in hydro‐bio‐geomorphological system engineering.