Quantitative Study On The Erosion Process Of River Bank Under The Influence Of Vegetation Roots

Desert riparian vegetation plays an important role in reducing riparian erosion and preventing soil erosion.In order to explore the quantitative impact of different root system characteristics on the river bank scouring process,the local dominant shrub Tamarix ramosissima and arbor Populus euphratica root system were selected as the research object.Through the indoor generalized water tank test,the quantitative effects of different root system characteristics on the river bank scouring process in different soils were revealed.It provides a supplement for basic research on riparian erosion under the influence of desert vegetation roots in arid areas.The main conclusions are as follows:（1）In the case of non-cohesive river banks,the main types of bank collapses are landslides.The collapse forms mainly include collapse,tensile and shear failure.The collapse mechanism is that the upper soil layer’s suspension width reaches a critical value and then rotates.Collapse;in the presence of vegetation,collapse is mainly caused by collapse.The mechanism is that small vertical cracks first appear at the top of the bank slope,and then the root-soil cement block collapses along the crack surface,mostly flat sliding failure.The mechanism of bankruptcy of the sticky river bank under the action of the root system is that small grooves are formed at the foot of the slope,and the root-soil bond on the upper part of the groove collapses along the slippery surface,and arc sliding failure often occurs.（2）The effect of the root network on the riparian soil consolidation is significant.In non-cohesive river banks,the soil-fixing capacity of the river banks has increased by 18%to 45%;in cohesive river banks,the soil-fixing capacity of the river banks has increased by 30%-56%.There is a logarithmic relationship between non-cohesive bank collapse and root surface area density(R_SAD);the relationship between cohesive bank collapse and root surface area density(R_SAD)decreases first and then increases.the trend of.Between the non-cohesive river banks and the same planted root system,the V-shaped root network acts more than vertical roots.The soil-fixing effects of the Tamarix ramosissima and Populus euphratica roots increased by 105.3%and 118.7%,respectively.Among different vegetation root systems,under the same vertical and V-shaped root shape Compared with Populus euphratica,Hongliu increased by39.6%and 30.4%respectively.Compared with Populus euphratica,the root-fixing effect of Tamarix ramosissima increased by 35.1%on average.Under the same plantation on the sticky river bank,the V-type root network acts more than vertical roots.The soil-fixing effects of the Tamarix ramosissima and Populus euphratica roots increased by 27.1%and 18.6%,respectively.Under different vegetation in the same vertical and V-shaped form,the Tamarix ramosissima were compared to Populus euphratica It increased by19.6%and 28.1%,and the soil-fixing effect of the Tamarix ramosissima root system increased by 24.2%on average.（3）The effect of root guarding has a significant impact on the nearshore flow field.The average velocity in the mainstream direction has gradually changed from an order of magnitude greater than the lateral and vertical velocity to the same order of magnitude.Under non-cohesive riparian roots,the near-shore water flow velocity decreases by 0.2 to 0.33 times without roots;in viscous riparian banks,it decreases by 0.45 to 0.67 times,and its turbulent energy decreases by 0.75 to 0.91 times.（4）The accumulation of bank collapses at the foot of the slope under the action of the root system is a triangle,and the slope of the triangle is basically equal to the underwater repose angle of the sediment;compared with the bank without roots,the bank of the bank with the root system after the bank collapses,The proportion increased significantly.The decomposition rate of the root soil cementation/bonding collapse body in the river channel is the Tamarix ramosissima root soil cementation/bonding body<Populus euphratica root cementing/bonding body<plain soil.（5）During the decomposition process of non-cohesive riparian soil cement,the V-type root’s pulling protection is better than vertical roots;the root system’s traction protection coefficient of the riverbed in the riparian banks can be estimated according to 1.15².52 in practice.The stronger the root pulling action in the cohesive river bank,the longer the root-soil bond is decomposed;the pulling action of the Tamarix ramosissima root system is greater than that of the Populus euphratica root,and the contribution of the root system to the riverbed protection has increased by about 20%on average.The cumulative sedimentation rate on the riverbed is positively correlated with the root length density(R_LD).The greater the root length density,the greater the cumulative sedimentation rate and the greater the amount of sedimentation on the riverbed.