Effects Of Soil Bioengineering Techniques Applied In Riverbank Ecological Restoration

River construction and management plays an important role in social and economic development of China. The main reason for the river system degradation is construction engineering designing. In the past, rubble stone, dry stone, cast-in-place concrete, precast concrete were used in river construction engineering. The river cross section was designed singularity. These methods caused the river natural attribute disappeared. Nowadays, river ecological restoration developed quickly in Beijing. According to the key problem existed in the degraded river ecological restoration, the paper introduce soil bioengineering techniques to Beijing area. The research results will apply a new river restoration method for Beijing and supply a reference and theory basement for soil bioengineering application in Beijing and other areas in China.In order to select suitable plants for soil bioengineering construction in Beijing,8 different kinds of plant materials were selected. The research content include plant material suitability, root characteristics and soil reinforcement, stem flexibility were studied. Meanwhile, in order to evaluate the suitability of soil bioengineering techniques used in Beijing,6 different techniques were applied in three river reaches in Huairou district, Beijing. At last, the environment effects of soil bioengineering were researched. The main research resuts show below:1. The suitability and root characteristics research results of Populus canadensis Moench, Salix alba var. Tristis, Salix purpurea, Salix matsudana cv Umbraculifera Rehd, Vitex negundo var. heterophylla and Amorpha fruticosa L. show that:considering survival rate, Vitex negundo var. heterophylla had no plant survival, Amorpha fruticosa L. survival rates were under 20%, Populus canadensis Moench, Salix alba var.Tristis, Salix purpurea, Salix matsudana cv Umbraculifera Rehd survivial rates reached up to 90%; considering shoots development, Populus canadensis Moench developed fast than other plant materials, Amorpha fruticosa L. shoot had the lowest development; considering root biomass development, Amorpha fruticosa L.> Salix matsudana cv Umbraculifera Rehd.> Populus canadensis Moench> Salix purpurea> Salix alba var.Tristis.2. The pull-out research results of Salix matsudana cv Umbraculifera Rehd, Amorpha fruticosa L., Populus canadensis Moench, Salix purpurea and Salix alba var.Tristis show that:Salix matsudana cv Umbraculifera Rehd had the highest pull-out force, its had the highest soil reforcement ability; the pull-out force between Amorpha fruticosa L., Populus canadensis Moench, Salix purpurea and Salix alba var.Tristis had no significant differnce. All morphological characteristics of Salix alba var.Tristis had no significant correlation with maximum pull-out force (P>0.05). The shoot biomass and root number of Salix matsudana cv Umbraculifera Rehd, Amorpha fruticosa L., Populus canadensis Moench and Salix purpurea had significant correlation with maximum pull-out force (P<0.05).The results from 1 and 2 show that:Salix matsudana cv Umbraculifera Rehd is the best plant material for soil bioengineering techniques, then are Populus canadensis Moench, Salix purpurea, Salix alba var.Tristis and Amorpha fruticosa L.. Vitex negundo var. heterophylla is not suitable used for live staking.3. The pull-out research results of 4-year Salix alba var.Tristis live staking and young age Salix matsudana Koidz show that:both plants had significant correlation between plant height, basal diameter and maximum pull-out force.4. The bending test results of Salix alba var.Tristis, Salix matsudana Koidz, Amorpha fruticosa L. and Vitex negundo var. heterophylla show that:from the mechanical point, Salix alba var.Tristis and Amorpha fruticosa L.are the best soil bioenigeering plant materials, then is Salix matsudana Koidz, Vitex negundo var. heterophylla is at last.5. From the response of soil bioengineering techniques applied in three river reaches, the results show that:soil bioenigeering techniques as live staking, bush mattress, live fascine, wattle fence, rooted cutting and vegetated riprap are all suitable used in Beijing river bank restoration; Salix alba var.Tristis are not suitable used as rooted cutting techniques in moisture serious absence river riparian area; Salix cheilophila live staking in diameter "1.5cm～3.0cm" developed better than other two diameter "1.0～1.5 cm" and "3.0～5.0 cm". Salix alba var.Tristis live staking in diameter "3.0～5.0cm" developed better than other two diameter "1.0～1.5 cm" and "1.5～3.0 cm". Vitex negundo var. heterophylla could be applied for rooted cutting techniques, however, its shoots had the poorest development; Amorpha fruticosa L. developed as well as Salix alba var.Tristis used in live staking, but its root grown faster than the last one.7. The research results of soil bioengineering environment effects show that:soil bioengineering had significant runoff delay effects and soil intercept effects; set up plants on near water area could improve human comfort degree; soil bioengineering caused water level elevated remarkably, water level elevated higer with vegetation coverage area increased.