Hydraulic erosion tests on river bank slope units in middle and lower reaches of Yangtze River

The river banks in the middle and lower reaches of the Yangtze River are facing severe hydraulic erosion. To explore the hydraulic erosion characteristics of bank slope soils, the single face soaking-immersion erosion tests and lateral erosion tests by flowing are conducted. By analyzing the morphology of erosion gullies, measuring the mass of single units, investigating the lateral depth and height loss by flowing erosion and studying the influences of roots and grid-vegetation layers on the erosion and destruction of soil units, the feasibility of using tree roots combined with grid-vegetation layers to prevent erosion on the bank slopes is studied. The test results show that both wetting erosion and flowing erosion jointly cause the erosion and destruction of bank slope soils. With the increase of the water depth, flow velocity and erosion time, the lateral depth and height of the lost unit by flowing erosion continuously increase. Under the small unit size of the tests, the effects of simulating roots with coarse tree roots on reducing the erosion and destruction of units are limited. The preferential flow effects of root-soil gaps actually increase the lateral erosion depth to some extent. The anchoring effects of roots on cohesive soil are significantly stronger than those on sandy loam, which can delay the collapse of the upper soil. After setting up the grid-vegetation layer, the lateral erosion depth of the unit can be effectively reduced, and the erosion resistance effects are significant. The research results can provide reference for ecological bank protection.