Study on the facilities and procedures for meltwater erosion of thawed soil

High erosion rate of seasonal thawed soils by snow-and ice-melting runoff in the high altitude and latitude cold regions has great impacts on ecological systems,industries,agriculture and various manmade infrastructures as well as people's lives.The facilities and procedures are of great importance for the studies on simulating erosion processes of melt-frozen soil.This study focuses on the method and facility for simulating the thawing process of frozen soil.The facility includes soil freezing system,meltwater supply system and experimental flume system for thawed soil erosion.The soil freezing system provides enough space to freeze soil columns in flumes.The water supply system deliveries snow-or icemelting water flow of constant-rate at 0℃.The soil flumes of 200 or 300 cm long,10 cm wide and 12 cm high are designed to be assemble and convenient for soil freezing before they are thawed in one-dimensional manner from top to bottom.The one-dimensional thawing process is realized as follows.The frozen soil flume is put on ice boxes and thermally insulated with heat-insulating materials all around to prevent frozen soil from being thawed from sidewalls and bottom.The soil thaws with this system shows that it can meet the requirements of simulating the process of soil thawing from top to bottom.The thawed soil flumes are connected from end to end to form rills of 6–8 m long to run the erosion experiments under different designed hydraulic condition.The equipment provides facility,method and operation process for simulating one-dimensional soil thawing to serve research on the effect of thawed soil depth on erosion process.

Measuring flow velocity on frozen and non-frozen slopes of black soil through leading edge method

Flow velocity is a major parameter related to hillslope hydrodynamics erosion.This study aims to measure flow velocity over frozen and non-frozen slopes through leading edge method before being calibrated with accurate flow velocity to determine the correct coefficient for convenience of flow velocity measurement.Laboratory experiments were conducted on frozen and non-frozen soil slopes with flumes involving four slope gradients of 5°,10°,15°,and 20°and three flow rates of 1,2,and 4 L/min with a flume of 6 m long and 0.1 m wide.The measurements were made with a stopwatch to record the time duration that the water flow ran over the rill segments of 2,4 and 6 m long.Accurate flow velocity was measured with electrolyte trace method,under pulse boundary condition.The leading edge and accurate flow velocities were used to determine the correction coefficient to convert the former to the latter.Results showed that the correction coefficient on frozen soil slope was 0.81 with a coefficient of determination(R2)of 0.99.The correction coefficient on non-frozen soil slope was 0.79 with R2 of 0.98.A coefficient of 0.8 was applicable to both soil surface conditions.The accurate velocities on the four frozen black soil slopes were approximately 30%,54%,71%,and 91%higher than those on non-frozen soil slopes.By contrast,the leading edge flow velocities on the frozen soil slopes were 23%,54%,67%,and 84%higher than those on non-frozen soil slopes.The flow velocities on frozen soil slopes increased with flow rate at all four slopes,but they increased from 5 to 15°before getting stabilized.Therefore,rill flow velocity can be effectively measured with leading edge method by multiplying the leading edge velocity with a correction coefficient of 0.80.This study provides a strategy to measure rill flow velocity for studies on soil erosion mechanisms.