Sediment transport mechanisms and selective removal of soil particles under unsteady-state condition

• 作 者: Elham Sirjani Majid Mahmoodabadi Artemi Cerdà
• 机 构: Department of Soil Science,Faculty of Agriculture,Shahid Bahonar University of Kerman,Kerman,Iran;De
• 出 处: 国际泥沙研究（英文版）
• 发表日期: 2022年2期
• 关键词: Aggregate breakdown Bed load Stream power Suspension-saltation Tilting flume

Selective removal of particles and nutrients by water erosion is a key factor in soil erosion studies.Most agricultural soils are located on gentle slopes where fertility is high;however,until now,the main attention on sediment transport mechanisms was paid to high-slope gradients,where soil erosion is intense,but soils are less productive.Despite the importance of sediment size distribution (SSD) and transport mechanisms under unsteady-state conditions,few studies have been done on this issue.Higher sediment concentrations in the early stages of the runoff indicate the need to deal with unsteady-state conditions.To address this issue,sheet erosion experiments were done using a 0.2 m by 1 m tilting flume under controlled laboratory conditions.Six inflow rates (75,100,125,150,175,and 200 mL/s) were applied on two contrasting soils,including an adjacent agricultural soil and a not cultivated soil (namely Cropland soil and Control soil,respectively) at two low slope gradients (1.5％ and 2％).No rill formation was observed during the experiments.The sediment-laden runoff was sampled during unsteady-state flow to determine the SSDs and sediment transport mechanisms of eroded particles for unsteady-state conditions.The results indicated different trends in the selective removal of sediment particles depending on hydraulic conditions and soil aggregate size.The contribution of suspension-saltation (SS)to the total sediment load for the Cropland and Control soils varied from 22％ to 68％ and from 35％ to 59％,respectively,while up to 78％ and 65％ of soil particles were transported by bed load (BL),respectively.However,SS and BL indicated a reverse trend with stream power.The Cropland soil showed a single peak in the SSD at low stream powers because of the selective removal of fine particles (0.042 mm),whereas the SSD was shifted to a bimodal distribution at higher stream powers with the selective depletion of both fine (≤ 0.084 mm) and coarse (1.5 mm) particles.The Control soil experienced a unimodal SSD in a range of sizes between 0.109 and 0.175 mm for all stream powers.The findings of the current study highlight the need for further study on the erosion of low-slope agricultural soils,where small stream powers can remove fine and fertile soil particles.