Hydrodynamic process of soil erosion in steep slope of engineering accumulation

Abstract: Soil erosion newly derived from engineering accumulation severely threatens ecological safety of construction sites and surrounding areas. It is of great necessity to carry out researches on hydrodynamic process of soil erosion originated from engineering soil deposits, and develop prediction model of soil erosion in production and construction areas. A set of field pouring water scouring experiments were conducted on the experimental plot with 72.7% gradient and 12-meter length, which lies in a steep slope of a typical spoil ground along the line of Shenfu freeway, to investigate the hydrodynamic process of soil erosion of the engineering accumulation. At the upper slope of runoff plot, a watering system consisting of submersible pump, water segregator, valves, flowmeter，overflow tank and impermeable fabric was set up achieve desired discharges. Inflow discharges were designed according to calculated unit discharge occurred on experimental plot under a certain rainstorm frequency and determined by pre-experiment. During the whole experimental process, 4 evenly spaced observation sections were down slope arranged to conduct soil sampling, flow velocity measurement and water-crossing section observations. At the bottom of experimental plot, a bucket was designed to collect all the runoff and sediment, and take samples during different intervals at different stages of experimental process. The process of runoff producing and sediment yielding can be deduced and calculated from the water level recording in the bucket and samples. A single trial persisted 40-50 minutes. Preliminary result reveals that: 1) relationships between flow shear stress, stream power, flow kinetic energy and soil detachment rate under sheet flow erosion all can be expressed by linear equation, except that effects of unit stream power and unit energy of water-carrying section on sheet flow erosion rates are not significant; 2) soil detachment rate under rill erosion conditions can be described with log-linear equation of runoff kinetic energy, and also linearly relates to flow shear stress, stream power, and unit energy of water-carrying section respectively; 3) stream power is the best hydrodynamic parameter simulating changing trend of soil detachment, and should be the power source of slope erosion; 4) critical unit stream power for rill erosion is 3 N·m-1·s-1, the value of rill erodibility parameter is 8×10-3 s2·m-2. In terms of fitting effect, the parameters tested should be ranked in the order of stream power>runoff kinetic energy>flow shear stress>unit energy of water-carrying section>unit stream power for sheet flow erosion, and stream power>unit energy of water-carrying section>unit stream power>flow shear stress>runoff kinetic energy for rill erosion, which indicates that mechanics parameters and energy parameters have different advantages on descriptions of dynamic process of soil erosion in steep slope of engineering soil deposit, which should be determined on practical considerations instead of lumped together. The result obtained may lay the foundation for the establishment of process-based model of soil erosion initiated by engineering accumulation, and provide scientific guidance for comprehensive control of newly arising soil & water loss in production and construction areas.