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PurposeSediment transport plays a vital role in the development of soil erosion process models. The primary purpose of this study is to establish new sediment transport capacity formulas and evaluate their applicability to sediment.Materials and methodsIn this study, we collected three different soil types from Loess Plateau. Simulated sediment transport experiments were carried out in indoor flumes with energy gradients ranging from 6.9 to 20.8% and unit flow discharge rates ranging from 0.00014 to 0.00111 m2 s−1.Results and discussionWe found an exponential relationship between sediment transport capacity, energy gradients, and unit flow discharge rates. The sediment transport capacity increased with increasing energy gradient and unit flow discharge, and the unit flow discharge had a more significant influence on sediment transport capacity compared with energy gradient. We used each composite force predictor and measured the sediment transport capacity according to the nondimensional principle, and the resulting data corresponded to different soils distributed in zones, as sediment transport capacity is controlled by a critical starting condition. After including soil clay particle content and volume sediment content in our formula, we were able to derive an accurate equation for calculating sediment transport.ConclusionsAmong the dimensionless composite force predictors, the dimensionless effective stream power was the most reliable predictor. The sediment transport capacity and effective stream power were related exponentially (R2 = 0.953).

Critical depth is an essential parameter for the design, operation, and maintenance of conduits. Circular, arched, and egg-shaped sections are often used in non-pressure conduits in hydraulic engineering, irrigation, and sewerage works. However, equations governing the critical depth in various sections are complicated implicit transcendental equations. The function model is established for the geometric features of multiple sections using the mathematical transform method and while considering non-dimensional parameters. Then, revised PSO algorithms are implemented in MATLAB, and the right solution’s formula for the critical depths in various non-pressure conduit sections is established through optimization. The error analysis results show that the established formula has broad applicability. The maximum relative errors of the formula for critical depths are less than 0.182%, 0.0629%, and 0.170% in circular, arched, and egg-shaped sections, respectively, which are more accurate than those of existing formulas; the form of the formula proposed in this work is also more compact than that of the existing formulas. The results of this research may be useful in design, operation, and maintenance in conduit engineering.

Existing research on soil erosion primarily focuses on the individual effects of factors such as rainfall intensity, slope gradient, grass cover, and soil characteristics, with limited exploration of the interactions among these factors. This study investigated the mechanisms of soil erosion on overland covered with vegetation in the Loess Plateau region through indoor artificial simulated rainfall experiments. The experiments included six levels of grass coverage (0, 30%, 40%, 50%, 60%, 70%), five grass distribution patterns (DP, CP, VP, SP, HP), five rainfall intensities (60, 80, 90, 100, 120 mm/hr) and three slope gradients (5°, 10°, 15°) to explore the effects of experimental design factors and hydraulic parameters on the overland soil erosion mechanisms. The results show that as the grass coverage increases, the soil erosion rate on the overland decreases. Under different grass distribution patterns, horizontal grass distribution played an important role in inhibiting overland soil erosion rate. The overland soil erosion rate increased following a power function relationship with rising slope steepness and rainfall intensity, with erosion rates being more sensitive to changes in rainfall intensity than slope gradient. Among the six hydraulic parameters, dimensionless stream power was the optimal hydraulic parameters for predicting overland soil erosion rate under grass cover. Furthermore, an overland soil erosion model under the influence of grass cover and rainfall intensity was established based on general dimensionless hydraulic parameters (KGE = 0.931, R2 = 0.912). The model satisfactorily simulates overland soil erosion rate under grass cover and helps to reveal the mechanism of overland soil erosion. Plain Language Summary Grass cover has a complex influence on overland soil erosion. This study quantified the impact of grass cover on overland soil erosion using a dimensionless water flow path index. It systematically analyzed the response mechanism among overland soil erosion, slope gradient, rainfall intensity, and hydrodynamic parameters, aiming to identify the optimal hydrodynamic parameters capable of characterizing overland soil erosion. A predictive model for soil erosion was constructed based on general dimensionless water flow intensity parameters, comprehensively evaluating the mechanism of soil erosion on grass‐covered overland under simulated rainfall conditions. The results indicate that the model constructed using dimensionless parameters exhibits strong adaptability and can be effectively validated in other experiments. Key Points Systematically analyze the response mechanism of overland soil erosion concerning experimental design factors and hydrodynamic variables Dimensionless stream power is the most effective hydrodynamic parameters for predicting overland soil erosion under grass cover Develop an overland soil erosion prediction model using general dimensionless flow strength parameters

The rapid expansion of construction land has been a common phenomenon worldwide, which resulted in the loss of high-quality arable land and severe land degradation. Here, a statistical analysis, together with a field investigation, was carried out in China to address the challenges. This study has gathered data on the reduction of land amount and quality caused by construction activities and has collected the relevant policies to control land deterioration caused by those activities. The increasing amount of farmland and open space are occupied by construction use. The annual growth of construction land from 2001 to 2017 was 43.64 × 104 hm2, with an annual average of about 38 × 104 hm2 of cultivated land being converted to construction land in China. Construction activities usually cause a deterioration of the physico-chemical properties in and around construction site soils. The organic matter of post-construction soil was lower than the pre-construction by 257.4~879.8%. A lack of strong economic incentives for developers, limited effectiveness of measures to control land degradation, and weak requirements and enforcement of relevant laws and regulations allow land degradation from construction activities to remain at a significant level. For more efficiency and success, the study proposes effective measures to control the hazards that occur so widely in China.

Overland flow is the initial driver of slope surface erosion. To discover resistance characteristics of overland flow influenced by rainfall intensity and roughness, indoor simulated rainfall experiments with six kinds of roughness, five flow discharges, and five rainfall intensities were investigated. Results showed that overland flow over rough surfaces could be considered as laminar and turbulent flow when using flow Reynolds number. According to roll waves observed, flow regimes belonged to the laminar transitional zone based on the viscosity-to-depth ratio. A critical water depth formula for overland flow was re-derived, and it showed that this test water flow consisted of supercritical flow in most cases, and subcritical flow in only a few cases. The flow resistance coefficient increased with increasing roughness, whereas it decreased as rainfall intensity increased. Considering the ‘increasing resistance’ phenomenon, this study focused on frictional resistance, thickness of the viscous sublayer, pressure drag and roll waves. Finally, a formula for sheet flow resistance was proposed based on resistance segmentation and multi-element linear regression. These findings are of significance both for understanding the characteristics and development of overland flow and overland flow dynamics.