Search

Land use and rainfall are two important factors affecting soil erosion processes. The red soil region of southern China is a representative region with high rainfall amounts and rapidly changing land use patterns where the water erosion process is sensitive to changes in land use and rainfall. To comprehensively understand the water erosion response to land use and rainfall in this region, a 6-year in situ experiment based on eight plots (bare land and seven typical land uses) was conducted from 2015 to 2020. The 320 rainfall events were divided into 4 types, and there were 3 main rainfall types. The runoff of different rainfall types was primarily determined by the rainfall amount, while the soil erosion of different rainfall types was primarily determined by the rainfall intensity. High-intensity rainfall contributed the most to both total runoff and soil erosion. Compared with bare land, the seven typical land uses reduced runoff and soil erosion by more than 75%. Grassland, cropland, and forest with low vegetation coverage experienced high runoff and soil erosion, while shrubland most effectively reduced runoff and soil erosion. The combination of land use and rainfall type significantly affected the annual average runoff depth, soil erosion modulus, and soil loss coefficient. Rainfall types can change the relationship between runoff and soil erosion for different land uses. The runoff and soil erosion of bare land were highly correlated with rainfall characteristics, while vegetation weakened this relationship under short- or moderate-duration rainfall. To effectively reduce water erosion, high-intensity rainfall should receive special attention, and all land uses should ensure that vegetation is well developed, especially understory vegetation. [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicle (UAV)-based nap-of-the-object photogrammetry techniques can be utilized to periodically monitor the erosion of nearly vertical cliffs. However, the broader applicability of such techniques is hindered by the necessity of deploying multiple ground control points around collapsing walls. This study aims to accurately assess Benggang erosion before and after the rainy season by analyzing the optimal flight proximity distance using close-range photogrammetric techniques. The assessment centers on positioning accuracy, point cloud data, and digital surface model (DSM) data. Nap-of-the-object photogrammetry techniques are integrated with control-free image methods to conduct aerial surveys of Benggang, generating high-resolution three-dimensional (3D) DSMs. The feasibility of this control-free-image-based nap-of-the-object photogrammetry technique is evaluated based on positioning accuracy and measurement errors, comparing the generated DSMs with real-time kinematic (RTK) measured coordinate data. The results indicate that a flight proximity distance of 20 m is optimal for obtaining data in the Benggang area using control-free-image-based nap-of-the-object photogrammetry. This scheme yields an average reprojection error of approximately 0.01 pixels in data processing before and after rainfall, showing strong consistency in the spatial distribution of the two-stage 3D models. The mean absolute error in planar accuracy is between 0.01 m and 0.02 m, and that in elevation accuracy is approximately 0.03 m, with the lowest errors reaching the millimeter level. Therefore, control-free images combined with nap-of-the-object photogrammetry techniques can meet relevant demands for monitoring landslide erosional areas, providing technical support for extensive, safe, and efficient Benggang erosion monitoring. [ABSTRACT FROM AUTHOR]

A precise estimation of sediment transport capacity (Tc) is key to establishing process‐based erosion models. However, few data are available for estimating transport capacity on steep slopes and test materials sorted at high coarse grain values of >2 mm. Colluvial deposits with loose, coarse material and steep slopes make up the packed materials underlying the collapsing walls in benggang, which collapse due to hydraulic pressure and gravity. The objectives of this study were to investigate how flow discharge and slope steepness affect Tc and to examine relationships between Tc and flow velocity, shear stress, stream power, and unit stream power for colluvial deposits found on steep slopes. A nonerodible rill flume of 4 m long and 0.12 m wide was used. Slope steepness values ranged from 18% to 84%, and unit flow discharge values ranged from 0.56 × 10−3 to 4.44 × 10−3 m2 s−1. Tc increased as a power function with flow discharge and slope steepness with a Nash–Sutcliffe model efficiency (NSE) value of 0.99, and the effects of flow discharge were stronger than those of slope steepness. Tc was overestimated for a colluvial deposit when the equations of the ANSWERS, Zhang et al. and Wu et al. models were considered and when Tc exceeded 5 kg m−1 s−1, as the slope steepness used in our study was much higher than those used (<47%) in the other models. Regression analyses show that Tc can be predicted from linear equations of flow velocity, stream power, and unit stream power, and Tc can be fit to shear stress with power function equation. Flow velocity optimizes to predict Tc with NSE = 0.97, and stream power and shear stress can also be successfully related to Tc (NSE = 0.91 and NSE = 0.81, respectively); however, unit stream power performs poorly (NSE = 0.67). These results provide a basis for establishing process‐based erosion models on steep colluvial slopes. [ABSTRACT FROM AUTHOR]

Eroded sediment is an important feature of permanent gully's development; however, obtaining the specific characteristics of the sediment transport in the gully can be difficult. Thus, a composite fingerprinting technique, incorporating uncertainty analysis, has been employed to investigate the mean relative contribution of sediment sources in permanent gullies. In this study, 31 tracers were measured at 62 different sampling sites from three layers of a gully wall [surface layer (SL), sandy soil layer (SSL), and semi-weathering rock layer (SWL)] and 36 sediment samples from the slumping deposit and alluvial fan of the gullies. The sediment source tracing procedure was therefore used to assess the relative contribution of each source. The mean relative contribution from the SL to the sediment of the slumping deposit is higher in the active gully (G1), and is relatively lower in the potentially stable (G2) and stable gullies (G3); thus there was no obvious gully bank retreat in G2 and G3. In different places of the G1 alluvial fan, the mean relative contribution of the SL, SSL and SWL ranged from 9–11, 36–43 and 46–55%, respectively. However, the sediment contribution of the SL increased in G2 and G3 due to the changes in the erosion type. The mean relative contributions of the SL were 33 ± 5 (G2) and 30 ± 3% (G3). These findings have important implications for the establishment of a scientific basis for permanent gully sediment transport management and control policies. [ABSTRACT FROM AUTHOR]