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By observing the processes of infiltration, flow generation, water flow characteristics and the spatial distribution of erosion in a designed rainfall test, and analyzing the infiltration, flow generation characteristics, water content change characteristics, soil moisture parameters change characteristics, and changes in the spatial patterns of erosion and sediment yield, this study draws the following conclusions: under different rainfall densities, the initial runoff generation time of sand-covered slope is 1~12 min longer than that of loess slope, the initial soil infiltration velocity of sediment-covered slope is about 1.23 times that of loess slope, and the time to reach stable infiltration of loess slope is shorter than that of sediment-covered slope. Under different rainfall densities, the rising time of the water content curve of sand-covered slope is earlier than that of loess slope. For the same duration of rainfall, the vertical infiltration performance of soil water of sand-covered slope is higher than that of loess slope, and when the rainfall density on the slope increases by 0.5 mm/min, the increase in runoff shear stress of the sediment-covered slope is about 1.5 times that of the loess slope, and the runoff power is about 1.13 times that of the loess slope. [ABSTRACT FROM AUTHOR]

In this study, two typical watersheds, i.e., the Dalihe watershed in the loess hilly-gully region of, and the Hailiutuhe watershed in the windy-sandy region of the Wudinghe Basin, were selected as study objects to evaluate the relationship between landscape indices and runoff and sediment, with the long-series data of runoff, sediment, and land use, using the GIS and Fragstats platforms. The results showed that between two watersheds showed that all of the contagion index, Shannon's diversity index, and patch cohesion index exhibited an ascending trend in the Dalihe watershed, and a descending trend in the Hailiutuhe watershed. In the Dalihe watershed, only Shannon's diversity index had a very significantly negative correlation with the runoff, whereas in the Hailiutuhe watershed, the contagion index had a significantly negative correlation with the runoff, and all of the Shannon's diversity index, the Shannon's evenness index, and the Simpson's evenness index had a significantly positive correlation with the runoff. In respect of correlation of sediment with landscape pattern, the sediment had a very significantly negative correlation only with Shannon's diversity index in the Dalihe watershed, whereas in the Hailiutuhe watershed, the sediment had a significantly negative correlation with all of the number of patches, the patch density, and the landscape shape index, and a very significantly positive correlation with the aggregation index. The importance of each landscape index in the regression equation and the positive or negative correlations indicated that erosion in watersheds could be reduced by strengthening the control function of the dominant patch, thoroughly improving the evenness of the landscape patch types, enriching the landscape types, reducing the physical connectivity between patches, and enhancing the degree of aggregation in landscape patches. [ABSTRACT FROM AUTHOR]

• Factors contribution to runoff, sediment in different seasons and spatial scales. • Contribution of precipitation and underlying surface to runoff and sediment. • Assess the group relationships between different types of influencing factors. The changes in runoff and sediment are the most active parts of river systems. Identifying the effect of precipitation, vegetation coverage (VC), landscape metrics, land-use and land-cover changes (LUCC) on runoff and sediment variations is essential for understanding hydrological processes and the environmental evolution mechanisms of watersheds. This study selected four watersheds located in the Qinling Mountains in China to quantify the effects of different driving forces on runoff and sediment variations at different scales. The results showed that VC increased significantly in the study watersheds (p < 0.05) by more than 16 % since 1990. Obvious increases in forest area were the main features of land use change after 2000. The annual sediment transport and sediment concentration in the wet season showed downward trends. The change of underlying surface contributed more than 58 % to reductions in runoff and sediment concentration in controlled watersheds in Xiangjiaping and Jingziguan. The factors influencing runoff and sediment variations displayed obvious spatial and temporal differences. The 2000 m buffer scale could better explain the runoff and sediment variations than other spatial scales. Rainfall and VC were the main factors affecting runoff and sediment variations at different spatial scales during the wet season, while the aggregation index at the watershed-scale and VC were the main influencing factors in the dry season. Moreover, the intersections between precipitation and landscape pattern, between precipitation and LUCC & VC, and between landscape pattern and LUCC & VC in the dry season and wet season were −31.9 %, −27.6 %, −29.0 % and −18.7 %, −11.1 % and −2.3 %, respectively. Therefore, multi-scale differences in the impact of driving factors and the group relationships between measures should be considered for effective runoff and sediment regulation. [ABSTRACT FROM AUTHOR]

Wind-water compound erosion is a complex process that affects 260,000 km in China. Understanding the effects of wind erosion deposition on water erosion is essential to soil and water conservation and ecological construction. In this study, runoff and sediment yield on sand-covered slopes (SS) and bare loess slope (LS) were studied under simulated rainfall experiments. The results showed that runoff in response to 1.0 and 1.5 mm/min rainfall intensities on SS began 31.1 min and 17.5 min later than on LS, respectively, and that runoff start-time increased as the sand-covering thickness increased. The impact of rainfall intensity on the runoff process of SS was greater than that of LS. Sand-covering had a greater effect on increasing sediment yield than runoff amount. Analysis of variance (ANOVA) indicated that the runoff amount and sediment yields of the three sand-covering thicknesses (0.5, 1.0 and 1.5 cm) of SS were all significantly larger than those of LS under 1.5 mm/min rainfall ( p < 0.01). However, the runoff and sediment did not increase strictly with increasing sand-covering thickness. The total sediment yields from SS under 1.0 and 1.5 mm/min rainfall intensities were 23 times and 13 times greater than those from LS, respectively. The relationships between cumulative runoff and sediment yield on LS and SS could be fitted well by linear functions ( R > 0.98, p < 0.01). The sediment yields showed strong positive correlations with runoff amount on SS ( p < 0.01). In conclusion, the sand-covered slopes greatly increased soil erosion when compared to the loess slope. [ABSTRACT FROM AUTHOR]

The sediment problem is a globally occurring problem that has long been a focus of research. The sediment-reducing effect of check dams and the safety problem after check dam breaks have always been a common concern of the society. This study analyzed the runoff change and sediment source during rainstorms in a small watershed using a multivariate mixed model and a comparative analysis of watersheds. The problem of sediment loss from dammed farmland after check dam break during rainstorms was evaluated. The results showed that the flood peak lag time (PLT) was significantly influenced by pre-soil moisture in case of small amounts of rainfall but not during rainstorms. Ecological construction significantly reduced the linear correlation between rainfall and runoff modulus (RM). The reduction of sediment delivery modulus (SDM) by check dam was stronger than that of the RM. The reduction in RM and SDM under rainstorm conditions were 16%~74% and 53%~93%, respectively. The contributions of inter-gully and gully lands to the sediment deposited in dammed farmland during the large rainstorm on July 26, 2017 were 38.07% and 61.93%, respectively. The increase in vegetation coverage in hillslope increased the proportion of sediment from gully lands. Check dam breaches have accounted for a loss of only 1.2% of the total area of the dammed farmland, and thus have not caused a large loss of sediment. However, the breaches of the check dams clearly increased the coefficient of variation of RM and SDM. Therefore, Check dams have a critical effect on controlling sediment delivery in watershed scale. Dam break will not result in a large percentage of sediment loss from the dammed farmland. [ABSTRACT FROM AUTHOR]

Revegetation and check dam construction are two widely applied soil erosion control measures on the Loess Plateau of China. They play important roles in sediment yield reduction. However, it remains unclear how these large-scale land-use changes and in-channel structures affect water yield and sediment load on the watershed scale. A combination of field work and modeling exercises were used to quantitatively assess the effects of land-use changes and check dam construction on hydrological processes in the Wuding River watershed. The study area suffered important land-use changes with increases in forestland and grassland, coupled with decreases in cropland, from 1980 to 2010. A large number of check dams were constructed from 1970 to 1980. Runoff and sediment yield in the watershed showed significant decreasing trends, with change points occurring in the early 1970s. Human activity contributed to 75% and 89% of runoff and sediment changes, respectively. The simulations showed that in a scenario without check dams, runoff and sediment increased by 12% and 11.7%, respectively. Vegetation recovery reduced runoff and sediment yield. 'Grain for Green' resulted in decreasing runoff and sediment levels, and reforestation had more hydrological regulatory effects compared with scenarios involving the conversion of cropland to grassland. Moreover, the combination of revegetation and check dam construction had a greater impact on water yield and sediment transportation. Check dams provide short-term flood control and sediment reductions, whereas land-use changes are long-term sustained soil 24 erosion control measures. It may be more efficient to combine check dam construction with revegetation strategies. [ABSTRACT FROM AUTHOR]