Search

Both vegetation coverage rates and arrangement patterns have important influences on erosion. Very little previous research focuses on the impacts of spatial vegetation distribution patterns on erosion. The slope-gully system was taken as the research object, which is composed of a 5.0 m long hillslope with a slope gradient of 20° and a 3.0 m long gully slope with a gradient of 50°. A series of scouring experiments with two inflow discharges (3.2 L min−1, 5.2 L min−1) was carried out. The effects of the flow discharges, spatial grass arrangement patterns (US, MS, and DS represent the presence of grass covering on up-hillslope, middle-hillslope, and down-hillslope, respectively) and grass coverage rates (0%, 30%, 50%, 70%, and 90%) on runoff and sediment were studied in this paper. The results indicated that either runoff or sediment yielding was significantly decreased with the grass coverage rates increasing and with the variation of grass arrangement patterns on a hillslope. While grass coverage had more effectiveness in controlling erosion compared with runoff reduction, and DS can control erosion more effectively than US and MS erosion controlling. For the gully slope, erosion significantly increased with the grass coverage rates increasing no matter how the grass arrangement patterns on the hillslope. Therefore, both different grass coverage and different grass arrangement patterns have an influence on erosion processes; any research that only takes care of the single factor mentioned above is not enough to reveal the effects of grass on erosion. In the process of erosion control in the Loess Plateau, taking effective measures both on the hillslope and gully slope will be effective methods of reducing soil erosion. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Summary Land cover and rainfall regime are two important factors that affect soil erosion. In this paper, three land cover types – grass cover, litter cover and bare land – were employed to analyze surface runoff, subsurface flow and sediment loss processes in relation to the rainfall regimes in the red soil region of China. Five rainfall regimes were classified according to 393 rainfall events via a k-means clustering method based on the rainfall depth, duration and maximum 30-min intensity. The highest surface runoff coefficient and erosion amount were found on bare land in all five rainfall regimes, and the lowest were found on grass cover. The litter cover generated the highest subsurface flow rate, followed by the grass cover; the lowest was on bare land. For grass cover and litter cover plots, rainfall events of rainfall regime IV which had the longest duration, greatest depth and lowest intensity had the highest surface runoff coefficient, soil erosion amount and subsurface flow rate. For bare land, storm rainfall events of rainfall regime V had the highest intensity, lowest depth and duration, had the highest surface runoff coefficient and soil erosion amount, but the lowest subsurface flow rate. The highest subsurface flow rate of bare land happened in rainfall regime IV. Surface cover was urgently needed to reduce soil erosion. When the lands under dense surface cover, more attention should be paid to rainfall events that of long duration, high depth but low in intensity which commonly occurred in spring. The interactions of surface–subsurface flow and its effects on soil erosion and nutrient loss were worth considering in the red soil region. [ABSTRACT FROM AUTHOR]

Soil erosion changes after China's Grain‐for‐Green Program (GGP) have attracted widespread attention. Many studies have reported positive contributions of the GGP to sediment reduction; however, GGP effects on runoff remain under debate. The objective of this study was to identify runoff and sediment changes and estimate the contribution of human activities to soil erosion decreases in the Mang River basin (MRB) in the southeastern Loess Plateau. The temporal trends of the rainfall‐runoff‐sediment series between 1960 and 2017 and the contribution of human effects to runoff and sediment changes were determined using time‐series analysis methods. The main transformations in land‐use types were from farmland to forestland in the upstream MRB and farmland to built‐up land in the downstream MRB. Rainfall remained in a relatively steady state, while runoff and sediment had descending trends, both of which began to mutate in 1990 and 1994, respectively. The average runoff (sediment load) decreased by 33 × 104 m3 (5 × 104 t yr−1), of which the human effect contributed to 79% (93%) of the decreases. During the descending period, the human effects on runoff and sediment increased with time. Sediment experienced a much larger reduction effect than runoff because of increased forestland area, which can greatly reduce soil erosion, in the MRB upstream of our study site; however, runoff was increased in the MRB downstream of our study site because urbanization led to the expansion of impervious surfaces. Our results provide new lessons for assessing the reduction effects of the GGP on soil erosion in an urbanized basin. [ABSTRACT FROM AUTHOR]

Soil erosion has become more serious in semiarid areas around the world. However, the discrimination of the impact of concurrent climate change and human activity on soil erosion in a particular study area remains a challenge. Check dams are important engineering measures to prevent soil erosion on the Chinese Loess Plateau, and the dam sediments, as the product of soil erosion, are related to both climate change and human activities in a small watershed. The present study selected a check dams sediment profile in the upper Jinghe Basin on the Chinese Loess Plateau as a case study. Based on AMS 14C dating and 137Cs measurement, we established the soil erosion timescale and employed multiple methods including magnetic susceptibility, particle size, and minerals to trace the soil erosion history. We compared them with a local hydrometeorological record in the Jinghe Basin to explore the relationship between soil erosion and human activities. AMS 14C and 137Cs results indicated that the profile was deposited since 1953. The results of magnetic susceptibility, particle size, and minerals revealed 3 soil erosion phases during the last 60 years. Soil erosion in this region is not only related to precipitation changes, but also closely related to human activities. Prior to the Reform and Opening-up in China in 1978, climatic change played a leading role in check dams sedimentation and hydrological changes. Subsequently, despite accelerated soil erosion associated with the family contract responsibility system, the check dams, afforestation and a warmer climate mitigated the soil erosion to some extent, runoff and sediment load continued to decrease. Since 1999, China's Grain for Green project has greatly reduced the runoff and sediment load. However, the policy of filling gullies and creating land since 2010 should be reconsidered carefully in terms of all aspects, including the eco-environment, hydrological cycle, and economics. [ABSTRACT FROM AUTHOR]

Abstract: Vegetation recolonization has often been used to control roadside slope erosion, and in this paper, four restoration models – Natural Restoration, Grass, Grass & Shrub, Sodded Strip – were chosen to recolonize the plants on a newly built unpaved roadside slope in the Three Gorges Reservoir Area. After eight months growth, eight rainfall simulations (intensity of 90mmh−1 for 60min) and in-situ soil shear strength test were then carried out to identify the impacts of vegetation on roadside slope erosion and soil shear strength. The erosion on cutslopes was higher than that on fillslopes. The runoff coefficient and soil detachment rate were significantly lower on the Grass & Shrub model (4.3% and 1.99gm−2 min−1, respectively) compared with the other three, which had the highest surface cover (91.4%), aboveground biomass (1.44kgm−2) and root weight density (3.94kgm−3). The runoff coefficient and soil detachment rate on roadside slopes showed a logarithmic decrease with the root weight density, root length density and aboveground biomass. The soil shear strength measured before and after the rainfall was higher on Grass & Shrub (59.29 and 53.73kPa) and decreased on Grass (46.93 and 40.48kPa), Sodded Strip (31.20 and 18.87kPa) and Natural Restoration (25.31 and 9.36kPa). Negative linear correlations were found between the soil shear strength reduction and aboveground biomass, root weight density and root length density. The variation of soil shear strength reduction was closely related to the roadside slope erosion, a positive linear correlation was found between runoff coefficient and soil shear strength reduction, and a power function was shown between soil detachment rate and soil shear strength reduction. This study demonstrated that Grass and Grass & Shrub were more suitable and highly cost-effective in controlling initial period erosion of newly built low-volume unpaved road. [Copyright &y& Elsevier]

Severe soil erosion in the Loess Plateau region and associated large sediment discharge downstream in China have been of great concern for years. A physically based distributed model, the Digital Yellow River model (DYRIM), was developed in 2007 for land management at the basin scale in this region. In DYRIM, an explicit sediment yield equation was derived based on simple assumptions where sediment discharge would increase nonlinearly with the slope length, leading to unrealistic results as the spatial scale increases. The main aims of this study were to reformulate the module of DYRIM in comparison with other process-based erosion models; to develop a generic framework for erosion prediction and simulation of erosion and sediment delivery processes within storm events; to validate the new hillslope erosion module for improved performance across a range of spatial scales; and to evaluate parameter consistency among different runoff events. Observed flow and sediment discharge data for 16 runoff events and three runoff plots with different slope lengths (20, 40, and 60 m) for each runoff event from the Tuanshangou experimental site in the Loess Plateau region were used to calibrate the new module for a 20 m slope and the calibrated parameter values were then used to predict the sediment discharge for slope lengths of 40 and 60 m at the same site. For calibration, the Nash-Sutcliffe coefficient of efficiency (NSE) was 0.92 on average for the 20 m plot. For prediction, the average NSE values were 0.87 for 40 m plot and 0.90 for the 60 m plot. There is a marked improvement over the existing module, for prediction with the existing module, the average NSE values were only -0.86 for the 40 m plot and -6.3 for the 60 m plot. Whereas the calibrated parameter values vary from event to event, results show that using a common set of parameter values for all runoff events to predict sediment discharge, the overall NSE values using the combined data set are as high as 0.89 for the 40 m plot and 0.90 for the 60 m plot. This research shows that it is absolutely imperative to include a control term involving the sediment transport capacity, even for the highly erodible region of the Loess Plateau in China. [ABSTRACT FROM AUTHOR]

ABSTRACT The spatial scale effect on sediment concentration in runoff has received little attention despite numerous studies on sediment yield or sediment delivery ratio in the context of multiple spatial scales. We have addressed this issue for hilly areas of the Loess Plateau, north China where fluvial processes are mainly dominated by hyperconcentrated flows. The data on 717 flow events observed at 17 gauging stations and two runoff experimental plots, all located in the 3906 km2 Dalihe watershed, are presented. The combination of the downstream scour of hyperconcentrated flows and the downstream dilution, which is mainly caused by the base flow and is strengthened as a result of the strong patchy storms, determines the spatial change of sediment concentration in runoff during flood events. At the watershed scale, the scouring effect takes predominance first but is subordinate to the downstream dilution with a further increase in spatial scale. As a result, the event mean sediment concentration first increases following a power function with drainage basin area and then declines at the drainage basin area of about 700 km2. The power function in combination with the proportional model of the runoff-sediment yield relationship we proposed before was used to establish the sediment-yield model, which is neither the physical-based model nor the regression model. This model, with only two variables (runoff depth and drainage basin area) and two parameters, can provide fairly accurate prediction of event sediment yield with model efficiency over 0·95 if small events with runoff depth lower than 1 mm are excluded. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article presents a study that validates the performance and feasibility of the Soil and Water Assessment Tool (SWAT). This model was used to simulate the transport of runoff and sediment into the Miyun Reservoir in Beijing, China. The study suggests that the SWAT performs the best and could accurately simulate both daily and monthly runoff and sediment yield.

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.