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This study uses the Global Assessment of Soil Degradation (GLASOD) to map sediment sources and erosion process types within the Congo Basin as part of a scoping study to guide a basin wide sedimentation study. The GLASOD map is validated using information from literature and published sediment concentration data at the Brazzaville gauging station, which includes over 95% of the basin area. Validation is complemented by analysis of timelapse satellite images and surface water transition maps derived from Landsat images. The upper catchments are shown to be the main sources of sediment, with the largest exporter by quantity being the Upper Congo sub-basin followed by the Kasai. In terms of severity, the Kasai has the highest specific sediment production rates at 8.92 t/km2/year, followed by the Sangha and Upper Congo at 8.52 t/km2/year and 7.61 t/km2/year, respectively. The dominant erosion/degradation type is the loss of topsoil through water erosion (sheet erosion), occurring in 32% of the entire Congo Basin area, followed by loss of nutrients and organic matter through chemical degradation, 21% of area. The mapping also shows that a large proportion of the Basin (39%) consists of stable terrain under natural conditions, without any human induced erosion. The erosion levels in the Basin are generally low with the predominant mapped erosion processes occurring mostly infrequently and with low levels of severity. The GLASOD map performs satisfactorily as a tool for mapping erosion sources and process types, but fails to explain the process dynamics within the sub-basins, for example, the high sediment exportation rates published for the Sangha sub-basin despite consisting mainly of stable natural terrain (84%). Analysis of satellite images shows an increase in sediment concentration in the Congo River's waters over the years. However, this temporal increase in sediment concentration is neither reflected in the GLASOD map nor the quantitative studies reviewed for this paper, pointing to the urgent need for future research on sediment dynamics in the Basin. Questions are also raised on the roles of the Malebo Pool and Cuvette Centrale in the sediment transport processes of the Basin. The questions raised, and observations made from this study have been used to identify strategic sampling sites for further field studies.

In this paper, we examine the effect of vegetation on soil erosion, runoff generation and sediment transport on saline rangeland hillslopes. Rainfall simulations were conducted at a fixed 114 mm/h intensity on 6 m × 2 m erosion plots with varying degrees of vegetation. Plots were grouped into three categories (L, M and H) based on their canopy cover (L: 19%) and selected to limit variations in slope across canopy cover groups. Runoff and sediment samples were combined with three dimensional (3D) reconstruction data used to monitor soil surface microtopographic changes. Runoff initiation was significantly delayed on the L plots but cumulative runoff after 20 min of rainfall simulation indicated a positive effect of vegetation on infiltration processes. Cumulative sediment after 20 min of rainfall was similar across vegetation cover categories. The 3D data suggest that vegetation reduced net sediment delivery from the plots by primarily increasing opportunities for deposition while marginally affecting gross soil erosion. Plots with H vegetation cover experienced lower 3D-estimated erosion volumes but average erosion depth on L plots was lower than that on plots with M and H vegetation covers. Lower runoff volumes on M and H plots may have been compensated by greater runoff erosivity on these plots as runoff was concentrated in a narrower inter-patch space compared to L plots. This study highlights the need for an increased integration between traditional runoff measurement techniques and 3D reconstruction methods.

Global warming and intensified climate variability have greatly affected Earth’s surface processes and continental sediment evacuation. River suspended sediment is a sensitive indicator for tracing seasonal surface erosion, but details of the rates of sediment generation and evacuation, and their connections with nowadays warming climate are not entirely clear, particularly in Tibet and other high–altitude areas where field observations remain scarce. Here, we investigate daily to seasonal river sediment transport dynamics between the cold, permafrost–dominated northeastern Tibetan Plateau and warm, non–permafrost Sichuan and Taiwan regions. Our results show that at a given river water discharge, greater river suspended sediment was evacuated during the pre–monsoon season (April–Mid June) relative to other seasons in the cold NE Tibetan catchments. In contrast, no such phenomenon was observed in the warm, non–permafrost regions. These comparisons likely indicate a center role of freeze–thaw processes on loose sediment generation, which enhanced sediment output. Hydrometeorological records show up to ∼2 °C warming in the NE Tibetan Plateau since the past 30 years, coupled with an 8-fold increase in sediment transport. We suggest that continuous warming climate may further accelerate sediment and soil carbon release in the Tibetan Plateau and other global permafrost–dominated areas, which in turn influences climate feedback.

The Wenchuan earthquake and subsequent strong rainfall triggered extensive mass wasting, which caused sufficient landslide sediment to be continuously transferred out of the alpine basin. Effective sediment management in earthquake areas requires a full understanding of how landslide sediment is transferred out of alpine basins. In this study, field investigations and remote sensing interpretations indicated that the bedrock or hillslope surface materials were transferred downstream of the hillslope through falls, slides, fall slides, slide falls, and slide flows. Subsequently, field investigations and box model tests showed that the loose landslide sediment was transferred to the channel mainly through three typical processes (erosion driven by torrents or debris flow, saturation, and surface runoff), which occurred simultaneously in the first several years after the Wenchuan earthquake. However, surface runoff erosion was the main transfer process in the following period. Using the number and area of effective landslides, the length and area of landslide sediment in channels, and the effective basin as indicators, we present observational evidence of the landslide sediment transport process based on a remote sensing image time series from 2005 to 2018. The trends of the indicators suggested that the sediment transfer process in the alpine basin was intense during the first 5 years after the Wenchuan earthquake; then, it gradually weakened without the influence of extreme rainfall, but it may last 20 years or longer before returning to the pre-earthquake level.

South Korea experiences numerous local sedimentation problems, such as landslides, upland erosion, aggradation and degradation, and flood plain sediment deposition. This has necessitated the development of a reliable and consistent approach for modeling sediment processes in the country. In this study, samples obtained from 35 gauging stations at five alluvial river basins in South Korea were used together with the modified Einstein procedure and series expansion of the modified Einstein procedure to determine the total sediment load at the sampling locations. Using two different methods, the total sediment load of majority of the 35 considered rivers were found to be typically 50–300 ton/km2·yr. A model tree data mining technique was used to develop a model for estimating the specific degradation based on certain meaningful parameters, namely, the 1) elevation at the middle relative area of the hypsometric curve [m], 2) percentage of wetland and water, 3) percentage of urban land, 4) mean annual precipitation [mm], 5) main stream length [km], and 6) watershed form factor [km2/km2]. The root mean square error of the predictions of the proposed model was found to be 55 ton/km2·yr less than those of existing statistical models. Erosion loss maps obtained by the revised universal soil loss equation (RUSLE), satellite images, and aerial photographs were also used to represent the geospatial features affecting erosion and sedimentation. The results of the geospatial analysis indicated that the transport of sediment into the alluvial rivers was affected by the wetlands located near the rivers, and also enabled clear delineation of the unique erosion features of construction sites in the urban areas. In addition, the watershed morphometric characteristics could be used to accurately represent the sediment transport. The proposed data mining methodology promises to facilitate the solution of various erosion and sedimentation problems in South Korea. The geospatial analysis procedure would also enable the understanding of spatially varied erosion and sedimentation processes under different conditions.

Sediment bodies produced during historical periods of human land use, sometimes referred to as legacy sediment, may be found in various locations within drainage basins, and potentially remobilized by hydrogeomorphic processes accompanying land use change. The amounts and locations of stored legacy sediment can be significant factors in modern drainage basin function and should be accounted for when possible. In this study, late nineteenth-century erosion and sediment storage were investigated and used to construct approximate sediment budgets for two small Blue Ridge Mountain drainage basins in North Carolina (USA). Erosion was quantified using a distributed implementation of the Universal Soil Loss Equation (USLE), and calibrated on the separate bases of soil profile truncation data and recent published rates for long-term erosion in the region. Sediment yield information was reconstructed from pond sediments trapped behind a mill dam. Alluvial sediment storage was quantified using field studies of streambank and floodplain sediment profiles and digital elevation data. Colluvial storage was calculated as a residual in the sediment budget, and further evaluated using soil profile studies of footslope deposits, and soil survey maps. The proportions of erosion accounted for by the different budget terms in the most reliable budget are: 28% sediment yield (i.e., a sediment delivery ratio of 0.28), 69% colluvial storage, and 3% alluvial storage. Blue Ridge basins with low levels of ground disturbance erode like Piedmont basins at high levels of ground disturbance, primarily due to higher slope angles. Sediment delivery ratio is high relative to those given for much larger basins in the adjacent and more frequently studied Piedmont province, and generally in accordance with published sediment delivery curves that reflect higher hydrogeomorphic connectivities within smaller basins. Low values for alluvial storage in Blue Ridge basins may be explained by high sediment transport within steep channels. Colluvial storage values have high uncertainties because of the well known problem of error accumulation in residual budget terms. Field data on colluvial deposits reported here are not sufficient to correct for this problem, and in general, the acquisition of accurate field data on historical colluviation remains an important methodological issue in historical sediment budgeting.

A rainfall simulator is an ideal tool for infiltration, soil erosion, and other related research areas for replicating the process and characteristics of natural rainfall. In this study, a laboratory-scale rainfall simulator is developed. Rainfall characteristics including the rainfall intensity and its spatial uniformity, raindrop size, raindrop velocity, and kinetic energy confirm that natural rainfall conditions are simulated with sufficient accuracy. Pressure nozzles are used to spray water corresponding to rainfall intensities ranging from 45 to 105 mm h(-1). The simulator produces rainfall with uniformity coefficient changing between 82 and 89%. The raindrops falling with an initial velocity from a height of 2.43 m have median diameters of 2.2-3.1 mm. The impact velocities of the median size raindrops deviate from their terminal velocities with a relative error between 6 and 15%. The accompanying erosion flume can be given slope up to 20% in lateral and longitudinal directions. During the experiments, flow measurement is taken from two outlets at the end of the flume to distinguish the contribution of interrill areas into rills. Experiments result in typical rainfall-induced hydrographs and sedigraphs observed under natural conditions. This shows the ability of the rainfall simulator for use in sediment transport processes over hillslopes. (c) 2012 Elsevier B.V. All rights reserved.

Treating the dynamics of sediment transport as two-dimensional on interrill-areas and as one-dimensional in rill sections, areally averaged sheet sediment transport equations are developed. The two-dimensional sheet sediment transport equation is averaged over an individual interrill-area width and then along the interrill-area length to obtain local-scale areally averaged interrill-area sheet sediment transport equation (local-scale areal averaging). Similarly, the cross-sectionally-averaged rill sediment transport equation is averaged along an individual rill length to obtain local-scale areally averaged rill sediment transport equation (local-scale areal averaging). In order to minimize computational effort and economize on the number of model parameters, the local-scale areally averaged equations are then averaged over a whole hillslope section (large-scale areal averaging). These equations constitute the areally averaged model. The expectations of the terms containing more than one variable are obtained by the method of regular perturbation. In the large-scale areal averaging it is assumed that all the randomness in the state variable is due to the randomness in the parameters of the process. Comparison of the results obtained from the areally averaged model with those of the point-scale model indicates that the areally averaged model uses far less data and yet it performs as well as the point-scale model. The results of the developed model indicate that on a rilled-surface most of the sediment loads comes from rill sections. The developed model is successfully tested against experimental data obtained from a bare rilled hillslope. It predicted measured runoff and sediment rates with mean absolute errors of 11.07 l/min and 0.382 kg/s, respectively.

The understanding of soil erosion processes and the development of accurate erosion prediction models require understanding of detachment, deposition, and sediment transport in rills. The objectives of this study were to determine whether sediment transport capacity is a unique value for given soil, flow rate, and slope, and to determine if equilibrium sediment concentration in the rill obtained by detachment was different from that observed under depositional conditions. Experiments on a Carmi loam (fine, mixed, mesic Typic Hapludalf) simulated rill erosion under net detachment and net deposition conditions. Two discharge rates of 6 and 9 l min � 1 and two sediment input regimes of 0 and excess of transport capacity were tested on soil beds with lengths of 2, 4, 6, 7, and 8 m at 7% slope. Sediment load reached steady state conditions within the 8-m distance on the rill. At 9 l min � 1 discharge, 8 m length, and excess sediment added to the flow, sediment delivery was 71 g l � 1 versus 31 g l � 1 for the corresponding case with no sediment added. Overall, for the conditions tested, rill flow transported two times more sediment than it could detach. The flow did not reach its maximum potential transported load through detachment of soil due in part to changes in the sediment size distribution under deposition and possibly to the protective action of bedload particles moving along the rill bottom and/or changes in flow turbulence associated with sediment laden flow. D 2003 Elsevier Science B.V. All rights reserved.

The object of the study is to compare the importance of soil and nutrient losses from plots in an ever green oak ( Quercus ilex ) woodland under different environmental conditions; namely under undisturbed forest and at sites that had been clear felled and burnt under controlled conditions. At each site, the plots were instrumented with 10 Gerlach troughs located at the footslope of each plot, and with 12 troughs in the upper part of the burned plot inserted at regular intervals from the water divide. Raingauges were subsequently added and data on rainfall intensity collected at a nearby station. Results indicate that burning has a significant effect with respect to runoff and nutrient and sediment losses. The impact of clear-felling is much less. Sediment transport on the slope is not only caused by surface runoff but by other agents of erosion as well.