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The influence of land use/cover patterns on soil erosion and sediment transport can be one of the most important indicators to optimize the soil and water conservation measures in a watershed. However, it is still lacking in the quantitative evaluation of the land use/cover pattern and their impacts on soil erosion and sediment yield at the watershed scale. This study aims to explore the long-term changes in the sediment yield on the interannual and intermonthly temporal scales from 1982 to 2020, together with their responses to the land and use/cover pattern. A typical watershed was selected in the Loess Plateau, and the Lyuergou watershed. The M-K trend analysis was employed to elucidate the long-term temporal trends of annual rainfall, runoff, and sediment yield in the study area. An investigation was explored on the changes in the runoff and sediment under different vegetation patterns using the land use/cover pattern. The index of connectivity was chosen to characterize the impacts of the land use/cover pattern on soil erosion and sediment yield. Accordingly, quantitative relationships were also established between the index of connectivity and sediment yield. In addition, the monthly rainfall amount, the maximum daily rainfall amount, and erosive rainfall days were selected as the indices to classify the rainfall types. The results indicated that the Lyuergou watershed experienced cropland abandonment and vegetation restoration, where the index of connectivity decreased significantly during 1982-2020. Consequently, the whole study period was divided into four stages: 1982-1985, 1986-1990, 1991-2000, and 2001-2020, corresponding to the land use/cover pattern Ⅰ, Ⅱ, Ⅲ, and Ⅳ, respectively. The average annual sediment yield varied consistently, as the land use/cover pattern changed. Significantly downward trends were found in the average annual sediment yield and runoff depth, whereas, the annual rainfall amount showed no significant changing trend. Specifically, the annual runoff depth and sediment yield of land use/cover pattern Ⅳ decreased by 74.5% and 68.1%, respectively, compared with the land use/cover pattern Ⅰ, respectively. The average monthly runoff depth and sediment yield in the flood season were 11.7, 5.9, 1.8, 4.0 mm and 713.4, 377.4, 112.0, 317.9 t/km² in the land use/cover pattern Ⅰ, Ⅱ, Ⅲ, and Ⅳ, respectively. The runoff depth and sediment yield under the later land use/cover pattern (Ⅲ and Ⅳ) were significantly lower as opposed to those in the early land use/cover pattern Ⅰ. The erosive rainfall in the flood season was classified into four types: type A (minor rainfall amount, and weaker rainfall erosivity), type B (medium rainfall amount, and weaker rainfall erosivity), type C (great rainfall amount, and medium rainfall erosivity), and type D (great rainfall amount, and larger rainfall erosivity). Type A, B and C contributed to the most sediment yield on the small watershed. However, there was no significant difference in the monthly runoff depth and sediment yield among different land use/cover patterns under type C. The sediment yield on both interannual and intermonthly scales increased exponentially with index of connectivity, whereas the relationships were weaker under type C. The finding can provide a strong reference to the optimal allocation of land use/cover patterns and soil and water conservation measures in arid and semi-arid areas. [ABSTRACT FROM AUTHOR]

The projected climate change for Norway through the 21st century predicts that the temperature will increase significantly. Events with heavy rainfall will be more intense and occur more frequently. Rain floods will increase in magnitude and also occur more frequently. Extreme flooding and heavy rain will significantly impact the sediment dynamics in rivers. In the mountain areas, floods are often associated with erosion, transport and deposition of coarse sediment along the streams. These processes are related to bed load transport and pose a hazard in addition to the elevated water discharge and have to be included in management plans for river basins. This article studies the bed load delivery from sources that contribute the most to the sediment budget in the Gudbrandsdalslågen river basin during the large magnitude floods in 2011 and 2013. More than 100 debris slides and debris flow were triggered in the tributary river Veikleåi by the heavy rain and snowmelt during these floods. The volume of the contribution from debris flows and erosion and deposition of the river bed was determined by subtracting digital elevation models acquired during repeated airborne LIDAR surveys. In the river Dørja the supply of sediment from a number of debris flows caused extensive aggradation and channel changes. In their new position, lateral erosion by these channels triggered slides on the adjacent slopes. The contributing volumes of debris flows, lateral erosion, and river bed erosion and deposition were determined from the LIDAR surveys. Relations obtained from studies of sediment transport in modern glacier rivers were used to obtain estimates of the ratio of bed load versus suspended load derived from the Pleistocene moraine deposits. Several monitoring stations using conventional methods for measuring bed load and suspended load recorded very large volumes of sediment delivery during both of the extreme floods. The results of the study may be used to identify necessary locations for check‐dams and erosion protection works in order to adapt to climate change. [ABSTRACT FROM AUTHOR]

Sediment associated carbon and nitrogen loss under rainfall, an important cause of soil quality degradation and water eutrophication, strongly depends on the intrinsic properties of original soil types. Relative to total loss, the transport behaviors of organic carbon and nitrogen among sediment size classes and response to soil types remain poorly understood. The concentrations of organic carbon (OC) and total nitrogen (TN) in different sediment size classes (>1, 0.25–1, 0.10–0.25, and <0.10 mm) and their contributions to total sediment load during rainfall erosion were determined under field plot rainfall simulation (at 90 mm h−1) on three contrasting soil types (Luvisol, Alisol and Ferralsol) with increased aggregate stability. During rainfall erosion, the concentrations of OC and TN in total and different sized sediments decreased first and then reached a steady state. The variability of OC and TN concentrations (coefficient of variations in 4.2–53.1% and 6.6–41.9%) among sediment size classes decreased from Luvisol to Ferralsol. Compared to original soils, sediments exhibited larger C/N ratios for Luvisol, and smaller values for Alisol, indicating the more selective transport of labile organic matter for weaker aggregated soils. Among sediment size classes, fine particles (<0.10 mm) accounted 69–88% of total OC and TN losses for Luvisol, and decreased to 30–39% for Ferralsol; and the main transport mechanisms of sediment associated OC and TN shifting from suspension-saltation (<0.10 mm) to rolling (>0.25 mm) with increased aggregate stability. Among original soil properties, inorganic cementing agents (including amorphous iron oxides and clay minerals) showed closer relationships with sediment OC and TN losses (|r| = 0.61–0.89, p < 0.001) than organic matter properties (|r| = 0.55–0.87, p < 0.001), further implying the important role of soil aggregate stability across soil types. This study provides an in-depth understanding on soil carbon and nitrogen losses and their divergent characteristics among soil types deserves consideration in the development of erosion model and land management in agricultural systems. • Variability of OC and TN concentrations among sediment sizes decreased from Luvisol to Ferralsol. • Suspension-saltation (<0.10 mm) dominated OC and TN losses for weak aggregated soils. • Contribution of coarse particles by rolling to OC and TN losses increased with aggregate stability. • Runoff rate, iron oxides and sediment size controlled the loss characteristics of OC and TN. [ABSTRACT FROM AUTHOR]

• Mass movement is an important erosion mode and sediment source in gully network. • Mass movement increased sediment concentration and led to peak sediment concentration. • Mass movement was prone to be triggered by rainfall with a medium-duration and moderate-intensity. • Rainfall amount and slope gradiet determined the trigger and total volume of mass movement. Mass movement erosion on the gully sidewalls is recognized as an important erosion mode and sediment source in hilly and gully watersheds. However, the trigger of mass movement erosion and transport of gravity-detached material remain poorly understood. A series of rainfall simulation experiments were conducted on six loess gully sidewall models, with a height (1 m), three rainfall (60 mm, 48 mm and 24 mm) and two slope gradients (70° and 80°), to quantitatively explore the sensitivity factor and transport mechanisms of mass movement. Results revealed that the accumulation volume and initiation of the mass failure were significantly influenced by rainfall amount. The accumulative volume of failure events was observed to increase in a linear pattern with increasing rainfall amount. The minimum cumulative rainfalls for the initiation of mass failure on the loess gully sidewalls were approximately 43.6, 28.2 and 65.6 mm for short-duration and high-intensity, medium-duration and moderate-intensity and short-duration and moderate-intensity rainfalls, respectively. This implied that the initiation of mass failure was more prone to rainfall events with a medium-duration and moderate-intensity than those with a high intensity and short duration. Rainfall amount and initial slope gradient were the most sensitive elements driving the number and volume of the mass movement erosion. Mass movement erosion raised sediment concentration, but the eroded material was unable to be transported by runoff in a timely manner. Average sediment concentrations at the model outlet increased by 1.9–11.9 times following the occurrence of mass failures compared to those before. A low instantaneous sediment delivery ratio of 0.032 for the mass movement erosion. The experimental findings help comprehend the influence of mass movement erosion on sediment supply on the gully sidewall in the hilly and gully network, i.e. the Loess Plateau. [ABSTRACT FROM AUTHOR]

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: <5%, M: 5–19%, H: >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. [ABSTRACT FROM AUTHOR]

• Effective sediment sizes were determined along a gradient of soil structural stability. • Sediment average size exhibited a unimodal variation with soil structural stability. • Suspension-saltation dominated sediment transport for low and high stable soils. • Suspension-saltation and rolling jointly dominated erosion for medium stable soils. • Soil structural stability determined rainfall intensity effect on sediment transport. Sediment transport patterns (suspension, saltation and rolling) not only depend on flow hydrodynamic characteristics, but also on sediment properties, both of which are largely influenced by soil structural stability. However, how sediment sizes and transport patterns response to original soils over a wide range of structural stability remains unclear. Herein, field plot rainfall simulation experiments on five soils along an increased gradient of structural stability were conducted at two rainfall intensities of 45 and 90 mm h−1 to investigate effective sediment size characteristics and associated transport patterns in sheet erosion. Differing from runoff and sediment yield, sediment sizes were most influenced by soil structural stability (F = 386.9) rather than rainfall intensity (F = 246.7, p < 0.001). Mean weight diameter of sediment (0.16–0.84 mm) and the proportion of coarse particles (>0.25 mm) exhibited a unimodal variation with increased soil structural stability. The effective sediment size distribution shifted from unimodal with the peak at < 0.10 mm for low and high stable soils to bimodal with two peaks at < 0.10 mm and 0.5–1 mm for medium stable soils. Correspondingly, suspension-saltation (>74 %) dominated sediment transport for low and high stable soils, which was determined by fine sized fragments from aggregate breakdown and small flow transport capacity, respectively; while both suspension-saltation (<0.10 mm) and rolling (>0.25 mm) jointly contributed to sediment transport for medium stable soils, which was controlled by the interaction between fragment size and flow transport capacity. Moreover, the positive effect of rainfall intensity on sediment sizes was more remarkable for the medium than for the low and high stable soils. A conceptual model of sediment transport mechanisms in response to soil structural stability is firstly proposed, which merits consideration in the future development of erosion modeling and soil conservation techniques. [ABSTRACT FROM AUTHOR]

• Demonstration of rise and fall of carbon discharge with time. • Demonstration of enrichment of sand in loose layer above soil. • Demonstration of no carbon enrichment is sediment at the steady state. Soil carbon losses from sheet and interrill erosion areas have an impact on the global carbon cycle. Sediment discharged in many experiments where artificial rainfall has been applied to sloping soil surfaces show greater proportions of carbon in the sediment than found in the cohesive soil source. In many cases, conclusions drawn from these experiments fail to recognise that the enrichment of carbon in the sediment discharge is a result of unsteady conditions that occur before the steady state develops. It is known that particles of sand of different sizes move at different rates when raindrop induced salation occurs with the result that initially the particle size distribution is finer than the source but tends towards that of the source as time progresses. The presence of carbon in aggregates influences the density of aggregates. Here a qualitative model of sediment transport of sand and coal particles by raindrop induced saltation is used to demonstrate time varying enrichment of coal resulting from the effect of carbon on particle settling velocity. The model also demonstrates how the layer of loose particles that develops on top of the cohesive soil surface influences the relative amounts of carbon and sand in the sediment discharges. The steady state is not achieved until the slowest moving particle detached at the farthest distance from the downslope boundary is discharged. That may not be achieved in many of the experiments reported in the literature. [ABSTRACT FROM AUTHOR]

A series of large rainfall simulator experiments was conducted in 2002 and 2003 on a small plot located in an experimental catchment in the North Island of New Zealand. These experiments measured both runoff and sediment transport under carefully controlled conditions. A physically based hydrological modelling system (SHETRAN) was then applied to reproduce the observed hydrographs and sedigraphs. SHETRAN uses physically based equations to represent flow and sediment transport, and two erodibility coefficients to model detachment of soil particles by raindrop erosion and overland flow erosion. The rate of raindrop erosion also depended on the amount of bare ground under the simulator; this was estimated before each experiment. These erodibility coefficients were calibrated systematically for summer and winter experiments separately, and lower values were obtained for the summer experiments. Earlier studies using small rainfall simulators in the vicinity of the plot also found the soil to be less erodible in summer and autumn. Limited validation of model parameters was carried out using results from a series of autumn experiments. The modelled suspended sediment load was also sensitive to parameters controlling the generation of runoff from the rainfall simulator plot; therefore, we found that accurate runoff predictions were important for the sediment predictions, especially from the experiments where the pasture cover was good and overland flow erosion was the dominant mechanism. The rainfall simulator experiments showed that the mass of suspended sediment increased post-grazing, and according to the model this was due to raindrop detachment. The results indicated that grazing cattle or sheep on steeply sloping hill-country paddocks should be carefully managed, especially in winter, to limit the transport of suspended sediment into watercourses. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Steeghs, L. and Healy, T., 2007. Tidal inlet configuration and bathymetric changes resulting from active sedimentation, Buffalo Bay, New Zealand. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 716 – 720. Gold Coast, Australia, ISSN 0749.0208 The Whitianga tidal inlet lies within Mercury Bay, on the northeast coast of New Zealand. The Whitianga Estuary harbours many recreational and commercial vessels. Terrestrial sediment inputs into the Whitianga Estuary catchment are high, due to the erodible tertiary sediments and the steep nature of the catchment, which suffers intense rainfall that results in high sediment influxes, much of which becomes deposited within the estuary. In recent years active shoals have appeared in Buffalo Bay and the inlet channel has noticeably shallowed, both of which inhibit the use of the inlet by boat traffic. The past and present bathymetry of Buffalo Bay is compared to establish changes in morphology and zones of accretion and erosion within Buffalo Bay. The outcomes of this research contribute to a larger research programme which aims to use numerical model simulations to identify sediment transport pathways and patterns within Buffalo Bay. This research will particularly provide information which can be used to calibrate a sediment transport model. Comparison of the Buffalo Bay bathymetries over the 38 year period from 1938 to 1979 and Whitianga inlet bathymetries between 1979 and 1995, show extensive accretion in the ebb discharge channel which is predominantly associated with the migration of the tidal inlet channel and growth of the ebb delta, and within the inner inlet area which are attributed to the growth of the flood delta system. [ABSTRACT FROM AUTHOR]