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Water erosion, a notorious major threat to food security and ecosystem sustainability, is strongly conditioned by spatial and temporal scale effects. This paper systematically reviews the scale issues in runoff and sediment delivery (SIRSD) as a research field by integrating the traditional review approach and bibliometric analysis. This review summarises SIRSD's roots and the scale effect on runoff and sediment delivery. Then, we provide quantitative insights into the SIRSD domain's development history, thematic structure, geographic distribution, international cooperation, and methodologies. Findings show that: i) SIRSD arises from the gap between the non-linearity of runoff and sediment delivery across scales and our ability to measure it. Point-based and short-term measurements cannot capture the non-linearities from the spatio-temporal heterogeneities and cross-scale interactions of factors or processes. ii) Previous literature provides evidence that the spatial scaling of specific runoff (r), soil erosion (SE), sediment yield (SSY), or sediment delivery ratio (SDR) with drainage area (A) or slope length (L) exhibits contrasting patterns due to distinct mechanisms. Infiltration-excess and saturation-excess processes account for inverse and positive r - A relations, respectively. Interrill-erosion and rill-erosion cause inverse and positive SE-L relations. Hillslope-erosion and channel/bank-erosion explain inverse and positive SSY-A relations. Downstream increasing deposition and additional sediment inputs drive inverse and positive SDR-A relations. These scaling relationships can be nonlinear or complex due to spatial heterogeneities in land use, vegetation, topography, climate, lithology, and soil characteristics. Hence, applying an empirical scaling equation developed from the region with distinct environmental contexts is not recommended. Furthermore, the existing scaling patterns or equations may require updating given global climate and land use change. iii) SIRSD is a complex and multidisciplinary issue investigated by scientists from 93 countries since 1928. International research has substantially facilitated the understanding of SIRSD; still, more collaboration should focus on less-developed countries with high soil and water loss risks and urgent conservation needs, such as those in Africa and South America under cropland expansion. iv) Scale mismatch and scale break have discredited large-scale erosion and sediment assessments. Incorporating gully and bank erosion into modelling, extending the scale range of the L factor, and expanding the sediment scaling scope from watershed to slope may make a difference. Therefore, more research with nested design incorporating multiple scales is necessary for cross-scale analysis and scalable modelling. Addressing global climate change requires improving real-time urban flood forecasting and integrating downscaled climate models with hydrology, erosion, and sediment transport models. • A bibliometric review of the global SIRSD research for the first time. • SIRSD is rooted in the gap between natural nonlinearity and our measuring ability. • Scaling of specific runoff, erosion, sediment yield, and SDR has diverse patterns. • Scale mismatch and scale break discredit large-scale modelling and assessments. [ABSTRACT FROM AUTHOR]

• Calculation unit division induced soil spatial aggregation in SWAT model. • Effect of soil spatial aggregation on simulation was separated and quantified.Soil spatial aggregation caused a significant increase in annual runoff and sediment load. • The effect of soil spatial aggregation on sediment load was greater than on runoff. • Optimal sub-watershed division scheme was discussed. Distributed hydrological model divides watersheds into distinct calculation units to simulate hydrological processes. Within the model, different calculation unit division schemes induce input elements, such as soil and land use, to certain degrees of generalization, thus affecting the simulation result. Analyzing the effect of the calculation unit division on the simulation result is an important methodology to reduce uncertainty and improve the simulation accuracy of the model. Previous researchers have focused on the comprehensive effect of underlying surface generalization (such as soil, land use, and terrain generalization) caused by the calculation unit division on the simulation results, while it did not separate the effect of the generalization of the individual input factor on the simulation result. In this paper, the Dongjiang headwater region in southern China was selected as the study area. The single type of land use and slope were input into the Soil and Water Assessment Tool (SWAT) model to fix the effects of land use and terrain caused by calculation unit division on the simulation results. Eleven calculation unit division schemes were used to analyze the impact of soil spatial aggregation on runoff and sediment load simulations. The calculation unit division schemes included 11 sub-watershed division schemes and their hydrological response unit (HRU) thresholds were set at 8 %. The drainage area thresholds of the 11 sub-watershed division schemes were 30 ha, 60 ha, 120 ha, 240 ha, 480 ha, 1000 ha, 1600 ha, 2200 ha, 2800 ha, 3400 ha and 4000 ha. The results demonstrated that the soil spatial distribution showed an obvious aggregation with an increase in the drainage area threshold in the SWAT model. Of these, the Krasnozem soil type which covers the largest area in the watershed, increased significantly with an increase in the drainage area threshold. However, the areas of all the other soil types decreased significantly. The Lioth soil type covers the smallest area in the watershed decreased and even disappeared when the threshold in the SWAT model was greater than 1000 ha. Furthermore, soil spatial aggregation caused a significant increase in the annual runoff and sediment load (P < 0.05), with the sediment load (Re = 29.78 %) increasing at a greater rate compared to runoff (Re = 1.74 %). Increased soil aggregation significantly increased the sediment loads in the maximum 1-day, the continuous maximum 5-day, the continuous maximum 7-day, and the sediment load in flood processes (P < 0.001). Refining the calculation unit division scheme will cause a significant increase in the number of calculation units. Due to the computer processing power limitations, we cannot further refine the calculation unit division scheme. Based on our current operational calculation unit division scheme, we did not identify the optimal division scheme in the study region. These results can provide reference information for future research into hydrological model uncertainty and can improve the SWAT model simulation accuracy. [ABSTRACT FROM AUTHOR]

Abstract: Numerous reports of “flash floods”, “mud torrents” and “landslides” in burnt landscapes of south-east Australia were only recently linked to debris flows and recognised as a significant process that warrant more detailed investigation. This paper provides a systematic documentation of high-magnitude erosion events after wildfire in south-east Australia, focusing on small (<5km2), upland catchments in eastern Victoria that were burnt by wildfire between 2003 and 2009. The aims of the study were to i) collect and show evidence of debris flow occurrence after wildfire; ii) quantify erosion rates from debris flows and; iii) identify rainfall thresholds and key hydrological properties. The result showed that 13 out of the 16 recorded high-magnitude erosion events were runoff generated debris flows. These occurred in dry eucalypt forests burnt at high or very high severity in steep headwater catchments throughout the eastern uplands of Victoria. The debris flows were triggered by intense, short duration rainfall events (I 30 35–59mmh−1) with annual exceedance probability in the order of 20%. This is the first paper to document the occurrence of post-fire runoff generated debris flows in Australia, so the discussion draws on literature from the western USA, where a large body of research has been dedicated to evaluating the risk posed by post-fire debris flows and their role in landscape processes. Typical features common to both systems include low infiltration capacity of burnt catchments; widespread sheet erosion and levee lined rills on steep upper hillslopes; and severe channel erosion initiated in response to convergent flow in previously un-scoured drainage lines. The depth of sheet erosion on surveyed slopes in the upper catchments (4.6±0.96 mm to 18.4±2.7mm) indicates that hillslope material provides an important source of sediment. The average channel entrainment rate of three debris flows ranged from 0.6 to 1.4m3 m−1. Runoff generated debris flows were not recorded in wet or damp forest types suggesting that this process is unlikely to operate in these forest environments. One isolated case of mass failure generated debris flow was recorded in wet forest. The outcome of the study indicates that runoff generated debris flows in dry eucalypt forest are an important process to be considered during post-fire risk assessment of hydrological hazards. [Copyright &y& Elsevier]

Explaining scale effects for runoff and erosion improves our understanding and simulation ability of hydrological and erosion processes. In this paper, plot scale effects on event runoff per unit area ( Q e ), sediment concentration ( C e ) and soil loss per unit area ( SL e ) were checked at El Teularet-Sierra de Enguera experimental site in Eastern Spain. The measurements were carried out for 31 events occurring in the years 2005 and 2007 in bare ploughed plots ranging from 1 to 48 m 2 . The analysis established the scaling relationship by dimensional analysis and self-similarity theory, and tested this relationship at different temporal scales ranging from event to annual scale. The dimensional analysis and the incomplete self-similarity condition allowed us to establish a power scaling relationship which was found to also be usable for the moments of k (1, 2, 3, 4) order. The power scaling relationship was theoretically deduced applying a boundary condition which is based on the hypothesis that sediment delivery processes do not occur at the selected plot scale. The simple scaling invariance condition was always verified (i.e. for each temporal horizon) for runoff and soil loss while the same hypothesis was not perfectly acceptable for sediment concentration. The analysis of the scaling relationships at event temporal scale showed that the spatial scale effects were less frequent for the composite variable (soil loss = sediment concentration × runoff) than the constituting variables. For 48% of the events, a statistically significant scale effect was detected for all tested variables. With reference to the statistically significant relationships, both runoff and soil loss always decreased and sediment concentration always increased in the passage from the reference area (1 m 2 ) to the largest one (48 m 2 ). The analysis at aggregated temporal scales suggested that annual scale effects for soil loss per unit area should be temporally more stable than those for both runoff and sediment concentration. Finally, at mean event scale the three investigated variables have a similar behaviour in terms of simple scaling invariance. [ABSTRACT FROM AUTHOR]

• The annual flood events contributed 64%∼99% of annual total sediment load. • The causes of flood-event sediment load variations were explored. • The high flow condition carried the same amount of sediment as previous period. • The peak sediment concentration in Tuo and Fu Rivers didn't reach the saturation. • Flood events exerted a notable impact on the operation of Three Gorges Reservoir. Understanding the change in sediment load at a flood-event scale helps to enhance channel regulation and optimize reservoir operation. This is particularly true in the Upper Yangtze River basin where a few flood events contribute most of the annual sediment load. This paper collected field data from representative hydrological stations and applied statistical analysis to investigate the change in runoff and sediment load during flood events in the Upper Yangtze River, including both the mainstream (Jinsha River) and its major tributaries (Min, Tuo, Jialing, and Wu Rivers). The results show that flood events contribute more sediment load than runoff volume to the annual statistics. A general decreasing trend occurs in sediment load in all river basins, which is closely related to soil conservation efforts and dam construction. The series of sediment load modulus of each stations present abrupt change. The variations in sediment load modulus in low flow are more significantly than those in high flow at different abrupt-change period, indicating high flows during flood event have been found to still carry the same amount of sediment as their predecessors in the Upper Yangtze River. An "abnormal" increase in sediment load in recent years (2013–2020) has been observed at the Fushun station in Tuo River, and three factors, i.e., earthquake, high-intensity rainstorm and local scouring, were identified to be responsible for such increase. The findings of our study are helpful for better management of basin-scale sediment resources and regulation of reservoirs in the Upper Yangtze River. [ABSTRACT FROM AUTHOR]

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]

This paper assesses annual and seasonal trends in runoff and sediment load resulting from climate variability and afforestation in an upland Mediterranean basin, the Ribera Salada (NE Iberian Peninsula). We implemented a hydrological and sediment transport distributed model (TETIS) with a daily time-step, using continuous discharge and sediment transport data collected at a monitoring station during the period 2009–2013. Once calibrated and validated, the model was used to simulate the hydrosedimentary response of the basin for the period 1971–2014 using historical climate and land use data. Simulated series were further used to (i) detect sediment transport and hydrologic trends at different temporal scales (annual, seasonal); (ii) assess changes in the contribution of extreme events (i.e. low and high flows) and (ii) assess the relative effect of forest expansion and climate variability on trends observed by applying a scenario of constant land use. The non-parametric Mann–Kendall test indicated upward trends for temperature and decreasing trends (although non-significant) for precipitation. Downward trends occurred for annual runoff, and less significantly for sediment yield. Reductions in runoff were less intense when afforestation was not considered in the model, while trends in sediment yield were reversed. Results also indicated that an increase in the river's torrential behaviour may have occurred throughout the studied period, with low and high flow events gaining importance with respect to the annual contribution, although its magnitude was reduced over time. [ABSTRACT FROM AUTHOR]

Summary Modelling hydrology and sediment yield and its scale dependency has been limited by the quantity and quality of instrumental data. This paper aims to apply alternative methods to estimate runoff and sediment production rates at the event-scale and to characterize the hydro-sedimentary response of a highly torrential Mediterranean catchment to historical changes in land use and vegetation. A selection of well-dated and spatially-distributed check dams within the catchment were used to calibrate and validate a hydro-sedimentary distributed model (TETIS). Sediment volumes deposited by individual runoff events and trapped in check dams were estimated on the bases of detailed stratigraphic descriptions and subsequent GPS/TLS surveys. The model results showed a good agreement with the observed water flows and sediment volumes deposited behind several check dams. Management and land uses proved to be a decisive factor in the hydrological behaviour of the catchment, especially affecting erosion and sediment yield. It was observed that while the hydrological response of the catchment was sensitive to the percentage of each land use type, the sedimentary response was more dependent on the spatial distribution of land use. These differences between hydrology and sedimentary behaviour imply that the optimal soil use distribution for soil conservation may differ from the optimal soil use scenario oriented to attenuate flood peaks. This study suggest that soil use policies and erosion mitigation strategies should consider a holistic hydro-sedimentary approach, in order to become an adaptive option to reduce and mitigate the effects of erosion and flood peaks under global change. [ABSTRACT FROM AUTHOR]

[Display omitted] • MUSLE is able to predict sedimentary response and mitigation measures in burnt areas. • High-severity fire increase soil erosion and sediment load at the basin scale. • Emergency stabilization and soil erosion barriers are effective to reduce soil erosion. • SWAT model may be a post-fire management decision tool. The present paper contributes to bridging the gaps in modelling post-fire impact and mitigation measures on soil erosion. The specific aims were to predict the effects of forest fires and post-fire mitigation measures on runoff and specific sediment yield (SSY) in a river basin (Celone, S-E Italy). The Soil and Water Assessment Tool model, calibrated with field observations, was used to evaluate runoff and SSY for the current land use (baseline) and six post-fire scenarios. From 1990 to 2011, at the basin scale, the average annual SSY was 5.60 t ha- 1yr−1 (SD = 3.47 t ha-1yr−1). 20% of the total drainage area showed a critical value of SSY (>10 t ha−1 yr−1). The effects of different fire-severity levels were predicted for one year after the fire, acting on a limited area (2.3% of the total basin area). At the basin scale, the post-fire effect on surface runoff was negligible for all scenarios (<0.4%), and the impact on SSY increased from 5.86 t ha−1 yr−1 up to 12.05 t ha−1 yr−1. At the subbasin scale, the post-fire logging scenario showed the highest increase of soil loss (SSY increased from 9.48 t ha−1 yr−1 to 57.40 t ha−1 yr−1). Post-fire mitigation treatments like straw mulching and erosion barriers effectively reduced soil erosion in high- and moderate-severity fires (19.12 t ha-1yr−1 and 20.93 t ha−1 yr−1, respectively). At the hydrological response unit level, the SSY estimated for the forest in the baseline ranged from 1.18 t ha- 1yr−1 to 2.04 t ha−1 yr−1. SSY increased more than one order of magnitude for the high-severity fire scenarios and ranged from 4.33 to 6.74 t ha−1 yr−1 in the very low-severity fire scenario, underlining the scale effect from the HRU to the basin scale. [ABSTRACT FROM AUTHOR]

This paper reviews the main physical laws proposed in landscape evolution models (LEMs). It discusses first the main partial differential equations involved in these models and their variants. These equations govern water runoff, stream incision, regolith--bedrock interaction, hillslope evolution, and sedimentation. A synthesis of existing LEMs is proposed. It proposes three models with growing complexity and with a growing number of components: two-equation models with only two components, governing water and bedrock evolution; three-equation models with three components where water, bedrock, and sediment interact; and finally models with four equations and four interacting components, namely water, bedrock, suspended sediment, and regolith. This analysis is not a mere compilation of existing LEMs. It attempts at giving the simplest and most general physically consistent set of equations, coping with all requirements stated in LEMs and LEM software. Three issues are in particular addressed and hopefully resolved. The first one is a correct formulation of the water transport equation down slopes. A general formulation for this equation is proposed, coping not only with the simplest form computing the drainage area but also with a sound energy dissipation argument associated with the Saint-Venant shallow water equations. The second issue arises from the coexistence of two competing modes, namely the detachment-limited erosion mode on hillslopes, and the transport-limited sediment transport on river beds. The third issue (linked to the second) is the fact that no conservation law is available for material in these two modes. A simple solution proposed to resolve these issues is the introduction, as suggested by several authors, of an additional variable for suspended sediment load in water. With only three variables and three equations, the above-mentioned contradictions seem to be eliminated. Several numerical experiments on real digital elevation models (DEMs) illustrate the discussion and show results of landscape evolution with the proposed synthetic models. [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]

Abstract: Despite the fact that the microcatchment scale allows us to evaluate the real complexity of soil protection in fields, few studies have been carried out in olive groves. This paper explores, on annual and event scales, the hydrological and erosive patterns observed in an olive microcatchment of about 6ha under non-tillage with spontaneous grass cover, where data series of runoff and sediment load have been measured in a contrasting hydrological period of over 5years. Firstly, the features of the data series acquired in the study station and its temporal context were explored through statistical analysis (statistics, histograms and correlation test), the intensity–duration–frequency relationships and the annual values of MOPREDAS dataset (1946–2005). In addition, annual and seasonal patterns were checked through Principal Components Analysis (PCA) to characterize the impact of rainfall variability and management techniques. Events with return periods of under 3years caused sediment loads between 7.2 and 17.0Mg., which implies that very high soil losses can be expected from frequent events. Although the contribution of a few events to the annual runoff and sediment load is substantial, a different distribution characterized by prolonged rainfall periods and very high soil losses was observed for a “rainy year” 2009–2010 (with an accumulated frequency of annual rainfall close to 79%). The PCA illustrated a seasonal pattern of events where low values of soil losses and sediment concentration were observed in spring. This is probably associated to lower soil moisture and to sediment being trapped by the grass cover. Finally, the minimal cost of the spontaneous cover for soil protection encourages its use, despite the fact that could be inefficient when inter-rill erosion is either not the main source of sediment in the catchment or it is not well-established. [Copyright &y& Elsevier]

Abstract: The spatial scale dependency of runoff generation and sediment yield and accuracy to extending the results of experimental plots to surrounding watersheds is rarely taken into account. The present paper aimed to evaluate the accuracy of soil erosion plots with different lengths in estimation of runoff and soil loss from a small watershed in Iran. Towards this attempt, two similar sets of experimental plots with lengths of 2, 5, 10, 15, 20 and 25 and fixed width of 2m were installed on two north and south facing slopes (i.e. 6 plots on each slope and totally 12 plots) in Sanganeh watershed, Razavi Khorasan Province with an area of ca. 1ha. Runoff and sediment was collected at the outlet of each plot as well as main outlet of the watershed associated with 12 storm events occurred during November 2006 to June 2007. The results verified that the accuracy of plot estimates on sediment and runoff improved while the plot length increased. The optimal lengths for estimation of sediment and runoff parameters were found 15 and preferably 20m for plots located on southern slope. No significant difference was also proved among estimates obtained from plots established on north facing slope and those measured at the main outlet of the watershed. [Copyright &y& Elsevier]

Abstract: It is recognised that the hydrological and erosion processes in watersheds are very much conditioned by the (inter)action of a number of variables. This paper covers a 15-year period of studying those factors that have a major influence on the sediment yield and transport during individual hydrological events in a small Mediterranean agricultural watershed. Multivariate statistical techniques such as cluster analysis and principal component analysis were applied for the interpretation of datasets. In addition, the relationships between suspended sediment concentration and discharge (hysteretic loops) were also analysed. The hydrological response of the studied watershed is mainly controlled by the antecedent condition of the flow. Most of the runoff and sediment are generated during the wet season when vegetation cover is scant and saturation overland flow occurs promptly as a response to almost any rainfall events. In contrast, during the dry seasons even if high-intensity rainfalls normally occur, very scant runoffs are, however recorded, at the exit of the watershed. Most of the eroded sediment seems to come from riparian areas. The discharge registered at the watershed outlet up to 1h prior to the flood is a very good surrogate for antecedent soil moisture. [Copyright &y& Elsevier]

Abstract: The Great Barrier Reef (GBR) is a World Heritage Area and contains extensive areas of coral reef, seagrass meadows and fisheries resources. From adjacent catchments, numerous rivers discharge pollutants from agricultural, urban, mining and industrial activity. Pollutant sources have been identified and include suspended sediment from erosion in cattle grazing areas; nitrate from fertiliser application on crop lands; and herbicides from various land uses. The fate and effects of these pollutants in the receiving marine environment are relatively well understood. The Australian and Queensland Governments responded to the concerns of pollution of the GBR from catchment runoff with a plan to address this issue in 2003 (Reef Plan; updated 2009), incentive-based voluntary management initiatives in 2007 (Reef Rescue) and a State regulatory approach in 2009, the Reef Protection Package. This paper reviews new research relevant to the catchment to GBR continuum and evaluates the appropriateness of current management responses. [Copyright &y& Elsevier]

Summary: In many cultivated areas of the loess belt in Northern Europe, loamy soils are particularly sensitive to runoff and erosion. Those processes may not be continuous within a catchment, and runoff and erosion responses to rainfall events differ depending on the study scale at which they are examined. Many of the underlying mechanisms of this scale effect are still unknown and/or not well described. The objective of this paper is to identify and quantify the scale effects on runoff and erosion, from the field scale to the catchment scale in the context of the Austreberthe catchment, located in Normandy, in an agricultural area of the loess belt. Based on extensive information compiled at the hillslope and the catchment scales, the runoff and erosion budgets are compared between both scales, showing a more important decreasing effect for erosion (95%) than for runoff (85%) when moving from the hillslope to the catchment scale. The reduction due to the scale change is linear for runoff but not for erosion, underlining the complexity of erosion processes. Comparison of these budgets between both scales shows a significant effect of the vegetation cover as an important connectivity parameter at the hillslope scale, but not at the catchment scale. The importance of the connectivity is also quantified when comparing runoff and erosion budgets between two states of the catchment connectivity: the connectivity without soil and water conservation measures and a modified connectivity (with soil and water conservation measures). This change of connectivity in the catchment was estimated to lead to a decrease in discharge and erosion rates of 50% and 90%, respectively. Finally, the sediment budget analysis from the field to the river basin scale shows that 80% of the mobilised sediments on the slopes are deposited before reaching the Austreberthe River. From the Austreberthe catchment (215km2) to the Seine River Basin (more than 65,000km2 the calculated reduction of the erosion rate is only 25%. In this context, the scale effect is more important on hillslopes, where there is not any permanent river channel and where connectivity depends on rainfall events and landscape organisation, than in catchments drained by perennial rivers. [ABSTRACT FROM AUTHOR]

Abstract: Contempoary research on the soil and water conservation benefit mainly focus on the benefit calculation after a certain harnessing stage. However, little was known about how the harnessing messures affect the runoff and sediment during the harnessing process.This paper takes Lianshui watershed as the research object to analyze 32 years’ monitoring data of the outlet station in this watershed by virtue of Mann-Kendall Test and calculate quantificationally the contribution of long-term soil and water conservation measures harnessing to the runoff and sediment yield of this watershed in different stages by virtue of mathematical model, thus to identify the influence on long-term long-scale soil and water conservation measures harnessing on runoff and sediment yield variation. The results have showed that: After the 3 soil and water conservation harnessing stages during the period from 1983 to 2002, the sediment yield of Lianshui watershed has significantly decreased, however, the annual runoff hasn’t been changed along with the extension of the harnessing period, with regard to the influence on sediment reduction in the watershed, the contribution rate of water and soil conservation measures was 41.41% compared with the natural factors after 1st harnessing stage (1991-1998), 49.74% after 2nd harnessing stage (1999-2002), and in 3rd harnessing stage (2003-2009) it reached 67.68%, it can be seen that the influence of water and soil conservation measures on watershed sediment yield can gradually increase along with the extension of harnessing period and continuous expansion of harnessing scale and eventually become the dominant factor. [Copyright &y& Elsevier]

Abstract: Olive orchards located in mountainous or hilly landscapes in Southern Spain have been identified as one of the major sources of sediments for streams in the region. This paper presents a modeling study of the magnitude and spatial distribution of sources of sediment within a small 6.1ha olive orchard forming a microcatchment in a mountainous area. The model used was SEDD, which was calibrated using rainfall, runoff and soil erosion patterns monitored over a 3-year period. Although the data series are incomplete, 46 events were observed. SEDD permitted an analysis of the erosive behavior and the sediment delivery ratio (SDR) in the catchment on an event scale. High variability in catchment responses was observed, due to differences in the characteristics of storms and the seasonal ground cover. A small group of two or three erosive events, occurring mainly in autumn, were responsible for most annual runoff and sediment loads, while the impact of spontaneous grass cover was apparent in events occurring in spring, where, despite high runoff depth, the sediment loss was low. This bimodal tendency justified the calibration of the SEDD model through the medians of β-values in both the periods September–January and February–June. The results of the calibration (E =0.97 and RMSE =0.03tha−1) confirmed the applicability of SEDD to predict soil loss in the microcatchment and to allow us to complete the data series. Although the annual mean of SDR in the catchment for the study period was 3.8%, high spatial variability was found in the geomorphological units identified, with SDR values between 0.3% and 21.7%. On the event scale, probabilities of 50% for surpassing an SDR value of 10% were calculated for only 6% of the catchment area. The location of these most significant sources of sediment will permit the design of more efficient management plans in order to reduce sediment discharge into streams. [Copyright &y& Elsevier]

Abstract: An increasing number of studies have indicated that soil erosion, sediment redistribution and water discharge during the Holocene have varied greatly under influence of environmental changes. In this paper we have used a modeling approach to study the driving forces for soil erosion and sediment redistribution on the one hand, and water discharge on the other hand, during the Holocene for the Belgian Dijle catchment. Soil erosion and sediment redistribution was modeled using the spatially distributed Watem/Sedem model. Several scenarios of past land use and climate were used to model soil erosion, colluvial sedimentation and sediment export to the fluvial system, and those scenarios were combined with a sensitivity analysis. Modeling results are validated based on an available time differentiated field-based sediment budget. Water discharge was modeled using the spatially distributed STREAM model with a daily time step. The model was calibrated based on contemporary discharge data. The results indicate that soil erosion has increased between the early Holocene and the current situation by ca. 9% due to climatic variations, and by ca. 6000% due to changes in land use. The average discharge has increased by ca. 7%, mainly due to land use changes, and the discharge also shows more peaks. The decrease in cropland area and increase in built up area since 1775 CE has resulted in a decrease in soil erosion and in a further increase in discharge, showing the difference in sensitivity of both processes to land use changes. [ABSTRACT FROM AUTHOR]

Summary: In many agricultural regions investments are made into improved land management and catchment restoration with the aim of reducing sediment and nutrient delivery to downstream water bodies. This paper presents the results of an 8year field study that evaluated the impact of improved grazing land management (GLM) on a 14km2 sub-catchment of the Burdekin River in northern Australia. Land condition recovery and changes to runoff and sediment yield were measured on hillslopes (using three flumes) and at the end of the catchment (using automatic water sampling). Ground cover was monitored at the beginning of the wet season at hillslope and catchment scales using direct measurement and Quickbird satellite imagery. At the catchment scale, improved GLM resulted in an increase in mean ground cover between 2003 and 2007, relative to a control grazing property. However, the total suspended sediment yield from hillslopes did not decline due to the disproportionately high yields from low (<10%) cover sites particularly in high runoff years. In 2007, when there was above-average rainfall, 97% of the hillslope derived fine sediment was coming from less than 3% of the catchment. Catchment sediment yield also increased, associated with higher rainfall and runoff in latter years of the study. In years of above-average rainfall, it is estimated that less than 40% of catchment sediment yield was derived from hillslope erosion. Channel erosion is considered to contribute the remaining sediment. Rehabilitation of hillslope scalds and gullies is likely to be an important companion to improved GLM to reduce catchment fine sediment yields in this landscape. Evaluation of gully and hillslope scald rehabilitation techniques is required, including the economic feasibility of such options. [Copyright &y& Elsevier]

Summary: Poor land condition resulting from unsustainable grazing practices can reduce enterprise profitability and increase water, sediment and associated nutrient runoff from properties and catchments. This paper presents the results of a 6year field study that used a series of hillslope flume experiments to evaluate the impact of improved grazing land management (GLM) on hillslope runoff and sediment yields. The study was carried out on a commercial grazing property in a catchment draining to the Burdekin River in northern Australia. During this study average ground cover on hillslopes increased from ∼35% to ∼75%, although average biomass and litter levels are still relatively low for this landscape type (∼60 increasing to 1100kg of dry matter per hectare). Pasture recovery was greatest on the upper and middle parts of hillslopes. Areas that did not respond to the improved grazing management had <10% cover and were on the lower slopes associated with the location of sodic soil and the initiation of gullies. Comparison of ground cover changes and soil conditions with adjacent properties suggest that grazing management, and not just improved rainfall conditions, were responsible for the improvements in ground cover in this study. The ground cover improvements resulted in progressively lower runoff coefficients for the first event in each wet season, however, runoff coefficients were not reduced at the annual time scale. The hillslope annual sediment yields declined by ∼70% on two out of three hillslopes, although where bare patches (with <10% cover) were connected to gullies and streams, annual sediment yields increased in response to higher rainfall in latter years of the study. It appears that bare patches are the primary source areas for both runoff and erosion on these hillslopes. Achieving further reductions in runoff and erosion in these landscapes may require management practices that improve ground cover and biomass in bare areas, particularly when they are located adjacent to concentrated drainage lines. [Copyright &y& Elsevier]

Abstract: The sealing of surfaces in urban areas makes storm water management compulsory. The suspended solids from surface runoff water accumulate in infiltration basins and may impact on water infiltration. This paper describes a study of the effect of the settlement of sedimentary layers on the water infiltration capacity of two urban infiltrations basins. In situ water infiltration experiments were performed (1) to quantify the effect of sediment on water infiltration at local scale and (2) to derive the complete characterization of the unsaturated hydraulic properties of sediments and subsoils by using the BEST algorithm. These properties were used to model the effect of sediments on 1D water infiltrations at basin scale, simulating real operating conditions for three model rainfalls (shower, rainfall and light rainfall) and the full year 2008. The results clearly prove that sediments reduce local water infiltration capacities, due to their lower saturated hydraulic conductivities (K s ). Moreover, numerical results have shown that this finding could have a drastic impact on water infiltration at the basin scale through increasing the number and duration of water pondings. From the technical point of view, this study underlines the need for efficient monitoring of infiltration basin sedimentation and its impact on water infiltration capacity. [Copyright &y& Elsevier]

Abstract: In this paper, different characteristics of runoff and eroded sediments were investigated as well as changes in textural composition of the original soil, on experimental plots. The objectives were to investigate the particle size distribution of the eroded sediments, as a function of soil, crop, and meteorological variables, and changes in texture due to water erosion over time. The study was performed on experimental plots in the Apennines mountain range, in northern Italy, where an automated system for measuring runoff water and sediment was installed. Runoff water, sediment yield and sediment mean diameters were analyzed as a function of land cover, rainfall kinetic energy and stream power. In particular, the study investigated: (a) the sediment particle size distribution using laser diffraction, (b) the effect of rainfall kinetic energy, stream power and crop coverage on runoff, sediment yield and sediment particle size distribution and (c) the changes in soil texture on the cultivated field plots, over a period of 15years. The results of this study showed: (a) the particle size distribution of the eroded sediment was generally unimodal and the dominant fraction characterizing the eroded sediments was the one with a mean particle diameter ranging from 4.3 to 13.1μm, comprised in the silt range, (b) the mean particle diameter changed depending on the rainfall kinetic energy and the stream power, with a positive correlation between particle diameter and rainfall kinetic energy under bare soil, and (c) the effect of long-term erosion showed that the original soil textural composition experienced a statistically significant change over a period of 15years, with a decrease in the silt fraction and a relative increase in the clay fraction, due to losses of silt in the eroded sediments. [Copyright &y& Elsevier]

Summary: Nutrient transport in surface runoff associated with sediment constitutes an important nutrient loss in Tigray, Northern Ethiopia, but little information is available on this aspect. This paper analyses runoff coefficient, runoff volume, sediment yield and sediment-associated nutrient losses under different land uses (cultivated, grazing, eucalyptus plantation, and exclosure lands) in the Tigray highlands. Two years data on rainfall, runoff volume, sediment yield and sediment-associated nutrient losses were collected from 31 runoff plots of 20m2. Results show that runoff coefficient, runoff volume and sediment yield are significantly higher in cultivated land than in the other land uses. On average, runoff volume from cultivated land is two times higher than in open grazing land at Gum Selassa, but at Maileba it is 5, 6, 16 times higher than in plantation, open grazing, and exclosures, respectively when extreme rainfall events were excluded. The respective values for sediment yield from cultivated land at Maileba are 4, 5 and 27 times higher. Variation in total rainfall amount that produced runoff explained 69% of the annual runoff volume variability, and this in turn explained 76% of the annual sediment yield variability. Among the plot variables, vegetation ground cover was significantly and negatively correlated with runoff coefficient; and runoff generation tends to be negligible when the ground cover exceeds 72%. Concentration of sediment-associated nutrient losses decreased with increasing sediment yield, supposedly related to the important nutrient dissolution effect of high runoff volumes. Rainfalls with low amount and intensity are important for selective removal of nutrient-rich sediments. Annually, on average, nutrient and OC losses varied between 14.4 and 263.4kgha−1 y−1 for OC, 2.1–32.8kgha−1 y−1 for N, 0.02–0.2kgha−1 y−1 for available P and 0.35–5.25kgha−1 y−1 for available K, with the lowest values in all cases on exclosures and highest on cultivated land. The present study demonstrates the effectiveness of exclosures and plantation in controlling runoff, sediment and sediment-associated nutrient losses on steep degrading lands of the region. [Copyright &y& Elsevier]

[Display omitted] • Future impacts of LULC and climate on the streamflow and erosion by new approaches. • SWAT model was applied to estimate future runoff-erosion. • Future climate data generated using GCM coupled to regional circulation model. • The methodology contextualizes potentially significant hydrological changes. • The changes may impact the sustainability of water resources management. Water management in the Caatinga/Atlantic forest ecotone in Brazil is critically dependent on better understanding of potential future changes in streamflow and sediment dynamics. This paper evaluates both the future impacts of land use and land cover (LULC) changes and the impacts of climate change on the streamflow and sediment yield in the Tapacurá River basin in northeastern Brazil, using a novel combination of approaches. Projected climate data derived using global circulation model HadGEM2-ES were coupled to regional circulation model ETA-CPTEC/HadCM3 for two representative concentration pathways (RCP 4.5 and 8.5), with bias correction. Two future LULC scenarios were generated: (a) optimistic (current LULC), and (b) pessimistic (land use change trends continue), using the multilayer perceptron algorithm (MP). The Soil and Water Assessment Tool (SWAT) model was used to estimate future streamflow and erosion for different periods (2011–2040, 2041–2070 and 2071–2099). The SWAT model was calibrated for period of 1995–2003 and validated for 2004–2013. The results showed good accuracy in relation to R2, NSE and PBIAS for the calibration and validation of the runoff, as well as for the verification of the sediment yield. Simulations indicated significant increases in erosion for the pessimistic scenario under RCP 8.5, followed by the pessimistic scenario and RCP 4.5. Lower sediment yields occurred for the optimistic and RCP 8.5, with lower still for the optimistic and RCP 4.5. However, the latter estimates are still considerably higher than baseline conditions. Although higher flows are found for some scenarios, the increases in sediment yield have serious implications for reservoir siltation and storage reduction. Despite modeling uncertainty, the results demonstrate that the proposed methodology has promising scope to contextualize potentially significant regional hydrological changes which have implications for land and biodiversity management and the sustainability of water resources in the Caatinga/Atlantic forest ecotone. [ABSTRACT FROM AUTHOR]

Summary: Annual runoff and annual suspended sediment loads of hydrological gauging stations along the mainstream of the Yangtze River basin (Pingshan station, Yichang station, Hankou station and Datong station) and main tributaries (Beipei station in Jialingjiang River, Wulong station in Wujiang River and Huangzhuang station in Hanjiang River) were analyzed with the help of Mann–Kendall trend analysis and linear regression analysis. Research results indicate that (1) changing patterns of runoff and sediment loads are different in different parts of the Yangtze River basin. No significant trend is detected for annual runoff at all stations at >95% confidence level. Changes of sediment loads, however, demonstrate different pictures in the Yangtze River basin. The sediment loads are in increasing trend in Pingshan station- the most upstream station on the Yangtze River basin (this increasing trend is significant at >95% confidence level after about 1990), but are in decreasing trend at other stations (including stations in the tributaries studied in this paper). This decreasing trend becomes more obvious from Yichang station to Datong station. (2) Water reservoirs exerted more influences on changes of sediment loads than on runoff, which is the main reason for the decreasing trend of sediment loads found in most stations. (3) Influences of water reservoirs on sediment loads are more obvious in the tributaries than in the mainstream of the Yangtze River basin, while in the mainstream the variation patterns of sediment loads are determined by multiple factors. [Copyright &y& Elsevier]

Abstract: Hydrological connectivity is a term often used to describe the internal linkages between runoff and sediment generation in upper parts of catchments and the receiving waters. In this paper, we identify two types of connectivity: direct connectivity via new channels or gullies, and diffuse connectivity as surface runoff reaches the stream network via overland flow pathways. Using a forest road network as an example of a landscape element with a high runoff source strength, we demonstrate the spatial distribution of these two types of linkages in a 57 km2 catchment in southeastern Australia. Field surveys and empirical modelling indicate that direct connectivity occurs primarily due to gully development at road culverts, where the average sediment transport distance is 89 m below the road outlet. The majority of road outlets were characterised by dispersive flow pathways where the maximum potential sediment transport distance is measured as the available hillslope length below the road outlet. This length has a mean value of 120 m for this catchment. Reductions in sediment concentration in runoff plumes from both pathways are modelled using an exponential decay function and data derived from large rainfall simulator experiments in the catchment. The concept of the volume to breakthrough is used to model the potential delivery of runoff from dispersive pathways. Of the surveyed road drains (n=218), only 11 are predicted to deliver runoff to a stream and the greatest contributor of runoff occurs at a stream crossing where a road segment discharges directly into the stream. The methodology described here can be used to assess the spatial distribution and likely impact of dispersive and gullied pathways on in-stream water quality. [Copyright &y& Elsevier]

This paper addresses some fundamental problems related to the structure and function of catchment areas in general and for seasonal (weekly, monthly) mass balance calculations of radionuclides (and metals, organics and nutrients) in particular. A new catchment area model has been developed and critically tested. This modelling approach is based on mechanistic principles. The catchment area is differentiated into inflow (∼dry land) areas and outflow (=wetland) areas. The model also accounts for time-dependent fixation of substances in the catchment related to single-pulse fallouts. The model has a general structure. It is simple to use since there are only two soil type classes and three categories for the outflow areas. In critical tests, the model was put within a framework where it is intended, i.e., within a more comprehensive lake model. Radiocesium was used as a tracer in these tests. Modelled values were compared to empirical data from 23 lakes (351 data on 137Cs in water, as well as in sediments, small fish and on suspended particles) covering a very wide limnological domain (latitudes from 42 to 61 °V, altitudes from 0 to 1090 m ASL, catchment areas from 0.17 to 114,700 km2, precipitation from 430 to 1840 mm/year, lake areas from 0.042 to 1147 km2, mean depths from 1.1 to 90 m, pH from 5.1 to 9 units, potassium concentrations from 0.23 to 27.5 mg/l, total P concentrations from 8.3 to 100 μg/l and theoretical water retention times from 0.02 to 137 years). When modelled values were compared to empirical data, the slope was almost perfect (0.99) as well as the coefficient of determination (r2=0.96). [Copyright &y& Elsevier]

Understanding of the impacts of key influential factors on RDS related heavy metal (HM) contamination is crucial for developing effective RDS management strategies to support the stormwater pollution mitigation. In this paper, three factors (i.e. traffic condition, slope of road and antecedent dry period) were considered to investigate their influences on the accumulation of RDS and adsorbed HMs. Positive correlations between truck and Zn/Ni content in RDS, car and Cu/Pb content in fine RDS, as well as bus and Cu content in coarse RDS were observed. Relative to sloping stretches, RDS from level stretches generally presented finer size distributions and aggravated HM contamination in fine fractions. Moreover, the fine RDS and adsorbed HMs increased significantly with the accumulation of RDS. Based on these findings, optimized RDS management strategies were proposed to enhance the removal of washable RDS in pollution hotspots. For example, tandem sweeping technologies, performing high efficiency in capturing fine particles, are suggested to be employed during the steady period of RDS accumulation, in order to reduce fine RDS effectively. The outcomes of this study provide useful reference for the source control of stormwater runoff pollution. • Vehicles of different types were indicative of specific HM contamination. • RDS on level stretches showed heavier HM contamination. • RDS presented aggravated HM contamination during the steady period of accumulation. • Optimized RDS management strategies were proposed. [ABSTRACT FROM AUTHOR]