Sediment Detachment Research Articles

Soil detachment and transport under the combined action of rainfall and runoff energy on shallow overland flow

Rainfall and runoff energy results in soil erosion. This paper presents new the concepts of rainfall and runoff energy and analyzes the relationship of rainfall energy and runoff energy with sediment transport based on the conversion theory of kinetic and potential energy using artificial rainfall and mechanical calculation. The results show that the ratio of sediment detachment in sloping fallow overland flow increases with the slope gradient, rainfall energy and runoff energy, while the sediment detachment ratio under raindrop impact are significantly higher than those under no raindrop impact. The sediment concentration increases with the slope gradient and rainfall energy; when the slope gradient and rainfall energy are constant, the sediment concentration decreases as the runoff energy increases. Rainfall disturbance coefficients have a logarithmic correlation with the rate of rainfall energy and runoff energy. On the same slope gradient, when the rainfall energy is constant, the disturbance coefficient decreases as the runoff energy increases, while when the runoff energy is constant, the disturbance coefficient increases as the rainfall energy increases. Rainfall energy results in sediment detachment, and runoff energy is the transportation for erosion sediment. This showed that rainfall energy and runoff energy are important in the sediment detachment and transportation of shallow overland flow.

Assessing hillslope-channel connectivity in an agricultural catchment using rare-earth oxide tracers and random forests models

Soil erosion from agricultural areas is a large problem, because of off-site effects like the rapid filling of reservoirs. To mitigate the problem of sediments from agricultural areas reaching the channel, reservoirs and other surface waters, it is important to understand hillslope-channel connectivity and catchment connectivity. To determine the functioning of hillslope-channel connectivity and the continuation of transport of these sediments in the channel, it is necessary to obtain data on sediment transport from the hillslopes to the channels. Simultaneously, the factors that influence sediment export out of the catchment need to be studied. For measuring hillslope-channel sediment connectivity, Rare-Earth Oxide (REO) tracers were applied to a hillslope in an agricultural catchment in Navarre, Spain, preceding the winter of 2014-2015. The results showed that during the winter no sediment transport from the hillslope to the channel was detected.To test the implication of the REO results at the catchment scale, two contrasting conceptual models for sediment connectivity were assessed using a Random Forest (RF) machine learning method. The RF method was applied using a 15-year period of measured sediment output at the catchment scale. One model proposes that small events provide sediment for large events, while the other proposes that only large events cause sediment detachment and small events subsequently remove these sediments from near and in the channel. For sediment yield prediction of small events, variables related to large preceding events were the most important. The model for large events underperformed and, therefore, we could not draw any immediate conclusions whether small events influence the amount of sediment exported during large events. Both REO tracers and RF method showed that low intensity events do not contribute any sediments from the hillslopes to the channel in the Latxaga catchment. Sediment dynamics are dominated by sediment mobilisation during large (high intensity) events. Sediments are for a large part exported during those events, but the system shows a memory of the occurrence of these large events, suggesting that large amounts of sediments are deposited in and near the channel after these events. These sediments are gradually removed by small events. To better understand the delivery of sediments to the channel and how large and small events influence each other more field data on hillslope-channel connectivity and within-channel sediment dynamics is necessary.

Sediment detachment and transport processes associated with internal erosion of soil pipes

AbstractSubsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping. The development of perched water tables fosters lateral flow that can result in seepage at the surface and/or formation of soil pipes by internal erosion of preferential flow paths. Continued internal erosion of soil pipes can lead to gullies, dam and levee failures. However, the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented. This paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes. Knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes. Copyright © 2017 John Wiley & Sons, Ltd.

The Importance of Scientific Publishing: Teaching an Undergraduate How to Swim the Entire Length of the Pool

The Importance of Scientific Publishing: Teaching an Undergraduate How to Swim the Entire Length of the Pool

Detachment characteristics of root-permeated soils from laboratory jet erosion tests

The influence of vegetation on flow and sediment dynamics at various spatial and temporal scales has been well documented. Vegetation may be one of the most effective measures in streambank stabilization. Traditionally, research on the influence of vegetation roots on streambank stabilization has focused on mechanical reinforcement and reduced applied shear stress due to above ground biomass. Few studies have investigated the effect of roots on fluvial detachment of sediment. This study conducted 36 mini-jet erosion tests (mini-JETs) on bare soil samples and 29 mini-JETs on root-permeated soil samples (average root diameters of 0.5 to 1.7mm) to determine the role of roots in erosion resistance. The research also estimated parameters of the linear excess shear stress model (erodibility coefficient, kd, and critical shear stress, τc) and a nonlinear detachment model called the Wilson Model (b0 and b1) and investigated the correlations between parameters of the two models and root characteristics. Root-permeated soil samples were more erosion resistant at higher shear stress as the τc and b1 parameters were on average higher for the vegetated samples than the bare soil samples. As root diameter increased in the soil samples, erosion rates at high shear stress decreased. The erodibility coefficient parameters (b0 and kd) of both the linear and nonlinear detachment models were negatively and significantly correlated to root diameter through power functions. No significant correlation was detected between critical shear stress or b1 and root parameters which supports conclusions of previous studies. Significant correlations were observed among the parameters of the excess shear stress model and the nonlinear detachment model; especially high correlation was observed between τc and b1 for the vegetated samples. In conclusion, root-permeated soils exhibited lower erosion rates primarily through increasing the required shear stress before detachment.

The impact of typhoons on sediment connectivity: lessons learnt from contaminated coastal catchments of the Fukushima Prefecture (Japan)

AbstractSediment connectivity characterizes the physical transfer of sediment through different geomorphic compartments in catchments due to sediment detachment, transport and deposition. Quantifying and modelling sediment connectivity is therefore a key prerequisite to improving our understanding of the dispersion of particle‐borne contaminants, especially in catchments exposed to highly erosive climates. The objective of this study is to provide novel insights into typhoon impacts on sediment connectivity from hillslopes to rivers. The dispersion of particle‐bound caesium‐137 (137Cs) was investigated in two coastal catchments draining the main contamination plume from the Fukushima Daiichi Nuclear Power Plant accident. Five sampling campaigns were carried out from November 2011 to November 2015, after each typhoon season. The spatial and temporal evolution of 137Cs contamination was investigated through the calculation of 137Cs enrichment ratios in sediment relative to nearby soils. Rainfall erosivity (EI30) associated with the main typhoons that occurred prior to each sampling campaign were computed, mapped, and finally used to improve a topographic‐based index of connectivity. From 2011 to 2015, mean contamination levels in Mano and Niida catchments decreased from 11.9 kBq kg−1 to 3.3 kBq kg−1 and from 34.1 kBq kg−1 to 8.0 kBq kg−1, respectively. Regional mean EI30 ranged from 262 MJ mm ha−1 h−1 for typhoon Jelawat (in 2012) to 1695 MJ mm ha−1 h−1 for typhoon Roke (in 2011). Typhoons Roke (2011) and Etau (2015) showed the highest connectivity from contaminated sources to the rivers, and induced a significant export of sediment to the ocean. In 2013 a slight increase in 137Cs levels in river sediments occurred, likely resulting from initial decontamination works and the occurrence of two consecutive typhoons. Importantly, this research provides new insights into the connectivity of the main sources of sediments contaminated with radiocaesium in Fukushima Prefecture and their temporal evolution, which will help with ongoing decontamination efforts. Copyright © 2016 John Wiley & Sons, Ltd.

Quantifying the Sediment Transport Capacity in Eroding Rills Using a REE Tracing Method

AbstractQuantifying the sediment transport capacity is crucial for better understanding of water erosion process. The limit for quantifying soil erosion process is due to a lack of spatially distributed sediment data. The rare earth elements (REEs) are a group of elements with unique properties for the potential study of soil sediment transport capacity, due to its characteristics as being strongly bound to soil particles and not interfere with sediment detachment, and transportation processes. The objective of this study was to estimate the sediment transport capacity in eroding rills using the REE tracing method. Ten REE oxides (Ho2O3, Tb4O7, Eu2O3, Yb2O3, Dy2O3, Sm2O3, La2O3, Tm2O3, CeO2, and Nd2O3) were used as tracers mixed with soil. A flume experiment combined with five slopes and four flow rates was conducted. Water flow rates of 2, 4, and 8 L min−1 (L min−1) were taken for the three steeper slopes in the experiment, and flow rates of 4, 8, and 12 L min−1 were taken for the two gentle slopes. Water flow was pumped to a tan and introduced to the inlet of a flume with 8‐m long and 0·1‐m wide, which were divided into ten equal segments, with each segment containing a tabbed REE‐soil mixture. The sediment load along different length rills was calculated from the REE concentrations in the eroded material and its background reference value. With an exponential rise to maximum equation between sediment loads with the downslope distance along eroding rills, we developed a method to quantify the sediment transport capacity. The results obtained by the REE tracing method confirmed that sediment transport capacity increased as a power function with flow rate and slope gradient, with a determination of coefficient (R2) of 0·93 (p < 0·001). Sediment transport capacity was more dependent on the flow rate and less on the slope gradient with larger exponent for the flow rate. The results from this study showed that the REE method is helpful to estimate the sediment transport capacity in a concentrated flow on the sloping cropland, and to improve understanding the processes of water erosion. However, the feasibility of using the REE for quantifying sediment transport should be further investigated at the field scale on complex landscapes and under natural rainfall. Copyright © 2016 John Wiley & Sons, Ltd.

Comparison of Linear and Nonlinear Models for Cohesive Sediment Detachment: Rill Erosion, Hole Erosion Test, and Streambank Erosion Studies

AbstractCohesive sediment detachment is typically modeled for channels, levees, spillways, earthen dams, and internal erosion by using a linear excess shear stress approach. However, mechanistic nonlinear detachment models, such as the Wilson model, have recently been proposed in the literature. Questions exist as to the appropriateness of nonlinear relationships between applied shear stress and the erosion rate. Therefore, the objective of this research was to test the appropriateness of linear and nonlinear detachment models for cohesive sediment detachment using three data sets: (1) rill erodibility studies across a limited range of applied shear stress (0.9–21.4 Pa), (2) hole erosion tests (HETs) across a wide range of applied shear stress (12.6–62.0 Pa), and (3) streambank erodibility as quantified by jet erosion tests (JETs) for the linear excess shear stress equation and the nonlinear Wilson model across a small range of shear stress (1–4 Pa). The Wilson model was also incorporated into the bank st...

Effects of vegetation cover on sediment particle size distribution and transport processes in natural rainfall conditions on post-fire hillslope plots in South Korea

Sediments were collected from four slow vegetation recovery plots, six fast vegetation recovery plots and five unburned plots at a post-fire site on a rainfall event basis and sorted for size distribution. The aim was to evaluate the effects of vegetation cover, soil aggregate stability, slope and rainfall intensity on sediment size distribution, transport selectivity and erosion processes between the burned and unburned treatment plots. Sediment detachment and transport mechanisms and the particle size transport selectivity of the eroded sediment were assessed based on enrichment ratios (ER) and mean weighted diameter (MWD) methods. The most eroded particle size class in all treatment plots was the 125–250μm class and, generally, the percentage of eroded particle sizes did not increase with slope and rainfall intensity. Higher MWD of the eroded sediment was related to a higher percentage of bare soil exposed and gravel content associated with high soil burn severity and soil disaggregation in the slow vegetation recovery plots. The enrichment of finer clay silt particle sizes increased with varying maximum 30-min rainfall intensity (I30) in the slow vegetation recovery plots, and reflected increased aggregate breakdown and transport selectivity, whereas no good relationship was found in the fast vegetation recovery and unburned plots with varying I30. A minimum I30 of <3.56mmh–1 and a maximum of 10.9mmh–1 were found to be the threshold rainfall intensity values necessary for aggregate breakdown and transport of finer particles by both rainsplash and rainflow in the slow vegetation recovery plots, whereas the response was weak in the fast vegetation recovery and unburned plots following varying I30 dominated only by rainsplash transport closer to the plot sediment collector. The results show that higher vegetation cover in the fast vegetation recovery and unburned plots reduces erosive rainfall energy by 5.6- and 17.7-fold respectively, and runoff energy by 6.3- and 21.3-fold respectively, limiting aggregate breakdown and transport selectivity of finer particles compared with the slow vegetation recovery plots.

Use of barley straw residues to avoid high erosion and runoff rates on persimmon plantations in Eastern Spain under low frequency–high magnitude simulated rainfall events

Soil and water losses due to agricultural mismanagement are high and non-sustainable in many orchards. An experiment was set up with rainfall simulation at 78 mm h–1 over 1 hour on 20 paired plots of 2 m2 (bare and straw covered) in new persimmon plantations in Eastern Spain. Effects of straw cover on the control of soil and water losses were assessed. An addition of 60% straw cover (75 g m–2) resulted in delayed ponding and runoff generation and consequently reduced water losses from 60% to 13% of total rainfall. The straw cover reduced raindrop impact and thus sediment detachment from 1014 to 47 g plot–1 h–1. The erosion rate was reduced from 5.1 to 0.2 Mg ha–1 h–1. The straw mulch was found to be extremely efficient in reducing soil erosion rates.

Application of microbially induced calcite precipitation in erosion mitigation and stabilisation of sandy soil foreshore slopes: A preliminary investigation

Eroding foreshores endanger the floodplains of many estuaries, as such, effective and environmentally friendly interventions are sought to stabilise slopes and mitigate erosion. As a step in forestalling these losses, we developed laboratory microcosms to simulate tidal cycles and examined the mechanisms of erosion and failure on sandy foreshore slopes. As an experimental aim, we applied microbially induced calcite precipitation (MICP) to selected slopes and compared the effectiveness of this microbial geo-technological strategy to mitigate erosion and stabilise slopes.To assess shoreline stability, thirty cycles of slowly simulated tidal currents were applied to a sandy slope. Significant sediment detachment occurred as tides moved up the slope surface. For steeper slopes, one tidal event was sufficient to cause collapse of the slopes to the soil's angle of repose (~35°). Subsequent tidal cycles gradually eroded surface sediments further reducing slope angle (on an average 0.2° per tidal event). These mechanisms were similar for all slopes irrespective of initial slope inclination.MICP was evaluated as a remedial measure by treating a steep slope of 53° and an erosion-prone slope angle of 35° with Sporosarcina pasteurii and cementation solution (0.7M CaCl2 and urea) before tidal simulations. MICP produced 120kg calcite per m3 of soil, filling 9.9% of pore space. Cemented sand withstood up to 470kPa unconfined compressive stress and showed significantly improved slope stability; both slopes showed negligible sediment erosion. With efforts towards optimisation for upscaling and further environmental considerations (including effect of slope saturation on MICP treatment, saline water and estuarine/coastal ecology amongst others), the MICP process demonstrates promise to protect foreshore slope sites.

Model analysis of check dam impacts on long-term sediment and water budgets in Southeast Arizona, USA

The objective of this study was to evaluate the effect of check dam infrastructure on soil and water conservation at the catchment scale using the Soil and Water Assessment Tool (SWAT). This paired watershed study includes a watershed treated with over 2000 check dams and a Control watershed which has none, in the West Turkey Creek watershed, Southeast Arizona, USA. SWAT was calibrated for streamflow using discharge documented during the summer of 2013 at the Control site. Model results depict the necessity to eliminate lateral flow from SWAT models of aridland environments, the urgency to standardize geospatial soils data, and the care for which modelers must document altering parameters when presenting findings. Performance was assessed using the percent bias (PBIAS), with values of ±2.34%. The calibrated model was then used to examine the impacts of check dams at the Treated watershed. Approximately 630tons of sediment is estimated to be stored behind check dams in the Treated watershed over the 3-year simulation, increasing water quality for fish habitat. A minimum precipitation event of 15mm was necessary to instigate the detachment of soil, sediments, or rock from the study area, which occurred 2% of the time. The resulting watershed model is useful as a predictive framework and decision-support tool to consider long-term impacts of restoration and potential for future restoration.

Availability and performance of sediment detachment and transport functions for overland flow conditions

Soil erosion is a global environmental problem. To quantify water erosion rates at the field, hillslope or catchment scale, several spatially-distributed soil erosion models have been developed. The accuracy of those models depends largely on the sediment detachment and transport functions used, many of which were developed from empirical research. In this paper, the physical basis of the available sediment detachment and transport functions is reviewed, and their application boundaries determined. Well-known and widely-used sediment detachment and transport functions are discussed on the basis of composite force predictors, i.e. shear stress, stream power, unit stream power and effective stream power, and their suitability is elucidated based on information in the literature. It was found that only a few sediment detachment functions are available, and those have been poorly tested. Most erosion models ignore direct calculation of sediment detachment, but use the sediment transport capacity deficit approach to estimate detachment rate. Many more sediment transport functions are available that also tested better for overland flow conditions. However, our tests did not result in a single function that appeared to perform best under a range of experimental conditions. The unit stream power-based functions developed by Govers seem to be the most promising ones for water erosion modelling. It is therefore recommended to evaluate the performance of existing sediment transport functions with more detailed field and laboratory datasets.Editor Z.W. Kundzewicz

Structural and functional connectivity as a driver of hillslope erosion following disturbance

Hydrologic response to rainfall on fragmented or burnt hillslopes is strongly influenced by the ensuing connectivity of runoff and erosion processes. Yet cross-scale process connectivity is seldom evaluated in field studies owing to scale limitations in experimental design. This study quantified surface susceptibility and hydrologic response across point to hillslope scales at two degraded unburnt and burnt woodland sites using rainfall simulation and hydrologic modelling. High runoff (31–47 mm) and erosion (154–1893 g m–2) measured at the patch scale (13 m2) were associated with accumulation of fine-scale (0.5-m2) splash-sheet runoff and sediment and concentrated flow formation through contiguous bare zones (64–85% bare ground). Burning increased the continuity of runoff and sediment availability and yield. Cumulative runoff was consistent across plot scales whereas erosion increased with increasing plot area due to enhanced sediment detachment and transport. Modelled hillslope-scale runoff and erosion reflected measured patch-scale trends and the connectivity of processes and sediment availability. The cross-scale experiments and model predictions indicate the magnitude of hillslope response is governed by rainfall input and connectivity of surface susceptibility, sediment availability, and runoff and erosion processes. The results demonstrate the importance in considering cross-scale structural and functional connectivity when forecasting hydrologic and erosion responses to disturbances.

Soil surface roughness: comparing old and new measuring methods and application in a soil erosion model

Abstract. Quantification of soil roughness, i.e. the irregularities of the soil surface due to soil texture, aggregates, rock fragments and land management, is important as it affects surface storage, infiltration, overland flow, and ultimately sediment detachment and erosion. Roughness has been measured in the field using both contact methods (such as roller chain and pinboard) and sensor methods (such as stereophotogrammetry and terrestrial laser scanning (TLS)). A novel depth-sensing technique, originating in the gaming industry, has recently become available for earth sciences: the Xtion Pro method. Roughness data obtained using various methods are assumed to be similar; this assumption is tested in this study by comparing five different methods to measure roughness in the field on 1 m2 agricultural plots with different management (ploughing, harrowing, forest and direct seeding on stubble) in southern Norway. Subsequently, the values were used as input for the LISEM soil erosion model to test their effect on the simulated hydrograph at catchment scale. Results show that statistically significant differences between the methods were obtained only for the fields with direct seeding on stubble; for the other land management types the methods were in agreement. The spatial resolution of the contact methods was much lower than for the sensor methods (10 000 versus at least 57 000 points per square metre). In terms of costs and ease of use in the field, the Xtion Pro method is promising. Results from the LISEM model indicate that especially the roller chain overestimated the random roughness (RR) values and the model subsequently calculated less surface runoff than measured. In conclusion, the choice of measurement method for roughness data matters and depends on the required accuracy, resolution, mobility in the field and available budget. It is recommended to use only one method within one study.

Turbulence statistics of flow through degraded channel bed of sand–gravel mixture

This paper describes the results of an experimental study on the turbulence characteristics of flow through bed profile of a laboratory channel that was degraded by detachment of its bed material consisting of sand–gravel mixture. The measurements of velocity and turbulence characteristics over the degraded bed profile were made at three locations along the degraded bed profile using an ADV. The maximum value of turbulence intensity and the Reynolds shear stress were found to occur at the level of bed surface existing before the detachment and these values decreased towards the flow surface. The magnitude of turbulence intensities and Reynolds shear stress are observed to reduce, as one moves towards the downstream along the degraded bed profile which signifies that vortex structure weakened by bed profile degradation. Quadrant analysis was performed which demonstrated the importance of ejection and sweep phases in sediment detachment and transport. Highest occurrence probabilities are found for sweep and ejection event. The other two events i.e. outward and inward interactions are found to have very small occurrence on the probabilities. Variation of occurrence probability with hole size (H) is also discussed.

Study of sediment movement in an irrigated maize–cotton system combining rainfall simulations, sediment tracers and soil erosion models

Summary Although soil erosion is one of the main threats to agriculture sustainability in many areas of the world, its processes are difficult to measure and still need a better characterization. The use of iron oxides as sediment tracers, combined with erosion and mixing models opens up a pathway for improving the knowledge of the erosion and redistribution of soil, determining sediment sources and sinks. In this study, magnetite and a multivariate mixing model were used in rainfall simulations at the micro-plot scale to determine the source of the sediment at different stages of a furrow–ridge system both with (+T) and without (–T) wheel tracks. At a plot scale, magnetite, hematite and goethite combined with two soil erosion models based on the kinematic wave approach were used in a sprinkler irrigation test to study trends in sediment transport and tracer dynamics along furrow lengths under a wide range of scenarios. In the absence of any stubble cover, sediment contribution from the ridges was larger than the furrow bed one, almost 90%, while an opposite trend was observed with stubble, with a smaller contribution from the ridge (32%) than that of the bed, at the micro-plot trials. Furthermore, at a plot scale, the tracer concentration analysis showed an exponentially decreasing trend with the downstream distance both for sediment detachment along furrows and soil source contribution from tagged segments. The parameters of the distributed model KINEROS2 have been estimated using the PEST Model to obtain a more accurate evaluation. Afterwards, this model was used to simulate a broad range of common scenarios of topography and rainfall from commercial farms in southern Spain. Higher slopes had a significant influence on sediment yields while long furrow distances allowed a more efficient water use. For the control of runoff, and therefore soil loss, an equilibrium between irrigation design (intensity, duration, water pattern) and hydric needs of the crops should be defined in order to establish a sustainable management strategy.

Testing the Effects of Detachment Limits and Transport Capacity Formulation on Sediment Runoff Predictions Using the U.S. Army Corps of Engineers GSSHA Model

The physics-based Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model was developed by the U.S. Army Corps of Engineers for hydrologic, sediment transport, and water quality analyses. GSSHA simulates erosion and transport of sediments on the overland flow plain based on rainfall intensity and overland flow depth and velocity. The original sediment transport capabilities in GSSHA were taken from the GSSHA predecessor, CASC2D-SED. Independent testing of the sediment transport methods in CASC2D-SED by researchers identified several deficiencies in the formulation that caused significant overestimation of sediment yield during hydrologic events that were much larger than a calibration event. Sediment detachment limits and a variety of overland sediment transport equations were incorporated into the GSSHA model to address these deficiencies. This paper presents an evaluation of these modifications in terms of GSSHA sediment yield predictions of both single-event and summer growing season sediment yields. Simulation results are compared with research-quality sediment discharge data set from the USDA Goodwin Creek Experimental Watershed (GCEW). Results show that the reformulated GSSHA sediment transport model predicts event-total sediment discharge volume within (±) 50% over hydrologic events that vary by three orders of magnitude. The transport capacity method selected for use in the simulation had a large effect on the model results.

Rangeland hydrology and erosion model (RHEM) enhancements for applications on disturbed rangelands

AbstractThe rangeland hydrology and erosion model (RHEM) is a new process‐based model developed by the USDA Agricultural Research Service. RHEM was initially developed for functionally intact rangelands where concentrated flow erosion is minimal and most soil loss occurs by rain splash and sheet flow erosion processes. Disturbance such as fire or woody plant encroachment can amplify overland flow erosion by increasing the likelihood of concentrated flow formation. In this study, we enhanced RHEM applications on disturbed rangelands by using a new approach for the prediction and parameterization of concentrated flow erosion. The new approach was conceptualized based on observations and results of experimental studies on rangelands disturbed by fire and/or by tree encroachment. The sediment detachment rate for concentrated flow was calculated using soil erodibility and hydraulic (flow width and stream power) parameters. Concentrated flow width was calculated based on flow discharge and slope using an equation developed specifically for disturbed rangelands. Soil detachment was assumed to begin with concentrated flow initiation. A dynamic erodibility concept was applied where concentrated flow erodibility was set to decrease exponentially during a run‐off event because of declining sediment availability. Erodibility was estimated using an empirical parameterization equation as a function of vegetation cover and surface soil texture. A dynamic partial differential sediment continuity equation was used to model the total detachment rate of concentrated flow and rain splash and sheet flow. The enhanced version of the model was evaluated against rainfall simulation data for three different sites that exhibit some degree of disturbance by fire and/or by tree encroachment. The coefficient of determination (R2) and Nash–Sutcliffe efficiency were 0.78 and 0.71, respectively, which indicates the capability of the model using the new approach for predicting soil loss on disturbed rangeland. By using the new concentrated flow modelling approach, the model was enhanced to be a practical tool that utilizes readily available vegetation and soil data for quantifying erosion and assessing erosion risk following rangeland disturbance. Copyright © 2014 John Wiley & Sons, Ltd.

Assessment of 80 years of ancient‐badlands restoration in Saldaña, Spain

ABSTRACTThis paper presents the history of badland generated in the Saldaña region, Spain; as well as the main responses eight decades after the start of restoration – in terms of vegetation, soil and erosive processes. The restoration consisted of intense reforestation and construction of more than 100 check dams and numerous wattle fences. Presently, the dense vegetation (87% cover) contrasts markedly with the degraded landscape from the early 20th century (5% cover). The thickness of litter and the natural presence of some species (Quercus pyrenaica, Paeonia broteroi and Lactarius deliciosus) clearly indicate the recovery of the site. The development of the forest cover shows that the intervention has the potential to recover almost 90% of the area. There is also evidence of soil regeneration, although some properties (erodibility, resistance to penetration and shear‐strength resistance) are not that different between the forested and degraded areas. In the restored zones, runoff is negligible, since a thick layer of moss covers the spillways of all the check dams. Erosion has almost been stopped by the effects of vegetation cover, litter and higher infiltration rates (infiltration rate in forested slopes is 43.4 times greater than in bare slopes). Sediment detachment, such as landslides, mudflows and piping, still occur, but are restricted to the degraded zones. Furthermore, even when sediments are mobilized from the upper degraded hillslopes during the larger storms events (2000–2010), check dams and the lower elevation restored forest‐buffers effectively work to reduce the sediment yield into the Carrión River by almost three orders of magnitude (<102 mg L‐1), compared with data from the 1930s and 1940s (>105 mg L‐1). Copyright © 2014 John Wiley & Sons, Ltd.