Increase In Erosion Rate Research Articles

3D photogrammetry as a tool for studying erosive processes at a Roman coastal site: the case of the Roman fish-salting plant at Sobreira (Vigo, Spain)

Rising sea levels, along with other biological and human factors, have increased erosion rates at a number of important sites located along the Atlantic coastline. Project GaltFish implemented a series of contingency measures to record some of these sites before they degraded further or totally disappeared. This process involved detailed photogrammetric recording of some of the sites under threat over a set period of time. One of the sites selected for this project was Sobreira (Vigo, Galicia): a Roman fish-salting factory which was partially destroyed by building activity in the 1980s and the remains of which are under threat from marine erosion and human action. In order to study the site, two photogrammetric models were created to examine the effect of erosive processes across the course of one year. The results illustrate that photogrammetry is an efficient tool for recording and analysing the issue of erosion. The data compiled helped in designing additional action in the factory, which was subject to a rescue excavation to record and help protect the site from further damage. This paper presents the results of this project, as well as the methodology used to produce the models, the data generated and their analysis. It is argued that the methodology can be used to collect and analyse data from other sites, and that this data could inform the political/administrative decision-making processes which concern the future management and preservation of archaeological sites under threat.

РАЗМЫВЫ ПОЙМЕННЫХ БЕРЕГОВ ОБИ И ИРТЫША И ИХ СВЯЗЬ С МОРФОЛОГИЕЙ РУСЛА1

This is the first study to provide generalized description of dangerous channel processes – riverbank erosion, conditions and patterns of its development for the Middle and Lower Ob (from the mouth of the Tom River to the city of Salekhard) and the Lower Irtysh (from the confluence with the Tobol River to the mouth). The geological and geomorphological conditions for the formation of the river channels and changes in the water content of the rivers downstream entail a change in the rate of riverbank erosion. On the Middle and Lower Ob, with a wide variety of channel types, the most active re-formations can be seen along the channel bends and the bends of the branches of the floodplain-channel branching and the bifurcated channel. On the Lower Irtysh, which has a predominantly meandering channel, riverbank erosion is confined to the free bends of the channel. The parameters of the channel forms, which determine the hydraulics of the flow, affect the characteristics of riverbank erosion (speed and length of the front). With an increase in the degree of bend development, the riverbank erosion rates increase with a simultaneous reduction in the length of the erosion front. On flat bends, there is no directional trend in the change in the riverbank erosion rates, but there is an increase in the length of the erosion front. The elongation of the riverbank erosion front is also traced for bends and forks of the channel with a larger step. The increase in the order of the river, which characterizes its water content, is accompanied by an increase in the rate of riverbank erosion on the Lower Irtysh. On the Ob, a significant contribution is made by the dispersal of the water runoff along the branches of the forks and forked channels, as well as the diversion of part of the runoff into floodplain channels (branches) and onto the inundated floodplain. The data obtained are of great importance for the development of water resources and the riverine areas of the Ob and Irtysh.

Erosion and sedimentation analysis due to land use changes in the Krueng Pase watershed

Human interactions with watershed can have positive and negative impact. The positive impact can improve socio-economic conditions. However, the negative impact is the degradation of the watershed function. For example, it’s continued increase in erosion rate on the land. The purpose of this study is to analyze erosion and sedimentation due to land use changes using the Universal Soil Loss Equation (USLE) and Modified Universal Soil Loss Equation (MUSLE) methods. Data collecting to determine erosion and sedimentation values are rainfall, soil erodibility and soil moisture, land use, and river water samples. The biggest decreased land use changes occurred in forest by 5.87%, followed by agriculture which decreased by 0.65% and water body 0.047%. On the other hand, built-up area increased by 0.65% and land used for agriculture increased by 6.15%. Furthermore, the level of erosion hazard in the Krueng Pase watershed from 2009 to 2019 increased in area, the mild level of erosion hazard increased by 7.9% and the moderate level erosion hazard by 27.4%. The amount of sedimentation obtained using the MUSLE method in 2019 was 6,869,98 tons and in 2009 was 41,692,97 tons. Erosion valuein 2019 is relatively small compared to other years. It’s really depends on the rainfall and the discharge that occurs. Therefore, a good land management system, proper and appropriate technology used, eco-hydrology concept and the monitoring of land use change regularly are needed, so damage that impact the Krueng Pase watershed can be prevented and minimize.

Modelling the effects of water chemistry and flowrate on clay erosion

Clay buffer is a key component of the engineered barrier system (EBS) for geological disposal of higher activity radioactive waste. Experimental observations indicate the possibility of buffer erosion at the interface with host rock due to interactions with groundwater. Existing models for clay erosion are very limited in terms of addressing the hydro-chemical effects, while the assessment of the long-term performance of clay buffer requires robust predictive models covering expected environment conditions and multiphysics phenomena involved in the erosion process. The work presented here is a step towards such a predictive capability, which considers clay expansion, detachment of clay particles and transport of detached particles by groundwater within a single modelling framework. The effects of solution chemistry and flowrate on the penetration, extruded mass and particle release rate of clay buffer are investigated in this paper. A series of experimental data are used to validate the swelling and erosion model developed in this study. The results show that the extrusion distance, which is controlled by both clay swelling and detachment processes, is nearly linearly dependent on the water flowrate irrespective of the water chemistry. Similar linear dependence of the erosion rate on water flowrate is observed for flowrates less than 10−5 m/s. Higher water flowrates are shown to induce nonlinearly increasing erosion rates in accordance with experiments. A flowrate threshold is found above which the erosion behaviour of compacted bentonite can be significantly affected. A concept of tolerance time for clay buffer is introduced as a failure criterion. The results indicate that the coupled effect of water chemistry and velocity requires further investigation for ionic concentrations below 1 mM.

Effects of human occupation on soil loss over the past two millennia in the Teotihuacan Valley, central Mexico

Soil erosion is one of the greatest risks worldwide for land degradation. Avoiding it is one of the greatest socio-environmental and economic challenges within sustainable development in connection with food production and maintenance of soil functions in the context of climate change. This study will allow us to answer how long-term occupation dynamics influenced by notable changes in the landscape have led to soil erosion through time. We used Geographical Information Systems to apply the Revised Universal Soil Loss Equation to assess soil erosion on prehispanic and present occupation scenarios that differ in climate and land use management in the Teotihuacan Valley, central Mexico. We analyzed how a heterogeneous landscape and its occupation dynamics over the last two millennia were affected by soil erosion in order to identify which biophysical and anthropogenic components affect soil loss. The settlements extended during Aztec periods over previously forested hillslopes which caused an increase in erosion rates. The greatest soil loss occurred during the humid Aztec period, followed by the Modern period. The differences between average erosion and potential erosion of these periods demonstrate greater effectiveness in controlling erosion during the Aztec period. The most relevant factors involved were land use and soil management, followed by climate and support practices. Our results indicate that in the face of climatic variations, soil management has a significant impact, even greater than rain erosivity. Our results suggest that pre-Hispanic cultures in the highlands of central Mexico may have caused soil erosion at least at rates similar to or even higher than those at present. The comparisons of the scenarios enable researchers and decision makers to identify high-risk areas and to implement sustainable measures against soil erosion.

Hilltop curvature as a proxy for erosion rate: wavelets enable rapid computation and reveal systematic underestimation

Abstract. Estimation of erosion rate is an important component of landscape evolution studies, particularly in settings where transience or spatial variability in uplift or erosion generates diverse landform morphologies. While bedrock rivers are often used to constrain the timing and magnitude of changes in baselevel lowering, hilltop curvature (or convexity), CHT, provides an additional opportunity to map variations in erosion rate given that average slope angle becomes insensitive to erosion rate owing to threshold slope processes. CHT measurement techniques applied in prior studies (e.g., polynomial functions), however, tend to be computationally expensive when they rely on high-resolution topographic data such as lidar, limiting the spatial extent of hillslope geomorphic studies to small study regions. Alternative techniques such as spectral tools like continuous wavelet transforms present an opportunity to rapidly document trends in hilltop convexity across expansive areas. Here, we demonstrate how continuous wavelet transforms (CWTs) can be used to calculate the Laplacian of elevation, which we utilize to estimate erosion rate in three catchments of the Oregon Coast Range that exhibit varying slope angle, slope length, and hilltop convexity, implying differential erosion. We observe that CHT values calculated with the CWT are similar to those obtained from 2D polynomial functions. Consistent with recent studies, we find that erosion rates estimated with CHT from both CWTs and 2D polynomial functions are consistent with erosion rates constrained with cosmogenic radionuclides from stream sediments. Importantly, our CWT approach calculates curvature at least 103 times more quickly than 2D polynomials. This efficiency advantage of the CWT increases with domain size. As such, continuous wavelet transforms provide a compelling approach to rapidly quantify regional variations in erosion rate as well as lithology, structure, and hillslope sediment transport processes, which are encoded in hillslope morphology. Finally, we test the accuracy of CWT and 2D polynomial techniques by constructing a series of synthetic hillslopes generated by a theoretical nonlinear transport model that exhibit a range of erosion rates and topographic noise characteristics. Notably, we find that neither CWTs nor 2D polynomials reproduce the theoretically prescribed CHT value for hillslopes experiencing moderate to fast erosion rates, even when no topographic noise is added. Rather, CHT is systematically underestimated, producing a power law relationship between erosion rate and CHT that can be attributed to the increasing prominence of planar hillslopes that narrow the zone of hilltop convexity as erosion rate increases. As such, we recommend careful consideration of measurement length scale when applying CHT to estimate erosion rate in moderate to fast-eroding landscapes, where curvature measurement techniques may be prone to systematic underestimation.

Bias and error in modelling thermochronometric data: resolving a potential increase in Plio-Pleistocene erosion rate

Abstract. Thermochronometry provides one of few methods to quantify rock exhumation rate and history, including potential changes in exhumation rate. Thermochronometric ages can resolve rates, accelerations, and complex histories by exploiting different closure temperatures and path lengths using data distributed in elevation. We investigate how the resolution of an exhumation history is determined by the distribution of ages and their closure temperatures through an error analysis of the exhumation history problem. We define the sources of error, defined in terms of resolution, model error and methodological bias in the inverse method used by Herman et al. (2013) which combines data with different closure temperatures and elevations. The error analysis provides a series of tests addressing the various types of bias, including addressing criticism that there is a tendency of thermochronometric data to produce a false inference of faster erosion rates towards the present day because of a spatial correlation bias. Tests based on synthetic data demonstrate that the inverse method used by Herman et al. (2013) has no methodological or model bias towards increasing erosion rates. We do find significant resolution errors with sparse data, but these errors are not systematic, tending rather to leave inferred erosion rates at or near a Bayesian prior. To explain the difference in conclusions between our analysis and that of other work, we examine other approaches and find that previously published model tests contained an error in the geotherm calculation, resulting in an incorrect age prediction. Our reanalysis and interpretation show that the original results of Herman et al. (2013) are correctly calculated and presented, with no evidence for a systematic bias.

Enhanced Quaternary Exhumation in the Central Three Rivers Region, Southeastern Tibet

The roles of tectonics and climate in the global increased erosion rates during the Quaternary have been the subject of active debate. The Three Rivers Region, strongly influenced by continental convergence between India and Eurasia and change in Asian monsoon climate, is an ideal place to study the interactions between tectonics and surface processes. Here we report new apatite (U-Th)/He data from an elevation transect that reveal a phase of rapid exhumation since ∼2.6 Ma in the Dulong batholith in the central Three Rivers Region, southeastern Tibetan Plateau. Based on stream profile analysis and compiled thermochronological data in the region, we demonstrate that the tectonic uplift caused by the high-strain at the corner of Indian-Eurasia convergence is responsible for the enhanced exhumation in the central Three Rivers Region in the Quaternary. Our new results highlight that the continuous plate convergence towards the plateau interior has dominated the uplift and deformation in the southeastern Tibet in the Quaternary.

Tectonic Accretion Controls Erosional Cyclicity in the Himalaya

AbstractThe evolution of Earth's climate over geological timescales is linked to surface erosion via weathering of silicate minerals and burial of organic carbon. However, methodological difficulties in reconstructing erosion rates through time and feedbacks among tectonics, climate, and erosion spurred an ongoing debate on mountain erosion sensitivity to tectonic and climate forcing. At the heart of this debate is the question of whether late Cenozoic climate cooling has increased global erosion rates or not. The Himalaya plays a prominent role in this debate as its erosion produces a large fraction of global sediments delivered to ocean basins. We report a 6‐Myr‐long record of ‐derived erosion rates from the north‐western Himalaya, which indicates that erosion rates in this region varied quasi‐cyclically with a period of ∼1 Myr and increased gradually toward the present. We hypothesize that the observed pattern of erosion rates occurred in response to the tectonic growth of the Himalaya by punctuated basal and frontal accretion of rocks from the underthrusting Indian plate and concomitant changes in topography. In this scenario, basal accretion episodically changes rock‐uplift patterns, which brings landscapes out of equilibrium and results in quasi‐cyclic variations in erosion rates. We used numerical landscape evolution simulations to demonstrate that this hypothesis is physically plausible. We attribute the long‐term increase in erosion rates to the erosional response of topography due to frequent basal accretion relative to frontal accretion. Because tectonic accretion processes are inherent to collisional orogenesis, they likely confound climatic interpretations of erosion rate histories.

Soil modeling for soil loss tolerance estimations: Exploring natural baselines and long-term variations

Quantification of soil stocks and ecosystem services (ES) under changing climate need time series of climate and soil data. Here, we propose a new approach combining process-based soil and climate simulations to obtain such time series, and apply it onto a recent interglacial, Marine Isotope Stage (MIS) 5e. We combined the LOVECLIM climate model and the SoilGen2 soil evolution model to simulate soil development under two scenarios: dust addition plus erosion and erosion-only (both with five erosion rates corresponding to low, natural erosion rates: 0, 0.5, 1.0, 1.5 and 2.0 Mg ha −1 y −1 ). We quantified five target variables: two soil stocks, Exchangeable Bases (EB) and Soil Organic Carbon (SOC), and three ES: Carbon Sequestration Capacity (CSC), Water Yield (WY) and the ratio of actual over potential evapotranspiration (Ω) at four sites on an aridity gradient on the Chinese Loess Plateau (CLP). We used the obtained time series of these target variables to estimate Soil Loss Tolerance (SLT) threshold values over the full extent of MIS 5e (22 ka). Under increased erosion, EB increases while SOC always declines in both scenarios. In both scenarios, the simulated CSC increases with erosion; contrastingly, the WY decreases with increasing erosion rates. Both CSC, WY and Ω gradually decrease towards the northwest CLP (semi-arid region). For EB and SOC, the determined SLT thresholds are relatively higher in the dust addition than in the erosion-only scenarios, and strictly follow the climate gradient in the CLP. Combined performance index for (1-CSC), WY and Ω, showed that soil ES performance is worse above 1.0 Mg ha −1 y −1 . This implies that benchmark levels must be chosen carefully. Our research highlights the potential of using SoilGen2 with LOVECLIM for quantifying soil-based ES and SLT. • Combined soil and climate models quantified soil stocks and ecosystem services. • Effects of natural soil erosion and dust deposition rates were compared. • Reference values for soil loss tolerance estimations should be carefully chosen.

Immediate Artificial Urinary Sphincter (AUS) Reactivation at the Time of Urethral Cuff Exchange is Not Associated with Increased Erosion Rate

ObjectiveTo retrospectively evaluate the outcomes of immediate artificial urinary sphincter (AUS) reactivation in patients after urethral cuff replacement. It is common practice to delay reactivation of an AUS for four to six weeks following surgery to replace a failed urethral cuff. This is due to concerns about local tissue edema risking obstruction and concerns for urethral erosion. Despite these concerns, there are no published data to support this practice. MethodsRetrospective chart review of single surgeon procedures performed from 2005-2020. Patients with urethral cuff replacement for recurrent stress incontinence due to compression or mechanical failure were included. ResultsThirty-four patients were identified who had immediate reactivation of the AUS following urethral cuff exchange. Thirty of these patients (88.2%) had radical prostatectomy and five patients also underwent further radiation therapy (14.7%). At 6 months follow-up, there was no reported events of erosion. Likewise, 32/34 (94%) of patients had no complications and reported expected urinary function of the AUS. Urinary retention was not observed. One patient required further re-exploration for a complication within his AUS system (2.9%), and another was ultimately unsatisfied with their unchanged baseline continence despite a fully functioning AUS (2.9%). ConclusionIn this series, we observe that immediate reactivation of the AUS after urethral cuff exchange is a safe and reasonable management approach. Limitations of this analysis include a single institution, retrospective study. However, early AUS reactivation after device revision has not been reported in the literature and warrants further investigation given the impact on patient quality of life.

Projections of soil loss by water erosion in Europe by 2050

Changes in future soil erosion rates are driven by climatic conditions, land use patterns, socio-economic development, farmers’ choices, and importantly modified by agro-environmental policies. This study simulates the impact of expected climatic and land use change projections on future rates of soil erosion by water (sheet and rill processes) in 2050 within the agricultural areas of the European Union and the UK, compared to a current representative baseline (2016). We used the Revised Universal Soil Loss Equation (RUSLE) adjusted at continental scale with projections of future rainfall erosivity and land use change. Future rainfall erosivity is predicted using an average composite of 19 Global Climate Models (GCMs) from the Coupled Model Inter-comparison Projects (CMIP5) WorldClim dataset across three Representative Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5). Concerning future land use change and crop dynamics, we used the projections provided by the Common Agricultural Policy Regional Impact Analysis (CAPRI) model.Depending on the RCP scenario, we estimate a +13 %-22.5 % increase in the mean soil erosion rate in the EU and UK, rising from an estimated 3.07 t ha−1 yr−1 (2016) to between 3.46 t ha−1 yr−1 (RCP2.6 scenario) and 3.76 t ha−1 yr−1 (RCP8.5 scenario). Here, we disentangle the impact of land use change and climate change in relation to future soil losses. Projected land use change in the EU and UK indicates an overall increase of pasture coverage in place of croplands. This land use change is estimated to reduce soil erosion rates (-3%). In contrast, the increases in future rainfall erosivity (+15.7 %–25.5 %) will force important increases of soil erosion requiring further targeted intervention measures.Given that agro-environmental policies will be the most effective mechanisms to offset this future increase in soil erosion rates, this study proposes soil conservation instruments foreseen in the EU Common Agricultural Policy (CAP) to run policy scenarios. A targeted application of cover crops in soil erosion hotspots combined with limited soil disturbance measures can partially or completely mitigate the effect of climate change on soil losses. Effective mitigation of future soil losses requires policy measures for soil conservation on at least 50 % of agricultural land with erosion rates above 5 t ha−1 yr−1.

Degradation of Armco iron caused by cavitation: Part I – Correlation with flow

Cavitation erosion resistance of Armco iron was studied using a tunnel equipped with a system of barricades at two flow conditions, inlet pressure of 1000 and 1200 kPa, and outlet pressure of 125 and 130 kPa, respectively. In order to analyse the mechanism of mass losses, numerical investigations concerning the flow behaviour in the vicinity of the samples were carried out. After 480 min of testing, the increase in inlet pressure from 1000 to 1200 kPa caused an approximately two-and-a-half-fold increase in the erosion rate of samples located closest to the upper barricade that served together with the lower barricade as a cavitation generator. The surface degradation depended on the test conditions: for the test at 1000 and 125 kPa, single pits were formed, while for the test at 1200 and 130 kPa, a large number of pits contributed to the formation of micro-undulation on the entire surface of the sample. Taking into account the time required for the water stream to reach samples’ surface from the low-pressure region and erosion rates, an exponential correlation with a determination coefficient R2 = 0.9247 was obtained. The erosion rate also increased exponentially with turbulence intensity and turbulent dissipation rate. The study of turbulence intensity showed that as the turbulent velocity fluctuations are larger than the mean velocity, the erosion rate increases more intensively, which indicates an increase in the aggressiveness of cavitation.

Poly(l-Lactic Acid)-co-poly(Butylene Adipate) New Block Copolymers for the Preparation of Drug-Loaded Long Acting Injectable Microparticles.

The present study evaluates the use of newly synthesized poly(l-lactic acid)-co-poly(butylene adipate) (PLA/PBAd) block copolymers as microcarriers for the preparation of aripiprazole (ARI)-loaded long acting injectable (LAI) formulations. The effect of various PLA to PBAd ratios (95/5, 90/10, 75/25 and 50/50 w/w) on the enzymatic hydrolysis of the copolymers showed increasing erosion rates by increasing the PBAd content, while cytotoxicity studies revealed non-toxicity for all prepared biomaterials. SEM images showed the formation of well-shaped, spherical MPs with a smooth exterior surface and no particle’s agglomeration, while DSC and pXRD data revealed that the presence of PBAd in the copolymers favors the amorphization of ARI. FTIR spectroscopy showed the formation of new ester bonds between the PLA and PBAd parts, while analysis of the MP formulations showed no molecular drug–polyester matrix interactions. In vitro dissolution studies suggested a highly tunable biphasic extended release, for up to 30 days, indicating the potential of the synthesized copolymers to act as promising LAI formulations, which will maintain a continuous therapeutic level for an extended time period. Lastly, several empirical and mechanistic models were also tested, with respect to their ability to fit the experimental release data.

Using Engineering With Nature® (EWN® ) principles to manage erosion of watersheds damaged by large-scale wildfires.

The US Army Corps of Engineers (USACE) manages hundreds of reservoirs and thousands of miles of navigation channels that provide invaluable flood control, commercial transport of materials, water supply, recreation, and stream flow regulation. This capability is being threatened by the continued occurrence of large-scale wildfires across the western United States. The wildfires damage watersheds in part by denuding landscapes, reducing infiltration rates, and increasing runoff rates, thereby dramatically increasing the potential for the erosion of denuded slopes, destabilizing stream channels, increasing the infilling potential of reservoirs and, hence, reducing their capacity. The increased erosion rates highlight the need to develop innovative solutions to reduce erosion of watersheds laid bare after wildfires engulf the area. The Santa Clara Pueblo in northern New Mexico extends from the top of the eastern Jemez Mountains to the floodplains of the Rio Grande River. The Pueblo designed and constructed thousands of structures built from natural materials, consistent with Engineering With Nature (EWN) principles for erosion control incorporating low-cost and readily available materials such as logs, mulch, vegetation, and local rock to stabilize highly erodible parts of the watershed. The watersheds where these natural structures were constructed were monitored after construction to assess their effectiveness, guiding a series of recommendations for broader implementation. As part of a continued emphasis on updating USACE engineering guidance, research, and development, funding has been focused on developing sustainable and resilient project designs using natural materials like those implemented by the Santa Clara Pueblo. This paper focuses on the innovative EWN-based watershed stabilization practices that were implemented in the upper section of this wildfire affected canyon and tributary streams. Recommendations for future implementation based on lessons learned from this project are also provided. Integr Environ Assess Manag 2021;17:1194-1202. Published 2021. This article is a US Government work and is in the public domain in the USA.

Cosmogenic in situ 14C-10Be reveals abrupt Late Holocene soil loss in the Andean Altiplano

Soil sustainability is reflected in a long-term balance between soil production and erosion for a given climate and geology. Here we evaluate soil sustainability in the Andean Altiplano where accelerated erosion has been linked to wetter climate from 4.5 ka and the rise of Neolithic agropastoralism in the millennium that followed. We measure in situ cosmogenic 14C directly on cultivated hilltops to quantify late Holocene soil loss, which we compare with background soil production rates determined from cosmogenic 26Al and 10Be. Our Monte Carlo-based inversion method identifies two scenarios to account for our data: an increase in erosion rate by 1–2 orders of magnitude between ~2.6 and 1.1 ka, or a discrete event stripping ~1–2 m of soil between ~1.9 and 1.1 ka. Coupled environmental and cultural factors in the Late Holocene signaled the onset of the pervasive human imprint in the Andean Altiplano seen today.

Comparing the Hydrological Response of Forested Headwaters (Unregulated and Regulated with Check Dams) under Mediterranean Semi-Arid Conditions

This study has evaluated the runoff and erosion rates in torrents of Southern Italy, two forested headwaters with very similar climatic, hydrological and geomorphological characteristics; in one headwater, 15 check dams were installed in the mid-1950s, while the other is not regulated with engineering works. To this aim, the hydrological variables have been modeled over 15 years after check dam installation using the HEC-HMS (Hydrologic Engineering Center-Hydrologic Modeling System) model coupled to the MUSLE (Modified Universal Soil Loss Equation) equation. The model simulations have shown that check dams have not played a significant role in reducing the surface runoff compared to the unregulated torrent; in both catchments, the well-developed forest cover determined very low runoff coefficients (lower than 0.3%) with a scarce runoff generation capacity. Additionally, the reduction in peak flow due to the check dams was not significant, on average −7.4% compared to the unregulated headwater. Check dams have retained sediments for about 8–10 years after their installation, reducing erosion by about 35%, although soil loss was much lower than the tolerance limit in both catchments. After the sediment retention capacity of the dam sediment wedge was depleted, the sediment yield in the regulated torrent was even higher (by about 20%) compared to the unregulated catchment. Overall, the study has shown that the use of check dams as a catchment management strategy of forested headwaters under semi-arid Mediterranean conditions should be considered with caution, since the structures could be ineffective to reduce water and sediment flows during floods or, in some cases, check dams may increase erosion rates.

Erosion analysis and experimental research of gas-liquid-solid soft abrasive flow polishing based on cavitation effects

Traditional soft abrasive flow (SAF) polishing is limited by its low material removal rate and its applicability to large workpieces. To address this issue, an innovative technique of a cavitation-based gas-liquid-solid abrasive flow polishing (CGLSP) process is proposed. The energy generated from cavitation effects is employed to increase the kinetic energy of abrasive particles in the fluid flow and the random movement of abrasive particles near the surface. The CGLSP mechanism is first introduced, and then, the cavitation erosion characteristics and material removal mechanism of brittle-plastic materials during polishing are investigated using a coupling computational fluid dynamics model. The simulated results show that erosion of the workpiece surface mainly occurs in the spiral area of the polishing tool. Furthermore, the erosion rate and erosion depth increase with increasing cavitation intensity. Subsequently, polishing experiments are conducted to verify the validity of the CGLSP method. The polishing results are verified by scanning electron microscopy (SEM) images of the polished surface. After polishing with the CGLSP method, most of the surface irregularities, such as microcracks and massive structures, are removed. The experimental results demonstrate that controlled polishing with cavitation erosion and abrasion can achieve a much higher quality surface on a large workpiece.

Erosion effects on soil carbon and nitrogen dynamics on cultivated slopes: A meta-analysis

Soil carbon (C) redistribution within cultivated landscapes is strongly controlled by soil erosion and sedimentation and it is widely appreciated that C is preferentially transported during erosion. In contrast, it remains elusive whether erosion induced transport of C and N is coupled although changes in the balance between C and N strongly affect soil C and N dynamics. We therefore reviewed the literature on carbon and nitrogen redistribution by erosion.Twenty-nine studies reported results on C and N enrichment of freshly eroded sediments after erosion events. Thirty-nine studies reported results on C and N contents and stocks along eroded slopes.Eroded sediments were enriched in C and N by 51.3% and 50.6% indicating that both elements are stored in soil fractions that are preferentially eroded. Slope gradient and soil texture strongly affected C and N enrichment. Decreasing C and N enrichment in fine-textured soils was counterbalanced by increasing erosion rates in these soils. This suggests similar SOM losses independent of textural class. The C/N ratio increased by 9.9%, pointing to preferential movement of C-rich particulate organic matter (POM) compared to N-rich mineral associated organic matter (MAOM). Breakdown of aggregates by rainfall energy possibly released POM which is then preferentially eroded. Soil C and N contents and total stocks showed similar percentage increases from upslope to depositional sites, indicating that downslope C and N stocks were largely driven by enrichment, rather by than increases in depth or bulk density.Altogether, our findings confirm that quantification of soil loss alone is not sufficient to estimate erosion-induced changes in soil fertility, because soil organic matter and plant nutrients are selectively moved during erosion. This leads to a shift in C and N dynamics in different slope positions and thus to an increase in the spatial variability of the C and N along the slope.

Flume Experiments on the Erosive Energy of Bed Load Impacts on Rough and Planar Beds

AbstractUnderstanding bed load impact dynamics on exposed bedrock in rivers is crucial to quantifying the erosive energy of a stream. Observations of the bed load saltation trajectories and impact energies are lacking, particularly in channels with nonplanar bed topography. In this study, we performed four flume experiments of saltating gravel to offer new insights on the dependence of particle impact dynamics on transport stage and bed topography. Our experiments used two different boundary shear stresses (τb = 36.5 and 25.4 Pa) and two different bed configurations, planar and nonplanar (bedrock disks uniformly oriented at 10° from the bed surface). For each experiment, we indirectly estimated the impact energies from the trajectories of particles with high‐speed video imaging and measured the erosion rates of rock samples embedded in the flume floor. The planar and nonplanar beds had negative and constant relationships, respectively, between energy delivered to the bed and transport stage. The nonplanar bed had a heavier tailed distribution of impact energy than the planar bed, which implies a greater number of rare highly erosive impacts. Probabilistic formulations of particle trajectories better predict the increase or decrease in erosion rate across experiments than deterministic regression equations. Our findings suggest that bedrock erosion models should consider a distribution of possible bed load impact energies, particularly for natural river channels that have rough surfaces.