Surface Erosion Processes Research Articles

Effect of a surface roughness on the erosion kinetics of Ba35 brass used in potable water pipelines: Experiments and mathematical modeling

AbstractThe purpose of this work is to establish the relationship between surface roughness and erosion processes of Ba35brass pipes subjected to abrasive particles. Brass samples were prepared with different levels of surface roughness, obtained by polishing using abrasive papers of various grain sizes: P80, P120, and P320. These samples were eroded using a recirculating erosion test bench. To analyze the erosion kinetics, the surface roughness values (Ra and Rz) as well as the cumulative mass loss were measured at specified time intervals. In parallel, mathematical models were developed to simulate the evolution of surface roughness and cumulative mass loss, based on optimization methods. The results show that rougher surfaces, such as those prepared with P80 grit paper, record a higher erosion rate, reaching 0.47 mg/h, compared to smoother surfaces, such as those obtained with P320 paper, whose rate is 0.19 mg/h. The developed mathematical models indicate that the surface roughness follows an exponential decrease, while the cumulative mass loss shows a logarithmic growth. Furthermore, a linear correlation was highlighted between the erosion rate and the surface roughness. This study highlights the crucial importance of surface roughness in erosion processes and provides guidelines for optimizing the design and maintenance of cast iron pipes.

Enhanced crop yields as a potential mitigator of soil organic carbon losses under elevated temperature in erosional and depositional landscape

The dynamics of agricultural soil organic carbon storage have been considerably influenced by the evolution of crop species, offering promising opportunities for restoring soil organic carbon under elevated temperatures through yield improvements. However, the intricate interplay between climate change and surface erosion processes poses challenges in understanding agricultural soil carbon dynamics in hilly landscapes. This study aimed to address these challenges by assessing the effects of climate change on soil organic carbon dynamics under the Shared Socioeconomic Pathways 245 and 585. We utilized projections from 12 distinct global climate models, covering the period from 2015 to 2100. Additionally, we investigated the potential for improving soybean yields by 100 %, 200 %, and 300 % linearly by 2100 to offset the anticipated soil organic carbon losses. Using a coupled landscape and biogeochemical model, our analysis focused on a soybean field in Nenjiang County, China. Our findings revealed a distinct soil organic carbon profile in deposition areas, characterized by relatively low levels of soil organic carbon in surface layers, attributed to carbon influx from adjacent erosion areas with typically low carbon content. We modeled decreases in soil CO2 fluxes with escalating climate change, corresponding to expected decreases in soil organic carbon levels, despite concurrent rises in soil microbial activity linked to increasing temperatures. Erosion areas emerged as particularly vulnerable zones under elevated temperatures due to their higher proportion of soil CO2 fluxes relative to soil organic carbon levels compared to deposition areas. As a soil organic carbon restoration strategy, improvements in soybean yields showed promise in mitigating soil organic carbon losses through enhanced litter inputs and the cooling effects induced by shading the soil. This study underscored the potential for achieving the dual benefits of food security and soil organic carbon restoration in the coming decades through a unified approach to enhancing soybean yields.

Efficient Depolymerization of Poly(ethylene 2,5-furanoate) Using Polyester Hydrolases.

Poly(ethylene 2,5-furanoate) (PEF) is considered to be the next-generation green polyester and is hailed as a rising star among novel plastics. It is biobased, is nontoxic, and has comparable or improved properties compared to polyethylene terephthalate (PET). Biobased PEF offers lower life-cycle greenhouse gas emissions than PET. However, with its industrial production starting soon, relatively little is known about its actual recyclability. This work reports on the near complete depolymerization of PEF using two efficient PET hydrolases, FastPETase and leaf compost-cutinase (LCC), at loadings 4.5-17 times lower than previously reported. FastPETase and LCC exhibited maximum depolymerization of PEF, measured by weight loss and 2,5-furandicarboxylic acid (FDCA) production, using potassium phosphate-NaOH buffer at 50 and 65 °C, respectively. The 98% depolymerization of 13 g L-1 PEF film was achieved by three additions of the LCC in 72 h, while 78% weight loss was obtained using FastPETase in controlled conditions. Nonetheless, 92% weight loss was obtained with FastPETase when using only 6 g L-1 PEF. The main reaction products were identified as FDCA, ethylene glycol, and mono(2-hydroxyethyl)-furanoate. LCC performed better than FastPETase, in terms of both FDCA release and weight loss. The effect of crystallinity was evident on the enzymes' performance, as only 4% to 7% weight loss of crystalline PEF (32%) was recorded. Microscopy studies of the treated PEF films provided information on the surface erosion processes and revealed higher resistance of the crystalline phase, explaining the low level of depolymerization. The study presents important insights into the enzymatic hydrolysis of biobased PEF material and paves the path toward more viable applications within biopolymer waste recycling.

Holocene process-based hydroclimate evolution coupled with human behaviours in Dian Lake basin, Southwest China

Lakes are considered excellent archives for the reconstruction of sedimentary processes and related hydroclimatic variations. Dian Lake in south-western China was selected to demonstrate the impacts of Indian summer monsoon-induced water and sediment availabilities on land surface changes and human behaviours. A new sediment core from Dian Lake in the vicinity of Hebosuo village was analyzed by grain size composition, geochemical content, and minerals to detect land-lake processes that responded to hydroclimatic variations and human impacts through the Holocene. Our data suggest that Dian Lake levels during the last 9.8 cal. ka BP were controlled by the variations of the Indian summer monsoon moisture supply according to the displacements of the Intertropical Convergence Zone. A low lake level stage of ∼ 4 m lower than present was determined between 3.1 and 1.73 cal. ka BP, allowing the residents of the Dian culture to occupy the low terrains for settlement and farmland cultivation. With lake level rise at around 1.73 cal. ka BP (220 CE) the high input of clay-fine silt-sized sediments rich in rubidium and barium indicates intensified soil erosion in the Dian Lake basin. Former paddy farmlands and mountain slopes were drained by artificial and natural channels towards the lake in response to strengthened rainfalls covering low terrains by coarse and red alluvial sediments that fostered the residents to abandon the lowlands in the southern basin until 1368 CE. However, the surface erosion process during this period promoted the elevation of the south-eastern delta so that it could be re-occupied since Ming Dynasty. The Indian summer monsoon influence comparable to the modern pattern was responsible for lake level rise to the present level since then but also triggered high seasonality in flood and drought events to foster manual regulation of flood discharge during the last centuries.

In Vitro and In Vivo Degradation of Photo-Crosslinked Poly(Trimethylene Carbonate-co-ε-Caprolactone) Networks.

Three-armed poly(trimethylene carbonate) (PTMC) and poly(trimethylene carbonate-co-Ɛ-caprolactone) (P(TMC-co-ε-CL)) macromers with molecular weights of approximately 30kgmol-1 are synthesized by ring-opening polymerization and subsequent functionalization with methacrylic anhydride. Networks are then prepared by photo-crosslinking. To investigate the in vitro and in vivo degradation properties of these photo-crosslinked networks and assess the effect of ε-caprolactone content on the degradation properties, PTMC networks, and copolymer networks with two different TMC:ε-CL ratios are prepared. PTMC networks degraded slowly, via an enzymatic surface erosion process, both in vitro and in vivo. Networks prepared from P(TMC-co-ε-CL) macromers with a 74:26 ratio are found to degrade slowly as well, via a surface erosion process, albeit at a higher rate compared to PTMC networks. Increasing the ε-CL content to a ratio of 52:48, resulted in a faster degradation. These networks lost their mechanical properties much sooner than the other networks. Thus, PTMC and P(TMC-co-ε-CL) networks are interesting networks for tissue engineering purposes and the exact degradation properties can be tuned by varying the TMC:ε-CL ratio, providing researchers with a tool to obtain copolymer networks with the desired degradation rate depending on the intended application.

Erosion‐Driven Isostatic Flow and Crustal Diapirism: Analytical and Numerical Models With Implications for the Evolution of the Eastern Himalayan Syntaxis, Southern Tibet

AbstractThe Eastern Himalayan Syntaxis (EHS) is one of the fastest exhuming regions on Earth since ∼10 Ma, and the mechanism of its fast exhumation is under debate. Different from many other studies based on tectonics‐driven models, we performed analytical analysis and numerical simulations to investigate an erosion‐driven system. Our results show that fast and focused surface erosion alone is able to exhume the lower crust on the timescale of ∼10 Myr. This process leads to the formation of a domal structure, an elevated geothermal gradient, rapid cooling of crustal rocks, and decompression melting in the lower crust. In the upper‐mid crust, the uplift of crustal rocks is caused by isostatic flow driven by pressure gradient, whose rate is limited by the driving erosional forcing. In the mid‐lower crust where decompression melting occurs, rocks entrained in a buoyant diapir experience fast uplift rate exceeding the erosional forcing. Our erosion‐driven model demonstrates an intricate coupling between surface erosion and crustal processes. Positive feedback between surface erosion and rock uplift is possible under certain conditions and crustal diapirism plays a key role in the feedback. Our study shows that both isostatic and diapiric flows play important roles in the uplift and exhumation of crustal rocks in the EHS. We highlight that erosion‐driven crustal diapirism can be one of the missing pieces explaining the evolution of the Eastern Himalayan Syntaxis.

Spatial variation of surface erosion rate in a fault zone and its controlling factors

Topographic relief and bedrock fractures caused by fault activity can accelerate surface erosion, suggesting that erosion rates increase with decreasing distance to the fault core. To test this hypothesis, we used 10Be cosmogenic nuclides to quantify catchment-wide erosion rates at various distances from a fault in the footwall of the Daqing Shan fault system, a 200-km-long active normal fault in Inner Mongolia, northern China. In addition, in order to examine the influence of topography and bedrock fractures on the surface erosion processes in the fault-weakened zone, their relationships with hillslope erosion, fluvial sediment grain size and transport efficiency, erosion rates, and erosion coefficients were studied. The resulting catchment-wide erosion rates ranged from 0.01 ± 0.00–0.13 ± 0.01 mm yr−1. These erosion rates and coefficients were unaffected by distance from the fault. The analysis of topography, bedrock fractures, and hillslope erosion yielded distinct hillslope erosion processes at different distances from the fault. Rapid mass wasting events, such as landslides, occurred at <15 km from the fault in steep, rocky hillslopes with abundant bedrock fractures. In contrast, at >15 km from the fault, hillslopes gradually become more gentle and soil-mantled. These spatial-slope configuration differences result in a decrease in sediment grain size delivered to river channels with increasing distance from the fault. Once sediments enter river channels, they impact fluvial transport capacity by influencing the initial motion threshold of sediment. Correlation analyses revealed that sediment transport efficiency in channels directly controls the catchment-averaged erosion rate and coefficient. This mechanism explains why the erosion rate remains insensitive to variations in topography and bedrock fractures in fault-weakened zones.

High speed water droplet impact erosive behavior on dry and wet pulsed waterjet treated surfaces

During water droplet impact onto a dry or wet rough solid surface, several phenomena affect the surface erosion process, such as splashing, crown formation, and small droplet emission to name a few. These phenomena have been extensively studied for various simple target surface geometries. However, droplet impact studies on complex irregular and asymmetric target surface topographies resulting from a waterjet treatment have never been conducted. Furthermore, very limited reports are found on the role of target surface topography and water droplet deformation development on the resulting target stress state. In the present study, high speed droplet impingements on surfaces exhibiting coarse topographical features associated with ultrasonic pulsed waterjet treatment are modeled to understand the underlying mechanisms causing erosion. Impacts on surfaces with various roughness values and water film thicknesses are modeled using a three-dimensional coupled Eulerian–Lagrangian approach. A detailed comparative analysis of the model with experimental ultrasonic pulsed waterjet erosion features and material loss is provided. It was found that the synclastic curvature of the modeled coarse surface features increases the shock wave's strength as many compression wavelets are simultaneously emitted at each water droplet contact location with the surface, resulting in concentrated high-pressure zones. The ultrasonic pulsed waterjet treated surface features and water film thickness also greatly influence the onset of water droplet splashing, subsequent finger, secondary droplet characteristics, and crown stability. According to the numerical results, strong splashing patterns and droplet breakup are generated and create high stress zones capable of accelerating surface erosion, explaining the enhanced performance of ultrasonic pulsed waterjet process.

Erosion mode and history of Eastern Adamaoua landscapes (Cameroon): Superimposed lateritic weathering of granites and basalts

Landscapes of eastern Adamaoua highlands have been shaped by successive weathering and erosion processes of Pan-African crystalline rocks and Neogene volcanics cover. Basalts have outpoured through major inherited structural discontinuities mostly in shallow incisions of lateritic pediplains previously shaped on the granitic basement. That has resulted in formation of a singular composite lateritic weathering profile on basalt superimposed to a truncated profile composed of mottled clays and saprolite on granite. The composite profile studied here is little evolved, mostly kaolinised on granite while basalt is weakly to moderately lateritised owing to differences in silica and iron oxide contents of the two contrasted parent rocks. During lateritic weathering, Cu, Ni, and Co are enriched in profile on granite but depleted on basalt, while Zr/Ti is relatively constant. Behavior and fractionation of REE are comparable except higher Eu* and Ce* anomaly on granite profile than on weathered basalt, owing to parent minerals differences, mostly feldspars in granite versus plagioclase and Fe-Mg minerals in basalt. The contrast in Eu* is also linked to differences in the Index Of Laterization (IOL) in weathered horizons of the two parent rocks. Beyond quite classical litho-dependent geochemical differences in the composite profile, persistence of per-humid climate and good drainage over Neogene have sustained rock-weathering and local surface erosion processes upon volcanic outpours and their contact surface with pediplains formed on Pan-African granitoids of Adamaoua highland.

Study on erosion and stability of the ecological slope

Rainfall is the main influencing factor causing slope erosion, landslide, and instability in loess; thus, it is vital to comprehend the process of rainfall erosion on various slope surfaces and water penetration inside the slope. In this paper, the loess sample is from Heifangtai in Gansu Province, and triaxial shear tests were conducted on loess with roots under varying water contents to evaluate the slope-reinforcing impact of roots. The slope surface erosion process was analyzed using a soil moisture sensor and matric suction meter to monitor the variation of matric suction in the middle slope and slope foot in response to varying precipitation levels. The numerical simulation approach is utilized to analyze the fluctuation of slope stability under the effect of varying rainfall intensities and humid heat, and the analytical solution of the safety factor is compared to the model solution. The results indicate that the shortest generation time for bare slope runoff is 6 min, whereas the greatest generation time for the Bermuda grass slope is 12 min; the shorter the period, the less water penetration and the simpler it is to reach the slope erosion stage. The slope’s rise increases runoff velocity, strengthening water resistance on the slope surface. When the test slope is 30°, the maximum mass of scouring sediment on the bare slope is 15.2 g from 24 to 36 min, compared to 14.7 g from 24 to 36 min when the test slope is 60°. The amount of scouring reduces as the slope increases. The slope safety factor declined from 3.51 to 2.84 after 24 h of heavy rain, and the loss rate accelerated as the rainfall intensity increased.

Late Oligocene - Miocene morpho-tectonic evolution of the central Gangdese batholith constrained by low-temperature thermochronology

The morpho-tectonic evolution of the Tibetan Plateau is controlled by complicated interactions between tectonic uplift and surface erosion. The Gangdese batholith in the southern Lhasa terrane is a key orogenic belt for exploring the complicated morpho-tectonic evolution of the Tibetan Plateau. In this contribution, we apply apatite fission track (AFT) thermochronology to constrain the thermo-tectonic evolution of the central segment of the Gangdese batholith. Twenty-four granitoid samples were collected from both river valleys (e.g., the Yarlung and Xiang Rivers) and from the internal batholith areas located farther from river drainage (and/or local faults) networks. All samples exhibit Miocene AFT ages between ∼19.9 and ∼ 6.1 Ma. Inverse thermal history modeling results reveal that the central Gangdese batholith underwent a two-stage accelerated basement cooling in the Miocene. The first cooling stage took place during the late Oligocene to middle Miocene (∼25–15 Ma), this period of moderate to rapid basement cooling coincides with activity along the Gangdese thrust and Great Counter thrust system, and the Oligocene-Miocene delamination of the Lhasa lithosphere and concomitant asthenosphere upwelling. These tectonic processes acted as first-order control on regional basement uplift, denudation and exhumation. Second, a middle-late Miocene (∼14–5 Ma) rapid cooling is widely recognized in the whole Gangdese batholith. We suggest that this middle-late Miocene cooling is due to exhumation in response to tectonic and surface erosion processes such as N-S normal faults and enhanced river incision induced by the intensification of Asian monsoon. Finally, in combination with published low-temperature thermochronological and paleoaltimetry data, it is deduced that the present-day low-relief landscape of the southern Lhasa terrane resulted from a long-term balance between intense regional tectonic activity and surface erosion.

Riprap Protection Exposed to Overtopping Phenomena: A Review of Laboratory Experimental Models

There are increasing demands from dam safety regulations and guidelines to upgrade the rockfill dams, especially in Norway where over 180 large rockfill dams are present. To protect the hydraulic structure against overtopping events or leakages, it is important to use defence mechanisms such as a protective layer of riprap on the downstream slope. In this article, we display 9 experimental setups of riprap, conducted at the hydraulic laboratory of NTNU (Trondheim) and subjected to overtopping phenomena with increasing water discharge, until the complete failure of the model. These tests were performed on models with dumped and placed riprap, with or without toe support, with or without the downstream rockfill shoulder, and finally on models with a full dam profile. The models with downstream rockfill shoulder as well as with full dam profiles allowed for throughflow. The model behaviour during these experimental tests is described and discussed, according to their respective critical discharge values and associated failure mechanisms. Limitations are also discussed. The results bring to light the benefit of placed riprap compared to dumped riprap structures. As the results show a placed riprap can withstand a significantly higher overtopping discharge than a dumped riprap. Also, the use of toe support enables a significant increase of resistance against overtopping of placed riprap structures. However, toe supports have not proven any significant improvement in stability for dumped riprap structures. This research also puts forward that dumped riprap undergoes a surface erosion process with smaller slides. Placed riprap undergoes a sliding failure mechanism when unsupported at the toe, and a buckling deformation when supported.

3D geodynamic-geomorphologic modelling of deformation and exhumation at curved plate boundaries: Implications for the southern Alaskan plate corner

Plate corners with extreme exhumation rates are important because they offer a perspective for understanding the interactions between tectonics and surface processes. The southern Alaskan margin with its curved convergent plate boundary and associated zones of localized uplift is a prime location to study active orogeny. Here, we present the results of fully-coupled thermo-mechanical (geodynamic) and geomorphologic numerical modelling, the design of which captures the key features of the studied area: subduction of oceanic lithosphere (Pacific plate) is adjacent to a pronounced asymmetric indenter dipping at a shallow angle (Yakutat microplate), which in turn is bounded to the east by a dextral strike-slip shear zone (Fairweather fault). The resulting first-order deformation/rock uplift patterns show strong similarities with observations. In particular, relatively young thermochronological ages are reproduced along the plate-bounding (Fairweather) transform fault and in the area of its transition to convergence (the St. Elias syntaxis). The focused exhumation of the Chugach Core also finds its equivalent in model predicted zones of high rock uplift rates in an isolated region above the indenter. From these results, we suggest that the general exhumation patterns observed in southern Alaska are controlled by mutually reinforcing effects of tectonic deformation and surface erosion processes.

Long-term effects of different arable cropping systems on surface erosion processes and C-factor in hilly Mediterranean environment

Soil erosion is an environmental threat strongly amplified by agricultural activity and, in the last decade, by climate change; it affects many European countries and in particular Italy. Water erosion is currently considered the most important cause of soil degradation. The vegetation cover represents a natural soil protection against water erosion phenomena as it reduces the rainfall impact energy, hinders surface runoff and promotes soil infiltration. For these reasons, identifying appropriate crop systems able to reduce soil loss is a key issue for proposing economical solutions in management planning. This work reports the results of a long-term study (12 years) aimed at determining the vegetation cover effectiveness, diversified by structure and duration of the crops in rotation, and the soil tillage impact on erosion and surface runoff. The C-factor determination, without resorting to very detailed measures, is provided by the indirect application of Universal Soil Loss Equation (USLE). Five different soil managements were included in this study. Four experimental plots were cultivated with different cropping systems and intensification tillage degree (CS), and a standard plot (SP) maintained in bare conditions by up and down slope tillage operations. The annual value of soil loss, calculated as mean for the five treatments, was 35.84 t ha-1, and ranged between 4.11 and 72.07 t ha-1. The results showed that CS4 and CS1 presented, on average, the lowest soil loss values of 9.38 and 13.93 t ha-1, respectively. The soil conservative management (minum tillage, strip tillage, shredded crop residues and grassy crops) allowed, in these two CS, to reach, on average, a soil cover degree (≥ 50 %) for 260 and 210 days and to obtain a C-factor of 0.12 and 0.14, respectively. In the CS3 (mixed conservative and conventional) with a soil cover degree ≥ 50 % for 182 days and a C-factor of 0.19, the soil loss was equal to 18.65 t ha-1. The conventional farming system (CS2) recorded an average value of soil loss of 55.04 t ha-1 with a maximum value of 138.20 t ha-1 in 2015/16; this CS also presented the lowest number of days (135) with a land cover level ≥ 50 % and the highest C value (0.50). The analysis allowed consolidating previous information and identifying strategies to be adopted in the Mediterranean hillside environment to significantly reduce soil losses due to water erosion.

Earthquake-induced landslide erosion coupled to tectonics and river incision, and effects of ground motion on coupled patterns

Landslide erosion and long-term denudation for the natural surface erosion processes in tectonically active mountain ranges are coupled to tectonics and river incision. However, such relationships have rarely been quantified in earthquake-induced landslides. Here we assess seismic landslide erosion caused by the Wenchuan earthquake in the Longmen Shan and explore relationships between tectonic uplift, river incision, and earthquake-induced landslide erosion yields and thus evaluate the effects of ground motion on coupled patterns. We show that nonlinear correlations exist between seismic landslide erosion rates and topographic metrics (mean slope gradient and normalized channel steepness) under various shaking conditions (peak ground acceleration PGA > 0.4 g). The areas with stronger shaking cause greater landslide erosion yields, higher erosion efficiency, weaker nonlinearity, and lower mean landslide slope although they have a similar threshold hillslope. Taken together, these analyses support an emerging view that the stronger ground motion reduces the equivalent rock mass strength on the hillslope and breaks the topographic threshold, which consequently produces a systematic increase in landslide erosion below or above the threshold state and results in nonlinearity variation. Our finding demonstrates that earthquake-induced landslide erosion is coupled to tectonics and river incision under various shaking conditions and presents a quantitative relationship between seismic landslide erosion rates and topographic metrics, providing potentially important implications for mountain belt evolution.

Evaluation Method of Soil Surface Roughness after Ditching Operation Based on Wavelet Transform

Soil surface roughness (SSR) is an important parameter affecting surface hydrology, erosion, gas exchange and other processes. The surface roughness of the farmland environment is directly related to the tillage process. In order to accurately characterize the random roughness (RR) parameters of the surface after ditching, a three-dimensional (3D) digital model of the surface was obtained by laser scanning under the conditions of an indoor ditching test, and the influence of oriented roughness components formed by removing ridge characteristics on the RR of the surface was analyzed by introducing the wavelet processing method. For this reason, four groups of ditching depths and two types of surface conditions (whether the surface was agglomerated or not) were designed in this paper. By comparing the root mean squared height (RMSH) and correlation length (CL) data calculated before and after wavelet processing under each group of tests, it was concluded that the RMSH values of the four groups before and after wavelet processing all change more than 200%, the change amplitude reached 271.02% under the treatment of 12 cm ditching depth, meanwhile, the average CL value of five cross-sections under each group of ditching depths decreased by 1.43–2.28 times, which proves that the oriented roughness component formed by furrows and ridges has a significant influence on the calculation of RR. By further analyzing the roughness value differences of clods and pits in different directions and local areas before and after wavelet transform, it was shown that the wavelet transform can effectively remove the surface anisotropy characteristics formed in the tillage direction and provide a uniform treatment method for the evaluation of surface RR at different ditching depths.

Combining FDR and ERT for monitoring soil moisture and temperature patterns in undulating terrain in south-eastern Norway

The occurrence of freeze–thaw cycles modifies water infiltration processes and surface runoff generation. Related processes are complex and are not yet fully investigated at field scale. While local weather conditions and soil management practices are the most important factors in both runoff generation and surface erosion processes, local terrain heterogeneities may significantly influence soil erosion processes in catchments with undulating terrain.This paper presents a field-based investigation of spatial and temporal heterogeneities in subsurface soil moisture and soil temperature associated with freezing, thawing, and snowmelt infiltration. The field setup consists of a combination of traditional point measurements performed with frequency domain reflectometry (FDR) and electrical resistivity tomography (ERT). The transect was approximately 70 m long and spanned an entire depression with a north-facing slope (average slope of 11.5%) and a south-facing slope (average slope of 9.7%). The whole depression was entirely covered with stubble.Observed resistivity patterns correspond well to the measured soil moisture patterns. During the observation period, the north facing slope froze earlier and deeper compared with the south facing slope. Freeze–thaw cycles were less pronounced in the north-facing slope than in the south-facing slope. There were also differences in soil temperature and soil moisture patterns between lower and upper parts of the monitored depression. These indicate that initiation and development of runoff related processes, and consequently soil erosion, in regions with freeze–thaw cycles may differ significantly depending on local terrain characteristics. Consequently, it indicates that spatial terrain heterogeneities, especially slope aspects, may be important when studying soil erosion processes, water flow and nutrient leaching in lowlands where patchy snowpacks and dynamic freeze–thaw cycles are predominating.

Importance of grass stolons in mitigating runoff and sediment yield under simulated rainstorms

The influence of grass cover on surface runoff and erosion processes on hillslopes differs with plant morphology and grass components (e.g., leaves, stems and roots). However, the importance of grass components, especially stolons, in reducing runoff and sediment yield is not fully understood. Thirty field simulation experiments with rainfall intensities of 90 mm h−1 were performed to study the effects of three grass species (Trifolium repens, Cynodon dactylon and Eremochloa ophiuroides) and their aboveground and belowground components on runoff, hydrodynamic parameters and sediment reductions during rainstorms. To examine the effects of different grass components on soil erosion, three management treatments, intact grass plants (IG), grass stems and roots (SR) and only grass roots (OR), were applied to each grass species. The results showed that the three grass species effectively reduced runoff and soil erosion, and the erosion reduction was greater than the runoff reduction. The highest reduction in runoff (78.2%) and sediment yield (97.9%) was observed for E. ophiuroides, followed by the T. repens and C. dactylon plots. The overland flow velocity and runoff energy increased with the sequential removal of grass aboveground components and led to increasing runoff and erosion. The effects of grass components on runoff and erosion reduction varied with grass species and plant morphology. The aboveground components had a greater impact on runoff reduction, and the roots primarily contributed to sediment reduction in T. repens and C. dactylon, which have erect stems. However, the contribution rates of grass stems to runoff and erosion reduction were highest for E. ophiuroides with well-developed stolons at 41.51% and 61.04%, respectively, which were much higher than the leaves and roots. This finding indicated that grass stolons played an important role in reducing runoff and sediment with efficiencies of 32.44% and 59.79%, respectively. These results help guide the selection of grass species with the best traits for erosion control and highlight the importance of grass stolons in preventing water erosion caused by extreme rainstorms.

SMODERP2D—Sheet and Rill Runoff Routine Validation at Three Scale Levels

Water erosion is the main cause of soil degradation in agricultural areas. Rill erosion can contribute vastly to the overall erosion rate. It is therefore crucial to identify areas prone to rill erosion in order to protect soil quality. Research on rainfall-runoff and subsequent sediment transport processes is often based on observing these processes at several scales, followed by a mathematical description of the observations. This paper presents the use of a combination of data obtained by different approaches at multiple scales to validate the SMODERP2D episodic hydrological-erosion model. This model describes infiltration, surface retention, surface runoff, and rill flow processes. In the model, the surface runoff generation is based on a water balance equation and is described by two separate processes: (a) for sheet flow, the model uses the kinematic wave approximation, which has been parameterized for individual soil textural classes using laboratory rainfall simulations, and (b) for rill flow, the Manning formula is used. Rill flow occurs if the critical water level of sheet flow is exceeded. The concept of model validation presented here uses datasets at different scales to study the surface runoff and erosion processes on the Býkovice agricultural catchment. The first dataset consisted of runoff generated by simulated rainfall on plots with dimensions of 2 × 8 m. The second dataset consisted of the runoff response to natural rainfall events obtained from long-term monitoring of 50 m2 plots. These two datasets were used to validate and calibrate the sheet flow and infiltration parameters. The third dataset consisted of occurrence maps of rills formed during heavy rainfalls obtained using remote sensing methods on a field plot with an area of 36.6 ha. This last dataset was used to validate the threshold critical water level that is responsible in the model for rill flow initiation in the SMODERP2D model. The validation and the calibration of the surface runoff are performed well according to the Nash–Sutcliffe efficiency coefficient. The scale effect was evident in the 50 m2 plots where parameters lower than the mean best fit the measured data. At the field plot scale, pixels with measured rills covered 5% of the total area. The best model solution achieved a similar rill cover for a vegetated soil surface. The model tended to overestimate the occurrence of rills in the case of simulations with bare soil. Although rills occurred both in the model and in the monitored data in many model runs, a spatial mismatch was often observed. This mismatch was caused by flow routing algorithm displacement of the runoff path. The suitability of the validation and calibration process at various spatial scales has been demonstrated. In a future study, data will be obtained from various localities with various land uses and meteorological conditions to confirm the transferability of the procedure.

Numerical simulation of the airflow at the world’s largest concentrated solar power plant in a desert region

Concentrated solar power (CSP) plants in desert regions disturb the wind regime and blowing sand, thus altering surface erosion and accumulation processes. We investigated wind regimes around the largest central-tower CSP plant in the world in Dubai in a desert environment using computational fluid dynamics to simulate the flows for the entire area, the wind and sand barriers, the central tower, and the heliostats. Over the entire area, increased surface roughness caused by the heliostats reduced wind speed by 20%, but the wind gradually returned to its original speed and direction after the return-flow region. Wind and sand barriers significantly reduced wind speed within 100 m and up to 200 m after the barrier. The area downwind of these barriers showed obvious airflow disruptions, with wind speeds decreasing by more than 50% at a distance of 100 m. The heliostat array reduced wind speed by about 20% locally, but had no effect on the overall wind field. Upwind and downwind of the central tower, the pressure and wind changed greatly, resulting in upwind erosion and downwind sand accumulation. We provide several recommendations regarding the management and design of CSP plants in desert regions.