Stages Of Erosion Research Articles

Extracting the Critical Rooting Length in Plant Uprooting by Flow From Pullout Experiments

AbstractThe growth and establishment of riparian vegetation on river bedforms is of hydrological as well as ecological importance as it helps in enhancing spatial heterogeneity and thus the biodiversity of river corridors. Yet, during floods, flow drag and scouring may reduce the rooting length of plants determining plant mortality via uprooting. In order for uprooting to occur, bed scouring must proceed until the rooting length reaches a critical value and drag forces exceed root residual anchorage. Therefore, the critical rooting length of a plant represents a crucial parameter to estimate the probability of plant removal due to flow erosion. However, difficulties in quantifying such length at the field scale have limited so far the performances of biomorphodynamic models for river bed evolution. In this work, we propose to assess the critical rooting length from controlled plant pullout experiments. To this aim, a free‐body model of the forces acting on a flexible plant in a stream at different erosion stages is developed. At incipient uprooting, we conjecture that the root resistance at the critical rooting length equals that of a plant with equal rooting length when pulled out in static conditions. To illustrate our approach, we validate our model on three different data sets obtained from small‐ and real‐scale plant uprooting experiments. A comparison between modeling and experimental observations reveals that the model provides valid results, despite its deterministic approach. The critical rooting lengths are finally used to assess the probability density function of the time to uprooting via a physically based stochastic model.

Identification of soil erosion-susceptible areas using fuzzy logic and analytical hierarchy process modeling in an agricultural watershed of Burdwan district, India

Soil erosion is a natural process; it adversely impacts natural resources, agricultural activities, ecological systems, and environmental quality as it degrades landscapes and water quality, disrupts ecosystems, and intensifies hazards. Management strategies are needed that protect soil erosion in agricultural watersheds to achieve the sustainable land-use planning. This study maps soil erosion susceptibility using two GIS-based machine-learning approaches—analytical hierarchy process (AHP) and fuzzy logic modeling in the Kunur River Basin, West Bengal, India. Fifteen soil erosion conditioning variables were integrated with the modeling methods, remote sensing data, and GIS analysis. The relative importance of the conditioning variables was assessed for their capacities to predict susceptibility of locations to soil erosion. The soil erosion susceptibility maps generated from the two models used 70% of surveyed soil erosion sites. These models’ maps were validated with the characteristics of the remaining 30% of the soil erosion sites to produce a receiver operating characteristics curve. The results indicated that the fuzzy logic model has the higher prediction accuracy; the area under the curve (AUC) value was 91.4%. The AUC value of the AHP model was 89.7%. Both models indicated that study area contains regions of high to severe soil erosion susceptibility. Logistic regression was used to discern the variables’ importance in the assessment. Relief, NDVI, distance from a river, rainfall erosivity, and soil types were the most important variables. TWI, SPI, aspect, and a sediment transportation index were of least importance. Fuzzy-logic-generated SESMs can be effective tools to guide protective actions and land managers’ measures during the primary stages of soil erosion to control the development of soil degradation.

Morphologic modelling of tidal inlet on a barrier-lagoon coast: Case study of the Laolonggou tidal inlet in the Bohai Bay

Understanding the long-term morphodynamic evolution of tidal inlet systems and their control mechanisms has great significance in the management and sustainable development of coastal regions. This study addresses this issue by applying a process-based morphological model (Delft3D) to hindcast morphodynamic evolution of the Laolonggou tidal inlet (LTI) for a duration of 68 years and then analyze the mechanism of morphologic evolution and factors affecting it in tidal inlets. The morphodynamic model is validated against two periods, a natural stage (1938–1983), and a recent erosion stage with reservoir construction (1983–2006). Results show that the evolution pattern, sediment volume changes, and hypsometry curves simulated by the model agree well with field data. A series of scenarios were designed to analyze the mechanism of morphologic evolution and impacting factors. The model results reveal that the asymmetry of the tidal currents in the channels leads to tide residual sediment transport, which causes morphodynamic evolution. The inconsistency of tidal flow path, i.e., ebb dominance occurs in the west channel and flood dominance occurs in the east channel, is an important mechanism for the evolution of the whole system. In addition, the decrease of sediment supply caused by reservoirs in Luanhe River, and extension of the barrier island contribute to the evolution of LTI. Although this study is site-specific, the results are expected to provide valuable information for sustainable management of tidal inlet systems.

Two-phase flow simulation of scour beneath a vibrating pipeline during the tunnel erosion stage

A new numerical model is developed to simulate and investigate scour beneath a vibrating pipe during the tunnel erosion stage. This study is motivated by the fact that existing numerical models are not able to properly simulate scour under a vibrating pipeline, and the underlying physical mechanisms are not well understood due to the complex fluid-structure-sediment interaction. The present model incorporates the hybrid fictitious domain-immersed boundary method into a recently developed rheology-based two-phase model. The present model is validated against published experiment results of flow beneath a vibrating pipeline near a rigid boundary and scour beneath a fixed pipe. The flow velocity at the gap and the scour profile beneath the pipe are generally well produced by the model. Subsequently, the proposed model is applied to simulate scour under a vibrating pipe with different vibration amplitudes and frequencies. Among other things, it is found that maximum pipe acceleration has a dominant effect on the underlying physics that induce scour, irrespective of the combination of the vibration amplitude and frequency. An explanation for this finding is proposed based on various quantitative simulated results.

Effect of Heat Treatment on the Cavitation Erosion Performance of WC–12Co Coatings

WC–12Co coatings were deposited on 16Cr5Ni stainless steel substrate by high-velocity oxygen fuel (HVOF) process, followed by a one-hour heat-treatment in a tube furnace with a nitrogen atmosphere at 650, 800, 950, and 1100 °C, respectively. The influence of heat-treatment temperature on properties and cavitation erosion resistance of as-sprayed and heat-treated WC–12Co coatings was studied. The cavitation erosion test was carried out with ultrasonic cavitation erosion equipment. The porosity, microhardness, phase composition, as well as surface and cross-section morphology of the coatings were characterized. The coating heat-treated at 800 °C showed three typical cavitation erosion stages and exhibited the best cavitation erosion resistance. The cavitation erosion resistance was closely related to the coating microstructure and heat-treatment process. 3D optical microscopy was used to analyze the eroded surface of the coatings. The cavitation erosion mechanism of the coatings was discussed.

Resistance of curved surfaces to the cavitation erosion produced through high-pressure submerged waterjet

The aim of the present study is to reveal fundamental cavitation erosion characteristics of the curved surface. The submerged waterjet was used to produce cavitation. An experimental work was performed on a standard cavitation erosion test rig. The Al 5083 specimens with three curvature radii, 7.0, 9.0 and 10.0 mm, were selected as the target specimens. The flat surfaces were tested for comparison. The mass loss of the eroded specimens was measured. The cumulative erosion rate was calculated. Morphology of the eroded surfaces was observed using techniques of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The root mean square (RMS) surface roughness of the eroded specimen was obtained. The results indicate that the curvature radius has a significant effect on the cavitation erosion intensity. The surface with the largest radius of curvature exhibits the weakest resistance to the cavitation erosion. No explicit relevance is recognized between the curvature radius and the extent of the cavitation erosion. In the early stage of the cavitation erosion, the central region of the target surface is less eroded. As the cavitation erosion progresses, the mass removal in the central area manifests a layer-by-layer pattern. Large erosion pits are evidenced in such a region. The specimen of R = 9.0 mm, with the highest resistance to the cavitation erosion, is featured by a sharp decline of the skewness of surface height distribution in the early stage of the cavitation erosion.

Sand-Control Technology for Water Injectors Improves Well Performance

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 192840, “Field-Trial Results for New Sand-Control Technology for Water Injectors,” by Steven Fipke, SPE, Tendeka; J.E. Charles, SPE, Shell; and Annabel Green, Tendeka, prepared for the 2018 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 12–15 November. The paper has not been peer reviewed. In 2014, a research and development (R&D) project was initiated to increase the life expectancy of Gulf of Mexico (GOM) Miocene and Lower Tertiary water-injection (WI) wells, several of which had suffered a severe loss of injectivity within only a few years of completion. The solution was to find a way to prevent fine material from entering the completion while sustaining high injection rates, with no loss of injection pressure or requirement for additional horsepower. A new flow-control device (FCD) and completion system were developed along with intrinsic nonreturn valves (NRVs) that prevent any backflow or crossflow during•shut-ins. Developing the Flow-Control Technology Tubing-deployed injection valves and regulators have been available for many years. However, these cannot address the problem of annular flow. The most-damaging factor in solids production is likely crossflow, wherein differently pressured injection zones can flow between layers inside the tubing or casing annulus. Crossflow can be eliminated only by blocking the flow at the sandface. This solution also would mitigate the damaging effects of water hammer by blocking pressure waves from entering the lower completion. Check-valve components must fit within sand-control screens or be deployed across multiple zones of the injection tubing.• During the R&D phase of the project, researchers used extensive laboratory testing, flow-loop testing, and computational-fluid-dynamics modeling to develop a series of NRV prototypes. The technology was designed to handle a variety of well conditions, including erosion, plugging, temperature, and repeated checking cycles. All FCD components, including the NRV technology, are manufactured with high-alloy stainless steel and tungsten-carbide components to resist tortuous downhole conditions for up to 15 years. FCD prototypes and design iterations were tested over 18 months and a final design was qualified to withstand repetitive pressure- checking cycles reliably at 1,500 psi (and up to 10,000-psi static differential•pressure).• The laboratory testing conducted to finalize the project development stage is described in detail in the complete paper; it consisted of leak-rate, erosion, plugging, and screen-construction stages. One determination of this testing was that the placement of the screen over the FCD joint could cause erosive wear because of the placement of the screen ribs over the valves. An alternative rib wire was designed that could place the FCD between wires without compromising the strength of the screen. With laboratory and workshop testing completed by early 2017, the focus of the project shifted to identifying and organizing a field trial for the new technology in a low-cost, low-risk environment.

Appraisal of Geomorphic Diversity with Special Reference to Basin-Area Extremity in Central Lesser Himalaya

ABSTRACT The standard for the selection of two fourth order watersheds for intensive geomorphic study was extremity in basin-area to assess diversity in between two watersheds in regard to their geomorphic environment. The diversity in geological traits reveals that the Phalal watershed was characterized by contact zone of two lithological formations (Augun gneiss 95% and Rautgara quartzites 5%) separated by north Almora thrust (NAT) while the entire Siya watershed was developed only in one formation, i.e. Rautgara (quartzites) Formation. The diversity in geo-morphometric personality and geomorphic evolution speaks of a differential development of both watersheds in context of stage of erosion. The zone of critical-height above which the erosion is acute is 1700 to 1800 m in Phalal watershed, whereas 1500 to 1600 m in Siya watershed; the hypsometric integral determines Phalal watershed (49.96 %) under middle-mature stage while Siya watershed (57.07 %) achieved early-mature stage. Diversity in erosion status was observed along the varying altitudes of the watersheds under different land use/cover. Diversity in the spatial distribution of altitude, erosion intensity, average slope versus land use/cover status under both watersheds determines the impact of basin-area extremity. The hazardous geomorphic processes also indicate the impact of basin-area extremity as eleven types of geomorphic hazards were experienced by the Phalal watershed while only four types of hazards were experienced by Siya watershed. Phalal watershed was 18.42 % hazardous area while 21.04 % hazardous area was possessed by Siya watershed. The hazard of ‘surficial erosion’ covers maximum area, i.e. 13.78 % in Phalal watershed while 20.52 % area is possessed by Siya watershed. Likewise maximum study units attained degree 4 instability for Phalal watershed (80%) while degree 2 instability for Siya (50%) watershed. Thus, basin–area has direct posture on geological traits, geomorphic evolution, geomorphometric personality and hazardous geomorphic processes while land use/cover status has no bearing on basin-area extremity under the studied watersheds.

Stratigraphic Sequence and Sedimentary Systems in the Middle-Southern Continental Slope of the East China Sea from Seismic Reflection Data: Exploration Prospects of Gas Hydrate

Many evidences for gas hydrate bearing sediments had been found in the continental slope of the East China Sea, such as bottom simulating reflections (BSRs), undersea gas springs, pyrite associated with methane leakage, mud diapirs/mud volcanos, bottom-water methane anomalies and so on. In this study, six key stratigraphic interfaces including T0 (seafloor), T1 (LGM, 23 kyr B.P.), T2 (2.58 Myr), T3 (5.33 Myr), T4 (11.02 Myr) and T5 (16.12 Myr) were identified, and then five third-order sequences of SQIII1 to SQIII5 were divided. However, T5 in southern continental slope is not found, which shows that the middle-northern Okinawa Trough had begun to rift in the early Miocene, earlier than the southern segment. Four system tracts including lowstand systems tract (LST), transgressive systems tract (TST), highstand systems tract (HST) and falling stage systems tract (FSST) are further divided. The marine erosion interface of 11.02 Myr and regressive unconformity interface of 23 kyr B.P. indicate two large-scale sea level drop events in the research area. Seven typical seismic facies identified in the continental slope are continental shelf-edge deltas, littoral fluvial-delta plains, incised channels or submarine canyons, slope fans, submarine fans or coastal sandbars, littoral-neritic finegrained sediments, mud volcanos and some other geological bodies respectively. The minimum water depth for hydrate occurrence in the Okinawa Trough is 630 m, and the thickness of gas hydrate stability zone in continental slope is between 0 and 590 m. The calculated bottom boundary of hydrate stability zone is slightly deeper than BSRs on the seismic sections. The re-depositional turbidite sand bodies, such as canyon channels, slope fans and submarine fans developed in Quaternary strata, are the predominant hydrate reservoirs. According to developing process, the dynamic accumulation of hydrate systems can be divided into three evolutionary stages including canyon erosion and hydrate stability zone migration stage, sediments destabilizing and methane leakage stage, and channel filling and hydrate re-occurrence stage.

Flow dynamics in the vicinity of a gravel embedded vertical retaining wall: conditions corresponding to the initial stages of local erosion

The present study examines the turbulent flow characteristics in the vicinity of the leading edge of a vertical retaining wall structure embedded in a gravel bed. Conditions before and during the initial stages of local scour development were considered. To that end, three laboratory experiments were carried out: one with fixed boundaries as a reference case, a second one with an erodible bed, but immobile channel bank, and a third one characterized by an erodible channel bed and bank. Instantaneous and time-averaged flow features, and turbulence statistics associated with the three-component velocity fields, obtained with a stereoscopic particle image velocimetry system, were analyzed. Water surface examination determined that channel bank erosion alters flow behavior upstream of the retaining wall. This change is manifested through more frequent formation of eddies near the top corner of the junction between the upstream face of the protrusion and the channel bank. Time-averaged and instantaneous velocity vector fields demonstrate the presence of two counter-rotating vortices in the experiments with the fixed channel bank, one located near the junction of retaining wall and the channel bed and one away from it generated as a result of a strong downflow. The latter motion represents a section of a horseshoe vortex. During the channel bank erosion, however, these vortices are not as significant and persistent. The results also indicate that the coherency and magnitude of the streamwise vorticity field diminish as a result of scour. However, it was confirmed that local turbulent kinetic energy and shear stresses increase in the presence of scour due to enhanced local flow separation.

Fish‐scale pit effects on erosion and water runoff dynamics when positioned on a soil slope in the Loess Plateau region, China

AbstractSoil moisture construction is a very important way to reduce soil erosion and maintain crop growth in arid and semiarid regions of China. A microcatchment technique for soil erosion prevention widely used on soil slopes on the Loess Plateau are fish‐scale pits (FSPs). This technique is combined with afforestation techniques to store runoff, interrupt the dynamics of soil erosion, and help mitigate frequent water deficiencies encountered by forest trees. This study investigated the effects of FSPs on soil erosion dynamics including rill formation and runoff. A three‐dimensional (3D) laser scanner was used to evaluate the erosion resistance of a 15° slope treated with FSPs arranged in a triangular pattern and the hydraulic characteristics of the flow on this slope during several intermittent simulated rainfall events. The following results were obtained. (a) The FSP‐treated slope displayed eight progressive stages of erosion: splash erosion, sheet erosion, scouring by water streams, formation of the scour pits, rill erosion, down‐slope erosion, up‐slope erosion, and collapse of the pit walls. (b) As the rainfall duration increased, the runoff velocities at various locations on the slope fluctuated, but generally, the runoff velocities were significantly higher in the down‐slope positions than for the midslope and upslope positions. When the cumulative rainfall duration reached approximately 58 min and the total rainfall reached approximately 88.5 mm, the ability of the FSPs to intercept and store runoff rapidly decreased. In the first two rainfall events, both the runoff reduction benefits (RRB) and sediment reduction benefits (SRB) were positive, but following the third rainfall event, the SRB and RRB of the FSPs were negative. The accuracy of erosion parameters extracted using the 3D laser equipment and the ArcGIS software in comparison with the measured rill erosion parameters all less than 10%. The relative error between the measured sediment and the calculated sediment is within 5.66–22.13%. (c) During the rainfall process, the flow on the upslope was constantly in the laminar regime, but after the FSPs were completely filled with water, the laminar flow on the downslope transitioned into a turbulent flow. (d) As the cumulative rainfall duration increased, the degree of topographic relief and the number of rills increased, as did the measurements of surface roughness and flow resistance. In conclusion, the microcatchment methods reduced the rill erodibility and enhanced the soil's resistance to concentrated flow erosion.

In-situ multi-sensor characterization of soil cores along an erosion-deposition gradient

Soil landscape research is faced with wide-ranging questions of soil erosion, precision farming, and agricultural risk management. Digital Soil Morphometrics is a powerful tool to provide respective answers or recommendations but requires soil data from the pedon-to-field scale with high horizontal and vertical resolutions, including the subsoil. We present an efficient sampling and measurement method for easily obtainable soil driving cores with low-destructive preparation. Elemental contents and soil organic and mineral matter composition were measured rapidly and in large numbers using a multi-sensor approach, i.e., visible and near-infrared (Vis-NIR), diffuse reflectance infrared Fourier transform (DRIFT), and X-ray fluorescence (XRF) spectroscopy. The suitability of the approach with respect to three-dimensional soil landscape models was tested using soils along a slope representing different stages of erosion and deposition in a hummocky landscape under arable land use (Calcaric Regosols, Calcic Luvisols, Luvic Stagnosols, Gleyic-Colluvic Regosols). The combination of soil core sampling, pedological description, and three spectroscopic techniques enabled rapid determination and interpretation of horizontal and vertical spatial distributions of soil organic carbon (SOC), soil organic and mineral matter composition, as well as CaCO3, Fe, and Mn contents. Depth profiles for SOC, CaCO3, and Fe contents were suitable indicators for site-specific degrees of erosion and matter transport processes at the pedon-to-field scale. Fe and Mn profiles helped identifying zones of reductive and oxic domains in subsoils (gleyzation). Further methodical developments should implement plant-availability of nutrients, characterization of Fe-oxides, and calibration of the spectroscopic techniques to field-moist samples.

Effect of aluminate content in cement on the long-term sulfate resistance of cement stabilized sand

Durability of cement-based materials for marine/coastal structures is an increasingly challenging problem. Sulfate ions in seawater can react with aluminate in cement to form erosion products, causing cracks and spalling. When cement is used to stabilize loose erodible sand in coastal areas, the resistance to sulfate attack is questionable. In this study, four cements with different aluminate contents were used to stabilize sand. Cement stabilized sands were immersed in 5% Na2SO4 solution for 300-days to simulate long-term sulfate attack process. The deterioration of engineering performance was evaluated based on expansion ratio, mass change, uniaxial compressive strength, and ultrasonic velocity. The deterioration mechanisms were analyzed through mineralogical and microstructural observations including X-ray diffraction, EDS, scanning electronic microscopy, and nuclear magnetic resonance. The results showed that the development of macro-scale mechanical performances could be divided into two stages (initial stage and erosion stage) when subjected to 300-days immersion in 5% Na2SO4 solution. Sand stabilized by low-aluminate-content cement displayed better engineering performance especially at the erosion stage. Mechanistically, more ettringite was formed in high-aluminate-content cement stabilized sand, leading to swelling and cracking. The formation of ettringite and gypsum were accompanied with the consumption of portlandite, leading to further strength loss.

Apportioning contributions of individual rill erosion processes and their interactions on loessial hillslopes

Channels (rill, ephemeral gully, gully and river channel) exhibit a continuum of sizes and flow magnitudes. Rill erosion, as the initial stage of channel erosion, accounts for >80% of total eroded sediments on sloping farming lands in many parts of the world. Previous researches often regard rill erosion as an entirety or focus on individual rill erosion process separately. Few attentions have been paid to the contributions of individual processes including rill headcut advance, bed incision, sidewall expansion and their interactions to the over-all rill erosion. Thus, simulated upslope inflow experiments were designed to investigate the impacts of individual processes involved and their interactions in rill erosion under four inflow rates (1.0, 2.0, 3.0 and 4.0 L min−1) and two slope gradients (15° and 20°). Photogrammetry and manual sampling were used to measure hillslope morphology variation and sediment delivery, repectively. The results show that headcut advance, bed incision and sidewall expansion interact with each other and exhibit both independent and dependent features across spatial and temporal scales. Headcut advance interacts with bed incision and sidewall expansion before rill head advancing to a critical slope length. Initial rill depth and width are determined by initial headcut morphology. Bed incision and sidewall expansion dominate rill erosion before and after the non-erodible layer is exposed to concentrated flow, respectively. Headcut advance contributed the largest amount of rill erosion (44%–68%), followed by bed incision (27%–44%) and sidewall expansion (3.8%–12%). Headcut advance contributed more (63%–83%) to total rill width increment while bed incision contributed larger percentage (51%–65%) to total rill depth increment. Prediction equations for length, width and depth of a single rill on a loessial hillslope and empirical equations of rill erosion for the individual erosion processes were fitted and validated. Quantification and understanding of the contributions of individual rill erosion processes provides the necessary scientific basis for the development of process-based rill erosion models, and then, for preventions of soil losses and land degradation.

Shedding frequency in cavitation erosion evolution tracking

Cavitation erosion is a concern for most hydraulic machinery. An especially damaging type of cavitation is cloud cavitation. This type of cavitation is characterized by a growth-collapse cycle in which a group of vapor bubbles first grows together in a low-pressure region and then collapses almost simultaneously when the pressure recovers. Measuring the frequency of these collapse events is possible by acoustic emission (AE), as demonstrated in this study, in which a cavitation tunnel is utilized to create cloud cavitation in the vicinity of a sample surface. These samples were equipped with AE sensors, and the initially high frequency AE signal was demodulated to detect the relatively low frequency cloud cavitation shedding. It was found that when the cavitation number is increased, AE successfully detects the changes in this frequency, confirmed by comparing the results to video analysis and to simulations from literature. Additionally, the frequency increases when cavitation erosion progresses, thus providing means to track the erosion stage. It is concluded that the presented method is suitable for both detecting the transition from cloud to sheet cavitation and the erosion evolution in the experimental cavitation tunnel. The method could probably be extended to non-intrusive hydraulic machine monitoring, as this type of cloud cavitation is common in hydrofoils.

Sediment load change with erosion processes under simulated rainfall events

It is of great significance to quantify sediment load changing with erosion processes for improving the precision of soil loss prediction. Indoor rainfall experiments were conducted in 2 rainfall intensities (90 mm·h−1 and 120 mm·h−1), four slope gradients (17.60%, 26.80%, 36.40%, 46.60%) and 2 slope lengths (5 m, 10 m). Erosion processes are divided into five stages. Results show that sediment yield is mainly sourced from rill erosion, contributing from 54.60% to 95.70% and the duration of which is extended by slope gradients. Sediment load and sediment concentration are significantly different along erosion stages, with the highest values in rill development stage (SIV). Surface flow velocities (interrill and rill) demonstrate less significant differences along erosion stages. Rainfall intensity increases sediment load in all stages, with up to 12.0 times higher when changing from 90 to 120 mm·h−1. There is an increasing trend for sediment load and sediment concentration with the rising slope gradient, however, fluctuations existed with the lowest values on 26.80% and 36.40%, respectively, among different treatments. The slope gradient effects are enhanced by rainfall intensity and slope length. Results from this study are important for validating and improving hillslope erosion modelling at each erosion stage.

Investigation of sandstone erosion by continuous and pulsed water jets

The study compares the sandstone erosion manifestations (depth, width, and volume of the removed material) caused by continuous and pulsed water jets (WJs) with a frequency f = 20 kHz and 40 kHz. The WJ head follows an inclined trajectory at an angle of 45° to the horizontal surface. The starting point of the head was positioned 5 mm above the sandstone surface. The traverse speed of the head was varied from v = 0.25 mm/s to 1 mm/s. The structural changes and plastic deformation caused by the mechanical effect of the continuous and pulsed WJs were analysed using SEM and optical profilometer. The results showed that an optimal standoff distance was responsible for the maximum erosion effect under both continuous and pulsed regimes. The PWJ at f= 40 kHz showed better erosion performance in terms of depth (6.8 mm), width (6.83 mm) and volume removed (27.31 mm3) as compared to PWJ at f = 20 kHz and CWJ. The microstructural topography at varying standoff distance (z = 10 mm to 45 mm) showed erosion features such as micro-pits, cracks, perforated holes responsible for different erosion stages. On-line monitoring via means of acoustic emission was measured to evaluate the erosion phenomenon on the sandstone surface during the impact of the PWJ and CWJ. The correlation between the acoustic emission results and the erosion parameters showed the progression of the erosion process under different technological conditions.

Imaging Spectroscopy for Soil Mapping and Monitoring

There is a renewed awareness of the finite nature of the world’s soil resources, growing concern about soil security and significant uncertainties about the carrying capacity of the planet. Regular assessments of soil conditions from local through to global scales are requested, and there is a clear demand for accurate, up-to-date and spatially referenced soil information by the modelling scientific community, farmers and land users, and policy- and decision-makers. Soil and imaging spectroscopy, based on visible–near-infrared and shortwave infrared (400–2500 nm) spectral reflectance, has been shown to be a proven method for the quantitative prediction of key soil surface properties. With the upcoming launch of the next generation of hyperspectral satellite sensors in the next years, a high potential to meet the demand for global soil mapping and monitoring is appearing. In this paper, we briefly review the basic concepts of soil spectroscopy with a special attention to the effects of soil roughness on reflectance and then provide a review of state of the art, achievements and perspectives in soil mapping and monitoring based on imaging spectroscopy from air- and spaceborne sensors. Selected application cases are presented for the modelling of soil organic carbon, mineralogical composition, topsoil water content and characterization of soil crust, soil erosion and soil degradation stages based on airborne and simulated spaceborne imaging spectroscopy data. Further, current challenges, gaps and new directions toward enhanced soil properties modelling are presented. Overall, this paper highlights the potential and limitations of multiscale imaging spectroscopy nowadays for soil mapping and monitoring, and capabilities and requirements of upcoming spaceborne sensors as support for a more informed and sustainable use of our world’s soil resources.

Development of Quaternary travertines in the carbonate mountains of the western Costa del Sol, Málaga, southern Spain

AbstractThe predominantly carbonate nature of the mountains near the coast of Málaga and Marbella (Costa del Sol, southern Spain) and the presence of springs have favored the formation of travertine buildups during the Quaternary. The geomorphic characteristics of the slopes and the location of the springs have determined the development of three types of travertine growths: (1) spring travertines, located preferentially on the south mountainside, where the slope is steepest; (2) pool-dam-cascade travertines, which form along the north and east edges, far from the carbonate relief and with a gentler slope; and (3) river-valley travertines, formed in the courses of the springs of any sector. Field observations combined with new amino acid racemization (AAR) dating of Helicidae gastropods show that most of the travertine formations are polyphasic and that their development was interrupted by stages of erosion and incision. Five stages of travertine development are evident, most of which are related to warm, moist episodes corresponding to marine oxygen isotope stages (MIS) 7, 5, 3, and 1, although local travertine growth also occurred during MIS 6 and during the transition from MIS 3 to 2.

Effect of Slope Gradient on Erosion Evolution Process at Microtopographic Tillage Soil Surfaces

Slope gradient is one of the critically important factors which drive the erosional response of microtopographic surfaces. This study investigates the effect of slope gradient on the evolution of erosion under accumulative rainfall in laboratory experiments and calculates critical slope values that help evaluate land suitability for farming and similar purposes. Dynamics of accumulative runoff, accumulated sediment and their rates in each erosion stage are studied when the slope gradient varies. The critical slope value for the microtopographic surface was calculated according to the relationship between the sediment yield and slope gradient. The amount of eroded soil downhill in each erosion stage was calculated using DEM data of point cloud. Results show that 1) a steeper slope would increase cumulative runoff; 2) cumulative sediment increases rapidly initially and then stabilizes with the increase of slope; 3) the critical slope value for the whole erosion is determined as 10°. The findings of the dynamics of interrill erosion and sediment characteristics are useful information for future research of erosion prediction and conservation of soil and water in the Chinese Loess Plateau.