Local Erosion Research Articles

Structural framework of the Caswell Sub-basin, North West Shelf, Australia

The Caswell Sub-basin, situated within the Browse Basin in the North West Shelf constitutes one of Australia’s primary hydrocarbon producing regions, with notable gas-condensate producing fields including Ichthys and Prelude. Jurassic syn-rift sandstones are extensively distributed across the basin and serve as one of the major reservoirs. However, reservoir sequences are typically intensely faulted and exhibit heterogeneity in thickness and lithofacies, with some areas experiencing localised erosion on uplifted fault blocks (e.g. Northern Caswell Sub-basin). Hence, understanding the nature of the 3D fault patterns and their growth history is crucial for evaluating the reservoir characteristics for field development and additional exploration activities. This study, therefore, aims to evaluate the structural framework and the tectonic evolution of the Caswell Sub-basin. Detailed structural interpretation of Paleozoic and younger sequences was conducted using multiple 3D seismic datasets extending over Ichthys, Prelude, Lasseter, and Crown fields. Our study focuses mainly on Mesozoic faulting patterns and kinematics evaluated from interpreted structural maps, thickness changes of each stratigraphic interval and fault throw profiles of major bounding faults. The extensional phase during the Early–Middle Jurassic triggered the development of NE–SW trending faults and the deepening of the Brewster Graben. While, from the Late Jurassic to the Early Cretaceous, the development of E–W trending faults in the north of the Crown and Lasseter fields indicate a shift in the regional stress regime. We highlight the importance of evaluating the structural linkage from basement to cover sequences to achieve a comprehensive understanding of reservoirs and associated petroleum systems.

Estimation of vertical transport timescales of sediment in the Changjiang Estuary and its adjacent regions

The concept of resuspension age was employed to assess the timescales of vertical sediment transport in the Changjiang Estuary (CJE) and its adjoining areas. Resuspension age refers to the duration elapsed since particles last made contact with the seabed. Energetic tidal current in the study area results in a significant amount of sediment being eroded into the water during spring tides, causing the resuspension age to consistently remain lower during spring tides compared to neap tides. Spatially, consistently low resuspension ages occur in the North Branch and turbidity maximum because suspended sediment in these areas primarily originates from local erosion. While advective sediment dominates in the HZB, leading to highest resuspension age there. During the wet season, the South Branch experiences an average resuspension age surpassing 10 days, primarily due to particles predominantly transported from the river. Sediments deposited on the seabed during the wet season become the primary source of suspended sediment after being eroded into the water column during the dry season, leading to a reduction in resuspension age. Likewise, the decrease in resuspension age in the Subei Coast during the dry season is closely associated with the appearance of sediment mass advected by the northern branch plume. When stratification occurs, the upward diffusion of sediment is impeded, constraining newly eroded sediment close to the bed. As a result, these sediments exhibit lower ages than those in the upper water column, where sediment transport is primarily dominated by horizontal advection.

Effect of concave‐wall jets with circumferential multi‐inlet on liquid–solid separation

AbstractThis study combined numerical simulation and experiment to explore the influence of the concave‐wall jets with uniformly distributed tangential inlets in the cyclone separator on the liquid–solid separation characteristics and equipment. The results show that as the number of tangential inlets increases, the superposition effect of particle trajectories and flow fields becomes more significant. The superimposed flow field enhances the circumferential flow velocity of the fluid, causing the distribution of the jet along the radial and spanwise directions to shrink, greatly improving the uniformity of particle distribution and turbulent kinetic energy along the circumference, and effectively reducing the impact of particles on local areas near the jet inlet. Since the superposition of circumferential multi‐inlet jets enhances the swirling flow, the local disturbance and wall erosion effects near the jet inlet were reduced. Compared with double inlets, the flow rates of three inlets and four inlets were increased by 50% and 100%, respectively, the maximum turbulent kinetic energy increased by 14.5% and 56.2%, and the maximum escape time of particles was shortened by 3.2 and 3.3 s, respectively, the maximum erosion rates were reduced by 38.4% and 23.6%, respectively, and the separation efficiency and material handling capacity were significantly improved. This study supplemented the theory of concave‐wall jets' superposition characteristics and provided a theoretical basis for applying circumferential multi‐inlet devices in liquid–solid separation equipment.

Obliquely incident seismic response of subway stations following urban soil internal erosion

Urban groundwater infiltration resulting from tropical storm rainfall can lead to internal soil erosion and ground subsidence. The long-term effects of these phenomena may result in uneven settlement of the subway system, posing risks to its safety and operational integrity. Suffusion poses a significant hazard to long-term subway operation. It is a type of soil internal erosion characterized by the migration of fine particles from the pore channels between coarse particles. This study focused on the performance degradation of different gap-graded sands caused by internal erosion, observed through triaxial compression tests. Using the cap plasticity model and considering mechanical parameters before and after soil erosion, a refined two-dimensional finite element model of a soil subway station structure based on ABAQUS was developed to analyze the deformation and damage pattern of the subway structure resulting from soil internal erosion and earthquake. The results of this study demonstrated that localized internal soil erosion significantly contributes to uneven settlement in subway stations, potentially compromising their seismic performance during oblique seismic excitations.

Benthos as a key driver of morphological change in coastal regions

Abstract. Benthos has long been recognized as an important factor influencing local sediment stability, deposition, and erosion rates. However, its role in long-term (annual to decadal scale) and large-scale coastal morphological change remains largely speculative. This study aims to derive a quantitative understanding of the importance of benthos in the morphological development of a tidal embayment (Jade Bay) as representative of tidal coastal regions. To achieve this, we first applied a machine-learning-aided species abundance model to derive a complete map of benthos (functional groups, abundance, and biomass) in the study area, based on abundance and biomass measurements. The derived data were used to parameterize the benthos effect on sediment stability, erosion rates and deposition rates, erosion and hydrodynamics in a 3-dimensional hydro-eco-morphodynamic model, which was then applied to Jade Bay to hindcast the morphological and sediment change for 2000–2009. Simulation results indicate significantly improved performance with the benthos effect included. Simulations including benthos show consistency with measurements regarding morphological and sediment changes, while abiotic drivers (tides, storm surges) alone result in a reversed pattern in terms of erosion and deposition contrary to measurement. Based on comparisons among scenarios with various combinations of abiotic and biotic factors, we further investigated the level of complexity of the hydro-eco-morphodynamic models that is needed to capture long-term and large-scale coastal morphological development. The accuracy in the parameterization data was crucial for increasing model complexity. When the parameterization uncertainties were high, the increased model complexity decreased the model performance.

Clinicopathologic and endoscopic characteristics of ten patients with gastric hamartomatous inverted polyp: a single center case series

BackgroundGastric hamartomatous inverted polyps (GHIPs) are not well characterized and remain diagnostically challenging due to rarity. Therefore, this study aims to investigate the clinicopathologic and endoscopic characteristics of patients with GHIP.MethodsWe retrospectively reviewed clinicopathologic and endoscopic features of ten patients with GHIP who were admitted to Beijing Friendship Hospital from March 2013 to July 2022. All patients were treated successfully by endoscopic resection.ResultsGHIPs were usually asymptomatic and found incidentally during gastroscopic examination. They may be sessile or pedunculated, with diffuse or local surface redness or erosion. On endoscopic ultrasonography, the sessile submucosal tumor-type GHIP demonstrated a heterogeneous lesion with cystic areas in the third layer of the gastric wall. Histologically, GHIPs were characterized by a submucosal inverted proliferation of cystically dilated hyperplastic gastric glands accompanied by a branching proliferation of smooth muscle bundles. Inflammatory cells infiltration was observed in the stroma, whereas only one patient was complicated with glandular low-grade dysplasia. Assessment of the surrounding mucosa demonstrated that six patients (60%) had atrophic gastritis or Helicobacter pylori–associated gastritis, and four patients (40%) had non-specific gastritis. Endoscopic resection was safe and effective.ConclusionsGHIPs often arise from the background of abnormal mucosa, such as atrophic or H.pylori-associated gastritis. We make the hypothesis that acquired inflammation might lead to the development of GHIPs. We recommend to make a full assessment of the background mucosa and H. pylori infection status for evaluation of underlying gastric mucosal abnormalities, which may be the preneoplastic condition of the stomach.

Sources of suspended sediments in salt marsh creeks: Field measurements in China and the Netherlands

Marsh creeks are perceived as important conduits for transporting water and sediment between mudflats and marshes. In order to advance the understanding of the transport mechanisms in creeks, the source and ultimate sink of sediment which moves between mudflats and marshes through creek channels need further investigation. Therefore, two field campaigns were conducted in two intertidal systems with varying sediment availability. The water depth, flow velocity, suspended sediment concentration, and bed level change were measured simultaneously in a marsh creek and on the adjacent mudflat in Chongming Island (China) and in Paulina Saltmarsh (the Netherlands). Paulina Saltmarsh is much smaller, more frequently flooded, and has lower sediment concentration than Chongming. These contrasting conditions allow for a comparison of transport mechanisms and functioning of the creek. Both systems first show that the high suspended sediment concentration (SSC) measured in marsh creeks is mainly the consequence of sediment advection rather than local erosion. In addition, erosion in marsh creeks is usually limited during ebb tides, reducing the export of sediment through these creeks. However, differences have been observed between two systems. The measured SSC was highly asymmetric between flood and ebb tides in Chongming. Large peaks in SSC during the flood period can be observed for most tidal cycles. The marsh creeks in Chongming therefore function as conduits for sediment import. Additionally, there are distinct overbank and underbank tides in Chongming. Sediment was trapped and retained in creeks during underbank tides, which can then be eroded and transported to the marsh during subsequent overbank tides. We also observed that mudflats in Chongming quickly recovered after erosion. These mechanisms have not been observed in Paulina Saltmarsh, where net sediment export via the marsh creek was observed due to a lack of abundant sediment in suspension during flood tides. Furthermore, the remaining bed surface of mudflats after an erosion event was stronger than before, limiting further erosion in Paulina Saltmarsh. These findings from the two systems indicate that the role of creeks in sediment import/export depends on the availability of sediment from mudflats, shedding light on nourishment strategies for salt marshes.

Asymmetric deterioration of reinforced concrete marine piles subjected to nonuniformly localized corrosion: Experimental study

Reinforced concrete (RC) marine piles usually suffer from local stiffness deterioration caused by chloride attack in splash and tidal zones. Moreover, pre-existing concrete cracks and defects at the steel–concrete interface usually lead to nonuniformly localized corrosion, which has seldomly been discussed. In this study, the effects of nonuniformly localized corrosion on the lateral behaviours of piles were experimentally studied. The localized electrochemical chloride erosion (LECE) technique was employed, and the corrosion level was represented by the number of corroded steel bars and the length of the corroded sections. Results show that the nonuniform localized corrosion caused asymmetric force–displacement hysteresis curves and changed the failure mode of pile structure under cyclic loading. The highly contrast mechanical responses suggest the importance of the loading directions in assessing the mechanical behaviours of corroded piles. Skeleton curves, stiffness degradation and energy dissipation capacity were further analysed to investigate the bearing capacity of corroded piles. These findings can benefit the comprehensive understandings and assessment of the asymmetric stiffness deterioration of corroded marine RC piles.

Towards Automated Chinese Ancient Character Restoration: A Diffusion-Based Method with a New Dataset

Automated Chinese ancient character restoration (ACACR) remains a challenging task due to its historical significance and aesthetic complexity. Existing methods are constrained by non-professional masks and even overfitting when training on small-scale datasets, which hinder their interdisciplinary application to traditional fields. In this paper, we are proud to introduce the Chinese Ancient Rubbing and Manuscript Character Dataset (ARMCD), which consists of 15,553 real-world ancient single-character images with 42 rubbings and manuscripts, covering the works of over 200 calligraphy artists spanning from 200 to 1,800 AD. We are also dedicated to providing professional synthetic masks by extracting localized erosion from real eroded images. Moreover, we propose DiffACR (Diffusion model for automated Chinese Ancient Character Restoration), a diffusion-based method for the ACACR task. Specifically, we regard the synthesis of eroded images as a special form of cold diffusion on uneroded ones and extract the prior mask directly from the eroded images. Our experiments demonstrate that our method comprehensively outperforms most existing methods on the proposed ARMCD. Dataset and code are available at https://github.com/lhl322001/DiffACR.

Multimethod dating of ice-rafted dropstones reveals hidden localized glacial erosion in Wilkes Subglacial Basin, Antarctica

Abstract The Antarctic ice sheet blankets >99% of the continent and limits our ability to study how subglacial geology and topography have evolved through time. Ice-rafted dropstones derived from the Antarctic subglacial continental interior at different times during the late Cenozoic provide valuable thermal history proxies to understand this geologic history. We applied multiple thermochronometers covering a range of closure temperatures (60–800 °C) to 10 dropstones collected during Integrated Ocean Drilling Program (IODP) Expedition 318 in order to explore the subglacial geology and thermal and exhumation history of the Wilkes Subglacial Basin. The Wilkes Subglacial Basin is a key target for study because ice-sheet models show it was an area of ice-sheet retreat that significantly contributed to sea-level rise during past warm periods. Depositional ages of dropstones range from early Oligocene to late Pleistocene and have zircon U-Pb or 40Ar/39Ar ages indicating sources from the Mertz shear zone, Adélie craton, Ferrar large igneous province, and Millen schist belt. Dropstones from the Mertz shear zone and Adélie craton experienced three cooling periods (1700–1500 Ma; 500–280 Ma; 34–0 Ma) and two periods of extremely slow cooling rates (1500–500 Ma; 280–34 Ma). Low-temperature thermochronometers from seven of the dropstones record cooling during the Paleozoic, potentially recording the Ross or Pan-African orogenies, and during the Mesozoic, potentially recording late Paleozoic to Mesozoic rifting. These dropstones then resided within ~500 m of the surface since the late Paleozoic and early Mesozoic. In contrast, two dropstones deposited during the mid-Pliocene, one from the Mertz shear zone and one from Adélie craton, show evidence for localized post-Eocene glacial erosion of ≥2 km.

Interaction of surface processes and crustal flow in the Eastern Himalayan Syntaxis

The syntaxes at the eastern and western ends of the Himalaya located in the Tsangpo and Indus gorge regions provide examples of the interplay between tectonics and erosion. A previous borehole study along the Yarlung River in the Eastern Himalayan Syntaxis (EHS) revealed an ∼1 km thick sedimentary wedge upstream of the Tsangpo gorge with a >2.5 Ma depositional age. However, the mechanism of formation of this sedimentary wedge remains under debate. Here, we combine low-temperature thermochronology data and thermomechanical modelling to discuss how a sedimentary wedge formed at the highly eroded EHS. Our low-temperature thermochronology results show late Miocene fast cooling episodes focused at the Gyaca and Tsangpo gorges, which are interpreted to be related to coeval rifting at the former and rapid erosion and hot-crust upwelling at the latter. Constrained by the geological and geophysical observations, we apply thermomechanical models to illustrate the mechanism of formation of the sedimentary wedge and present high relief of the EHS. The numerical geodynamic model shows that localized erosion triggers middle ‘crust extrusion’ and regional topographic adjustment at the EHS. Supplementary material : Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.7008098 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Large‐Scale Channel Response to Erosion‐Control Measures

AbstractErosion‐control measures in rivers aim to provide sufficient navigation width, reduce local erosion, or to protect neighboring communities from flooding. These measures are typically devised to solve a local problem. However, local channel modifications trigger a large‐scale channel response in the form of migrating bed level and sediment sorting waves. Our objective is to investigate the large‐scale channel response to such measures. We consider the lower Rhine River from Bonn (Germany) to Gorinchem (the Netherlands), where numerous erosion‐control measures have been implemented since the 1980s. We analyze measured bed level data (1999–2020) around four erosion‐control measures, comprising scour filling, bendway weirs, and two fixed beds. To get further insight on the physics behind the observed behavior, we set up an idealized one‐dimensional numerical model. Finally, we study how the geometry and spacing of the measures affect channel response. We show that erosion‐control measures reduce the sediment flux due to (a) lack of erosion over the measure and (b) sediment trapping upstream of the measure, resulting in downstream‐migrating incision waves that travel tens of kilometers at decadal timescales. When the measures are in close proximity, their downstream effects may be amplified. We conclude that, despite fulfilling erosion‐control goals at the local scale, erosion‐control measures may worsen large‐scale channel‐bed incision.

The influence of driftwood debris in accelerating the regional scour near the bridge pier

Flood disasters caused by driftwood debris are increasing and becoming more severe due to rising rainfall, shifting forest conditions, and increased trees along rivers. Driftwood buildup in rivers leads to sedimentation, erosion, and rising water levels, necessitating precise prediction of its behavior to mitigate its harmful effects. This study utilizes a three-dimensional numerical model to investigate the influence of piled-up driftwood debris on the acceleration of local scour development in front of the bridge pier. Depending on their density, driftwood blockages can be deposition types, such as floating, suspended, and submerged materials. The floating driftwood debris types yielded broader and deeper scour holes, while the suspended driftwood debris produced narrower but deeper ones. The submerged driftwood debris obstructed the pier perimeter; consequently, the plunging and spiral horseshoe patterns deteriorated as the flow approached the pier. The horseshoe vortex’s intensity and diving flow are likely lower, producing shallower local erosion around the bridge pier.

Study on the Influence of Water Erosion on the Bearing Capacity and Function of the High Pile Foundation of the Wharf

High-pile foundation is a common form of deep foundation commonly used in ocean environments, such as docks and bridge sites. Aiming at the problem of bearing capacity of high pile foundations, this paper proposes the calculation of bearing capacity and the analysis of scour depth of high pile foundations under the action of scour based on the modified p-y curve. In this paper, three kinds of scour mechanisms—natural evolution scour, general scour, and local scour—are described; and the calculation methods of scour widely used at present are compared and analyzed. The solution of the vertical stress of soil around the pile under local scour is solved and applied to the β method to solve the lateral resistance of the pile under local scour. The local erosion is equivalent to the whole erosion, and the expression of the ultimate soil resistance before and after the equivalent is calculated, respectively, according to the principle that the ultimate soil resistance at a certain point above the equivalent pile end remains unchanged. The distance from the equivalent soil surface to the pile end can be obtained simultaneously, and then the equivalent erosion depth, p-y curve of sand at different depths, and high pile bearing capacity can be obtained. Finally, it is found that the bending moment of a single pile body varies along the pile body in the form of a parabola, and the maximum bending moment of the pile body is below the mud surface and increases with the increase in horizontal load. When the scouring depth is 30 m, the horizontal load is 25 KN, and the maximum bending moment of the pile body is about 150 N·m. The data with a relative error greater than 10% accounted for only 16.6% of the total data, and the error between the calculated value and the measured value was small. The formula can predict the erosion depth more accurately.

Ultrasonic cavitation erosion of CFRP composites

To date, cavitation erosion of carbon fibre reinforced polymer (CFRP) composites has attracted only limited scientific attention. This paper investigates this knowledge gap through a series of experiments, in which unidirectional and bidirectional (2x2 twill) CFRP composites were exposed to cavitation clouds produced by an ultrasonic transducer in distilled water. Both composites were bonded with epoxy resin. Cavitation erosion tests were conducted according to the ASTM G32-16 standard using a stationary specimen method. The effect of water absorption on monitoring erosion damage was studied using saturated and dry specimens. Specimen mass loss measurements and microscopy observations were done at regular intervals throughout testing. Erosion imprint topographies were studied using X-ray computed microtomography. Three distinct erosion stages were identified from the erosion process observations. Nonuniformities in surface geometry and properties facilitated nucleation and accelerated local erosion. Surface epoxy thickness, fibre diameter and packing, and thickness and layup of fibre bundles influenced the erosion process. The erosion mechanisms included cracking and debonding of epoxy, and tunnelling and trenching in fibre bundles. Research findings indicated that the composite internal structure can potentially be designed for reduced water absorption and increased erosion resistance. Acoustic impedance was most efficient in predicting material response to cavitation erosion.

Distribution of logjams in relation to lateral connectivity in the River Corridor

We examine the redistribution of logjams from the channel to the floodplain during a large flood following a wildfire in a forested montane catchment, conceptualizing redistribution with respect to changes in connectivity within the river corridor during and after the flood. A 2020 wildfire burned much of the 40 km2 Little Beaver Creek catchment at high severity. A flash flood in July 2022 completely inundated the river corridor and moved substantial amounts of large wood from the channel onto the floodplain. Floodplain logjams were largely absent prior to the flood. Forty-two channel-spanning logjams remained in the channel after the July 2022 flood, compared to 91 before the flood, and only 4 of these created backwater at base flow. Most of the large wood present in the river corridor was redistributed into 700 floodplain logjams, most of which were pinned against tree trunks. Multivariate linear models indicate that floodplain jam distribution density (number of logjams/ha surface area) correlates most strongly with floodplain forest basal area and floodplain/channel width ratio. Prior to the July 2022 flood, channel-spanning logjams limited longitudinal connectivity within the active channel but enhanced vertical connectivity via hyporheic exchange and lateral connectivity via formation of secondary channels and obstruction-inducing overbank flows. The enhanced transport capacity of the flood removed or altered most of these logjams, increasing longitudinal connectivity. Complete inundation of the floodplain during the July 2022 flood represented a transient increase in lateral connectivity. The formation of floodplain logjams and secondary channels, along with localized floodplain erosion and deposition, created more persistent alterations in lateral connectivity. Our observations suggest that logjams can increase lateral connectivity within the river corridor by deflecting flow in a manner that creates persistent secondary channels. Although secondary channels might have formed in Little Beaver Creek during the 2022 flood without the presence of logjams, the flow obstructions created by even relatively transient logjams likely increased the formation of a multichannel planform and the associated persistent lateral connectivity.

Numerical investigation of the instability of dry granular bed induced by water leakage

AbstractUnderground pipe defects or cracks under transport infrastructure can cause water leakage to upper soil layers (e.g. subgrade and capping), inducing local cavities or even failure of overlying road/railway formation. Although numerous studies on the instability of granular beds induced by injected water have been conducted, most of them focused on the behaviour of saturated granular beds, while research on dry granular beds is still limited. This paper aims to address this gap using a numerical model coupling volume of fluid method with discrete element method. We observed that dry granular beds go through three distinct regimes as water jet velocity increases including stationary, stable deformation with heave and fluidisation. However, the flow velocities required to deform and fluidise dry granular beds are significantly higher than those required for saturated beds. Increasing granular bed thickness can alter its failure mechanism from full depth to localised erosion, leading to cavity formation around pipe cracks prior to the bed fluidisation. The gravitational and frictional components of granular mass are identified as two main resisting forces of dry granular beds against water jet force, evidenced by the increase of critical jet velocities as particle density and friction coefficient increase. Nevertheless, the moblised zone of granular mass is practically independent of both the buried depth of dry granular beds.

Experimental Investigation of the Evolution Process of Suspended Pipelines through River Bottoms under Unsteady Flow Conditions

One of the major geological hazards that can cause harm to long-distance oil and gas pipelines are water-induced disasters. These disasters are quite common and widespread. Pipelines that cross river channels are at a higher risk of facing damage due to flood-induced erosion. To shed light on the evolution pattern of riverbeds adjacent to pipelines under the influence of unsteady flow conditions, a flume model test was conducted, and the underlying mechanisms of local scour were elucidated. The experimental results demonstrate that pipelines are more susceptible to suspension during flood conditions. The suspension process of pipelines under flood conditions could be broadly divided into five stages. In comparison to constant flow conditions, the evolution process of local scour and the suspension of pipelines under unsteady flow lacked the erosion pit expansion stage, and the scour duration was shorter. Each stage exhibited distinct erosion characteristics, and both the peak flow rate and the number of flood peaks significantly impacted the maximum range and depth of the erosion pit. During pipeline-laying projects, selecting a covering layer with a larger particle size can enhance the erosion resistance of the riverbed around the pipeline. The study of the local erosion process of underwater crossing pipelines under unstable flow conditions can provide a reference for pipeline engineering design and riverbed pipeline protection strategies.

Kinetic modeling of the plasma–wall interaction in the DTT divertor region

A precise estimate of the local energy fluxes and erosion profiles at the divertor monoblocks of a fusion reactor requires a kinetic modeling of the plasma–wall interaction. Here, a two-dimensional Particle-in-Cell code is used to quantify the particle and energy fluxes and ion impact distribution functions across the divertor monoblocks of the ‘Divertor Tokamak Test’ reactor, focusing on poloidal gaps with toroidal bevelling. The considered critical locations are close to the strike points at both Inner and Outer Vertical Targets. A worst-case scenario for particle fluxes corresponding to attached plasma conditions and featuring a single-null magnetic configuration is assumed. The separate and cumulative effects of including electron wall emission and ions/electrons collisions with a background neutral gas (recycled at the walls) are also assessed. It is found that a non-negligible energy flux affects the shadowed regions of the monoblocks, especially when accounting for collisions, and that the ion impact distribution functions are strongly influenced by the considered kinetic effects, with important implications on the induced sputtering yield.

Morphodynamic numerical modelling of bridge pier erosion induced by downstream check-dam partial collapse

The paper presents a case study in which a severe bridge pier erosion effect was triggered by a partial collapse of a downstream check-dam, due to a flood event in June 2020. The area under study is about 30 km east from the city of Udine (Italy), along the river Torre, which is the main tributary of the river Isonzo. In particular, it is 1 km downstream of the confluence between river Torre and its main tributary, river Natisone. The hydrodynamic complexity of the reach is further exacerbated by the presence of two bridges, close to each other and almost parallel (the new one is just upstream and it is under construction, although almost finished, while the old one is still in service). The result is that there are many bridge piers in the riverbed, determining some interference effects also increasing local erosion. The presence of a check-dam 600 m downstream of the old bridge had a stabilizing effect in this sense, although it was originally designed as a grade control structure of the river. The flood event determined a partial collapse of such structure, whose central portion was progressively excised by tipping. The backward propagation of the erosion reached the area of the bridges, determining a progressive general lowering of the river bed. As a consequence, many bridge piers of the old bridge were excavated, determining severe conditions for the stability of the structure (the traffic was interrupted). The paper presents the methodology adopted and the main results obtained by hydrodynamic and morphodynamic numerical analyses, which were conducted through a two-dimensional, finite volume, shallow water model able to determine the hydrodynamic fields (water depth and flow velocity) and the evolutionary trends of the river bed, allowing to identify the best retrofitting strategy for the design phase.