Stream Dynamics Research Articles

Aspect-ratio-dependent heat transport by baroclinic acoustic streaming

Standing acoustic waves have been known to generate Eulerian time-mean ‘streaming’ flows at least since the seminal investigation of Lord Rayleigh in the 1880s. Nevertheless, a recent body of numerical and experimental evidence has shown that inhomogeneities in the ambient density distribution lead to much faster flows than arise in classical Rayleigh streaming. The emergence of these unusually strong flows creates new opportunities to enhance heat transfer in systems in which convective cooling cannot otherwise be easily achieved. To assess this possibility, a theoretical study of acoustic streaming in an ideal gas confined in a rectangular channel with top and bottom walls maintained at fixed but differing temperatures is performed. A two time scale system of equations is utilized to efficiently capture the coupling between the fast acoustic waves and the slowly evolving streaming flow, enabling strongly nonlinear regimes to be accessed. A large suite of numerical simulations is carried out to probe the streaming dynamics, to highlight the critical role played by baroclinically generated wave vorticity and to quantify the additional heat flux induced by the standing acoustic wave. Proper treatment of the two-way coupling between the waves and mean flow is found to be essential for convergence to a self-consistent steady state, and the variation of the resulting acoustically enhanced steady-state heat flux with both the amplitude of the acoustic wave and the $O(1)$ aspect ratio of the channel is documented. For certain parameters, heat fluxes almost two orders of magnitude larger than those realizable by conduction alone can be attained.

Exploring the integrated potential of pyrolysis and low-temperature wet torrefaction for typical medical waste valorization: A multifaceted approach leveraging online TG-FTIR-MS, 2D-COS, iso-conversional kinetics, and reaction mechanisms

The rapid growth of medical waste, exacerbated by the COVID-19 pandemic and advancements in healthcare, has drawn increased public scrutiny regarding its proper disposal and treatment. This research aimed to characterize the wet torrefaction of a typical medical waste biomass (MWB) composition, comprising bamboo swabs, skewers, splints, cotton balls, tongue depressors, toothpicks, and chopsticks, followed by its co-pyrolysis with medical waste plastic (MWP) including catheter bags, drapes, IV tubing, IV bags, oxygen masks, syringes, and test tubes. The study employed thermogravimetric analysis, TG-FTIR, 2D correlation spectroscopy, iso-conversional kinetics, and mass spectrometry techniques elucidated the driving factors, behaviors, products, mechanisms, and pathways involved. The pyrolysis temperature ranges were 180.15 to 400 °C for TMWB and 380.04 to 550 °C for MWP, with average activation energies of 150.22 and 221.59 kJ/mol for their respective devolatilization processes. Incorporating 20 % and 40 % MWP into the co-pyrolysis process yielded the best performance, characterized by the lowest activation energy. The co-pyrolysis process promoted the release of cyclic hydrocarbons and chain hydrocarbons, but decreased the yields of alcohols, esters, ethers, phenols, and acids, through synergistic mechanisms. Unraveling the pyrolysis pathways and dynamics of these representative medical waste streams offers valuable insights into improving energy recovery, mitigating pollution, diminishing waste volumes, and optimizing industrial thermochemical conversion processes for safely treating these hazardous materials.

LMC-driven Anisotropic Boosts in Stream–Subhalo Interactions

Dark matter subhalos are predicted to perturb stellar streams; stream morphologies and dynamics can, therefore, constrain the mass distribution of subhalos. Using FIRE-2 simulations of Milky Way–mass galaxies, we demonstrate that the presence of an LMC analog significantly changes stream–subhalo encounter rates. The LMC analog brings in many subhalos, increasing encounter rates for streams near the massive satellite by 10%–40%. Additionally, the LMC analog displaces the host from its center of mass (inducing reflex motion), which causes a north–south asymmetry in the density and radial velocity distributions of subhalos. This asymmetry, combined with the presence of LMC-analog subhalos, causes encounter rates at the same distance to vary by 50%–70% across the sky, particularly in regions opposite the LMC analog. Furthermore, the LMC analog induces a density wake in the host's dark matter halo, further boosting the encounter rates near the LMC analog. We also explore how stream orbital properties affect encounter rates, finding up to a 50% increase for streams moving retrograde to the LMC analog’s orbit in the opposite quadrant. Finally, we report the encounter rates for Milky Way streams within the context of our simulations, both with and without the presence of an LMC analog. The dependence of encounter rates on stream location, orbit, and their position relative to the LMC has important implications for where to search for streams with spurs and gaps in the Milky Way.

Urbanization and Suspended Sediment Transport Dynamics: A Comparative Study of Watersheds with Varying Degree of Urbanization Using Concentration-Discharge Hysteresis.

Suspended sediment is a critical water quality parameter and an indicator of geomorphic processes, but suspended sediment dynamics in urban streams may not conform to the first-flush model widely used for other pollutants. We analyzed discharge and turbidity data for 367 events from three urban watersheds (impervious cover 16-45%) in Cleveland, Ohio (USA). Less intensely urbanized watersheds exhibit higher turbidity compared to that of the most highly urbanized watershed. Proportionally, more counterclockwise hysteresis is observed in the two less urbanized watersheds, and more clockwise hysteresis occurs in the highly urbanized watershed. However, hysteresis patterns are driven by different mechanisms in each watershed, and geomorphic analysis was critical to identifying the underlying mechanisms. In the least urbanized watershed, spatial rainfall variability controls sediment hysteresis. In the intermediate watershed, the erosion of upstream weathered shale banks during dry periods plays a significant role in the sediment supply and shaping hysteresis. In the most urbanized watershed, high eroding banks in downstream reaches lead to more frequent clockwise hysteresis. Overall, we suggest that as the impervious surfaces increase, the availability of instream sediments (bed and banks) plays an increased role in suspended sediment dynamics, and geomorphology remains essential for guiding management decisions.

Investigating laser beam shadowing and powder particle dynamics in directed energy deposition through high-fidelity modelling and high-speed imaging

Laser beam shadowing in directed energy deposition process occurs when in-flight powder particles partially block the laser beam, preventing it from fully reaching the melt pool. This blockage alters the beam's profile, introducing spatio-temporal randomness in heat transfer to the melt pool and affecting its stability. This study utilizes a novel high-fidelity multiphysics model to quantitatively analyze gas-powder stream dynamics and laser-particle interactions. It specifically focuses on dynamic variations in laser beam shadowing, attenuation, and reflection of the laser beam radiant energy, along with powder particles temperature prediction from in-flight heating, accounting for multiple reflection phenomena. Gas-particle dynamics is modeled using a fully coupled CFD-DEM approach, while laser-particle in-flight interactions are predicted using a ray-tracing-based photon discretization method. Modeling predicted that interactions between the laser beam and the in-flight powder stream could result in energy losses up to approximately 70 % due to shadowing and attenuation. The study comprehensively explored the spatio-temporal variations in the attenuated laser beam profile, revealing significant deviations from its initial Gaussian profile and substantial stochasticity and randomness over time. To confirm the modeling results and correlate computational predictions with experimental data, high-speed visible imaging of the powder stream, both with and without the melt pool, along with laser beam attenuation measurements using a photodiode system, were conducted. The model's predictions of particle velocity and laser beam attenuation characteristics aligned with the results from these experiments. Modeling and high-speed imaging demonstrated that in-flight heating caused some particles to melt and few others to reach the vaporization threshold. High-speed imaging further validated these numerical findings by examining the interaction of heated particles with the melt pool across different phases (solid, liquid, and partially vaporized). A significant observation was the increased velocities of partially vaporized particles due to recoil pressure from selective vaporization, which led to the formation of deep craters in the melt pool resulting from high-speed impact.

Assessment of fluvial response to landslide susceptibility and transient response of tectonically active upper Alaknanda River basin of Uttarakhand Himalaya, India

This paper focuses on the transient response of the upper Alaknanda River basin and landslide vulnerability analysis of tectonically active segments located between the Trans Himadri Fault (THF) and Main Central Thrust (MCT) in the higher central Himalayan domain. We applied the power law functions of the conventional bedrock incision proxies to decode erosionally balanced tectonic processes. The channel concavity and slope of the upper Alaknanda basin have been logarithmically evaluated to understand the balance between erosion/incision and tectonic events. Further, tectonically balanced erosional events along the trunk and tributary stream dynamics have been estimated using the Chi (χ) function law. The results of χ suggest a disequilibrium state of the trunk and tributary stream concerning steady state condition. Furthermore, the landform and longitudinal river profile have been analyzed to understand differential uplift/incision and impact of erosion in river profile between THF and MCT. Furthermore, we applied a geospatial technique for landslide susceptibility analysis. Our results show that approximately 94.45% of the basin area is highly vulnerable and has the potential for future landslides and glacial avalanches. Furthermore, we claim that this study is extremely helpful to identify the locations of future geohazards (landslide, avalanche, cloudburst etc.) and their impact on the downstream areas where population density is very high.

On the influence of rock glacier dynamics on the runoff in basin of the Ulken Almaty (Bolshaya Almatinka) River, Northern Tien Shan

The purpose of the work was to study the dynamics of mountain stone glaciers and streams flowing down from them for an understanding their hydrological significance. Two glaciers: Morenny and Gorodetsky, were analyzed, both located in the river Ulken Almaty (Big Almatinka) basin, Northern Tien Shan. On the average, the rate of surface displacement of the Morennoye glacier is higher than that of the Gorodetsky, which is associated with increased ice content of the last one. The increase in rates of surface displacement of both stone glaciers revealed in 2021–2022 when compared to previous years turned out to be consistent with the widely discussed idea of intensification of such glaciers dynamics under the present-day climate changes and glacier retreats. It was found that the stone glaciers have a pronounced influence on the water regime, temperature and chemical composition of watercourses formed by water running out from them. They are distinguished by the almost complete absence of intraday fluctuations in the level, temperature, and specific electrical conductivity of water, which are more pronounced in rivers and streams with glacial alimentation during the summer time. Some waterflows from the Gorodetsky glacier do not freeze in winter, which is indicative of significant groundwater reserves in its body. The waters of each of the above stone glaciers differ in their characteristic mineralization, temperature, and the ratio of the major ions. The stable water flow from such glaciers can play an important role in maintaining a river runoff during periods of the low stream discharge.

How much rainwater contributes to a spring discharge in the Guarani Aquifer System: insights from stable isotopes and a mass balance model

ABSTRACT Outcrops play an important role in groundwater recharge. Understanding groundwater origins, dynamics and its correlation with different water sources is essential for effective water resources management and planning in terms of quantity and quality. In the case of the Guarani Aquifer System (GAS) outcrop areas are particularly vulnerable to groundwater pollution due to direct recharge processes. This study focuses on the Alto Jacaré-Pepira sub-basin, a watershed near Brotas, a city in the central region of the state of São Paulo, Brazil, where groundwater is vital for supporting tourism, agriculture, urban water supply, creeks, river and wetlands. The area has a humid tropical climate with periods of both intense rainfall and drought, and the rivers remain perennial throughout the year. Therefore, the aim of this study is to investigate the interconnections between a spring and its potential sources of contribution, namely rain and groundwater, in order to elucidate the relationships between the different water sources. To achieve this, on-site monitoring of groundwater depth, rainfall amount, and stable isotope ratios (deuterium (2H) and oxygen-18 (18O)) from rain, spring discharge, and a monitoring well was carried out from 2013 to 2021. The results indicate that the mean and standard deviations for δ18O in rainwater exhibit higher variability, resulting in −4.49 ± 3.18 ‰ VSMOW, while δ18O values from the well show minor variations, similar to those of the spring, recording −7.25 ± 0.32 ‰ and −6.94 ± 0.28 ‰ VSMOW, respectively. The mixing model’s outcomes reveal seasonal variations in water sources contribution and indicate that groundwater accounts for approximately 80 % of spring discharge throughout the year. Incorporating stable isotopes into hydrological monitoring provides valuable data for complementing watershed analysis. The values obtained support the significance of the aquifer as a primary source, thereby offering critical insights into stream dynamics of the region.

Combined effects of herbicides and insecticides reduce biomass of sensitive aquatic invertebrates

The structure and biomass of aquatic invertebrate communities play a crucial role in the matter dynamics of streams. However, biomass is rarely quantified in ecological assessments of streams, and little is known about the environmental and anthropogenic factors that influence it. In this study, we aimed to identify environmental factors that are associated with invertebrate structure and biomass through a monitoring of 25 streams across Germany. We identified invertebrates, assigned them to taxonomic and trait-based groups, and quantified biomass using image-based analysis. We found that insecticide pressure generally reduced the abundance of insecticide-vulnerable populations (R2 = 0.43 applying SPEARpesticides indicator), but not invertebrate biomass. In contrast, herbicide pressure reduced the biomass of several biomass aggregations. Especially, insecticide-sensitive populations, that were directly (algae feeder, R2 = 0.39) or indirectly (predators, R2 = 0.29) dependent on algae, were affected. This indicated a combined effect of possible food shortage due to herbicides and direct insecticide pressure. Specifically, all streams with increased herbicide pressure showed a reduced overall biomass share of Trichoptera from 43 % to 3 % and those of Ephemeroptera from 20 % to 3 % compared to streams grouped by low herbicide pressure. In contrast, insecticide-insensitive Gastropoda increased from 10 % to 45 %, and non-vulnerable leaf-shredding Crustacea increased from 10 % to 22 %. In summary, our results indicate that at the community level, the direct effects of insecticides and the indirect, food-mediated effects of herbicides exert a combined effect on the biomass of sensitive insect groups, thus disrupting food chains at ecosystem level.

Testing MOND using the dynamics of nearby stellar streams

The stellar halo of the Milky Way is built up at least in part from debris from past mergers. The stars from these merger events define substructures in phase space, for example in the form of streams, which are groups of stars that move on similar trajectories. The nearby Helmi streams discovered more than two decades ago are a well-known example. Using 6D phase-space information from the Gaia space mission, recent work showed that the Helmi streams are split into two clumps in angular momentum space. This substructure can be explained and sustained in time if the dark matter halo of the Milky Way takes a prolate shape in the region probed by the orbits of the stars in the streams. Here, we explore the behaviour of the two clumps identified in the Helmi streams in a modified Newtonian dynamics (MOND) framework to test this alternative model of gravity. We performed orbit integrations of Helmi streams member stars in a simplified MOND model of the Milky Way and using the more sophisticated phantom of RAMSES simulation framework. We find with both approaches that the two Helmi streams clumps do not retain their identity and dissolve after merely Myr. This extremely short timescale would render the detection of two separate clumps very unlikely in MONDian gravity. The observational constraints provided by the streams, which MOND fails to reproduce in its current formulation, could potentially also be used to test other alternative gravity models.

Behavioural tendencies of the last British–Irish Ice Sheet revealed by data–model comparison

ABSTRACTIntegrating ice‐sheet models with empirical data pertaining to palaeo‐ice sheets promotes advances in the models used in sea‐level predictions and can improve our understanding of past ice‐sheet behaviour. The large number of empirical constraints on the last British–Irish Ice Sheet make it ideal for model–data comparison experiments. Here, we present an ensemble of 600 model simulations, which are compared with data on former ice‐flow extent, flow geometry and deglaciation timing. Simulations which poorly recreate data were ruled out, allowing us to examine the remaining physically realistic simulations which capture the ice sheets' behavioural tendencies. Our results led to a novel reconstruction of behaviour in the data‐poor region of the North Sea, insights into the ice stream, potential ice‐shelf and readvance dynamics, and the potential locations of peripheral ice caps. We also propose that the asynchronous behaviour of the British–Irish Ice Sheet is a consequence of the geography of the British Isles and the merging and splitting of different bodies of ice through saddle merger and collapse. Furthermore, persistent model–data mismatches highlight the need for model development, especially regarding the physics of ice–ocean interactions. Thus, this work highlights the power of integrating models and data, a long‐held aim of palaeoglaciology.

Integrated monitoring and modeling to disentangle the complex spatio-temporal dynamics of urbanized streams under drought stress

We have a poor understanding of how urban drainage and other engineered components interact with more natural hydrological processes in green and blue spaces to generate stream flow. This limits the scientific evidence base for predicting and mitigating the effects of future development of the built environment and climate change on urban water resources and their ecosystem services. Here, we synthesize > 20 years of environmental monitoring data to better understand the hydrological function of the 109-km2 Wuhle catchment, an important tributary of the river Spree in Berlin, Germany. More than half (56%) of the catchment is urbanized, leading to substantial flow path alterations. Young water from storm runoff and rapid subsurface flow provided around 20% of stream flow. However, most of it was generated by older groundwater (several years old), mainly recharged through the rural headwaters and non-urban green spaces. Recent drought years since 2018 showed that this base flow component has reduced in response to decreased recharge, causing deterioration in water quality and sections of the stream network to dry out. Attempts to integrate the understanding of engineered and natural processes in a traditional rainfall-runoff model were only partly successful due to uncertainties over the catchment area, effects of sustainable urban drainage, adjacent groundwater pumping, and limited conceptualization of groundwater storage dynamics. The study highlights the need for more extensive and coordinated monitoring and data collection in complex urban catchments and the use of these data in more advanced models of urban hydrology to enhance management.

A conceptual model on the influence of logjam formation on longitudinal and lateral sediment dynamics in forested streams

Large wood (LW) and log jams have important implications for sediment dynamics within river systems. Although many case studies explore this topic, far fewer synthesize these results at the reach and basin scales. In this paper, we present a conceptual model that relates valley setting and landscape history of forested, mountain streams to spatiotemporal patterns of sediment storage and transport via the formation and decay processes of logjams. This conceptual model explores the function of logjams as sediment transport moderators, significantly influencing sediment retention, channel morphology, and lateral and longitudinal connectivity. Detailed wood inventories, channel topographic surveys, and channel morphology from four case studies are used to illustrate the range of channel responses to logjam formation, evolution, and decay in different valley contexts. Valley setting is shown to influence logjam formation and dynamics by determining the mechanisms and timing of sediment and wood recruitment. In steep and narrow (and thus coupled, confined) reaches, colluvial processes are the dominant mechanisms of wood and sediment delivery, and logjams grow vertically as sediment is stored in a wedge behind the jam (longitudinal disconnectivity). In contrast, in unconfined reaches (decoupled hillslopes), wood and sediment recruitment occurs primarily through fluvial processes, and logjams grow laterally as the channel shifts across the valley bottom. These logjams have long lifespans, often over a century, and gradually release sediment as the logjam decomposes. Sediment deposits stabilized by riparian vegetation behind these structures may persist long after logjam decay. This conceptual model is a testable framework and practical tool that offers insight into wood-sediment interaction mechanisms within steep, forested basins.

Dynamical response of the southwestern Laurentide Ice Sheet to rapid Bølling–Allerød warming

Abstract. The shift in climate that occurred between the Last Glacial Maximum (LGM) and the Early Holocene (ca. 18–12 kyr BP) displayed rates of temperature increase similar to present-day warming trends. The most rapid recorded changes in temperature occurred during the abrupt climate oscillations known as the Bølling–Allerød interstadial (14.7–12.9 kyr BP) and the Younger Dryas stadial (12.9–11.7 kyr BP). Reconstructing ice sheet dynamics during these climate oscillations provides the opportunity to assess long-term ice sheet evolution in reaction to a rapidly changing climate. Here, we use glacial geomorphological inversion methods (flowsets) to reconstruct the ice flow dynamics and the marginal retreat pattern of the southwestern sector of the Laurentide Ice Sheet (SWLIS). We combine our reconstruction with a recently compiled regional deglaciation chronology to depict ice flow dynamics that encompass the time period from pre-LGM to the Early Holocene. Our reconstruction portrays three macroscale reorganizations in the orientation and dynamics of ice streaming followed by regional deglaciation associated with rapid warming during the Bølling–Allerød interstadial. Initial westward flow is documented, likely associated with an early set of ice streams that formed during the advance to the LGM. During the LGM ice streaming displays a dominant north to south orientation. Ice sheet thinning at ∼15 ka is associated with a macroscale reorganization in ice stream flow, with a complex of ice streams recording south-eastward flow. A second macroscale reorganization in ice flow is then observed at ∼14 ka, in which southwestern ice flow is restricted to the Hay, Peace, Athabasca, and Churchill river lowlands. Rates of ice sheet retreat then slowed considerably during the Younger Dryas stadial; at this time, the ice margin was situated north of the Canadian Shield boundary and ice flow continued to be sourced from the northeast. Resulting from these changes in ice sheet dynamics, we recognize a three-part pattern of deglacial landform zonation within the SWLIS characterized by active ice margin recession, stagnation and downwasting punctuated by local surging (terrestrial ice sheet collapse): the outer deglacial zone contains large recessional moraines aligned with the direction of active ice margin retreat; the intermediate deglacial zone contains large regions of hummocky and stagnation terrain, in some areas crosscut by the signature of local surges, reflecting punctuated stagnation and downwasting; and the inner deglacial zone contains inset recessional moraines demarcating progressive regional ice margin retreat. We attribute these macroscale changes in ice flow geometry and associated deglacial behaviour to external climatic controls during the Bølling–Allerød and Younger Dryas but also recognize the role of internal (glaciological, lithological and topographic) controls in SWLIS dynamics.

Disentangling effects of multiple agricultural stressors on benthic and hyporheic nitrate uptake

Agricultural land use alters nitrate (NO3–) uptake dynamics in streams, but the specific mechanisms linking individual agricultural stressors to benthic and hyporheic uptake remain unclear. Using stream-side mesocosms and 15N-nitrate additions, we examined the individual and combined effects of fine sediment (FS) and augmented light and phosphorus levels (L&P) on benthic and hyporheic NO3– uptake rates. In absence of FS, L&P stimulated uptake of autotrophic and heterotrophic biofilms, leading to a 12- and 7-fold increase in the benthic and hyporheic compartments, respectively. Under ambient light and nutrient conditions, FS reduced by 3-fold benthic uptake, but effects were not significant. Conversely, in the hyporheic compartment, FS induced anoxic conditions, likely stimulating denitrification and causing a 14-fold increase in hyporheic uptake. When these stressors were combined, they did not interact in the benthic compartment. Conversely, in the hyporheic compartment they interacted antagonistically, with L&P diminishing the increase in uptake induced by FS. Our results indicate that the previously observed increase of whole-stream NO3– uptake in agricultural streams is attributable to nutrients and light stimulating benthic uptake, while fine sediment effects and the role of the hyporheic compartment to total uptake are modest. Moreover, the finding that stressor interactions vary with ecosystem compartments calls for a consideration of all compartments and their contribution to whole-system functioning in multiple stressor studies. We are beginning to understand how multiple interacting stressors affect stream functioning, but more mechanistic evidence is needed to disentangle whether additive or non-additive effects prevail in human-altered ecosystems.

Large wood recruitment, retention and mobilization in low-order streams of the Brazilian Savanna

The delivery of wood to streams varies in space and time and may occur continuously or episodically. Once in a stream, wood may be retained or transported due to the balance between driving (water flow) and resisting forces (channel features and wood characteristics). Despite there being few studies directly measuring wood mobility, notable variations in annual transport rates and mean travelled distances have already been detected worldwide. In the tropics, due to wetter and warmer conditions and consequently higher decay rates and peak discharge, wood is believed that more readily degraded and transported downstream. However, there exists a knowledge gap regarding wood dynamics in tropical streams and even more considering tropical non-forested environments. In the present study, we aimed to document large wood (LW) recruitment, retention, and mobilization over a period of one year in eight low-order streams of the Cerrado (the South American Savanna) by tagging and tracing LW pieces. We detected high LW transport and recruitment rates in Cerrado streams, such that the total wood amounts remained constant over time. However, there were important differences between streams due to their distinct channel morphologies and the occurrence of episodic events. The LW length and diameter, original location and orientation were the most important factors in the prediction of the LW travelled distance, which ranged from zero to almost 100 m in one year. Our findings provide unprecedented information regarding wood mobility in tropical savanna streams in South America. To further advance knowledge about the dynamics of wood in Cerrado streams, future studies should characterize the great diversity of wood, especially with regard to densities that may strongly affect wood mobility. Furthermore, it is essential to perform long-term studies to document the dynamics of wood over years in these environments.

Retreat patterns and dynamics of the former Norske Trough ice stream (NE Greenland): An integrated geomorphological and sedimentological approach

A better understanding of past extent and dynamics of the Greenland Ice Sheet (GrIS) is required to provide context for present-day observations, to constrain numerical climate models and to predict future scenarios of ice-sheet response to recent climatic change. The presence of a grounded GrIS on the NE Greenland shelf during the Last Glacial Maximum (LGM) is supported by high-resolution seismic data combined with multi-proxy analyses of sediment gravity cores from Norske Trough. Our results indicate that an ice stream advanced to the outer shelf during the LGM. Recessional moraines and grounding zone wedges on the seafloor of the outer to middle shelf show that initial retreat was episodic, punctuated by two major stillstands. Pinning points for grounding-zone stabilization were controlled by pre-LGM trough topography. In contrast, preserved large-scale glacial lineations on the seafloor of the inner shelf, formed during the advance, indicate that ice retreat from the inner trough to the coast-proximal position was rapid in order to maintain the former carved morphology. Initial ice retreat was underway before 16.6 cal Kyr BP, earlier than previously known for this sector of the NE Greenland shelf. The inner shelf was free from grounded ice at least by 12.5 cal Kyr BP, and likely before. Retreat occurred in a glaciomarine setting and the ice sheet was fringed by a floating ice shelf. There is no evidence of grounded-ice readvances during the Younger Dryas, although a floating ice shelf with vigorous sea-ice and iceberg rafting production occupied the inner shelf at 11.3 cal Kyr BP. 14C dates reveal initial stepwise ice retreat followed by a fast retreat that coincides with Heinrich Stadial 1 and the Bølling-Allerød interstadial, respectively. During both periods there was increased inflow of warm Atlantic Water, indicating a strong ocean/climate control on the late deglaciation of Norske Trough. Following the late deglaciation, postglacial (Holocene) sedimentation records a change from an ice-distal glaciomarine environment, to an open marine environment and complete ice shelf disintegration. On the innermost shelf of the Norske Trough, the ice shelf disintegrated and reformed once before the final break-up occurred at 9.6 cal Kyr BP.

Characterisation of chaos and mean-motion resonances in meteoroid streams

Context. Dynamically linking a meteor shower with its parent body is challenging, and chaos in the dynamics of meteoroid streams may contribute to this challenge. For a robust identification of parent bodies, it is therefore necessary to quantify the amount of chaos involved in the evolution of meteoroid streams. Aims. Characterising chaos in meteoroid streams through the aid of chaos maps is still a new field of study. Thus, we examine two very different meteoroid streams, the Draconids and the Leonids, in order to obtain a general view of this topic. Methods. We used the method developed in a previous paper dedicated to Geminids, drawing chaos maps with the orthogonal fast Lyapunov indicator. We chose four particle size ranges to investigate the effect of non-gravitational forces. As the dynamics are structured by mean-motion resonances with planets, we computed the locations and widths of the resonances at play. We used semi-analytical formulas valid for any eccentricity and inclination and an arbitrary number of planets. Results. We pinpoint which mean-motion resonances with Jupiter play a major role in the dynamics of each meteoroid stream. We show how those resonances tend to trap mostly large particles, preventing them from meeting with Jupiter. We also study particles that manage to escape those resonances, for example, due to the gravitational perturbation of Saturn. Finally, we explain why non-gravitational forces do not disturb the dynamics much, contrary to what is observed for the Geminids.

Hydrochemical dynamics of stream following rainfall events at agricultural catchments in New Zealand

One of the prerequisites for efficiently managing lake water quality is reliable data regarding the quantity and quality of inflows water, mainly the export of nutrients from the catchment area during rainfall events. We investigated the dynamic characteristics of hydrochemicals concerning rainfall events in agricultural stream waters flowing into eutrophic lakes situated on the North Island’s central plateau of New Zealand. We utilized isotopic composition of water (δ2H-H2O and δ18O-H2O) and nitrate (δ15N-NO3- and δ18O-NO3-) along with high-frequency hydrochemical data for source identification of water and nitrate during a drought period (2020). Our findings indicate that it is essential to initially grasp the fundamental mechanisms associated with rainfall events to formulate effective strategies for minimizing nutrient losses. The methodology outlined in this research integrates stable isotope hydrology with water quality monitoring initiatives, facilitating the understanding and managing the primary governing mechanisms behind diverse contaminant losses from land to adjacent water bodies, explicitly focusing on nitrates. This approach establishes a framework that can assist in devising measures for water quality improvement capable of anticipating the repercussions of substantial rainfall events more effectively.

River channel dynamics and flooding: A case of motorable bridge collapse due to abrupt flood in Chhabdi Khola, Tanahun, Nepal

The monsoon season in Nepal brings calamitous events like riverbank erosion, toe cutting, and the structural failure of bridges due to floods. In July 2021, a motorable bridge in Bhadgaun, Tanahun district, Nepal, collapsed during a massive flood in Chhabdi Khola. The study aims to comprehensively document the aftermath, specifically focusing on the causal factors that led to the damage of the Chhabdi Khola Dovan Bridge. The study delves into an in-depth analysis of the stream's channel morphology, with the 5.85 kilometers Chhabdi Khola partitioned into 28 distinct segments, each spanning approximately 200 meters. These segments, sequentially labeled from Site 1 to Site 28, encompass the area extending from the upstream at Chhabdi Barah temple to the downstream at bridge’s location. Rigorous measurements of length, breadth, and depth at each site form the basis for volumetric assessments of the stream. The study revolves around contrasting paleo channel attributes with contemporary alterations within the Chhabdi Khola catchment. The analysis leverages precipitation data sourced from the Department of Hydrology and Meteorology (DHM) to discern precipitation trends within the Chhabdi Khola catchment area. The hydrographic data underwent trend analysis utilizing Mann-Kendall and Sen's slope method through R software (version 4.3.2). The collapse of the Chhabdi Khola Dovan Bridge resulted from intense water flow and debris due to heavy rainfall and a narrow outlet near the bridge, impacting the local population and land users facing the enduring aftermath of a catastrophic monsoon event. The study highlights the significance of understanding river dynamics in small streams and advocates for proactive disaster preparedness measures, even in seemingly small river channels.