Sediment Deposition Research Articles

GravelSens: A Smart Gravel Sensor for High-Resolution, Non-Destructive Monitoring of Clogging Dynamics.

Engineers, geomorphologists, and ecologists acknowledge the need for temporally and spatially resolved measurements of sediment clogging (also known as colmation) in permeable gravel-bed rivers due to its adverse impacts on water and habitat quality. In this paper, we present a novel method for non-destructive, real-time measurements of pore-scale sediment deposition and monitoring of clogging by using wire-mesh sensors (WMSs) embedded in spheres, forming a smart gravel bed (GravelSens). The measuring principle is based on one-by-one voltage excitation of transmitter electrodes, followed by simultaneous measurements of the resulting current by receiver electrodes at each crossing measuring pores. The currents are then linked to the conductive component of fluid impedance. The measurement performance of the developed sensor is validated by applying the Maxwell Garnett and parallel models to sensor data and comparing the results to data obtained by gamma ray computed tomography (CT). GravelSens is tested and validated under varying filling conditions of different particle sizes ranging from sand to fine gravel. The close agreement between GravelSens and CT measurements indicates the technology's applicability in sediment-water research while also suggesting its potential for other solid-liquid two-phase flows. This pore-scale measurement and visualization system offers the capability to monitor clogging and de-clogging dynamics within pore spaces up to 10,000 Hz, making it the first laboratory equipment capable of performing such in situ measurements without radiation. Thus, GravelSens is a major improvement over existing methods and holds promise for advancing the understanding of flow-sediment-ecology interactions.

The Pleistocene Witch Ground Ice Stream in the central North Sea

AbstractThe North Sea Basin has been covered by ice sheets originating from both the British Isles and Scandinavia at multiple times during the Pleistocene. The Witch Ground Basin (WGB) in the central northern North Sea is a critical location in terms of interpreting Late Pleistocene glacial to glacimarine history of the North Sea since it was the location of the Witch Ground Ice Stream that was active on multiple occasions during the Mid to Late Pleistocene. We map five mega‐scale glacial lineation flowsets corresponding to the changing ice flow direction of the Witch Ground Ice Stream and investigate the sedimentological fingerprint and corresponding subglacial depositional processes of this palaeo‐ice stream. We show that sorted sand layers within a subglacial traction till represent periodic hydraulic jacking and ice–bed decoupling at the base of the Witch Ground Ice Stream. In contrast to previous studies that have described glacitectonites deposited below the most recent grounded ice in the WGB, we present analysis of sediment cores that recovered primarily massive diamictons without any obvious deformation structures. The most recent ice cover in the WGB (~18–16 ka) was thought to have been sourced from a localized ice cap over Orkney and Shetland. The presence of chalk clasts sourced from NW of the WGB described in this study from the stratigraphically youngest till confirms this interpretation. The transition from subglacial to glacimarine deposition, while acoustically well defined (from opaque to laminated acoustic units), appears surprisingly uniform in the recovered sediment cores, but can be differentiated based on a change in colour including mottling and banding, presence of whole intact shells, and the increased number of silt and sand lenses. 14C dating of glacimarine muds indicate high sedimentation rates of between 80 and 260 cm ka−1. The transition from glacimarine to marine deposition is represented by a comparative decrease in sedimentation rate and deposition of Holocene age sandy mud. This study demonstrates a highly dynamic Witch Ground Ice Stream in the northern North Sea during the Late Pleistocene with evolving subglacial hydrology and depositional processes at the ice stream bed that left a distinct geomorphological and sedimentological fingerprint within the WGB.

Application of the DRASTIC Model to Assess the Vulnerability of Groundwater Contamination Near Zaporizhzhia Nuclear Power Plant, Ukraine.

Russia's invasion of Ukraine continues to have a devastating effect on the well-being of Ukrainians and their environment. We evaluated a major environmental hazard caused by the war: the potential for groundwater contamination in proximity to the Zaporizhzhia Nuclear Power Plant (NPP). We quantified groundwater vulnerability with the DRASTIC index, which was originally developed by the United States Environmental Protection Agency and has been used at various locations worldwide to assess relative pollution potential. We found that there are two major gradients of groundwater vulnerability in the region: (1) broadly higher risk to the northeast of the NPP and lower risk to the southeast driven by a regional gradient in water availability and water table depth; and (2) higher risk in proximity to the channels and floodplains of the Dnipro River and tributaries, which host coarser-textured soils and sedimentary deposits. We also found that the DRASTIC vulnerability index can be used to identify and prioritize groundwater well-network monitoring. These and more detailed assessments will be necessary to prioritize monitoring and remediation strategies across Ukraine in the event of a nuclear accident, and more broadly demonstrate the utility of the DRASTIC approach for prognostic contamination risk assessment.

Intensification of sediment flux by wind-induced residual currents in a heavily contaminated, micro-tidal bay.

Wind-induced currents are the major forces responsible for sediment resuspension and transport in micro-tidal bays. To reveal the impact of wind-induced residual currents on the sediment flux, in-situ measurements using acoustic Doppler current profilers (ADCPs) were conducted at two mooring stations in a heavily contaminated, micro-tidal Onsan Bay. During the mooring period, the suspended sediments at both stations were transported seaward (landward) at the surface (bottom) layer mainly through the residual currents (mean-flow flux Fmean: > 70% of the total flux). Under northerly winds, the landward bottom residual currents at both stations strengthened, resulting in the "intensification" of landward Fmean. This suggests that the northerly winds might be a primary factor intensifying the landward sediment fluxes, potentially resulting in the increased sediment deposition into the bay. The findings provide insights into managing sedimentation in contaminated coastal bays and highlight the importance of wind effects on sediment transport in micro-tidal bays.

Geochemical Analysis of Paleocene-Eocene Sediments from Subathu Formation, Dehradun District, Uttarakhand: Implication for Provenance, Tectonic Setting and Paleoclimate

The Palaeocene-Eocene Subathu Formation in the Nilkanth region near Rishikesh, Uttarakhand provides insights into the provenance, depositional environment, and tectonic setting prior to final India-Asia continent collision. Geochemical analysis of major oxides, trace elements, and rare earth elements from shale-dominated sedimentary rocks reveals a complex provenance. Discriminant function plots indicate the derivation of sediments from quartzose sedimentary sources, with minor input from mafic igneous sources. Trace element patterns suggest contributions from felsic igneous rocks, recycled sediments, and subduction-related components. The Chemical Index of Alteration (87.2*Avg.) indicates moderate weathering in the source area under semi-arid paleoclimatic conditions. Tectonic discrimination diagrams indicate that the deposition of sediments from Subathu Formation was occurred predominantly in an active continental margin setting. Rare earth element patterns exhibit varying degrees of fractionation, implying diverse sources ranging from mafic to felsic compositions. This multi-proxy geochemical study sheds light on the evolving paleoenvironmental conditions and sediment routing systems in the western Himalayan foreland basin leading up to the terminal India-Asia collision. Keywords: Geochemistry, Subathu Formation, Provenance, Tectonic Setting, Paleoclimate, Depositional Environment, Himalaya

Enhanced mercury deposition in Arctic Alaskan lake sediments coincides with early Holocene hydroclimate shift.

Substantial amounts of mercury (Hg) are projected to be released into Arctic watersheds as permafrost thaws amid warmer and wetter conditions. This may have far-reaching consequences because the highly toxic methylated form of Hg biomagnifies rapidly in ecosystems. However, understanding how climate change affects Hg dynamics in permafrost regions is limited due to the lack of long-term Arctic Hg records. Using a 27-ka Hg sediment record from Burial Lake, northwestern Alaska, we examine how well-characterized temperature, precipitation, and vegetation shifts affected Hg mobilization in a catchment underlain by permafrost. During the Last Glacial Maximum (29.6-19.6ka), Hg concentrations (63±5μg/kg) and Hg flux (8.6±2.2μgm-2yr-1) remain relatively stable. Abrupt warming trends, starting at 17.6ka, do not coincide with Hg levels. After 15ka, the ecosystem transitions to shrub tundra, Hg concentrations (101.2μg/kg) peak at 14.2ka, while flux (5.3±1.3μgm-2yr-1) declines and stabilizes. At ~11ka, increased precipitation coincides with a 72% rise in Hg concentrations and a 32% increase in Hg flux compared to average Hg levels since 15ka. These results suggest that summer rainfall was the primary driver of Hg mobilization from the catchment, while the vegetation shift influenced lake sediment Hg concentrations. At 1990CE, peak Hg levels represent an 88% increase in Hg concentrations (196.3μg/kg) and a sixfold rise in Hg flux (38.1μgm-2yr-1) above background levels, underscoring the need for further research to understand Hg dynamics driven by anthropogenic Hg emissions and climate change.

Multiple stressor effects act primarily on microbial leaf decomposers in stream mesocosms.

At the global level, stream ecosystems are influenced by multiple anthropogenic stressors such as eutrophication, habitat deterioration, and water scarcity. Multiple stressor effects on stream biodiversity are well documented, but multiple stressor effects on stream ecosystem processes have received only limited attention. We conducted one mesocosm (stream channel) and one microcosm (feeding trial) experiment to study how combinations of reduced flow, increased nutrient concentrations, and increased fine sediment coverage would influence fungal and macroinvertebrate decomposer assemblages and their active contribution to leaf decomposition. In the stream channels, increased fine sediment coverage significantly reduced fungal biomass, occurrence frequencies of most aquatic hyphomycete species, and microbial leaf decomposition rates compared to untreated controls. Macroinvertebrate-induced leaf decomposition rates were mainly correlated to total fungal biomass and community composition. Neither increased nutrient concentrations, nor reduced flow conditions significantly influenced leaf decomposer communities or decomposition rates. The feeding trials revealed significantly reduced leaf consumption in the freshwater amphipod Gammarus pulex when feeding on leaf material from treatments with increased fine sediment coverage in the mesocosm experiment. When offered a food choice between sterile, unconditioned leaf material and leaf material from treatments with increased fine sediment coverage, G. pulex foraged mainly on sterile material. This study showed that increased fine sediment coverage can alter the flux of energy and material in the detrital food chain through bottom-up regulation of leaf conditioning by fungal decomposers. Our results suggest that increasing attention should be given to mitigating fine sediment transport and deposition in stream systems to preserve ecosystem functioning within the detrital food chain.

Tracing the trail of eroded fertile soils during a high intensity rainfall event: A fingerprinting study in war-torn tropical mountains

The depletion of fertile topsoil presents a critical challenge in tropical mountain agroecosystems. Impacts are intensified during heavy storm events that strip unprotected topsoils and pose risks to downstream water ecosystems. To better understand such dynamics, we investigated an agricultural mountainous catchment located on the Democratic Republic of the Congo shore of Lake Kivu. This area is characterised by weak governance systems exacerbated by protracted violent conflicts, which have prevented the application of remediation practices to address extensive land use changes, including deforestation and monoculture proliferation, notably banana plantations. Additionally, the spread of Banana Xanthomonas wilt (BXW) has further augmented land use impacts. Herein the complete diseased mat uprooting (CDMU) method employed to combat the disease has resulted in significant erosion and sediment export rates. Following the recovery of banana plantations from CDMU, sediment export rates continued to increase without a clear responsible party but more as a legacy of past and present land degradation activities and embedded soil erosion and connectivity process pathways. To analyse the impact of high-intensity storm events coupled with the aftermath of conflict instability and the effects of BXW on erosion dynamics, the sediment fingerprinting technique was implemented. We collected 60 sediment source samples across a 42km2 catchment, predominantly cultivated since the mid-20th century. Samples spanned four main land uses/land covers: seasonal crops, banana plantations, bare or degraded soil, and channel banks. Additionally, mixture/target samples were collected at the summit of six fluvial terraces located at different altitudes along the vertical profile of the river after a high-intensity storm event. These terraces serve as natural indicators of sediment accumulation under different flow intensities, with higher terraces representing sediment deposition during higher discharge. Furthermore, sediment samples were collected via a gravity core in delta deposits at the river's inflow into the lake, allowing us to identify the main sources contributing to fine sediment export to the lake. This methodology enabled us to assess how sediment provenance has changed in response to varying discharge levels while elucidating the primary sources responsible for fine sediment inputs to the lake and the subsequent water quality decrease. Our analysis indicates increased contributions occurred from channel banks and degraded areas as discharge increased. Despite steep channel banks and degraded soils being primary sediment sources on the terraces, agricultural and banana sources predominantly contributed to the fine sediments exported to the lake. These findings underscore the hazards of high-intensity storm events in these fragile ecosystems and highlight the role of current banana plantation and cropland management in degrading land and water quality. Understanding the primary factors driving land degradation and sediment export is crucial for preventing further ecosystem degradation and mitigating heightened instability in conflict-affected areas. This research suggests that remediation practices should be incentivised to create buffer structures in upslope agricultural areas and protect the fertile sediments from banana plantations from being exported to the lake if socio-cultural and economic hurdles to implementation can be overcome.

Numerical and experimental investigation on vortex control and sedimentation suppression in a Y-shaped diversion channel with circular inlet tanks

A sudden angle change between the Y-shaped diversion channel and the inlet tank of the circular pump station often leads to boundary layer separation and large vortex formation. These flow patterns can cause significant sediment deposition in sediment-laden rivers, reducing pump efficiency. A mixture model is introduced to describe water-sediment two-phase flows. Simulation results analyze vortex characteristics and formation mechanisms, and evaluate potential sediment deposition areas. Without rectification, vortex areas cause significant sediment migration towards the sidewalls of the Y-shaped diversion channel and pump inlet. Diversion measures like sills and pressure plates are introduced to reduce flow vortices. Results show that sills generally optimize flow structures. Sills in the main Y-shaped diversion channel outperform those in other channels in terms of optimization. Pressure plates also optimize flow structures. Vortex structure and position are closely related to the distance between the pressure plate and the circular intake tank. Optimized measures with pressure plates significantly reduce the flow deviation angle and improve flow velocity uniformity. Numerical simulation accuracy is validated through experiments. Results reveal the formation mechanism of adverse vortices and their sedimentation effects, which are detrimental to pump stations. The proposed rectification scheme provides theoretical support for optimizing pump station operation.

Numerical investigation of non-overflow section stability

ABSTRACT Constructing dams is one of the human achievements in developing urban societies. In the last few decades, rapid growth in developing the Red Sea coast and Sinai in Egypt has taken place. According to the UN Nexus definition, water, energy, and food are the main sources of sustainable development. The dam gives the best structure that can fulfill these requirements. The geology of Egypt in the concerning areas in both the Red Sea and Sinai shows that both areas are mountainous areas. The wadies in these mountains suffer from being exposed to severe weathering conditions. Flash floods and wind blowing are the main causes of exposing sedimentary rocks in these Wadies to different degrees of weathering. The present paper focuses on studying the effect of weathering on the engineering behavior of dams intended to be constructed in these areas. The examined rock foundations cover mud-stone, Sand-stone, and limestone. A published numerical model for Longtan Dam was utilized as a reference case to construct a verified numerical model that was later employed in a parametric study to clear the effect of weathering on the studied sediment rock. The verification and parametric study were carried out using GeoStudio software. The results show the clear effect of the variation in weathering on the engineering parameters of the examined sedimentary rock deposits.

Metallogenic Evolution Related to Mantle Delamination Under Northern Tunisia

Mineralization processes in the Tell-Atlas of North Africa coincided with magmatism, extension, and lithospheric rejuvenation during the middle to late Miocene. This review examines the lead isotope compositions and Pb-Pb age dating of ore deposits in the region to elucidate the sources and timing of mineralization events. The data reveal a predominantly radiogenic signature in the ores, indicating that the primary component is from a crustal source, with a contribution from the mantle. Pb-Pb age dating suggests the ranges of mineralization ages, with late Miocene events being particularly significant, coinciding with proposed sub-continental mantle delamination following subduction of the African lithosphere. In this context, polymetallic mineralizations formed related to felsic magmatism, hydrothermalism driven by extensional faults, resulting in the formation of Mississippi Valley-Type, and Sedimentary exhalative deposits within associated semi-grabens and diapirism. The correlation between orogenic extensional collapse, magmatism, and mineralization underscores the importance of understanding the specific geological context of ore formation. The detachment of subducted slabs and subsequent influx of hot asthenosphere play pivotal roles in creating conducive conditions for mineralization. This study sheds light on the intricate interplay between tectonic mechanisms, mantle-crust interactions, and mineralization events in the Tell-Atlas, offering insights for further exploration in the region.

Sedimentation rates, coastal delta accretion, and stratigraphic datum of the Late Pleistocene–Mid-Holocene transition in the East Equatorial Atlantic: New concept from calcareous nannoplankton

This study examines the sedimentation rates (SR) during the last 20 kyr in the Niger Delta using selected biostratigraphic datum levels. Three gravity cores (GCs) collected at −40 m below sea level from the shallow offshore Niger Delta (GC1 = Western, GC2 = Central, and GC3 = Eastern) were analysed for their calcareous nannoplankton species ( Emiliania huxleyi, Gephyrocapsa oceanica, Helicophaera sellii and Reticulofenestra asanoi). Successive datums were established mainly from the informal biozones and ranges of Gephyrocapsa oceanica and Emiliania huxleyi marker species due to their abundance. By correlating the First Occurrence (FOC) and Last Occurrence (LOC) datums of the marker species in the cored sequences (GCs), SRs were reconstructed. Based on the constructions, the FOC of Gephyrocapsa oceanica (20 kyr) reflects a position towards the bottom of the GCs, the FOC of Emiliania huxleyi (11–8.5 kyr) delineates the middle of the GCs, and the LOC of Emiliania huxleyi (6.5 kyr) marks the uppermost part of the GCs. The sediment load by average calculated from each location in the Western, Central, and Eastern Niger Delta shows sequences of sedimentation rates of ~36.7 cm/kyr for the late Pleistocene, ~174 cm/kyr for the early Holocene, and ~18.6 cm/kyr for mid-Holocene time periods. Consequently, on average, ~229.3 cm/kyr of sediment were deposited at −40 m water level over the last 20 kyr, with the early Holocene experiencing the highest sedimentation rates (~174 cm/kyr) across the three locations. Additionally, this study provides evidence that the Niger Delta sink deposits responded to the West African Monsoon (WAM) driven sedimentation rates during the late Quaternary (20–6.5 kyr). Furthermore, this sediment deposit facilitated the development of a high-resolution age-depth and sedimentation rate model linked to the regional sea level of the Eastern Equatorial Atlantic that succinctly delineates the late Pleistocene and early Holocene boundary of the Niger Delta. The outputs of this study bridged the research gap and knowledge on the impact of coastal accretion and depositional processes on sedimentation rates in the shallow offshore Niger Delta.

Undulating stratigraphy of a carbonate inner ramp lagoon and associated architectural facies heterogeneity: An example from the Late Jurassic Hanifa Formation, Central Saudi Arabia

AbstractThis study offers new insights into the internal architecture of shallow marine carbonate sediments deposited in an epeiric sea formed on a broadly flooded passive margin continental shelf. The Ullayah Member of the Late Jurassic Hanifa Formation is exposed along the Tuwaiq Mountain Escarpment in Central Saudi Arabia and serves as an example. High‐resolution drone imagery over a 4 × 4 km2 wadi system, measured‐sections and thin‐section petrography are utilized to develop the three‐dimensional architecture of the lagoonal sediments deposited in an inner‐ramp setting. Parasequence sets have been mapped on the digital outcrop models that demonstrate a high degree of lateral and vertical thickness variability associated with stromatoporoid/coral buildups and inter‐buildup sediments. The stromatoporoid/coral buildups have been interpreted to be deposited during the late Transgressive Systems Tract and Highstand System Tract. The positive relief developed by the stromatoporoid/coral buildups resulted in hydrodynamic acceleration of currents in the inter‐buildup areas, which limited sediment deposition. The incomplete filling of the inter‐buildup areas led to an undulating topography, which significantly influenced depositional architecture in the next parasequence set. This theme of sediment filling, also referred to as compensational stacking, was repeated over the next two parasequence sets, with an overall decreasing accommodation towards the late highstand, eventually levelling the uneven topography at the top of the Ullayah Member. The study offers insights into the processes of sediment accumulation in an inner ramp lagoon and/or on a flat‐top shallow marine epeiric carbonate shelf. Although accumulation is cyclic, neither strict facies patterns nor uniform cycle thicknesses can be discerned on a kilometre scale. This insight potentially provides a reason for the frequently debated correlation of cycles and facies patterns in carbonate sequences in shallow epeiric seas.

Do ice-dam rupture events leave a distinctive signature in proglacial lake sediments?

Abstract Lake sediment provides a valuable record of past environmental change. However, the controls on sedimentation in proglacial lakes and their relation to glacier retreat remain poorly understood. In this study we analyze glaciolacustrine sediment production and deposition in Canal de los Témpanos, Lago Argentino, Argentine Patagonia. We associate temporal changes in the sedimentologic and geochemical characteristics analyzed from Lago Argentino cores with Late Holocene fluctuations of the Perito Moreno and Ameghino glaciers. We show that the dominant sediment source at our study site switched from Ameghino to Perito Moreno Glacier after the recession of Ameghino Glacier and the formation of the marginal ice-contact lake into which it currently calves. Spectacular ice-dam rupture events generated by Perito Moreno Glacier redistribute large volumes of water through the lake system but do not leave a significant sedimentary signature. Our results demonstrate that a detailed analysis of sedimentologic, petrophysical, and geochemical changes in lake cores can provide insight into regional glacial dynamics and sedimentary processes even in complex systems with multiple competing glacial sources and that changing glacier geometries during retreat can provide insights into the provenience of the sediments.

Of Fire and Water Microarchaeological Evidence of Mining, Rituals and Floods in North Tyrol's Kropfsberg Mine (Austria)

ABSTRACTKropfsberg, located near Reith im Alpbachtal, in North Tyrol (Austria), has been exploited for its copper ores for centuries, since at least the Early Iron Age. Excavations conducted in 2020 by the University of Innsbruck exposed the detailed stratigraphic sequence of the mine, leading to a surprising discovery: what was initially believed to be only a site for mineral extraction showed clear indications of ritual use during the Roman period and Late Antiquity. These cultic layers are characterised by abundant charcoals, animal bones and almost 200 votive coins, and suggest that the mine served during this period as a Mithraeum. Using micromorphology and µXRF, along with macroscopic, hydro‐ and geomorphological information about the mine and its surroundings, we reconstructed the processes that led to the deposition of sediments within this artificial cave. Our analyses indicate that remains of ceremonial fires and offerings were deposited within a cultic pit, rather than being spread over the floor. Also, evidence suggests that the cultic use of the mine likely ceased before the area surrounding the mine was flooded, potentially due to the damming of the Inn River caused by a significant rock fall during the Roman period. We also traced the phases following the inundation, including the cave's reopening after a period of abandonment, and identified a sequence of mining backfills that provide evidence of the site's subsequent secular use. Ultimately, the study sheds new light on the cultural and geomorphological dynamics of the Inn Valley during the Roman Period and the Late Antiquity, while underscoring the importance of integrating microarchaeological approaches to disentangle the complex interaction of cultural and environmental influences, even in historical (artificial) cave contexts.

De Geer moraine internal architecture based on sedimentological and geophysical investigations and implications for ice‐marginal reconstructions

De Geer moraines (DGMs) may act as valuable ice margin indicators; however, to date, their variable mode of formation has presented challenges for this utility. Morphometric investigations provide useful insights into formation processes, which can be developed using sedimentological and geophysical methods. Here we present sedimentological and ground penetrating radar (GPR) data of DGMs located in southwest Finland. Individual lithofacies were identified and interpreted using sediment architectural elements. These were correlated with neighbouring GPR radargrams and extrapolated across the wider study area. Generally, internal architecture presents a multi‐phase structure with lower units representing subglacial traction till and ice margin infill deposits, truncated by a larger prominent push unit, which is then successively deformed via the overriding of active ice. Significantly, there are notable differences between proximal and distal structures, with proximal sides characterized by silts, clays, and diamicton with laminae, stratification and thrust planes, and distal sides characterized by poorly consolidated diamicton and proglacial water current reworkings. Internal architecture of both prominent and intermediate ridges is very similar, reflecting similar formation processes, however, slight differences also reflect inter‐seasonal variations. Based on our findings, we present an integrated conceptual model for the genesis of DGMs whereby inter‐seasonal ridge forming processes occur within a sub‐aqueous ice‐marginal environment. Our model highlights that DGMs can be subcategorized as: (i) sediment deposition at an unstable margin during summer calving, and/or (ii) sediment pushing at a stabilized margin during a winter re‐advance. We do not find evidence of crevasse filling as a mechanism for DGM formation. We propose a landform assemblage classification whereby ‘De Geer terrain’ is used to describe series of parallel ridges arranged in a typical washboard‐like configuration. This classification identifies all DGMs derived within a sub‐aqueous ice‐marginal environment, whilst also capturing the equifinal characteristics between individual landforms.

A micro‐geoarchaeological investigation of a cultivation pit (maite) on Teti'aroa atoll, Central‐East Polynesia

ABSTRACTCultivation pits represented the principal form of horticultural features developed by past atoll communities in Central‐East Polynesia (CEP), and they are still utilised on some atolls in Oceania. The majority of information about the use of cultivation pits in CEP derives from ethnographic and preliminary archaeological investigations. The lack of excavations with rigorous stratigraphic sampling and analyses has constrained the recovery of environmental information associated with these agro‐technical features. Using a combination of geoarchaeological techniques, including field observations, physico‐chemical analyses and soil micromorphology, this study focuses on sedimentary deposits from a cultivation pit (MAITE‐01) on Teti'aroa atoll, in the Society Islands. We demonstrate how micro‐geoarchaeological investigations can advance research and offer new interpretations to study past human interactions within environments long considered “lost causes” to detailed archaeostratigraphic interpretation. High‐resolution geoarchaeological techniques reveal details about pit construction and provide indirect evidence of the integration of human‐animal interaction into the horticultural system.

Experimental Investigation of Hydraulic Characteristics for Open Channel Gates

As irrigation districts rapidly advance in terms of informatization, research on intelligent water quantity control technologies for open channels has gained increasing importance. This study aims to investigate the flow capacity and hydraulic characteristics of gates in open channels, focusing on the flow measurement and the hydraulic behavior around water-measuring structures. Although automated control in irrigation systems has achieved significant development, research on the flow characteristics near gates remains limited. To address this gap, an integrated approach combining indoor physical model experiments with theoretical analysis was used. This study explored the water surface profile, cross-sectional flow velocity distribution, vertical velocity distribution, and turbulent kinetic energy under various gate opening conditions and flow rates. The findings reveal that the water surface exhibits a sharp rise upstream of the gate, followed by a steep decline and stabilization downstream, influenced by the gate’s water-blocking effect. The flow velocities near the gate opening differ significantly in direction and magnitude from those in other cross-sections, affecting both longitudinal and vertical velocities. The turbulent kinetic energy is concentrated near the gate opening, and the turbulent kinetic energy is primarily concentrated near the sidewalls and the channel bottom; the gate’s opening size plays a crucial role in its diffusion and distribution. Linear regression analysis was utilized to fit the gate flow coefficient formula, and a comparative analysis of the measurement accuracy was conducted. The relative error between the calculated flow values and the actual measured values is within ±5%, which meets the precision requirements specified in the water measurement standards for irrigation canal systems in the irrigation district. This study pioneers an integrated approach for investigating the hydraulic characteristics of gates in open channels, merging physical model experiments with theoretical analysis. It provides novel insights into how gate openings affect water surface profiles, flow velocity distributions, and turbulent kinetic energy. This research also underscores the role of gate discharge in turbulent kinetic energy distribution, offering technical insights to enhance flow measurement accuracy and prevent sediment deposition, thereby optimizing gate applications for efficient water management. Overall, this study significantly advances the understanding of open channel flow dynamics and holds substantial significance for the refinement of water quantity control techniques in irrigation districts.

Data‐driven 3D modelling of long‐term Holocene delta evolution and sediment compaction: The Mekong Delta

SummaryThe Vietnamese Mekong River Delta (VMD) is one of the largest and lowest elevated deltas on Earth, shaped over the past thousands of years following delta progradation and sediment deposition. The geologically young delta sediments have high porosity and compressibility, resulting in high natural sediment consolidation (also known as autocompaction). Autocompaction is a natural intrinsic process that governs the spatio‐temporal morphological evolution and shallow compaction (i.e., land subsidence) in a delta. As a delta aggrades and progrades, the weight of accumulated sediments increases the effective stress experienced by underlying sediments, driving internal shallow compaction processes. Compaction of shallow sediments considerably contributes to land subsidence in the VMD, influencing the morphology and elevation of the delta plain and increasing the deltas exposure to natural hazards like flooding and relative sea‐level rise. In this study, we introduce a novel methodology to quantify sediment accumulation and autocompaction while taking into account the depositional history and heterogeneous nature of subsurface sediments in deltas like the VMD. We derived the depositional history, spatial heterogeneity and palaeo‐sedimentation rates by combining extensive datasets with lithological borelogs, sediment datings and geomechanical characterization of the delta's most representative lithologies. To simulate the spatio‐temporal formation and evolution of the delta over the last 4000 years, we employ the NATSUB3D finite element model to simulate sediment deposition and consolidation over time using an adaptive three‐dimensional mesh. The resulting 3D hydro‐stratigraphical and geomechanical characterization provides unique insights on past Holocene spatio‐temporal evolution of the VMD and current autocompaction dynamics. The model enables the prediction of shallow compaction rates under future sediment deposition and can facilitate process‐based quantification of delta elevation evolution under natural and human‐engineered sedimentation. This unlocks new opportunities to evaluate the effectiveness of nature‐based solutions and sediment enhancing strategies aimed to prevent elevation loss and combat relative sea‐level rise in the Mekong delta and similar lowly elevated coastal‐deltaic landforms elsewhere.

Riverbed Adjustments in Gravel–Sand Reaches Immediately Downstream of Large Reservoirs

The operation of large reservoirs significantly modifies flow–sediment regimes, and the reaches immediately downstream of the dams are the first to undergo responsive channel adjustments. Considering that the geomorphological responses are directly related to the flood control safety, channel stability and other sustainable functions of rivers, this paper explores the similarities and dissimilarities of the channel adjustments in the two reaches with gravel–sand beds immediately downstream of the Xiangjiaba reservoir and the Three Gorges Dam, respectively. The results show that major erosion primarily occurred during the initial years of reservoir impoundment. And then with the prominent reduction in washable sediment on the riverbed, the erosion intensity further weakened. It takes 6 to 13 years for the two reaches to reach a new state of relative equilibrium. In comparison, after the equilibrium state has been achieved, the reach with significant tributary sediment inflows exhibits alternating erosion and deposition dynamics, while the other remains relatively stable. The tributaries that transport a large amount of sediment during floods are the main sources of sediment deposition in the downstream reaches of the Xiangjiaba reservoir. However, the tributary inflow of the Qing River with low sediment concentrations has little impact on the riverbed evolution of the reaches from Yichang to Zhicheng immediately downstream of the Three Gorges Dam. These findings contribute to a deeper understanding of geomorphic adjustments near dams in response to upstream damming.