Downstream Section Research Articles

Study on the Morphological Distribution and Modeling Methods of River Particles in Upstream and Downstream Sections

This study investigates the morphological evolution of river particles and their mechanical behavior during sediment transport. River particles exhibit distinct shape differences between upstream and downstream sections, with particles becoming progressively rounded downstream. The rounding process is quantitatively described using morphological indices. The analysis reveals upstream particles are more angular, while downstream particles become increasingly rounded due to erosion and abrasion, modeled by a unified abrasion function. The Loop subdivision method effectively simulates this gradual rounding process. Additionally, the Discrete Element Method (DEM) calculates the natural angle of repose for particles with varying erosion levels, showing angles ranging from 38.2° for angular particles to 34.4° for rounded particles, closely matching field observations. The numerical results effectively demonstrate the interlocking effect caused by particle morphology. This research enhances the understanding of sediment transport dynamics and provides a robust framework for modeling particle shape evolution.

Ruin-of-the-rivers? A global review of run-of-the-river dams.

The classification of a hydropower scheme as run-of-the-river (or run-of-river; ROR) evokes an image of a low-impact installation; however, examination of eight case studies worldwide shows that substantial negative societal and ecological impacts are tied to them, albeit in somewhat different ways. We conclude that ROR dams not only potentially displace communities, disrupt livelihoods, and degrade environments in surrounding areas, but they also divert water from areas of need, impact aquatic ecology through habitat destruction and disruption of fish migrations, emit non-trivial amounts of greenhouse gases over the lifespan of the project, and disrupt streamflow in downstream river sections. While these negative impacts vary on a case-by-case basis, medium and large ROR dams consistently have multiple and cumulative impacts, even when not having appreciable reservoirs. We contend that many impactful dams do not qualify as low-impact ROR projects, despite being defined as such. Such mislabeling is facilitated in part by the ambiguous definition of the term, which risks the ROR concept being used by proponents of impactful structures to downplay their negative effects and thus mislead the public or gain status, including within the Clean Development Mechanism in relation to mitigating climate change.

Spawning Redd Habitat Use and Selection by Invasive Brown Trout (Salmo trutta) Along a Longitudinal Gradient in a Headwater Stream

ABSTRACTAs stream habitats change from upstream to downstream, choice of spawning redd sites by brown trout may shift as habitat availability changes. In a previous study, we examined the importance of overhead cover or shade in redd site selection. Here, we examined spawning site habitat use and selection by brown trout by assessing physical characteristics at redd sites in a 4.8‐km reach of Garvin Brook (southeastern Minnesota, USA) during each of five spawning seasons, 2016–2020. We measured redd dimensions, water depths, and current velocities, and compared these among four separate sections (900–1900 m in length) of the stream. We also assessed available habitats within each section to examine possible selection of habitats by spawning trout, plus quantified the size distribution of gravel substrate at redd sites within two stream sections. Habitat availability varied dramatically among stream sections. After analyzing 1844 redds from the five spawning seasons, brown trout displayed strong selection for water depths between 10 and 29 cm and current velocities between 10 and 49 cm/s. Preferred/selected water depths and current velocities increased by 7 cm and 10 cm/s, respectively, between upstream and downstream sections. All redds were located in gravel/cobble substrates, with variations in size distributions of gravels not correlated to redd dimensions or any measured habitat variable. Spawning site preferences of brown trout can change along a stream reach of moderate length, likely in relation to changing availability of various combinations of water depth, velocity, substrate, available cover, and trout abundance.

Vertical baffles in a fluidized bed reactor: Hydraulic assessment with a numerical and experimental approach

The hydrodynamics of a mini fluidizedbedreactor with and without vertical baffles has been studied with Computational Fluid Dynamics (CFD) and verified experimentally for several selected configurations. The CFD – Lagrangian Multiphase Method (CFD-LMM) approach was adopted. The gas was fed at a flow rate of 18Lmin−1 via twelve tangential inlets, creating a vortex flow around a cone in the downstream section, and additionally via a single vertical inlet (2Lmin−1) in the top plane of the cone. Relevant parameters on the friction factor, namely baffle height, inclination angle, arrangement of the baffles and the distance between the two baffle sets, have been studied. The results showed that increasing the number of baffles, the particle non-uniformity parameter decreases from 75 to 40 %. Moreover, the aligned arrangement was superior to staggered one by providing more fluid mixing. Finally, the trapezoidal baffles further improved the bed uniformity, allowing a decrease of the experimental particle non-uniformity index by more than four times as compared to the reactor without baffles tested in the same conditions.

Source distribution, ecological risks, and controlling factors of heavy metals in river sediments: Receptor model-based study in a transboundary river basin

In the context of transboundary rivers, which constitute intricate fluvial ecosystems, the persistent threat of heavy metals (HMs) contamination poses significant risks to ecosystem health. In this study, ecotoxicological hazards, governing factors, and the distribution of nine HMs (uranium (U), lead (Pb), cadmium (Cd), nickel (Ni), chromium (Cr), manganese (Mn), iron (Fe), zinc (Zn), and copper (Cu)), as well as sediment characteristics (sand, silt, clay, organic matter, and pH) are assessed within the sediment. The current investigation encompasses the analysis of twenty-seven sediment samples, utilizing inductively coupled plasma mass spectrometry, in the transboundary river basin of Bangladesh, specifically the Teesta River. Notably, the findings underscore the predominance of Cd as a contaminant, responsible for 51.85%, 81.84%, and 100% of the geo-accumulation index, contamination factor, and enrichment factor, respectively. The Teesta River emerges as moderately to highly polluted, with cumulative probabilities of 7.4%, 85.2%, and 7.4% denoting "medium", "high", and "priority" pollution levels, respectively. Regions in the upstream and downstream middle sections of the study area exhibit relatively higher pollution levels, particularly in proximity to Kaunia Upazila in the Rangpur district. Ecologically, the potential risk index indicates a low likelihood of ecological impacts at 77.8%, alongside a moderate risk observation of 22.2%. The current results attribute the distribution of these HMs to the pH and organic matter content within the sediment, serving as pivotal factors. To unravel the origins of the HMs, the positive matrix factorization (PMF) model successfully identifies four contributing factors, primarily from geogenic sources. Validation of the PMF model through Spearmen correlation and principal component analysis (PCA) reveals a consistent pattern, affirming its efficacy in this analysis. Within the region, HM sources are identified as originating from anthropogenic activities such as irrigation, industrial discharges, and domestic effluent, in addition to substantial inputs from geogenic sources. Recognizing the transboundary nature of metal pollution, the current study underscores the imperative for continuous and vigilant monitoring, coupled with the implementation of robust management practices. The interplay of both anthropogenic and geogenic factors necessitates a comprehensive approach to effectively and sustainably combat HM contamination.

Study on flood level forecasting of tidal reach in Puyang River basin

Abstract The downstream section of the Puyang River is a tidal river reach subject to both upstream floods and downstream tides. This combined impact results in an unstable relationship between water level and discharge at the forecast station, making flood level forecasting challenging. This paper took the Linpu station on the Puyang River in Zhejiang Province as the research object. Based on the historical flood data, the cause of high water levels at Linpu station was analyzed. The flood levels at Linpu station were decomposed into flood increments and basic tidal levels. Using the multiple regression method, the prediction formula for upstream flood-induced water level increments was obtained. A flood level forecasting method based on the flood increment was developed. The result of the scheme accuracy evaluation indicates that this method has good forecasting performance. The flood level forecasting method for the tidal channel proposed in this paper has a simple structure and high accuracy, which provides a scientific basis for the prevention and control of flood and drought hazards and the decision-making of project scheduling in the tidal river.

Mapping the Distribution of the Magnetic Field Strength along the NGC 315 Jet

We study magnetic field strengths along the jet in NGC 315. First, we estimated the angular velocity of rotation in the jet magnetosphere by comparing the measured velocity profile of NGC 315 with the magnetohydrodynamic jet model proposed by Tomimatsu and Takahashi. Similar to the case of M87, we find that the model can reproduce the logarithmic feature of the velocity profile and suggest a slowly rotating black hole magnetosphere for NGC 315. By substituting the estimated Ω F into the jet power predicted by the Blandford–Znajek mechanism, we estimate the magnetic field strength near the event horizon of the central black hole as 5 × 103 G ≲ B H ≲ 2 × 104 G. We then estimate magnetic field strengths along the jet by comparing the spectral index distribution obtained from very long baseline interferometry (VLBI) observations with a synchrotron-emitting jet model. Then we constrain the magnetic field strength at a deprojected distance z from the black hole to be in the range 0.06 G ≲ B(z) ≲ 0.9 G for 5.2 × 103 r g ≲ z ≲ 4.9 × 104 r g , where r g represents the gravitational radius. By combining the obtained field strengths at the event horizon and the downstream section of the jet, we find that the accretion flow at the jet base is consistent with a magnetically arrested disk. We discuss a comparison of the jet power and the magnetic flux anchored to the event horizon in NGC 315 and M87.

Investigating supercritical flow characteristics and movement of sediment particles in a narrow channel bend using PTV and video footage

This experimental study investigates the cause of nonuniform invert abrasion observed at sediment bypass tunnel (SBT) bends by examining the variations in velocity distributions, turbulence properties, bed shear stress, and bulk sediment movements under three supercritical bend flow conditions, detailed investigation of such flow is scarce. Using a laboratory-scaled model (1:22) of the downstream bend at Solis SBT, Switzerland, the research utilized particle tracking velocimetry and high-speed cameras with spherical sandstones and glass spheres representing sediments. The results indicate that as the secondary currents develop in the flow direction, the flow properties and sediments redistribute across the channel: the high-momentum fluids are directed toward the outer wall, the bed shear stress increases toward the outer wall, and the sediments are pushed toward the inner wall, which then follow this path downstream, even in straight sections, despite lower bed shear stress. This distribution of sediments, driven by secondary currents, leads to deeper invert abrasions toward the inner wall at SBT bends and downstream sections. Thus, these abrasions are primarily influenced by sediment movement rather than the bed shear stress alone. The study's findings are also valuable for validating future numerical simulations.

Assessing the impact of sediment characteristics on vegetation recovery in debris flow fans: A case study of the Ohya Region, Japan

What factors influence natural vegetation recovery in debris flow-prone areas, and how do sediment dynamics play a role? This study investigates these questions in the Ohya debris flow fan, Japan, utilizing various analytical techniques. Through the application of Support Vector Machine (SVM) classification, grain size analysis, accuracy assessment, debris flow analysis, and hotspot analysis, this study assess the distribution of sediments, vegetation classes, and the extent of debris flow events. The findings shed light on the dynamics of vegetation recovery and its relationship with sediment dynamic. The SVM classification outcomes reveal distinct trends in sediment and vegetation distribution along the flow path, particularly noting a significant decrease in vegetation cover from upstream to downstream sections. By employing SVM classification, this study successfully identified 3,282,910 sediment particles and determined their average, minimum, maximum, and standard deviation grain sizes as 7.3 cm, 0.27 cm, 415 cm, and 9.18, respectively. Accuracy assessments of image classification and grain size measurements demonstrate high levels of accuracy, with an overall classification accuracy of 98.82 % and a kappa coefficient of 0.977. Validation of grain size measurements reveals a strong correlation (R2 = 0.997 and y = 1.005× + 0.0661) between field-observed sediment sizes and sizes derived from classified images. Debris flow analysis reveals that the total area affected by debris flow in 2022 was 36,232.7 square meters, decreasing to 14,213.9 square meters in 2023. Hotspot analysis identifies regions of both high and low sediment size concentrations, providing valuable insights into sediment distribution patterns. Examining the natural recovery of vegetation, present study identifies vegetation spots across different study sections. Results show that 55 % of naturally recovering vegetation areas are located in regions unaffected by debris flow events between 2022 and 2023. Among the study sections, the area affected by debris flow in 2023 exhibits the lowest density of vegetation spots. Overall, this study highlights the new generation vegetation recovery and its association with sediment dynamic in the Ohya debris flow fan. The findings contribute valuable insights for understanding natural recovery processes in highly dynamic sedimentation areas, informing the development of effective strategies for ecosystem restoration and management in debris flow-prone regions.

Bacterial community and dissolved organic matter networks in urban river: The role of human influence

Human activities have significantly altered the biogeochemical cycles of carbon, nitrogen, and sulfur in aquatic ecosystems, leading to ecological problems.This study utilized 16S rRNA gene high-throughput sequencing and excitation-emission matrix parallel factor analysis (EEM-PARAFAC) to evaluate the bacterial community composition and dissolved organic matter structure in the upstream (less impacted) and downstream (severely impacted) sections of the river, with a focus on the interactions between bacterial diversity and dissolved organic matter (DOM) characteristics.Results indicated significant spatial diversity in bacterial communities, with a higher α-diversity upstream compared to the more polluted downstream sections. Environmental parameters, particularly total phosphorus (TP) and dissolved oxygen (DO), were found to significantly influence the distribution and composition of bacterial phyla through redundancy analysis. The pattern of bacterial community assembly has shifted from predominantly deterministic to predominantly stochastic as a result of human activities. The analysis of DOM through EEM-PARAFAC identified three main fluorescent components, reflecting varied sources and interactions with bacterial communities. Upstream, microbial activities predominantly contributed to autochthonous DOM, while downstream, increased inputs of allochthonous DOM from human activities were evident. Furthermore, the study revealed that through the introduction of various organic pollutants and nutrient loads that shift microbial metabolic functions towards increased degradation and transformation of complex organic compounds downstream. Structural equation modeling (SEM) revealed that upstream human activities primarily affected bacterial communities indirectly by altering DOM properties. In contrast, downstream activities had both direct and indirect effects due to higher pollutant loads and more complex environmental conditions. These interactions underline the profound effect of anthropogenic factors on riverine ecosystems and emphasize the importance of managing human impacts to preserve microbial biodiversity and water quality.

Detangling past and modern zinc anthropogenic source contributions in an urbanized coastal river by combining elemental, isotope and speciation approaches

The accumulation of trace metals in the environmental compartments of coastal rivers is a global and complex environmental issue, requiring multiple tools to constrain the various anthropogenic sources and biogeochemical processes affecting the water quality of these environments. The Valao fluvio-estuarine system (Rio de Janeiro, Brazil) presents a challenging case of a coastal river contaminated by both modern and historical anthropogenic metal sources, located in the land and in the intra-estuary, continuously mixed by tidal cycles. This study employed a combination of spatial distribution analysis of trace metals including gadolinium (Gd), zinc (Zn) isotopic analyses, and X-ray absorption spectroscopy (XAS) to distinguish between these sources. The concentrations of metals in both dissolved (water samples) and surficial sediment compartments (Suspended Particulate Matter and sediment samples) display an overall enrichment trend from upstream to downstream. Multivariate statistical analysis allows to discriminate geogenic elements derived from watershed geology (Ti, K, and Mg) vs anthropogenic contaminants from urban runoff and domestic sewage discharges (Cu, Cr, Pb, Zn, and Gd); and legacy metal contaminants (Zn and Cd) remobilized from ancient metallurgical wastes and transported upstream in the estuary during tidal cycles. The anthropogenic Gd concentration in the dissolved compartment increases along the watercourse, highlighting continuous ongoing sewage discharge. Zinc solid speciation also indicates that Zn contribution from legacy metallurgy waste is primarily associated with sulfide-Zn and Zn-phyllosilicate in the outlet estuary, while in upstream sediments of fluvio-estuarine system, Zn is found bound to organic matter. Zinc isotope systematically reveals a progressive downstream shift to heavier isotope compositions. Upstream, the relatively pristine site and the urbanized section of the river exhibit a relatively uniform δ66/64Zn value (+0.20 ± 0.07 ‰) in suspended particulate matter (SPM) and surficial sediments. These results indicate that domestic sewage discharges contribute to Zn enrichment in sediments of the Valao fluvio-estuarine system but without modifying its isotope signature in sediments. The sediment of the downstream estuarine section shows a heavier δ66/64Zn value (+0.48 ± 0.08 ‰), indicating the strong influence of the intra-estuarine source identified as the historical metallurgic contamination. An integrated view of the geochemical tracers allows thus inferring that the untreated sewage and legacy metallurgical contamination are the primary sources of anthropogenic Zn contamination. It highlights the progressive mixing along the estuarine gradient under tidal dynamics. The influence of the former source continuously expands from the headland towards the estuary.

Application of remote sensing and GIS to understand the spatio-temporal shifting of Bagmati River of Nepal

Geomorphology, hydrological conditions and human activities, alter river morphology and shift channels, causing environmental and socio-economic impacts. River shifting in Nepal is well-documented for large rivers like the Koshi and Karnali, while smaller rivers like the Bagmati have received less attention. This study employs geospatial tools and techniques to understand the morphological changes, quantify the spatio-temporal shifting, and erosion and deposition of the Bagmati River channel in Nepal over a 30-year period (1988–2018). The morphological changes were measured in terms of sinuosity index, river width and water area. The entire river maintained a generally sinuous character throughout the study period. The total average width of the river decreased by more than four times from 1287.17 m to 300.01 m from 1988 to 2018, and the water area also decreased by 6.59 km2 over the same period, reflecting a transition of the river into a narrower channel over the decades. Overall, the Bagmati River channel slightly shifted eastward in the upstream and downstream sections while significantly shifting westward in the midstream section with an annual rate of 9.94 m, 4.83 m and 41.5 m respectively. The annual rate of bank erosion was found to be one-fourth of the deposition (0.72 km2 per year), with the higher erosion and deposition in the east bank and midstream section of the river. This study highlighted the morphological changes, spatio-temporal channel shifting, and erosion and deposition of the Bagmati River located in the floodplain of Tarai region of Nepal.

Impacts of fish pond effluent on the water quality of an afrotropical stream: a comprehensive evaluation using the water quality index

This study highlights the importance of managing fishpond effluent to minimize its impact on aquatic environments. Fish effluents are a major concern worldwide in aquatic environments. It also provides information on the impacts of effluents on the water quality index of streams when released into aquatic environments. Streams and fishponds were sampled bimonthly for two annual cycles, covering different sampling stations both upstream and downstream of the fishpond effluents at 50-m intervals. Water quality parameters associated with in situ conditions were determined in the field. In the laboratory, other physicochemical parameters were determined via proper standard protocols. The results of the study revealed that water quality parameters such as turbidity, total suspended solids, total solids, conductivity, total dissolved solids, dissolved oxygen, biological oxygen demand and organic matter recorded in water samples collected from 50 m upstream at the point of effluent discharge were significantly (p < 0.05) different from those recorded at other sampling stations. The WQI value of the discharge point was higher than the WQI recorded in both the upstream and downstream sections of the stream. The findings of this study showed that the point of discharge of fishpond effluents is particularly concerning for the receiving stream compared with other sampling points. This localized area has experienced marked deterioration in water quality, posing significant threats to the health and biodiversity of aquatic ecosystems. The effluent's impact, though slight when dispersed in the receiving waterbody, underscores the necessity for adequate management practices to mitigate its adverse effects. Effective strategies, including regular monitoring, effluent treatment, and sustainable pond management, are imperative to ensure the long-term health and resilience of the aquatic environment.

Upstream heating history effects on heat transfer of supercritical R134a in transcritical organic Rankine cycle

A comprehensive understanding on the heat transfer of supercritical working fluid is critical for the design of vapor generator in transcritical Organic Rankine Cycles. The thermal entrance region under supercritical pressure conditions is relatively complex and remains unresolved. To this end, this study investigates heat transfer to supercritical fluids in heated horizontal flow, focusing on the impact of upstream heating history which has been rarely discussed. The Abe-Kondoh-Nagano (AKN) low Rek–ε turbulence model was employed, covering a wide range of upstream conditions: upstream heating length ranging from 10d (d is tube diameter) to 200d, and upstream heat flux up to 4.5 times that of the downstream test section. The results revealed that heating history didn't matter when upstream Grq/Grth < 5. For upstream mixed convection of Grq/Grth = 10–220, heating history had a significant effect on the downstream flow, causing a maximum 50 %–60 % increase in heat transfer coefficients within an affected length up to 100d. When the downstream flow was forced convection, thermophysical property variations mainly contributed to the above enhancement. Meanwhile for downstream mixed convection, upstream heating history notably enhanced turbulent intensity, further improving heat transfer. The upstream heating length was identified as a crucial factor influencing both forced and mixed convections downstream. Negligible differences were observed when the heating length was less than 20d. On the other hand, the radial distribution of flow and thermal fields remained constant beyond a critical heating length, indicating the achievement of a pseudo-fully-developed state with identical heat transfer behavior. Results of this work confirm that the effect of upstream heating history is closely tied to thermal developing length and holds significant importance in the thermal design of vapor generators.

A turbulent flow topology optimization method for diverging tee resistance reduction

The resistance of local components in piping and duct systems significantly affects the energy consumption of fans and pumps, accounting for 40–60 % of the total building energy consumption. In this paper, an improved topology optimization method for variable density turbulent flow is proposed to design a low-resistance diverging tee structure in piping and duct systems. The advantages of the improved optimization method over the traditional method are analyzed using finite element numerical simulation, and the applicability of the proposed method is verified in the Reynolds number range of 0.6 × 105–2.6 × 105. In order to ensure the resistance reduction effect of the topology diverging tee under multiple operating conditions, the local resistance coefficients under nine flow ratios were simulated and calculated using the finite volume method. The results show that the topology diverging tee can significantly reduce the resistance. Compared with the traditional tee, the maximum resistance reduction rates in the straight-through direction and branch direction reached 63 % and 59 %, respectively. In addition, the intensity of secondary flow in five downstream sections was analyzed based on the dimensionless parameter Se. Finally, the actual resistance reduction effect of the topology diverging tee was experimentally verified. The optimization method and analysis results proposed in this study can provide a reference for the optimal design of pipelines with low resistance in energy-saving operation of buildings and in engineering fields such as petroleum and chemical industries.

Effect of flameholding cavity geometry on the flowfield of a solid fuel scramjet

An optically accessible solid fuel scramjet was used to investigate the supersonic combustion of varying polymethyl methacrylate solid fuel grain geometries. The rear wall angle of the flameholding cavity was varied (30, 60, 75, and 90°) and an alternative geometry (flush fuel grain) containing the addition of a backwards facing step to the front of a conventional fuel grain was explored. Optical diagnostics including high-speed shadowgraph, CH* chemiluminescence, and HD video were used to analyze flammability characteristics and determine quantitative regression rates for each geometry. The optical results were supplemented by static pressure traces along the length of the combustor for the duration of a test firing. All tests were conducted with Mach 2 inlet flow into the combustor at nominal inlet conditions of 12.9 atm and 900 °C. Shadowgraph imaging for both cold flow and combusting flow was used to characterize the varying flow fields associated with their respective geometries and their core flow oscillatory frequencies were preliminarily inspected. Chemiluminescence data reveals increased heat release in the downstream constant area and expansion sections of the flush fuel grains compared to conventional geometries. This heat release appears to correlate with increased time-averaged regression rates in these regions while the varying cavity angle fuel grains demonstrate differing magnitudes of maximum regression along the rear cavity wall and onset of the constant area section. In addition to increased overall regression rates, flush geometries increase the flameholding capabilities and demonstrate self-sustained burning at lower inlet temperatures than similar geometries designed without a flush section.

Phosphorus prediction in the middle reaches of the Yangtze river based on GRA-CEEMDAN-CNLSTM-DBO

Accurate and rapid prediction of water quality is crucial for the protection of aquatic ecosystems. This study aims to enhance the prediction of total phosphorus (TP) concentrations in the middle reaches of the Yangtze River by integrating advanced modeling techniques. Using operational and discharge data from the Three Gorges Reservoir (TGR), along with water quality parameters from downstream sections, we used Grey Relational Analysis (GRA) to rank the factors contributing to TP concentrations. The analysis identified turbidity, permanganate index (CODMn), total nitrogen (TN), water temperature, chlorophyll a, upstream water level variation, and discharge from the Three Gorges Dam (TGD) as the top contributors. Subsequently, a coupled neural network model was established, incorporating these key contributors, to predict TP concentrations under the dynamic water level control during flood periods in the TGR. The proposed GRA-CEEMDAN-CN1D-LSTM-DBO model was compared with conventional models, including BP, LSTM, and GRU. The results indicated that the GRA-CEEMDAN-CN1D-LSTM-DBO model significantly outperformed the others, achieving a correlation coefficient (R) of 0.784 and a root mean square error (RMSE) of 0.004, compared to 0.58 (R) and 0.007 (RMSE) for the LSTM model, 0.576 (R) and 0.007 (RMSE) for the BP model, and 0.623 (R) and 0.006 (RMSE) for the GRU model. The model's accuracy and applicability further validated in two sections: YC (Yunchi) in Yichang City and LK (Liukou) in Jingzhou City, where it performed satisfactorily in predicting TP in YC (R = 0.776, RMSE = 0.007) and LK (R = 0.718, RMSE = 0.007). Additionally, deep learning analysis revealed that as the distance away from dam increased, prediction accuracy gradually decreased, indicating a reduced impact of TGR operations on downstream TP concentrations. In conclusion, the GRA-CEEMDAN-CN1D-LSTM-DBO model demonstrates superior performance in predicting TP concentration in the middle reaches of the Yangtze River, offering valuable insights for dynamic water level control during flood seasons and contributing of smart to the advancement of water management in the Yangtze River.

Theoretical modeling of process heat transfer mechanism in U-shaped molten salt heat exchanger

U-shaped tube molten salt heat exchanger (MSHE) plays an important role for further improving peak shaving capacity of coal-fired unit (CFU) coupled extraction thermal storage system (ETSS). Nevertheless, existing experimental approach cannot reveal process heat transfer characteristics (HTCs) of MSHE. Meanwhile, investigation exploring factors restricting heat transfer enhancement for MSHE in theory is still vacant. In this paper, a theoretical method for MSHE was developed to determine process mechanism of heat transfer to capture perspective of enhanced heat transfer. Heat transfer performance of U-tube MSHE was theoretically unpacked. Deliberating work was executed with inlet water flow rate of 69–139 kg/s, water temperature of 120–170 °C, salt flow rate of 28–58 kg/s and salt temperature of 350–400 °C. Whereupon, the process mechanism of heat transfer inside MSHE was obtained with redeeming lack of theoretical exploration.Research shows, total HTC respectively increases by 2.57 and 1.88 W/(m2·°C) with 10 °C increasing of molten salt inlet temperature (MSIT) and 14 kg/s ascension in condensate flow rate (CFR). It is signified thermal resistance of countercurrent section of MSHE mainly involving HTCs of MSHE with increment of MSIT and CFR. Such privileged sites are main factor restricting heat transfer enhancement. Moreover, total HTC respectively increases by 2.1 and 21.84 W/(m2·°C) with 10 °C upgrading in condensate inlet temperature (CIT) and 6 kg/s increment in molten salt flow rate (MSFR). Contrary to augmenting MSIT and CFR, HTCs changing of MSHE with CIT alteration and MSFR preferment mainly attributed to downstream section and inlet position of MSHE. Meanwhile, it is discovered significant impact is generated for HTCs of MSHE with specific heat changing in molten salt. Furthermore, it was proven that Bell method is suitable for calculating HTC of molten salt on shell side in U-shaped tube MSHE. The research contents in present work can provide reliable basis for optimal design and application of U-tube MSHE in CFU.

Neonicotinoids as emerging contaminants in China's environment: a review of current data.

Neonicotinoids (NEOs), the most widely used class of insecticides, are pervasive in the environment, eliciting concerns due to their hydrophilicity, persistence, and potential ecological risks. As the leading pesticide consumer, China shows significant regional disparities in NEO contamination. This review explores NEO distribution, sources, and toxic risks across China. The primary NEO pollutants identified in environmental samples include imidacloprid, thiamethoxam, and acetamiprid. In the north, corn cultivation represents the principal source of NEOs during wet seasons, while rice dominates in the south year-round. The high concentration levels of NEOs have been detected in the aquatic environment in the southern regions (130.25ng/L), the urban river Sects.(157.66ng/L), and the downstream sections of the Yangtze River (58.9ng/L), indicating that climate conditions and urban pollution emissions are important drivers of water pollution. Neonicotinoids were detected at higher levels in agricultural soils compared to other soil types, with southern agricultural areas showing higher concentrations (average 27.21ng/g) than northern regions (average 12.77ng/g). Atmospheric NEO levels were lower, with the highest concentration at 1560pg/m3. The levels of total neonicotinoid pesticides in aquatic environments across China predominantly exceed the chronic toxicity ecological threshold of 35ng/L, particularly in the regions of Beijing and the Qilu Lake Basin, where they likely exceed the acute toxicity ecological threshold of 200ng/L. In the future, efforts should focus on neonicotinoid distribution in agriculturally developed regions of Southwest China, while also emphasizing their usage in urban greening and household settings.

Comparative analysis of water quality index and river classification in Kereh River, Penang, Malaysia: Impact of untreated swine wastewater from Kampung Selamat pig farms.

The Kereh River in Penang, Malaysia, has faced severe pollution for over 40 years due to untreated wastewater from swine farms in Kampung Selamat, discharged via stormwater drains. Despite official claims that all 77 swine farms treat their wastewater to meet regulatory standards, local non-governmental organizations and villagers have challenged this, though their concerns lack scientific backing. This study evaluates the river's water quality by analyzing samples from upstream (US), midstream (MS), and downstream (DS), and from Parit Cina-Parit Besar, a conduit for untreated swine wastewater. Fourteen parameters were measured against Malaysia's National Water Quality Standards (NWQS). Significant differences were found in six parameters: ammonium nitrogen (AN), biochemical oxygen demand (BOD), chemical oxygen demand (COD), dissolved oxygen (DO), total suspended solids (TSS), and oil and grease (OG). While Dunn's post hoc pairwise comparison showed no significant differences among river segments, mean values indicated increased pollution downstream, particularly after the convergence with untreated swine wastewater. River classification worsened, with water quality index dropping from 69.88 ± 11.37 score (Class III) US to 38.49 ± 12.74 and 50.44 ± 3.14 scores (Class IV) MS and downstream, respectively. A significant positive correlation between E. coli and AN (r = 0.71, p < 0.01) suggests a common point source pollutant, particularly the untreated swine wastewater. The river exhibits low oxygen levels and high organic matter and nutrient concentrations, especially MS and downstream, highlighting substantial ecological and public health risks. Effective enforcement of waste treatment regulations and enhanced monitoring are crucial for mitigating pollution and restoring the river's ecosystem. Collaboration between authorities and pig farmers is essential to improve water quality and maintain the river's ecological balance. PRACTITIONER POINTS: Severe Kereh River pollution: Untreated swine wastewater from Kampung Selamat pig farms, primarily via Parit Cina-Parit Besar, has degraded the river for over 40 years. Regulatory non-compliance: Despite official claims, untreated swine wastewater continues to pollute the river, challenging regulatory standards. Significant pollution indicators: Elevated levels of AN, BOD, COD, DO, TSS, OG, and E. coli signal severe pollution midstream and downstream. Water quality index drop: WQI scores classify midstream and downstream sections as polluted, indicating worsening conditions downstream. Urgent need for action: Enforcing regulations, improving wastewater treatment, and relocating pig farms are crucial for restoring the Kereh River.