Downstream Section Research Articles

Microplastic Contamination of Fine-Grained Sediments and Its Environmental Driving Factors along a Lowland River: Three-Year Monitoring of the Tisza River and Central Europe

The hydro-geomorphological background in microplastic (MP) deposition and mobilization is often neglected, though the sampling environment is the key point in a monitoring scheme. The aim of the study was to analyze the environmental driving factors of MP transport over three years (2020–2022) along a 750 km-long section of the Tisza River, Central Europe. The mean MP content of the fresh clayey sediments was 1291 ± 618 items/kg in 2020, and then it decreased (2021: 730 ± 568 items/kg; 2022: 766 ± 437 items/kg). The upstream and downstream sections were the most polluted due to improper local sewage treatment. In 2020, 63% of the sites were hotspot (≥2000 items/kg), but their number decreased to one-third in 2021 and 2022. MP pollution is influenced by highly variable environmental factors. (1) The geomorphological setting of a site is important, as most of the hotspots are on side bars. (2) The tributaries convey MP pollution to the Tisza River. (3) The bankfull or higher flood waves effectively rearrange the MP pollution. (4) The dams and their operation influence the downstream trend of MP pollution in the reservoir. (5) Downstream of a dam, the clear-water erosion increases the proportion of the pristine sediments; thus, the MP concentration decreases.

Compartmentalization transformation of Fe2+, Mn2+ and NH4+ in groundwater: A comparative research containing experimental medium and functional genera profiling derived from experiment data

Contamination of soluble iron (Fe2+), manganese (Mn2+), and ammonium (NH4+) in groundwater is prevalent, particularly in Northeast China. This study aims to elucidate the intricate biological and physical-chemical reactions involved in the sequential transformation of three target contaminants. Two dynamic column simulations were used to compare quartz sand filtration (QSF) system with riverbank filtration (RBF) system to assess the interactions and respective contributions of the reactions involved in transforming process. Similar pattern of transformation vertical compartmentalization in two systems along the filter depth were founded, and the Fe2+ transformation was mainly distributed in the upper part, while NH4+ and Mn2+ occurred primarily in the downstream sections. The average transformation rate of Fe2+, Mn2+ and NH4+ in RBF system was 84.52 %, 47.68 % and 67.95 %, respectively, which was 5.20 %, 11.43 % and 23.06 % higher than in QSF system. The dominant transformation process for Fe2+ in RBF involved chemical oxidation, bio-oxidation and adsorption. The lower transformation rate for Mn2+ was attributed to abiotic homogenous oxidation limitation and negative affect derived from high concentration of NH4+ with high nitrification rate in RBF system. Nitrification by Nitrosomonas and Nitrospira was critical NH4+ transformation mechanism in RBF system, while the adsorption by iron and manganese oxide and aerobic denitrification were contributed strongly to NH4+ transformation in QSF system. Furthermore, the spatial distribution of functional bacterial genera was in good consistent with the transformation compartmentalization of three target contaminants in both systems, and similar microbial community structure reflected the domestication effect of groundwater chemistry on functional bacteria.

Aquatic Insects as Bioindicators of Water Quality in the Achenkovil River, Kerala, India.

The origin of the Achenkovil River, the Devarmalai of Western Ghats, is within the Konni reserve forest of Pathanamthitta district, flowing through Pathanamthitta, Kollam, and merging with the Pamba river in the Alappuzha district. This study included the spatial variation of aquatic insect fauna with respect to water quality. The bottom water samples and insect fauna were collected bimonthly using a Niskin sampler and D-frame nets for a period of one year (February 2019 to January 2020). The study yielded 10736 insect fauna under 8 orders, 21 families, 35 genera, and 36 species. How the quality of the water affects biodiversity of aquatic insects was examined using multivariate statistical techniques (PCA and CCA) and Pearson's correlation coefficient. The findings showed that the upstream portion of the river has a remarkable diversity and quantity of aquatic insect species. The major insect group in the collected sample was ephemeroptera. There were no pollution-sensitive taxa in the middle stream or downstream portions of the river, which suggests that the water quality was declining. The middle stream and downstream sections of the river did not contain any pollution-sensitive taxa, indicating deteriorating water quality. Human-caused factors like washing, cleaning cars, and washing cattle and disposal of garbage are common in these regions. Because most aquatic insects are sensitive to environmental fluctuations, they can be used as an efficient tool in biomonitoring studies.

Effect of kerosene injection states on mixing and combustion characteristics in supersonic combustor at high equivalent ratio

Previous studies have found that the difference in combustion characteristics of gaseous and liquid kerosene injection in supersonic combustor is sensitive to the equivalent ratio. In this paper, the previous work is extended to a high equivalent ratio to gain a deeper understanding of the effect of injection states on combustion performance via numerical computation. The simulation results match well with the experiments and demonstrate that due to the different jet structures, the cavity shear layer of liquid injection penetrates deeply into the cavity, forming two recirculation zones therein. As a result, the majority of droplets enter the cavity and exist at a low streamwise velocity, which is favorable to droplet vaporization and combustion. Therefore, when the liquid fuel is injected at a high equivalent ratio, the fuel residence time increases, the droplet evaporation distance decreases, and the fuel vapor accumulates in the cavity. Compared to the gaseous injection with the same equivalent ratio, the liquid injection exhibits similar mixing efficiency in the cavity but slightly higher mixing efficiency in downstream divergent sections. This unique fuel distribution causes the liquid injection to have a higher combustion efficiency than that of the gaseous injection. The weak advantage in mixing and combustion makes the liquid injection capable of compensating for the effects of the fuel atomization and evaporation on combustion performance. As a result, the combustion structure and static pressure distribution of liquid injection with the high equivalent ratio is similar to those of the gaseous injection.

Seasonal Variation Analysis of Microplastic Distribution in the Estuary of Brantas River

Every year, 0.48-1.29 million tonnes of plastic waste is estimated to enter the waters due to poor plastic waste management in Indonesia. Plastic waste has the potential to be degraded into smaller particles through ultraviolet (UV) radiation, weathering process, water currents, physical-mechanical and biodegradation. Plastics with particle sizes between >1 μm and <5 are categorized as microplastics (MP). Microplastic particles are mainly distributed in surface waters. Rivers are considered as the main route of plastic transportation from the land to the ocean. The Brantas River in Surabaya is the main downstream section of the Brantas River and plays an important role in providing clean water for Surabaya City, aquatic biota habitat, and irrigation. With extreme weather conditions such as long dry seasons and high rainfall in the rainy season distribution and abundance of microplastics in water bodies/rivers tend to vary. The study's goal is to determine the effect of seasonal water volume (dry and rainy) on the abundance and characteristics of microplastics in water and sediment samples from the downstream Brantas River (Surabaya city). Observations of the abundance of microplastics in water and sediment at three stations during the dry season revealed a trend of increasing abundance downstream. Microplastics were abundant in the water at sta 1 with an average of 0.8 particles/L, sta 2 with 1.25 particles/L, and sta 3 with 1.02 particles/L. The abundance of microplastics in the sediment at sta 1 averaged 0.2 particles/gr, sta 2 0.51 particles/gr, and sta3 0.25 particles/gr. Meanwhile, in the rainy season, the abundance of microplastics in water and sediment shows a higher abundance compared to the dry season. Abundance of microplastics in the water at sta 1 with an average of 0.9 particles/L, sta 2 1.24 particles/L, and sta3 1.17 particles/L. The abundance of microplastics in the sediment at sta 1 averaged 0.55 particles/gr, sta 2 0.56 particles/gr, and sta3 0.60 particles/gr.

Analysis of the low water level decline and its causes in the downstream section of Hanjiang River Xinglong Water Control Project near the dam

Analysis of the low water level decline and its causes in the downstream section of Hanjiang River Xinglong Water Control Project near the dam

Nutrient inputs shape ecosystem functioning gradients along the pristine, upper Neretva River, Bosnia and Herzegovina

Ecosystem functions are the backbone of ecosystem services that rivers provide to human societies. Ecosystem functioning emerges from the interaction between biological communities and their environment. As environmental conditions in rivers change along their longitudinal continuum, so does functioning. Sometimes, these changes do not follow smooth gradients but rather great discontinuities. This can be the case in calcareous, karstic rivers due to the sudden massive inputs of groundwater along the landscape, a typical phenomenon for Balkan rivers. Despite their high geodiversity and their great ecological value, Balkan rivers remain understudied. Here, we investigated how ecosystem functions and their diversity (estimated as multifunctionality) change along the continuum of the karstic, free-flowing Neretva River in Bosnia and Herzegovina. For this purpose, we measured a subset of fundamental ecosystem functions (ecosystem gross primary production, biofilm net primary production and enzymatic activities, organic matter decomposition) in 11 river reaches from the Neretva headwaters to river sections upstream of the Jablanica reservoir. We found different functions reached their maximum in different sections of the Neretva depending on nutrient inputs. While organic matter decomposition was highest in headwaters due to the input of nutrients from riparian vegetation, biofilm enzymatic activity expressed highest values at middle sections due to groundwater inputs of NH4+-N. Primary production was highest at the most downstream sections due to the accumulation of NO3--N and PO43--P within the catchment area. As a result, average multifunctionality peaked at sites with the highest nutrient concentration across the Neretva river continuum, indicating a stronger influence of nutrient inputs than network position. The pristine conditions of the Neretva result in oligotrophic conditions along its upper course. Our results emphasize the great sensitivity of ecosystem functioning in the Neretva to nutrient inputs and environmental discontinuities, either natural or human-made. Potential major, long-term impacts in the area might alter existing environmental gradients and thus ecosystem functioning in rivers at local and regional scale.

Prediction of critical heat flux in non-uniform heated rod bundle based on modified CHF empirical correlations

The accurate estimation of critical heat flux (CHF) continues to be a significant challenge in the study of radial and axial non-uniform heated rod bundles under NHR-200Ⅱ operating conditions. The present work develops the subchannel analysis code CTF algorithm that incorporates modified CHF empirical correlations to forecast CHF of non-uniform heated rod bundles preliminarily. The article selected experimental data from HTRF, which includes both uniform heated and non-uniform heated rod bundle CHF experiments, for preliminary validation and analysis of this method. The results demonstrated that the predicted results of modified Barnett correlation have the good agreement with the experimental values. Additionally, the modified Barnett correlation is used to predict the CHF of rod bundles under various power distribution. In different radial power distribution, the critical power of rod bundles decreases with the increase of radial power factor ratio. In different axial power distribution, the critical power in inlet and outlet peak distribution is lower than uniform heated rod bundle. Regarding the case of radial uniform heating and axial inlet peak distribution, CHF locations often occur near the central section of the heated rod height. In the axial intermediate peak distribution, CHF positions often emerge in the intermediate and downstream sections of the heated rod to the outlet. In a typical operating scenario of the NHR-200II, the CHF will occur towards the exit of the hot central subchannel, particularly near the radial heated rod exhibiting the maximum thermal power. The occurrence of CHF can be attributed to factors such as lower mass flux, higher local equilibrium quality, and heat flux.

Study on the Disaster Mechanism Analysis and Enlightenment of Dam Failure

With the continuous advancement of infrastructure construction, dam, as an important water conservancy project, plays the role of water storage, flood regulation and power generation. However, due to the influence of extreme weather and other reasons, there may be the possibility of dam failure accidents when the dams are put into operation. The dam break accident may bring great losses to the downstream dam section. The theme of this paper is the disaster mechanism analysis and enlightenment of dam failure. By combining the statistics of dam break data with the analysis of potential causes, the disaster mechanism of dam break is obtained. According to the disaster mechanism, the corresponding treatment plan and future development trend are discussed, with the aim of monitoring the design, construction and operation stages of the dam. Suggestions for improvements include improving the dam's ability to withstand extreme weather, carrying out precise construction according to specific steps, and improving the professionalism of managers. These suggestions can reduce the probability of dam break accidents and reduce the casualties and economic losses caused by dam break accidents.

Numerical simulations on the effect of swirler installation angle on outlet temperature distribution in gas turbine combustors

The higher demand for temperature rises and low-pollution combustion methods make it more problematic to regulate the outlet temperature distribution (OTD) of advanced gas turbines. The present investigation tackles the significant challenge of achieving uniform outlet temperature distribution in advanced low-emission gas turbine combustors devoid of dilution holes, a concern that directly impacts the service life of turbine blades. Differing from the reliance on dilution holes characteristic of conventional combustor designs, this study aims to control the OTD by adjusting the installation angles of the swirler blades. To this end, a thorough numerical analysis is conducted to assess the impact of swirler blade angles on the temperature distribution within the combustor. The findings reveal that an elevated swirl number drives the flame front and regions of high temperature toward the downstream section of the combustor. This downstream shift exhibits the dual effect of potentially improving heat exchange due to enhanced mixing and substantially reducing the outlet temperature distribution factor (OTDF). Quantitatively, the obtained results demonstrate that by fine-tuning the swirler blade angles, a reduction in the OTDF by approximately 33.6 % and a decrease in the radial temperature distribution factor (RTDF) by about 20.4 % can be achieved. These reductions represent a substantial improvement in controlling the temperature field inside the combustor, which is crucial for minimizing the thermal load on turbine blades. In summary, the research provides valuable insights into the design of gas turbine combustors, highlighting an innovative approach to achieving more uniform temperature distributions at the outlet without the exploitation of dilution holes. The results of this scrutiny contribute to extending turbine blade life and improving the overall performance of gas turbine systems, thereby advancing the development of environmentally friendly combustion technologies.

Integrating reaction pathways and downstream separation network for optimal sustainable process route selection

Reducing the environmental impact of chemical production has become a critical objective due to carbon emission regulations and the challenges the carbon market poses. Downstream separation network optimization, which can improve process sustainability by using complex heat exchanger networks, applying advanced separation techniques, optimizing the design/operating parameters, etc., has been researched for many years. However, most optimization work focuses solely on downstream separation sections without considering the selection of raw materials and different reaction pathways. This work aims to develop a mixed integer nonlinear programming (MINLP) optimization model, which integrates reaction pathway selection and downstream separation optimization, to select the optimal sustainable process route for utilizing raw materials or producing products. The objective is to maximize/minimize the process profit/cost. Decision variables such as binary variables, which represent the selection of separation task, key component, heating utility, and continuous variables, which influence the separation mass/energy balance, are considered. By giving parameters like reaction conversion rate, selectivity, and raw material/product price, this optimization model can identify the optimal process route for producing a target product or utilizing a raw material. The optimization model was applied to two case studies: one-step isobutylene and methanol utilization and two-step 1,4-butanediol (BDO) production. The process routes, using isobutylene for pivalic acid production and methanol for gasoline production, have the highest process profit per carbon emission. And the process route, which uses acetylene for BDO production, leads to minimum process cost.

Effects of flow reduction and artificial light at night (ALAN) on litter decomposition and invertebrate communities in streams: A flume experiment

River ecosystems are heavily impacted by multiple stressors, where effects can cascade downstream of point sources. However, a spatial approach to assess the effects of multiple stressors is missing. We assessed the local and downstream effects on litter decomposition, and associated invertebrate communities of two stressors: flow reduction and artificial light at night (ALAN). We used an 18-flow-through mesocosm system consisting of two tributaries, where we applied the stressors, merging in a downstream section. We assessed the changes in decomposition rate and invertebrate community structure in leaf bags. We found no effect of ALAN or its interaction with flow reduction on the litter decomposition or the invertebrate community in the tributaries. Flow reduction alone led to a 14.8 % reduction in decomposition rate in the tributaries. We recorded no effect of flow reduction on the macroinvertebrates community composition in the litter bags. We also observed no effects of the spatial arrangement of the stressors on the litter decomposition and macroinvertebrate community structure downstream. Overall, our results suggest the impact of stressors on litter decomposition and macroinvertebrate communities remained local in our experiment. Our work thus calls for further studies to identify the mechanisms and the conditions under which spatial effects dominate over local processes.

Influence of non-uniform grid plates on the vortex-induced vibration performance of twin-box girder section

The wind resistance design of long-span bridges necessitates addressing the issue of vortex-induced vibration (VIV) and implementing appropriate counter measures to mitigate it. The present study focused on the examination and comprehensive analysis of a self-anchored suspension bridge. Wind tunnel tests were conducted on sectional models to analyze the effect of wind attack angles on the VIV performance of the girder. Moreover, the investigation examined the impact of opening slot ratio and the configuration of grid plates on the trigger mechanism and performance of VIV. From the results, it is observed that the main girder displays vertical VIV when the damping ratio reaches 0.25%. At wind attack angle of − 3°, 0°, and + 3°, the dimensionless maximum amplitude of the vertical VIV normalized by the height of the girder section, represented as ymax/D, is measured to be 0.032, 0.033, and 0.023 correspondingly. When the opening slot ratio of the grid plates reaches 50%, and the grid plates are non-uniformly arranged on the opening slot, that is the sides of the opening slot position, the vertical VIV becomes non-existent. Furthermore, it is observed that when the grid plates are arranged uniformly with the same opening slot ratio, the suppression effect on VIV is relatively worse and the dimensionless maximum amplitude of the vertical VIV is reduced to 0.013 from 0.032. The flow structure mechanism is that the upside airflow is separated at the windward edge of the girder section, leading to the formation of a large upper vortex. The upper vortices interact with the airflow passing through the upper and lower portions of the central slot, colliding with the top and bottom surfaces of the downstream section. Eventually, the vortices are shifted towards the tail side of the girder section and eventually shed, causing VIV. After implementing grid plates, vortices with a certain size still form at the gap. The grid plate effectively separates the vortices from the upper and lower sections of the girder, reducing their impact on the downstream section and optimizing the VIV performance of the main girder. These research findings could serve as a guide for designing the two-box girder section.

Algal or bacterial community: Who can be an effective indicator of the impact of reclaimed water recharge in an urban river

Reclaimed water has been widely utilized for water resource replenishment, yet little is known regarding its impacts on various microorganisms in the receiving water. To address this knowledge gap, we systematically investigated the responses of bacteria and algae to the recharge of reclaimed water by using the high-throughput sequencing technology in the urban Chaobai River. After the inputs of reclaimed water, lower contents of NO2−-N, NH4+-N, and TP were observed in the downstream section compared to that of upstream without reclaimed water, indicating that reclaimed water could improve the water quality of the receiving water. Correspondingly, both bacterial and algal communities showed the decreased network complexity in the downstream section, but many common freshwater bacteria and typical bloom-forming algae were dominant in the downstream, potentially suggesting that algae were more sensitive to the local environmental conditions. More importantly, although nitrogen and phosphorus served as the paramount factors in shaping both bacterial and algal communities, environmental selection contributed more to algal rather than bacterial community, and simultaneously algal variations could further affect bacterial dynamics in the urban river. Overall, these findings revealed distinct characteristics of bacteria and algae in responding to the reclaimed water recharge, highlighting the superiority of algae in indicating environmental changes, especially in monitoring and regulating the replenishment of reclaimed water in urban rivers.

Abundance, Distribution and Mortality of Hydrobionts in the Section of the Gorky Reservoir Affected by Heated Waters of the Kostroma Hydroelectric Power Plant

The study was conducted in the river section of the Gorky reservoir in the zone affected by the heated water discharge from the Kostroma hydroelectric power plant during the growing season (May–November) 2021. The reduced species richness was observed in the sites of the maximum water heating, which, however, quickly returned to the initial values in the downstream section of the river. The lethal effect of warm waters on zooplankton is mainly manifested in the summer, when the natural warming of the river waters is influenced by the heated water discharge from the Kostroma hydroelectric power plant. In autumn, the warming effect of heated waters, on the contrary, promotes better survival of organisms. Fish reach a high abundance in the study area by the end of summer, when the grown juvenile sleave shallow waters. In the autumn period, the fish redistribution and a significant increase in the abundance occur in the area of heated waters compared to the back ground sites. The results obtained indicate the absence of an environmentally significant lethal effect. Local plankton losses are quickly compensated due to high reproduction rates and short-cycle development of invertebrates. The lethal effect of exposure to high temperatures on fish was not found.

Evolution Characteristics of Long Time Series of Secondary Perched River in Typical Reaches of the Lower Yellow River

Secondary perched rivers are extensively distributed in the lower section of the Yellow River, and their condition is grave, representing a significant peril to the flood control safety of this region. Consequently, conducting an analysis of their evolution characteristics holds immense engineering importance for ensuring the flood control safety of the lower reaches of the Yellow River. This study focuses on the downstream section of the Yellow River, specifically from Dongbatou-Taochengpu. This research is based on extensive data, including topographic measurements of large cross-sections and water and sand data from Huayuankou spanning from 1960 to 2022. The transverse slope of the beach, which indicates the level of development of the secondary perched rivers, was chosen as the calculation index. To analyze the trend and mutation of the transverse slope, statistical methods such as the Theil–Sen slope estimation, Mann–Kendall test, Pettitt test, and double cumulative curve method were employed. The findings indicate that the average transverse slope along the wandering section (Dongbatou-Gaocun) is 5.81‱, is significantly lower compared to the transitional section (Gaocun-Taochengpu), with an average transverse slope of 8.89‱. Furthermore, the range of fluctuation in the variation in the transverse slope along the wandering section (3.19–8.18‱) is considerably narrower than that observed in the transitional section (2.94–19.51‱). Prior to the implementation of Xiaolangdi, there was a significant increase in the transverse slope. Notably, the transitional section experienced a sudden change in 1975, while the wandering section experienced a sudden change in 1990. The abrupt alteration in the transitional section can be attributed to the substantial variation in the water and sand conditions. Conversely, the sudden change in the wandering section resulted from the insufficient flow rate of the flat beach. However, following the implementation of Xiaolangdi, the rapid increase in the transverse slope was effectively mitigated.

Local environmental and spatial factors are associated with multiple facets of riverine fish β‐diversity across spatial scales and seasons

Abstract Disentangling the factors governing community structure across various spatial and temporal scales is a core task in community ecology and biogeography, because it could provide valuable insights into biodiversity conservation and management. The relative role of environmental (a proxy for niche‐based mechanism) and spatial (a proxy for dispersal) effects in shaping ecological communities depends on diversity facets, network positions, seasonality and biological characteristics of the focal organisms. However, such patterns are not well understood for fish communities in large river systems, especially if all of these patterns are examined simultaneously. We investigated fish taxonomic, functional and phylogenetic total β‐diversity (and their turnover and nestedness phenomena) at different spatial scales (basin vs. section scales) and seasons (wet vs. dry seasons) in a subtropical river system (the Chishui River basin, China). We also quantified the relative importance of environmental variables and spatial factors in shaping fish β‐diversity by using generalised dissimilarity modelling. At the basin scale, fish taxonomic and phylogenetic β‐diversity across seasons mainly reflected turnover, yet turnover and nestedness contributed likewise to total functional β‐diversity. Taxonomic and phylogenetic β‐diversity were strongly correlated (r from 0.39 to 0.87), whereas functional and both taxonomic and phylogenetic facets were relatively weakly correlated (r from 0.27 to 0.65). Generalised dissimilarity modelling suggested that phylogenetic β‐diversity phenomena were consistently more influenced by environmental variables (wet 16.1%, dry 22.4%) than by spatial factors (wet 6.7%, dry 4.8%). However, for both taxonomic and functional facets, environmental variables (turnover 13.8%, nestedness 6.4%) and spatial factors (turnover 4.3%, nestedness 9.4%) accounted for a greater proportion of variations in turnover and nestedness, respectively. At the section scale, only phylogenetic total β‐diversity and nestedness, as well as taxonomic nestedness significantly differed between the headwater and downstream sections. Furthermore, headwater communities were primarily explained by spatial (15.7%) and environmental (12.7%) variables in the wet season, while environmental factors (25.9%; spatial 7.7%) dominated in the dry season. By contrast, downstream communities were more influenced by environmental factors (17.9%; spatial 8.3%) in the wet season, whereas environmental (11.0%) and spatial variables (11.5%) contributed likewise to β‐diversity in the dry season. Our results highlight that, compared with taxonomic β‐diversity, accounting for turnover and nestedness of functional and phylogenetic β‐diversity helps to reveal distinct biodiversity patterns, and potential environmental and spatial controls. Given that community–environment relationships and the relative contribution of environmental and spatial factors varied between seasons and between the basin and section scales, our study underlines the importance of long‐term dynamics and spatial scales in metacommunity studies. Our findings also suggest that maintaining environmental heterogeneity and adequate hydrological connectivity would be essential for the conservation of fish diversity. Overall, our study advances current knowledge of fish biodiversity patterns and their maintenance mechanisms by adding insights from multi‐faceted diversity and seasonality, which has rarely been done in large subtropical rivers.

Torrential Hazards’ Mitigation Measures in a Typical Alpine Catchment in Slovenia

Different sediment-related disasters due to torrential hazards, such as flash floods, debris flows, and landslides, can occur in an Alpine torrential catchment. When protecting infrastructure and human lives, different structural and non-structural protection measures can be used to mitigate permanent and future risks. An overview of the mitigation measures constructed near the Krvavec ski resort in northwest Slovenia (Central Europe) is presented. In May 2018, an extreme debris flood occurred in this area, causing significant economic damage. After the May 2018 event, different field investigations (i.e., geological and topographic surveys) and modeling applications (e.g., hydrological modeling, debris flow) have been conducted with the purpose of preparing the required input data for the design of protection measures against such disasters in future—due to climate change, more disasters are expected to happen in this torrential watershed. The mitigation includes the restoration of local streams, the construction of a large slit check dam for sediment retention, the construction of several smaller check dams and the construction of 16 flexible net barriers with an estimated ~8000 m3 retention volume for controlling in-channel erosion in steep torrential streams. Additionally, in order to observe and monitor potential future extreme events, an extensive monitoring system has been established in the investigated area. This monitoring system will cover measurements of flexible net corrosion, the estimation of concrete abrasion at check dams, periodical geodetic surveys using small drones (UAV), hydro-meteorological measurements using rainfall gauges and water level sensors. The recent extreme floods of August 2023 also hit this part of Slovenia, and this combination of technical countermeasures withstood the event and prevented large amounts of coarse debris from being transported to the downstream section and devastating infrastructure, as was the case in May 2018 during a less extreme event. Therefore, such mitigation measures can also be used in other torrential catchments in the Alpine environment.

A novel design of heat recovery system from exhaust stacks' silencers in a simple cycle gas turbine

This paper aims to evaluate the potential of heat recovery from the integrated heat exchanger within the exhaust stack silencer baffles in a simple cycle gas turbine. Heat transfer channels were incorporated into the upstream (nose) and downstream (tail) sections of the parallel silencer baffles in the exhaust stack. The gas turbine exhaust gas represents the hot side flow across the baffles' sections. The integrated heat exchanger system offered an advantage of extracting waste heat from the exhaust stream, while reducing pressure drop on the flow and improving acoustic attenuation.In this work, a series of parametric studies were carried out across a range of internal and external heat transfer area configurations within the silencers to maximize the heat transfer. Further enhancement opportunities were introduced and discussed based on the conducted parametric studies and practical aspects borne out of common industry practice. The proposed heat recovery system was implemented to power the gas fuel performance heater which is used to enhance the gas turbine cycle performance through utilization of the extracted waste heat while keeping lower exhaust pressure drop in the stack.The obtained results showed that the proposed integrated heat exchanger within the silencers has a potential of generating a 5.48 MW net gain from the gas turbine exhaust stacks which are normally lost to the atmosphere from the simple cycle exhaust stack. The proposed heat recovery system proved significant fuel savings that lead to economic benefits and reduction in CO2 emissions.

Hydrologic and Organic Carbon Quality Controls on Nitrous Oxide Dynamics Across a Variably Confined Karst Aquifer

AbstractAtmospheric concentrations of the potent greenhouse gas nitrous oxide (N2O) have increased approximately 20% since the pre‐industrial era. Riverine systems represent an important atmospheric source of N2O however, the influence of varying hydrogeological conditions and dissolved organic carbon (DOC) quantity and quality on N2O dynamics remains poorly understood. We investigate effects of these processes on N2O dynamics in the Santa Fe River watershed in north‐central Florida, USA where a gradient in DOC quantity and quality is caused by varying surface water‐groundwater exchange. The watershed is underlain by the karstic Floridan aquifer, which is confined in the headwaters and contains terrigenous recalcitrant DOC, while the unconfined lower reaches contain protein‐like labile DOC substrates. Where extensive surface water‐groundwater exchange occurs at the boundary between the confined and unconfined aquifer, incomplete denitrification raises N2O concentration to 6.1 μg N‐N2O L−1, approximately 20 times greater than the concentration expected from equilibration with atmospheric N2O. These elevated concentrations create average local fluxes reaching ∼950 μg N‐N2O m−2 hr−1 within the mixing zone. Summation of spatially explicit emission estimates for upstream, mixing zone, and downstream river sections yield a total average emission rate of ∼3,758 kg N‐N2O yr−1. Despite having the smallest surface area across the river transect (∼8%), emissions from the mixing zone account for 26% of the total river emission rate. These findings highlight the potential contributions from karst landscapes to N2O cycling caused by varying redox conditions during surface water‐groundwater exchange, which creates hotspots of N2O production and emissions.