Search Results (2,233)

Bacterial sourcing in urban watersheds is a critical water quality concern because elevated index bacteria concentrations routinely trigger beach advisories and closures in coastal Southern California and elsewhere. This study evaluates diurnal controls on dry-weather bacterial loading in a groundwater-fed storm drain within the Malibu Creek watershed using a 24 h monitoring campaign. Discharge, nutrients, major ions, stable water isotopes, and index bacteria (total coliforms and Escherichia coli) were measured at six time intervals. Storm drain discharge varied by more than an order of magnitude, with rapid nighttime increases of up to +91 L/min during irrigation periods. Total Dissolved Solids ranged from 1276 to 2175 mg/L, peaking during groundwater-dominated low-flow conditions. Nitrate–N ranged from 1.08 to 2.96 mg/L, and orthophosphate from 0.44 to 2.16 mg/L, with nutrient concentrations increasing as irrigation inputs increased. Total coliform concentrations ranged from 13,000 to 670,000 MPN/100 mL, and E. coli ranged from 300 to 120,000 MPN/100 mL, exceeding concentrations in tap water and recycled water runoff by up to two orders of magnitude. End member mixing analysis showed that storm drain flow consisted of approximately 45% groundwater, 23–26% tap water, and 30–33% recycled water during early morning peak flow, shifting to ~56% groundwater and <12% recycled water by mid-morning. The lowest bacterial concentrations occurred during groundwater-only flow, while the largest bacterial increases coincided with the greatest positive changes in discharge rather than with maximum absolute flow. These results support an irrigation-driven biofilm stripping mechanism as the dominant control on dry-weather bacterial loading, with groundwater seepage sustaining biofilm persistence but not peak bacterial release. The findings highlight the importance of internal storm drain processes for managing coastal bacterial exceedances and protecting beach health. Full article

Based on true triaxial loading experiments and particle flow numerical simulations (PFC3D), this study systematically analyzes the mechanical behavior and failure mechanisms of granite under the influence of stress difference (deviatoric stress). The experimental results indicate that increasing deviatoric stress reduces peak strength, axial strain, and lateral strain, promoting rock failure with less deformation and dilatancy. An energy analysis reveals that higher deviatoric stress suppresses peak energy accumulation, with a greater proportion of energy being dissipated through crack initiation and propagation. Macroscopic observations show that failure surfaces develop combined tensile-shear cracks, evolving into distinct “V” shapes as deviatoric stresses increase. Numerical simulations demonstrate that intermediate principal stress plays a dual role, initially facilitating, then inhibiting, and finally promoting rock failure with its continuous increase. Microscopically, tensile cracks dominate during pre-peak stages, while rapid crack coalescence in the post-peak stage leads to the formation of throughgoing V-shaped failure zones. Particle displacement analysis reveals that deformation concentrates along the minimum principal stress direction, with the displacement vectors ultimately forming a V-shaped boundary that delineates the failure zone. The research provides comprehensive insights into the macro-meso failure characteristics of hard rock under true triaxial conditions, offering valuable guidance for stability prediction and control in underground rock engineering projects such as water-sealed storage caverns. Full article

This study aims to address the limitations of dense polyvinylidene fluoride (PVDF) membranes grafted with vinyl ethyl imidazole tetrafluoroborate, which exhibit low hydrophilicity and ionic conductivity in vanadium redox flow batteries (VRFBs). To improve these properties, water-soluble β-cyclodextrin was introduced as a porogen to fabricate asymmetric porous membranes. The porous structure was controlled by varying the porogen content (10–50 wt%), and the resulting membranes were characterized using FTIR, SEM, TGA, and electrochemical tests. This unique architecture led to a significant enhancement in ionic conductivity (to 71.69 mS/cm, from 6.73 mS/cm for the dense membranes), porosity (up to 40.24%), and water uptake (up to 31.8%), while maintaining robust mechanical strength (tensile strength 14.96 MPa) suitable for VRFB assembly and operation. In single-cell performance tests across a range of current densities, clear trends emerged: Coulombic efficiency (CE) decreased with higher porosity, whereas voltage efficiency (VE) followed the opposite trend. Consequently, the optimal energy efficiency (EE) was achieved with the intermediate porogen content, successfully balancing conductivity and selectivity. This work demonstrates a green and scalable approach to developing high-performance porous membranes for VRFB applications. Full article

Riverbed topography in natural rivers commonly features sand dunes, whose morphological variations can alter the turbulent flow structure near the bed and thereby affect processes of channel scour, deposition, and sediment transport. In this study, a series of flume experiments was conducted using an acoustic Doppler velocimeter (ADV) to simulate fixed bedforms of different dune scales (ratio of wavelength to flow depth, λ/h) in a laboratory flume. Velocity measurements were taken along the water depth at the dune crest and trough for each test case. The near-bed distributions of mean flow velocity, Reynolds stress, turbulent kinetic energy (TKE), and turbulence intensity were obtained at the crest and trough under three flow conditions, allowing analysis of the vertical decay of turbulence intensity at different locations on the dune. The results show that the dune steepness (Ψ, defined as dune height over wavelength) is a key parameter controlling the near-bed flow structure. As Ψ increases, the near-bed velocity gradient, Reynolds stress, TKE, and peak turbulence intensity all increase significantly, with the peak positions shifting closer to the bed. The trough region, due to flow separation and vortex shedding, exhibits substantially higher values of all turbulence-related parameters than the crest, making it the primary zone of energy dissipation and turbulence production. This study provides experimental evidence and theoretical reference for understanding the mechanism by which sand dune morphology influences flow structure, and it offers insight for predicting riverbed evolution. Full article

Understanding the behavior of light non-aqueous phase liquids (LNAPLs) in urban subsurface environments is essential to developing effective pollution control strategies, designing remediation systems, and managing waste and resources sustainably. Oil leakage from urban industrial facilities, underground pipelines, and fueling systems often leads to contamination that is challenging to characterize due to complex soil structures, limited access beneath densely built infrastructure, and dynamic groundwater conditions. In this study, we integrate a large-scale soil tank experiment with multiphase flow simulations to elucidate LNAPL distribution mechanisms under fluctuating groundwater conditions. A 2.4-m-by-2.4-m-by-0.6-m soil tank was used to visualize oil movement with high-resolution multispectral imaging, enabling a quantitative evaluation of saturation distribution over time. The results showed that a rapid rise in groundwater can trap 60–70% of the high-saturation LNAPL below the water table. In contrast, a subsequent slow rise leaves 10–20% residual saturation within pore spaces. These results suggest that vertical redistribution caused by groundwater oscillation significantly increases residual contamination, which cannot be evaluated using static groundwater assumptions. Comparisons with a commonly used NAPL simulator revealed that conventional models overestimate lateral spreading and underestimate trapped residual oil, thus highlighting the need for improved constitutive models and numerical schemes that can capture sharp saturation fronts. These results emphasize that an accurate assessment of LNAPL contamination in urban settings requires an explicit consideration of groundwater fluctuation and dynamic multiphase interactions. Insights from this study support rational monitoring network design, reduce uncertainty in remediation planning, and contribute to sustainable urban environmental management by improving risk evaluation and preventing the long-term spread of pollution. Full article

Instability in dump slopes frequently induces landslides, a process governed by complex factors. To investigate the impact of gradation composition on dump slope stability, four distinct gradations were designed, and large-scale laboratory triaxial tests were conducted to characterize their strength and deformation behaviors under varying confining pressures. Concurrently, numerical models of dump slopes with these four gradations were established using Particle Flow Code (PFC) to simulate rainfall infiltration processes. Through a comparative analysis of particle contact force chains, pore water pressure evolution, particle displacement under varying rainfall durations, and safety factors under natural and rainfall conditions, the mechanisms governing the influence of gradation composition on slope stability were elucidated from both macroscopic and microscopic perspectives. Results indicate the following: (1) Gradation composition significantly affects the strength and deformation characteristics of dump materials. Sample group 3 (with a fine-to-coarse particle ratio of 4:6) exhibited the highest strength among the four test samples, with peak deviatoric stresses of 610 kPa, 1075 kPa, and 1539 kPa under confining pressures of 200 kPa, 400 kPa, and 600 kPa, respectively. Its corresponding shear strength parameters were a cohesion of 38.45 kPa and an internal friction angle of 32.55°. In contrast, sample group 4 (fine-to-coarse ratio of 6:4) showed the lowest strength, with peak deviatoric stresses of 489 kPa, 840 kPa, and 1290 kPa under the same confining pressures, and shear strength parameters of c = 25.35 kPa and φ = 30.02°. (2) Gradation modulates contact forces and failure modes via a “skeleton-filling” mechanism. (3) Gradation plays a critical role in controlling pore water pressure evolution and the seepage characteristics of the dump slope model. Among the four designed gradations and their corresponding numerical models, Model 3 was characterized by the highest contact forces and the lowest pore water pressure. It exhibited the highest stability under both natural and rainfall conditions, with safety factors of 1.70 and 1.22, respectively. Conversely, Model 4 showed weak particle contact forces and high pore pressure, demonstrating the poorest stability. It yielded safety factors of only 1.25 and 1.02 under natural and rainfall-saturated conditions, indicating that it represents the least favorable gradation composition. These findings provide valuable references for the optimization of dumping processes and stability control in similar engineering projects. Full article

Enhanced oil recovery (EOR) in fractured reservoirs presents significant challenges due to fluid channeling and poor sweep efficiency. In this study, a synergistic EOR system was developed with polymer-based weak gel as the primary component and foam as the auxiliary enhancer. The system utilizes a low-concentration polymer (1000 mg·L⁻¹) that forms a weakly cross-linked three-dimensional viscoelastic gel network in the aqueous phase, inheriting the core functions of viscosity enhancement and profile control from polymer flooding. Foam acts as an auxiliary component, leveraging the high sweep efficiency and strong displacement capability of gas in fractures. These two components synergistically create a multiscale enhancement mechanism of “bulk-phase stability control and interfacial-driven displacement.” Systematic screening of seven foaming agents identified an optimal formulation of 0.5% SDS and 1000 mg·L⁻¹ polymer. Two-dimensional visual flow experiments demonstrated that the polymer-induced gel network significantly improves mobility control and sweep efficiency under various injection volumes (0.1–0.7 PV) and gravity segregation conditions. Numerical simulation in a 3D fractured network model confirmed the superiority of this enhanced system, achieving a final oil recovery rate of 75%, significantly outperforming gas flooding (65%) and water flooding (59%). These findings confirm that weakly cross-linked polymer gels serve as the principal EOR material, with foam providing complementary reinforcement, offering robust conformance control and enhanced recovery potential in fracture-dominated reservoirs. Full article

Abrasive water jet machining (AWJM) is a non-traditional machining process that is increasingly employed for shaping hard-to-machine materials, particularly titanium (Ti)-based alloys such as Ti-6Al-4V. Owing to its non-thermal nature, AWJM enables effective material removal while minimising metallurgical damage and preserving subsurface integrity. The process performance is governed by several interacting parameters, including jet pressure, abrasive type and flow rate, nozzle traverse speed, stand-off distance, jet incident angle, and nozzle design. These parameters collectively influence key output responses such as the material removal rate (MRR), surface roughness, kerf geometry, and subsurface quality. The existing studies consistently report that the jet pressure and abrasive flow rate are directly proportional to MRR, whereas the nozzle traverse speed and stand-off distance exhibit inverse relationships. Nozzle geometry plays a critical role in jet acceleration and abrasive entrainment through the Venturi effect, thereby affecting the cutting efficiency and surface finish. Optimisation studies based on the design of the experiments identify jet pressure and traverse speed as the most significant parameters controlling the surface quality in the AWJM of titanium alloys. Recent research demonstrates the effectiveness of artificial neural networks (ANNs) for process modelling and optimisation of AWJM of Ti-6Al-4V, achieving high predictive accuracy with limited experimental data. This review highlights research gaps in artificial intelligence-based fatigue behaviour prediction, computational fluid dynamics analysis of nozzle wear mechanisms and jet behaviour, and the development of hybrid AWJM systems for enhanced machining performance. Full article

Discontinuous phase flooding (such as polymer microspheres) is an important method for enhancing oil recovery. With the hydration swelling and elastic properties, a unique “migration–entrapment–remigration” discontinuous flow behavior is identified during flooding. And a more pronounced conformance control effect is observed in high-permeability flow channels and deeper reservoir regions compared to continuous phase flooding. These complex seepage mechanisms pose significant challenges to reservoir numerical simulation. Based upon a chemical reaction framework, a multi-component mathematical model comprising oil, gas, water, pre-discontinuous phase, and discontinuous phase components is developed in this study. The discontinuous phase is generated through chemical reactions involving the pre-discontinuous phase. A minimum reaction porosity is first introduced in the chemical reaction process to enhance the discontinuous phase generation in high-permeability regions. A threshold pressure is incorporated into the discontinuous phase equation for the “migration–entrapment–remigration” discontinuous flow characteristics. The model is subsequently solved using a fully implicit finite volume method. A new numerical simulator implementing this approach is developed in C++. Validation through physical experiments confirms the method’s accuracy. The discontinuous migration process of “migration–entrapment–remigration” is clearly reflected through the injection pressure fluctuations during simulation. Mechanistic models and field-scale simulations both confirm that discontinuous phase flooding significantly enhances oil recovery efficiency, outperforming both water flooding and continuous phase flooding. The novel reaction specification enhances conformance control in high-permeability channels, as demonstrated by the simulation results. The proposed model accurately captures the migration characteristics of the discontinuous phase and holds important practical value for reservoirs with discontinuous phase flooding. Full article

Climate change is steadily reshaping hydrological regimes, and one of its clearest consequences is the growing disruption of the biogeochemical pathways that govern water quality across river basins. More frequent high-intensity rainfall events, prolonged dry spells, and shifts in seasonal runoff patterns are altering the timing and magnitude of nutrient, organic matter, sediment, and contaminant fluxes. These pulses of material often originate from short-lived episodes of enhanced connectivity between soils, groundwater, and surface waters, making water-quality responses more variable and harder to anticipate than in previous decades. This review describes the ecohydrological mechanisms underlying these changes, focusing on threshold behaviors, the functioning of transitional zones such as riparian corridors and floodplains, and the cumulative effects of legacy pollution. We also discuss the capacity of nature-based solutions (NbS) to buffer climatic pressures. Although NbS can improve retention and moderate peak flows, their performance proves highly sensitive to hydrological variability and landscape context. In the final part, we describe tools that can strengthen adaptive water-quality management, including high-frequency monitoring, event-focused early-warning systems, and modeling approaches that integrate hydrology with biogeochemical processing. This article addresses ecohydrological pathways for water quality under climate change and presents nature-based solutions for regulating pollutant flows within a general framework. Data from North America and Europe, among other areas, are used as primary examples. However, it is important to remember that the issues and proposed solutions vary depending on landscape conditions and climatic zones, which vary across the globe. This article provides an overview of the most common solutions. Full article

The Xinding Basin is located in the high-heat-flow geothermal anomaly zone in the north-central part of China. Revealing the geothermal origin mechanism of the basin is of great significance for filling the measurement gap in heat flow values in China and providing a scientific basis for the evaluation and utilization of regional geothermal resources. Based on the hydrogeochemical characteristics of thermal reservoirs and borehole data in the Xinding Basin, this paper analyzes water–rock interaction process between geothermal water and heat reservoirs and discusses the types of geothermal systems in the basin. The results indicate that the fault structures in the basin are well-developed. The hydrochemical type of typical geothermal fields is dominated by the Cl·SO₄-Na type. Geothermal water is mainly immature water and receives recharge from shallow cold water with relatively rapid circulation. The discovered magma intrusion residues in the basin indicate that sections of the upper mantle with a shallow burial depth serve as the dynamic heat sources for regional thermal reservoirs. Intense extensional stretching in the Cenozoic Era resulted in high terrestrial heat flow values and an upward arching phenomenon of the Curie isothermal surface in the basin. Neotectonic movement is active in the basin. The regional geothermal reservoirs in the Xinding Basin occur in the glutenite beds of the Cenozoic Erathem and the rock formations of the New Archaean Erathem. The thick-layered Cenozoic loose sediments serve as the thermal cap rocks in this area. An efficient heat-convergent geothermal system integrating a heat source, heat channel, thermal reservoir, and cap rock (the “four-in-one” system) has promoted the formation of geothermal resources in the Xinding Basin. Full article

Although blood transfusion eco-compensation—a metaphorical term in the Chinese eco-compensation literature referring to short-term direct compensation—can balance stakeholder interests in securing ecological flows (e-flows) in water-scarce rivers, it often fails to enhance the productivity of disadvantaged stakeholders or expand long-term development opportunities. To overcome this limitation, this study introduces hematopoiesis eco-compensation, a metaphorical term for capacity-building, longer-term development-oriented compensation that improves irrigation water-use efficiency and agricultural productivity through water-saving infrastructure upgrades, enhanced irrigation technologies, and technical training. Based on this distinction, we developed a hybrid eco-compensation mechanism integrating the two approaches using a cost–expenditure method and applied it to the mainstream section of the Weihe River and the Baojixia Yuanshang Irrigation District in Northwest China under typical hydrological conditions. The main findings are as follows: (1) Compensation standards for both approaches increase with higher ecological flow targets, with average values of 2762 CNY ha⁻¹ and 1386 CNY ha⁻¹, respectively. (2) The two approaches differ in terms of participants, standards, and implementation methods, yet they are complementary and indispensable under current conditions. (3) Hematopoiesis eco-compensation generates positive ecological and economic effects, increasing the annual value of riverine ecosystem services by approximately 126 million CNY and the annual economic benefits of the irrigation district by approximately 467 million CNY. This study provides a theoretical foundation and practical guidance for establishing long-term compensation mechanisms to maintain ecological flows in water-scarce regions. Full article

Declining recovery factors from mature oil fields, coupled with the technical challenges of recovering residual oil under harsh reservoir conditions, necessitate the development of advanced enhanced oil recovery (EOR) techniques. While promising, chemical EOR often faces economic and technical hurdles in high-salinity, high-temperature environments where conventional polymers like hydrolyzed polyacrylamide (HPAM) degrade and fail. This study presents a comprehensive numerical investigation that addresses this critical industry challenge by applying a rigorously calibrated simulation framework to evaluate a novel hybrid EOR process that synergistically combines an ionic liquid (IL) with HPAM polymer. Utilizing core-flooding data from a prior study that employed the same Berea sandstone core plug and Saudi medium crude oil, supplemented by independently measured interfacial tension and contact angle data for the same chemical system, we built a core-scale model that was history-matched with RMSE < 2% OOIP. The calibrated polymer transport parameters—including a low adsorption capacity (~0.012 kg/kg-rock) and a high viscosity multiplier (4.5–5.0 at the injected concentration)—confirm favorable polymer propagation and effective in -situ mobility control. Using this validated model, we performed a systematic optimization of key process parameters, including IL slug size, HPAM concentration, salinity, temperature, and injection rate. Simulation results identify an optimal design: a 0.4 pore volume (PV) slug of IL (Ammoeng 102) reduces interfacial tension and shifts wettability toward water-wet, effectively mobilizing residual oil. This is followed by a tailored HPAM buffer in diluted formation brine (20% salinity, 500 ppm), which enhances recovery by up to 15% of the original oil in place (OOIP) over IL flooding alone by improving mobility control and enabling in-depth sweep. This excellent history match confirms the dual-displacement mechanism: microscopic oil mobilization by the IL, followed by macroscopic conformance improvement via HPAM-induced flow diversion. This integrated simulation-based approach not only validates the technical viability of the hybrid IL–HPAM flood but also delivers a predictive, field-scale-ready framework for heterogeneous reservoir systems. The work provides a robust strategy to unlock residual oil in such challenging reservoirs. Full article

Understanding how nanocomposite gels regulate pore–throat structures and flow behavior is essential for improving profile control and flow diversion in deep-water tight reservoirs. In this study, a dual-structure-regulated nanocomposite gel (DSRC-NCG) was designed, and its structure–flow coupling behavior during gel injection, curing, and degradation was systematically investigated using multiscale flow configurations, including microfluidic models, artificial cores, and sandpack systems. Microstructural evolution and pore–throat connectivity were characterized using μCT imaging, mercury intrusion porosimetry, nitrogen adsorption, and image-based flow simulations, while macroscopic flow responses were evaluated through permeability variation, dominant-channel evolution, injectivity behavior, and quantitative indices including the structure regulation index (SRI) and pore–flow matching index (HCI). The results show that increasing SiO₂ content induces a progressive optimization of pore–flow matching by refining critical throats and suppressing preferential flow channels, whereas excessive nanoparticle loading leads to aggregation and attenuation of these effects. This study proposes a multiscale structure–flow coupling framework that quantitatively connects pore–throat regulation with macroscopic flow responses during nanocomposite gel injection and degradation. These findings offer mechanistic insights and practical guidance for the design of nanocomposite gels with improved flow-regulation efficiency and reversibility in deep-water tight reservoir applications. Full article

This study aims to investigate the feasibility and performance effects of using waste chestnut shells (CNS), derived from agricultural biomass, as a filler replacement material in hot mix asphalt mixtures. The influence of CNS on the mechanical behavior of hot mix asphalt mixtures was evaluated through a comprehensive experimental program. Initially, the physical and conventional properties of the B50/70 asphalt binder, aggregates, and CNS material were characterized to establish a reference framework for mixture design. The optimum asphalt content (OAC) for the control mixture was established using the Marshall mix design procedure. Mixture specimens incorporating CNS were produced by introducing the material at four different proportions, corresponding to filler substitution levels ranging from 5% to 20% by weight. The prepared specimens were evaluated through a series of mechanical and durability-related tests, including Marshall stability and flow, Retained Marshall, moisture damage, dynamic creep stiffness, indirect tensile strength (ITS), fatigue performance, and indirect tensile stiffness modulus (ITSM). The results indicated that mixtures with 10% CNS replacement exhibited notable improvements in stability, water sensitivity, ITS, ITSM, dynamic creep, and fatigue resistance, suggesting that CNS has the potential to enhance the performance characteristics of hot mix asphalt pavements. Full article