High Flow Conditions Research Articles

Fluid Dynamic and in Vitro Blood Study to Understand Catheter-Related Thrombosis.

Central venous catheters (CVCs) provide a direct route to the venous circulation but are prone to catheter-related thrombosis (CRT). A known CRT risk factor is a high catheter-to-vein ratio (CVR), or a large catheter diameter with respect to the indwelling vein size. In this study, the CVR's effect on CVC hemodynamics and its impact on CRT is investigated with in vitro and in silico experiments. An in vitro flow loop is used to characterize the hemodynamics around CVCs using particle image velocimetry. In addition, CRT is investigated using an in vitro flow loop with human blood and clinical catheters. The wall shear rate of flow around the CVC is computed numerically. CVRs of 0.20, 0.33, and 0.49 and Reynolds numbers of 200, 800, and 1300 are evaluated. No flow is used through CVC lumens to model chronic indwelling catheters. Results show CVR ≥ 0.33 promotes platelet-rich clot growth at the device tip and at an increased rate compared to lower CVR cases. A high wall shear rate gradient on the CVC tip and an extended wake distal to the tip exists for higher CVR cases, promoting the aggregation of platelets and subsequent stagnation for clot formation. Further, the combination of the CVR and Reynolds number are crucial to CRT potential, not the CVR alone. Specifically, thrombosis risk is increased with low (stasis driven) and/or high (platelet activation driven) flow conditions, with the CVR and CVC's geometry playing an additional role in promoting fluid mechanic driven thrombus development. A high CVR (≥ 0.33) and high flow condition (≥ 1300) results in the highest risk for clot growth at the tip of the device; other locations of the device are at risk for thrombus development in lower flow conditions, regardless of the CVR. The importance of the device geometry and flow in promoting thrombus and fibrin sheath formation is also shown for the device investigated. This work demonstrates that the CVR, flow, and device geometry affect CRT. For clinical cases with CVR ≥ 0.33 and/or Re ≥ 1300, the device tip may be monitored more consistently for clot formation. Thrombosis risks remain on the entire catheter, regardless of the flow condition, for a CVR = 0.49. Device placement should be chosen carefully with respect to the combination of the Reynolds number and CVR. Further study is needed on the effect of catheterization to confirm these findings.

The effect of stress history on the critical shear stress of bedload transport in gravel-bed streams

Critical shear stress is a pivotal parameter that describes the bedload transport and riverbed stability. Recent studies indicate that different interevent periods in gravel-bed streams can lead to a realignment of riverbed structures, thereby disrupting the bedload transport. In this research, a series of flume experiments were conducted to study the effect of stress history on the critical shear stress of bedload transport in a gravel-bed channel. The results reveal the temporal-spatial variation patterns of critical shear stress. The critical shear stress has an increased trend after interevent with low flow and long duration. Conversely, a decreasing trend in critical shear stress observed after low flow and short duration conditions. After interevent durations with medium to high flow condition, no matter the duration, critical shear stress shows a decreasing trend. A significant positive correlation between the flow magnitude of the interevent period and the critical shear stress of the subsequent flood period is shown. Besides, critical shear stress has a significant spatial variation pattern on the gravel bed due to the presence of microtopography as revealed by the correlation analysis results among the spatial density of microtopography with different protrusion heights, riverbed statistical parameters, and critical shear stress. Moreover, the stress history, by adjusting the position of fine particles on the riverbed surface through different magnitudes and durations of the interevent period, affects the spatial density of the microtopography, thereby influencing the critical shear stress. The conventional bedload transport equations are deficit by only considering the riverbed slope or standard deviation of bed surface elevation. An optimization of the critical shear stress calculation method, based on parameter correlation analysis, is proposed, potentially enhancing the calculation accuracy of bedload transport in mountainous rivers.

Piano Key Weir (PKW)—Improvement in Conventional Geometry for Augmented Discharge Capacity

The conventional piano key weir (PKW), characterized by a rectangularly cranked planform, is an effective discharge structure. Its hydraulic performance is primarily influenced by several geometrical parameters, including crest length, key width, and weir height. To enhance its hydraulic efficiency, each key is modified with an isosceles triangle at both the crest and the vertical base surface. In this way, the weir crest is extended both up and downstream; the key floor is lowered accordingly, resulting in a triangular prism-shaped floor. Laboratory tests are conducted to compare the hydraulic performance of this modified weir with that of the standard design. The results demonstrate that the geometrical adjustments noticeably improve the overflow discharge. With an equilateral triangle extending the crest length by ~23%, the discharge capacity is enhanced by 16–20% within the examined flow conditions. The modified weir outperforms the conventional design in terms of hydraulic performance. The improvements can be attributed to several factors: elongated crest length enhancing the flow capacity; triangular upstream overhangs improving the inflow condition along the inlet key’s height; lowered inlet key floor increasing the flow volume, promoting better flow movement towards the crest; lowered outlet key floor reducing the submergence effect under high flow conditions; and the triangular crest of the inlet key facilitating jet spreading and promoting air entrainment. These modifications make the redesigned PKW a promising option for improved hydraulic performance in engineering applications.

Task-Driven Tailored Covalent Organic Framework for Dynamic Capture of Trace Radioactive CH3 131I under High-Flow Rate Conditions.

The removal of radioactive gaseous iodine is crucial for sustainable nuclear energy development, safe spent fuel management, and secure disposal of radioactive waste and radioactive medical waste. However, the efficient capture of gaseous iodine, particularly methyl iodide, under conditions of low concentration and high-flow rate that are representative of real-world scenarios remains underexplored. Herein, we adopted a "theory-first" strategy to design adsorbents with a superior affinity for methyl iodide. The rigorous theoretical calculations for both physisorption and chemisorption have guided us to rationally design a piperazine-based covalent organic framework material (Pip-COF, Pip = piperazine). The pioneering hot-testing under dynamic conditions, featuring low concentrations of 5 ppm radioactive CH3 131I and a high-flow rate of 600 mL/min, demonstrated Pip-COF's exceptional capture performance. Pip-COF exhibits saturated capacities of 39 mg/g at 75 °C and 78 mg/g at 25 °C, significantly outperforming the previously reported best COF (COF-TAPT, 6 mg/g at 25 °C) in this scenario. The gradual process of methylation and the identification of specific high-affinity sites were elucidated by time-resolved FT-IR spectroscopy and density functional theory (DFT) analysis, consistent with the design philosophy. This study exemplifies rational material design in facilitating the separation of trace pollutants in challenging environments.

Influence of NH3 flow rate on the photoelectric properties of high Al content p-AlGaN.

High Al content (60%) p-AlGaN with different NH3 flow rates was grown using metal-organic chemical vapor deposition (MOCVD), and changes in its photoelectric properties were studied using the Hall effect tester (Hall) and cathodoluminescence (CL) spectrometer. The results show that the film resistivity increases from 3.8 Ω·cm to 46.5 Ω·cm with increasing NH3 flow rate. The impurity peak intensity of p-AlGaN grown under high NH3 flow conditions is particularly high, indicating numerous point defects. The results of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) show a large number of Ga interstitial atoms (Gai) at the interface. As Gai acts as a donor, this may be the main reason for the increase in resistivity. And under high NH3 flow conditions, a lattice distortion and a high density of dislocation occur between p-AlGaN and p-GaN, which can lead to enhanced carrier scattering and decreased mobility. Additional validation via LED growth experiments indicates that the luminescence intensity of samples with low ammonia concentration increased by more than 13000 times.

Density effects on the hydrodynamics and mixing at a large confluence with a compound channel tributary

Abstract Confluences are marked by converging streamlines, complex hydrodynamics features and mixing processes. Understanding such intricate flow patterns and their effects on the mixing at natural river junctions is difficult, particularly for large confluences with a compound channel tributary, due to the scarcity of field data. This research aims to assess the effects of density differences on hydrodynamics and mixing at the large river confluence between the Yangtze River and its tributary, the Poyang Lake, whose outflow channel has a large inner-side floodplain. Field data were collected during three surveys under various flow conditions to analyse how the alternate flow mechanism (compound channel vs single channel) of the Poyang Lake outflow channel influences the confluence mixing process. In high flow and relatively high flow conditions, the Poyang Lake outflow channel functioned as a compound channel and switched to a single channel in low flow. Acoustic Doppler current profiling (ADCP) was used in all three surveys to explore the features of hydrodynamics and the mixing process at the confluence, supplemented by water quality sampling to characterise the mixing patterns. Secondary flows observed during the field surveys were found to be affected by alterations in the flow mechanism (compound channel vs single channel) of the Poyang Lake outflow channel and the density effects, which were characterised using the densimetric Froude number Frd. Ultimately, the findings obtained in these field surveys confirm the role of density differences between the tributaries in significantly affecting hydrodynamics features and the mixing process at river confluences.

Hydraulic and axial force characteristics of large axial flow pumps under different flow conditions

Abstract Axial flow pumps often experience uneven distribution of axial force on the blades when deviating from design conditions, which can easily lead to local damage to the pump blades. In response to this issue, this article conducts a detailed study on the hydraulic and axial force characteristics of large vertical axial flow pumping stations in China based on constant and non-constant numerical simulation research methods. Research has found that under biased operating conditions, due to the angle between the water flow direction inside the impeller and the impeller blades, the water body collides with the blades, resulting in concentrated pressure distribution on both sides of the inlet side of the impeller blades. Under low flow conditions, the high axial force area of the impeller blade is concentrated in the middle and rear position of the suction surface, while under high flow conditions, the high axial force area is widely distributed. Under the conditions of 0.8 Q to 1.4 Q, the fluctuation of axial force on the impeller blades is mainly affected by the rotation of the impeller blades. However, under low flow conditions, due to the turbulence of the flow state, there is no obvious pattern of axial force variation on the impeller blades. In addition, under different flow conditions, there is no obvious pattern in the fluctuation of axial force on the guide vanes. This also proves that there are problems such as uneven axial force distribution and no periodic changes in the impeller blades under low flow conditions, which can easily lead to damage to the impeller blades. The above analysis can provide some reference for the design of impeller blades.

Jet centrifugal pump internal flow numerical simulation and structural optimization

Abstract Jet centrifugal pump is essential equipment in multiple systems such as agricultural irrigation and energy production. This paper investigates the internal flow characteristics of jet centrifugal pumps at different flow rates and the cavitation behavior under high flow conditions by numerical simulation methods. Additionally, two performance optimization strategies are proposed based on simulation results. The findings indicate that high-velocity regions and low-pressure zones exist within the nozzle. As flow rate increases, the outlet velocity of the nozzle gradually decreases, and large areas of low pressure are observed near the inlet of the impeller. Cavitation occurs to varying degrees at flow rates of 4.056 m3/h and 3.840 m3/h. The turbulent kinetic energy contours for these conditions reveal uneven distribution within the jet nozzle, with higher values near the jet mixing layer, inner wall of the jet nozzle and impeller inlet. Structural optimization using hemispherical bolts significantly reduces the turbulent kinetic energy around the bolts, resulting in an increase in head ranging from 1.68% to 6.70% across various flow rates. Shortening the clearance between the impeller and the rear cover reduces energy losses, leading to an increase in head ranging from 2.72% to 5.86%.

Analysis of Flood Resistance of Masonry Arch Bridges Combining Numerical Simulation and Probabilistic Analysis

ABSTRACT In the context of global climate change, extreme weather events such as heavy rainfall and floods are becoming more frequent. The safety of masonry arch bridges is facing unprecedented challenges. This study aims to explore the collapse mechanism of bridges in flood environments by combining numerical simulation and stochastic analysis. Taking the collapse of the Original Zhenhai Bridge caused by heavy rainfall in July 2020 as a specific case, a three-dimensional numerical model is established to analyze the mechanical response of the bridge under the combined action of flood scour and water flow loads. Additionally, predictions of scour depth are made using both theoretical formulas and stochastic methods, comparing the impact of stochastic analysis on the mechanical performance of arch bridges under the same flood conditions. The study reveals that compared to pure scour, the structural characteristics of the bridge undergo significant changes under the coupled effects of scour and water flow loads. In extreme flood events, stochastic analysis has a significant impact on the structural safety under high flow conditions. The research results provide case references and scientific methods for the safety analysis of masonry arch bridges in flood environments.

Performance of GPM-IMERG satellite precipitation for rainfall-runoff modeling in Indonesia

ABSTRACT Accurate discharge predictions are essential for effective water resource management, including irrigation, drinking water supply, hydropower, reservoir management, environmental flow, and flood assessment. Satellite precipitation data, such as GPM-IMERG, offers a viable solution for estimating river discharge, especially in ungauged or sparsely gauged watersheds. This study evaluates the use of GPM-IMERG data in the HEC-HMS hydrological model to predict discharge in the Mayang Watershed, Jember Regency, Indonesia. The study employs the Arithmetic, Polygon Thiessen, and Isohyet methods to analyze rainfall distribution. Results indicate that the Polygon Thiessen method, when paired with GPM-IMERG data, provides more reliable precipitation estimates due to its consideration of rain gauge proximity. Calibration and validation confirm the superiority of GPM-IMERG data over traditional observational data, particularly under high-flow conditions. Despite some limitations in detecting low-intensity precipitation, GPM-IMERG outperforms other satellite products like TRMM in terms of accuracy. Sensitivity analysis highlights the significant influence of parameters such as curve Number and time of concentration on model outcomes. Further research should explore emerging rainfall data products to improve hydrological modeling accuracy.

Season-dependent climate sensitivity of the surface runoff of major rivers in Changbai Mountain

Due to the sensitivity of runoff to changes in seasonal snowpack, the changes in surface runoff within high-latitude and high-elevation areas are more complex than in other areas. However, this sensitivity is often overlooked when correlating changes in runoff with meteorological variables. Here, we analyze changes in surface runoff during snowmelt and snowless periods and their sensitivity to climate change from 1960 to 2019 in the upstream watersheds of the Songhua, Yalu, and Tumen Rivers in Changbai Mountain. Most runoff indices, except for low flow in the Yalu River, exhibited decreasing trends during snowmelt and snowless periods. Precipitation was the primary variable responsible for surface runoff during snowless and snowmelt periods. Notably, rainfall replenished all runoff indices during snowless periods, particularly under high flow conditions. The average and high flows were also primarily supplemented by rainfall during snowmelt periods. However, low flow was positively correlated with snowmelt in the Songhua and Tumen Rivers and with temperature in the Songhua, Yalu and Tumen Rivers during snowmelt periods. Additionally, extreme runoff events were closely associated with extreme precipitation. These findings demonstrate the seasonal and index-dependent climate sensitivity of surface runoff within Changbai Mountain, offering insights into the surface runoff response mechanism to climate change in high-altitude mountainous areas. Under future climate change conditions, frequent and intense extreme precipitation events may increase the risk of flooding, owing to the high sensitivity of high flows to precipitation, posing a serious threat to regional ecological security.

Enrichment of dissolved metal(loid)s and microbial organic matter during transit of a historic mine drainage system

Water quality degradation by decommissioned mining sites is an environmental issue recognized globally. In the Ore mountains of Central Europe, a wide array of contaminants is released by abandoned under- and aboveground mining sites threatening the quantity and quality of surface and groundwater resources. Here, we focus on the less-explored internal pollution processes within these mines involving organic carbon and microorganisms in trace metal(loid)s mobilization processes. Over an 18-month period, we conducted hydrological and biogeochemical monitoring at the Reiche Zeche mine, a former lead-zinc-silver mine, in Germany, reaching 230 meters below ground, well below the critical zone. Our results show strong seasonal fluctuations in water availability, concentrations of metal(loid)s, pH, and dissolved organic matter (DOM) components across multiple depths. Excess metal(loid) presence during high flow conditions indicated mobilization behavior deviating from conservative dilution. Our findings reveal strong positive correlations between metal(loid) variability and pH (0.894), and between metal(loid) variability and the DOM fluorescent component C2 (-0.910), a proxy for microbial activity. Accordingly, the microbial processes may significantly contribute to the observed metal(loid) composition and fluxes. By elucidating the intricate roles of hydrological and biogeochemical factors in trace metal(loid) mobilization, our research offers a comprehensive framework for improving mine water management and remediation, potentially informing global environmental policies and sustainable mining practices.

Janus nanoparticles as efficient interface compatibilizer in blends of polylactide and elastomers: Importance of interfacial relaxation on toughening

For blending immiscible polymers, such as in the toughening modification of polylactide (PLA) via blending with rubbery materials, interfacial compatibilization is of great significance while the mechanism, especially the role of interfacial rheology, remains elusive. In this study, styrene-butadiene block copolymer elastomer (SBC) was employed to toughen PLA and a dumbbell-shaped Janus nanoparticle (JNP) consisting of polymethyl methacrylate and polystyrene spheres with equal size (∼80 nm) was used as the compatibilizer. Located at the interface, JNPs exhibited a great compatibilization efficiency in PLA/SBC blends, as demonstrated by the good morphology stabilization against droplet coalescence under static annealing and low shear flow conditions, as well as by the resistance against droplet breakup under high shear flow conditions. Moreover, as revealed from the linear viscoelasticity of JNP compatibilized blends, when JNP loading is more than 2 phr, aside from shape relaxation, an interfacial relaxation dominated by Marangoni stress was observed, indicating the possibility of particle redistribution on droplet surfaces. However, when loading is more than 4 phr, relaxations in the terminal zone no longer exist, implying the possible formation of a particle network on the droplet surface. This is consistent with the mechanical properties. The blend shows the greatest toughness at JNP loading around 3 phr, while the toughness is very poor when JNP loading is either too low or too high. This suggests interfacial relaxation to be crucial to guarantee a good toughening effect of SBC in PLA.

The Growth Mechanism of Layered Hexagonal Boron Nitride Crystal on Copper Foil

Abstract2D hexagonal boron nitride (h‐BN), which has a similar honeycomb lattice structure to graphene, is a promising dielectric material for a wide variety of applications. Herein, the growth of high‐quality and large‐size multilayer h‐BN crystals on Cu foils is reported by chemical vapor deposition (CVD) at atmospheric pressure. The size of an individual isolated hexagonal crystal of h‐BN is about 20 µm, and the thickness is 3 nm. This paper studies the variables that affect h‐BN growth during the process and the microstructure changes during the growth. Through analysis of the thermal and dynamic processes of chemical vapor deposition, relationships are derived between the mass of h‐BN grown in the gas phase and various temperature and pressure factors. This information is used to develop appropriate parameters for commercial copper foil growth. Finally, using optimized conditions, high‐quality h‐BN at high pressure and low gas flow conditions are grown.

Improving runoff simulation in the Western United States with Noah-MP and variable infiltration capacity

Abstract. Streamflow predictions are critical for managing water resources and for environmental conservation, especially in the water-short Western United States. Land surface models (LSMs), such as the variable infiltration capacity (VIC) model and the Noah LSM with multiparameterization options (Noah-MP), play an essential role in providing comprehensive runoff predictions across the region. Virtually all LSMs require parameter estimation (calibration) to optimize their predictive capabilities. Here, we focus on the calibration of VIC and Noah-MP models at a 1/16° latitude–longitude resolution across the Western United States. We first performed global optimal calibration of parameters for both models for 263 river basins in the region. We find that the calibration significantly improves the models' performance, with the median daily streamflow Kling–Gupta efficiency (KGE) increasing from 0.37 to 0.70 for VIC, and from 0.22 to 0.54 for Noah-MP. In general, post-calibration model performance is higher for watersheds with relatively high precipitation and runoff ratios, and at lower elevations. At a second stage, we regionalize the river basin calibrations using the donor-basin method, which establishes transfer relationships for hydrologically similar basins, via which we extend our calibration parameters to 4816 hydrologic unit code (HUC)-10 basins across the region. Using the regionalized parameters, we show that the models' capabilities to simulate high and low flow conditions are substantially improved following calibration and regionalization. The refined parameter sets we developed are intended to support regional hydrological studies and hydrological assessments of climate change impacts.

Ensemble hydrological predictions at an intraseasonal scale through a statistical–dynamical downscaling approach over southwestern Amazonia

ABSTRACT We developed and analyzed the performance of an ensemble forecasting system for the Madeira River basin, the largest sub-basin of the Amazon, with forecasts up to 30 days under different hydrometeorological conditions. We used outputs from the regional Eta model of precipitation and global climatological data as inputs to a large-scale hydrological model. Bias correction of precipitation through quantile mapping significantly improved the results, achieving a hit rate >70%. The system demonstrated the ability to discriminate between high, medium, and low flow conditions. Forecast performance is better for larger catchment areas. This system is expected to increase decision-making efficiency for flood and drought situations in the largest Amazon tributary.

The Influence of Lobe Top Clearance on the Performance of High-Speed Centrifugal Pumps

High-speed centrifugal pumps are widely used in several industries due to their high efficiency and small footprint. In actual applications, there are issues such as low operational efficiency and a small high-efficiency flow interval; particularly, the leakage occurring in the impeller channel gap presents a significant barrier to the pump’s performance and stability. This study takes the fully open impeller miniature high-speed centrifugal pump as the object and uses a numerical simulation calculation method. The objective of this research endeavor is to analyze the effects of different flow conditions on a high-speed centrifugal pump’s external characteristics, flow field characteristics, and energy loss. The findings indicate that lobe top clearance exerts a substantial impact on the efficiency of high-speed centrifugal pumps. Increasing the lobe top clearance will result in a reduction in pump head and efficiency, particularly under high flow conditions. The lobe top clearance has a significant impact on the complexity of the flow in the impeller, particularly the flow close to the suction surface of the impeller, according to an analysis of the flow field characteristics. The energy loss analysis further confirms the importance of reducing lobe top clearance for improving pump performance and reducing energy loss. These results provide valuable guidance for optimizing centrifugal pump designs with lobe top clearance.

Improvement of macroscopic turbulence model for subchannel analysis in the rod bundle array

The PRIUS program was established to generate an experimental database for the 6 × 4 and 12 × 6 rod bundle geometry. The database will be used to address the subchannel and CFD code analysis required for modeling and validation. This is necessary because Small Break Loss of Coolant Accident (SBLOCA) and Intermediate Break Loss of Coolant Accident (IBLOCA) present three-dimensional phenomena in the core due to the radial power profile, crossflow, and diffusion-dispersion. Therefore, specific experimental programs are required, especially during core reflooding, to investigate the large-scale three-dimensional effects. However, validating each sensitive model of the code separately in the presence of 3D effects is not possible due to the inability to implement instrumentation at high pressure and temperature steam-water flow conditions. The PRIUS test program uses a single-phase flow test to simulate a non-homogeneous velocity distribution and provide information on crossflow with radial mixing effects between subchannels. The CUPID code, which uses a macroscopic turbulence model, has been validated using the PRIUS-II experimental database. Existing macroscopic turbulence models were also validated for their prediction capabilities with different inlet flow conditions. However, the validation revealed significant errors in the shear region between subchannels. An improved macroscopic turbulence model showed promising results in predicting turbulence kinetic energy in porous media analysis.

Investigating a surface water quality monitoring approach for QwaQwa, South Africa, by combining biological in vitro tests and chemical analyses

IntroductionWater quality assessment is a fundamental requirement for comprehensive water management. Access to water is not exclusively a quantitative issue, as human activities often lead to negative impacts on water quality due to pollution. This results in a need for the systematic monitoring of water bodies to surveil ongoing pollution dynamics and, if needed, facilitate the implementation of suitable solutions for water quality management.MethodsTo that effect, in March 2022 and July 2023, we conducted two sampling campaigns in four headwater streams in QwaQwa, South Africa, to assess the water quality under high (summer) and low (winter) flow conditions. The overarching aim was to support local decision-makers with relevant information on water quality in a semirural and less studied area. Beside the hydrological characterization of the catchment, which drains the mountainous areas around Phuthaditjhaba (the main town of the region), physicochemical and biological monitoring were conducted, including in vitro tests detecting endocrine disruption, dioxin-like impacts, and genotoxic potentials in the water.ResultsThe elemental analysis showed that at several sampling sites, Al, Cu, Mn, Fe, and Zn were above the Target-Water-Quality-Range (TWQR) for aquatic ecosystems and Fe, Al, and Mn were additionally above the TWQR for domestic use. Interestingly, the organic micropollutants (OMPs) revealed a region with a high incidence of HIV infections, given the occurrence of the drugs efavirenz, its transformation product 8-OH-efavirenz and nevirapine, among other micropollutants. Possibly, the signals from the in vitro tests for endocrine disruption are also induced by the detected micropollutants. Our results ultimately show that even though anthropogenic impacts increase from upstream to downstream, none of the sampling sites are without concern. This indicates the urgent need for measures to increase the water quality of these headwater streams in this region.

Assessment of river recreation safety using hydrodynamic model and fuzzy logic: A spatial river recreational index approach

As demands for river recreational activities increases, assessing their safety has become essential to prevent accidents. The hydraulic conditions of the river critically influence the safety of in-water activities, such as sailing, paddling, and boating. Localized hazardous areas can emerge due to the spatial variability of hydraulic phenomena. This potential risk necessitates providing information about safe zones. Therefore, this study proposes a spatial river recreational index (SRRI) to assess the safety of river recreational activities over river spaces based on hydraulic factors. We reproduce the spatial distribution of the hydraulic parameters under various discharge conditions using a 3D hydrodynamic model and then estimate the SRRI by integrating all membership degrees and weights of these parameters using fuzzy synthetic evaluation (FSE). The application of the SRRI in the confluence of the Nakdong-Guemho River, South Korea, reveals that each hydraulic parameter contributes differently to safety levels, depending on discharge and morphological conditions. Specifically, the flow direction substantially decreases safety near the river confluence, whereas the water depth plays an important role in the meandering reach of the Nakdong River. Under high-flow conditions, velocity becomes a critical factor, especially for nonpowered activities (sailing and paddling/wading). The SRRI indicates that sailing is unsafe in the main flow zone and near the river confluence due to high sensitivity to discharge changes. In contrast, paddling/wading and leisure boating are less sensitive to discharge changes, allowing these activities to be partly allowable even under high-flow conditions, except in the deep-water zones of meandering reach. These results suggest that the SRRI can assist water recreational activity users in safely engaging in river recreational activities by providing spatial safety information based on various hydraulic conditions.