Journal of Hydro-environment Research最新文献

Sediment Bypass Tunnels (SBTs) are proven to be an effective measure to reduce or even stop reservoir sedimentation by bypassing sediment laden flows around reservoir dams to the downstream river reach. They are mostly used in Switzerland, Japan, and Taiwan. However, hydraulic and sedimentological operating conditions and the resistance of the invert materials against hydroabrasive erosion affect their cost-effectiveness. Hydroabrasion is a pressing issue at SBTs, other hydraulic structures and steep bedrock rivers exposed to high sediment transport rates under supercritical flow conditions. The present study was therefore conducted to address this issue by aiming at improving knowledge on abrasion mechanics and calibrating a mechanistic saltation abrasion model enhanced by Demiral-Yüzügüllü (2021). To this end, the abrasion resistance of fourteen different invert materials installed at Solis, Pfaffensprung and Runcahez SBTs in Switzerland was quantified by annual 3D laser scanning and the hydraulic conditions and sediment transport rates were regularly monitored between 2017 and 2021. The analysis of invert scans and hydraulic conditions revealed that Prandtl’s first and second kinds of secondary currents occurring in the bends and straight sections of the SBTs, respectively, and the observed abrasion patterns were strongly interrelated. The tested potassium aluminate cement and steel fibre concretes, granite, cast basalt and steel plates had better abrasion resistance against impact of sediment-laden flows compared to other materials. Sediment mineralogical composition i.e., bulk hardness relative to the invert material properties significantly affected hydroabrasion. The enhanced abrasion prediction model was calibrated with the present data and a quasi-constant abrasion coefficient of k_v = (4.8 ± 2.2) × 10⁴ was obtained. The enhanced model is well-suited for both laboratory and field scales. The present findings will contribute to the sustainable utilization and operational safety of hydraulic structures, optimization of SBT and reservoir operations regarding bypassing efficiency and reservoir lifetime and modelling of bedrock river erosion.

Urban flood vulnerability monitoring requires a large amount of socioeconomic and environmental data collected at regular time intervals. However, collecting such a large volume of data poses a significant constraint in assessing changes in flood vulnerability. This study proposed a novel method to monitor spatiotemporal changes in urban flood vulnerability from satellite nighttime light (NTL) data. Peninsular Malaysia was chosen as the research region as floods are the most devastating and recurrent phenomena in the region. The study developed a flood vulnerability index (FVI) based on socioeconomic and environmental data from a single year. This FVI was then linked to NTL data using an Adaptive neuro-fuzzy inference system (ANFIS) machine learning algorithm. The model was calibrated and validated with administrative unit scale data and subsequently used to predict FVI at a spatial resolution of 10 km for 2000–2018 using NTL data. Finally, changes in estimated FVI at different grid points were evaluated using the Mann-Kendall trend method to determine changes in flood vulnerability over time and space. Results showed a nonlinear relationship between NTL and flood vulnerability factors such as population density, Gini coefficient, and percentage of foreign nationals. The ANFIS technique performed well in estimating FVI from NTL data with a normalized root-mean-square error of 0.68 and Kling-Gupta Efficiency of 0.73. The FVI revealed a high vulnerability in the urbanized western coastal region (FVI ∼ 0.5 to 0.54), which matches well with major contributing regions to flood losses in Peninsular Malaysia. Trend assessment showed a significant increase in flood vulnerability in the study area from 2000 to 2018. The spatial distribution of the trend indicated an increase in FVI in the urbanized coastal plains, particularly in rapidly developing western and southern urban regions. The results indicate the potential of the technique in urban flood vulnerability assessment using freely available satellite NTL data.

In canopy flows, flow resistance mainly originates from vegetation drag and depends on vegetation characteristics and flow conditions. In the present study, a series of experiments were performed in various hydraulic scenarios with high stem Reynolds numbers (2641 $\le$ Re_d $\le$ 17333) using relatively sparse rigid canopies, represented with four different dimensionless vegetation densities (0.0044, 0.0098, 0.0174 and 0.0392), on a smooth bed. A novel drag plate mechanism was developed to measure the total flow resistance due to the emergent and submerged vegetation arrays in a staggered pattern under subcritical flow conditions. Manning’s roughness coefficient and Darcy–Weisbach friction factor were adopted to represent the total flow resistance in the analyses. Simple empirical relationships based on roughness concentration and submergence ratio were derived to determine the total flow resistance parameters within a broad range of stem Reynolds numbers. Although relationships were proposed in a simple form to be used for direct practical applications, they show similar or better performance in the prediction of total flow resistance parameters than the existing equations in the literature, which require considerable computational effort. Additionally, analyses demonstrated that the results of the present study and those of similar studies regarding canopy flow resistance are in good agreement. Accordingly, the novel drag plate looks promising for measuring flow resistance due to vegetation and bed conditions similar to those in nature.

In a spillway chute flow, the upstream flow is typically non-aerated and the flow becomes self-aerated when the turbulent stresses acting next to the water surface exceeds the combined resistance of gravity and surface tension. The inception region of air entrainment is a rapidly-varied region characterised by the transition from a monophase water to two-phase air–water flow. In this contribution, field observations were conducted at large dam spillways during major flood events, with a focus on prototype data for discharges between 100 m³/s and 6,000 m³/s and Reynolds numbers between 2.6 × 10⁶ to 1.1 × 10⁸. The onset of self-aeration was a complicated three-dimensional transient process, and the dimensionless location of the inception region was a function of the Reynolds number. Surface velocities obtained with an optical technique showed that the streamwise surface velocities were close to theoretical estimates, and the streamwise surface turbulent intensities in excess of 100 %, consistent with self-aerated measurements in laboratory. The current findings yield a couple of seminal questions: (a) what do we know about prototype spillway operation during major floods? (b) how large the Reynolds number of a prototype flow needs to be truly representative of large dam spillway self-aerated flows during major flood events?

The spatiotemporal structure of the flow field during particle–cloud sedimentation has not been sufficiently investigated. In this study, experiments on the sedimentation process of particle clouds in water are conducted using hydrogel particles with a refractive index similar to that of water as the settling particles. The flow field during the sedimentation process of particle clouds in water is measured using particle image velocimetry (PIV). Although the measurement conditions in this study are restricted to one condition owing to the limitations of the measurable area by our PIV system and the available hydrogel particles, the measurement target is novel because it has not been measured so far. The spatiotemporal structure of the turbulent flows is investigated by analyzing the turbulent flows induced by the sedimentation particles using the PIV system. Furthermore, the turbulent structure of the vortex formed by particle sedimentation is examined.

The effects of a vertical slot fishway slope (with slope values from 1.5% to 6%) on a flow field are numerically investigated, using a re-normalization group k – ε model. The distribution of the velocity, turbulence kinetic energy (TKE), average energy dissipation rate per unit volume (E), and vorticity for different slopes are systemically explored. The results indicate that, with an increase in slope, the appearance of downward flow in conjunction with an increase in vertical velocity results in three-dimensional flow characteristics. The recirculation region in H_s, at a 6.0% slope, was 20.9% less than that at a 1.5% slope. Meanwhile, the flow velocity in the vertical slot region grew with increasing slope, which would limit the passage of fish with burst speed lower than the velocity in the vertical slot region. The TKE and E may locally exceed the threshold at larger slopes. Furthermore, vorticity distribution shows little variability with increasing slope, but may interfere with the equilibrium of the fish in the vertical slot region. In addition, the change in water level has little effect on the flow field, which is changed by the increase in slope. These findings can aid vertical slot fishway designs especially in terms of the efficiency of fish passage.

Despite the widespread application of spur dikes in river training projects, the performance of the structure during flood events and its impacts on unsteady flow conditions have rarely been studied. In this experimental investigation, the influences of twelve unsubmerged unilateral and bilateral spur dike layouts on upstream flow conditions during flood movements were examined. Three hydrographs with varying unsteadiness intensities were generated and applied to all layout tests, including the no-spur condition for comparison purposes. The results revealed that discharge directly affected changes in flow depth upstream of the spur dike, while the flow rate trend exerted inverse influences. The Keulegan-Carpenter number was modified to assess the impact of unsteadiness intensity on the rating curve loop. Stage hysteresis analysis demonstrated an increase of more than thirty times compared to the no-spur scenario, highlighting the elevated risk of flooding in the upstream reach while delaying peak flood arrival time. This has implications for flood risk management and warning programs. The results underscore the significance of considering not only peak discharge but also unsteadiness intensity in spur dike design.

The present study investigated experimentally the dynamic interactions between surface waves and submerged vertical tensioned barriers with full and partial penetrations. The range of tension for the barrier was set within the flexible membrane regime in the experiments which measurements have not been reported in the literature so far. In addition, an extensive Internet of Things (IoT) system with five GoPro cameras was developed for the measurements to quantify both the surface wave transformation as well as dynamic response of the barrier. The cameras were synchronized through the IoT system to cover the entire wave flume, and the recorded videos were converted to spatial and temporal data using image processing techniques. The experimental results were found to agree with the analytical predictions based on the linear wave theory reasonably well. In particular, the measured reduction in the tensioning effect on the wave transmission and reflection with decreased barrier length was in close argument with the predictions. Similar good agreement was also observed for the dynamic response of the tensioned barrier during the wave interaction. However, additional energy loss was noted in the experiments possibly due to energy dissipation at the boundary ends of the experimental barrier and wave-induced flow separation with partial penetration which are not considered in the analytical analysis.

To investigate the flood-regional composition under changing environmental conditions in the middle reach of Hanjiang River (MHR), a data-driven hydrological simulation model and its related quantitative methods were developed. The flood-regional composition of Huangzhuang(HZ) in the MHR was quantitatively analyzed, and the influence of environmental changes on river flood routing was discussed. The primary research findings are as follows: ① A hydrological simulation model based on support vector regression machine (SVRM) is constructed to simulate the daily average flow process of HZ from 1965 to 2021. The Nash-Sutcliffe Efficiency (NSE) coefficient achieved values above 0.95, and the overall relative error (RE) was within ± 1 %, indicating excellent simulation performance. ② A quantitative analysis method has been proposed to identify the composition of flood areas. The results indicate that the upper reach of Hanjiang River (UHR) is the primary contributor to floods in the MHR, accounting for 60.62 % to 78.05 % of the total. The Tangbai River (TR) contributed between 14.1 % and 27.4 %, whereas the Nan River had a smaller contribution of only 6.83 % to 8.85 %. ③ Trend analysis indicates that the proportion of floods originating from the UHR increases in the summer flood season and decreases in the autumn flood season, while those changes of TR and Nanhe River (NR) are coincidental, especially in the autumn flood season, the proportion of floods in the TR increases significantly. The impact of floods from the UHR and TR cannot be ignored when implementing flood control measures. ④ A comprehensive analysis method has been proposed to quantify the integrated impacts of environmental changes. The results show that environmental changes had a relatively minor impact on flood routing and its flood-regional composition. However, they did affect the flood propagation process, resulting in earlier occurrences in peak flow, increased in peak discharge, and rapid rise and fall of floodwaters for floods exceeding 12,000 m³/s. These research findings provide strong foundational support for designing flood-regional, as well as flood control and disaster reduction systems in the MHR.

Seepage failure is a common problem in engineering, and the calculation and analysis of critical hydraulic gradient are of great significance for the safety and protection of engineering. Based on the principle of discrete element method and computational fluid dynamics, the fluid–solid coupled models were established to study the critical hydraulic gradient and particle loss rate of granular soils at seepage failure. The evolution of seepage failure was divided into four stages: seepage development stage, local damage stage, volume expansion stage and overall damage stage. The validity of numerical simulation was demonstrated by comparing the critical hydraulic gradient obtained by numerical simulation and by Terzaghi’s formula. According to the fabric damage and flow velocity variation of the models at seepage failure, the influences of model size and particle size on the critical hydraulic gradient and particle loss rate were analyzed. The results indicate that critical hydraulic gradient and particle loss rate were not sensitive to changes in model size. A wide particle size distribution range resulted in large critical hydraulic gradient and small particle loss rate at seepage failure. The discrete element numerical simulation can not only be used to determine the critical hydraulic gradient of geotechnical and hydraulic engineering, but also offer a visual portrayal of the evolution of seepage failure, serving as an important complement to comprehend the intricate microscopic mechanisms underlying soil seepage failure.