Journal of Hydro-environment Research最新文献

Hydraulic jump is a phenomenon with destructive effects on the river bed and downstream the hydraulic structures. This study, based on experimental findings, presents a new method that can be used to prevent the detrimental impacts of the hydraulic jump downstream of hydraulic structures and to design optimal structures. In this empirical research, 135 experiments were conducted in an experimental flume where submerged vanes with angles of attack of 30 and 60°, as a novel intuitive method, were used with two different configurations and adverse slopes (0, −1.5% and −3%) to control hydraulic jump in the range of 4.58 < Fr₁ < 9.14. Based on the obtained results, the sequent depth and length of the hydraulic jump were, at most, decreased by 26.6% and 31.9%, respectively, with increasing the angle of attack of submerged vanes and the adverse slope of the bed. Also, the energy loss increased up to 7.7% in the case of φ = 60°, d = 0.2 m, and S = −3%. To calculate the sequent depth and length of the hydraulic jump, new equations were expressed through the analysis of the effects associated with the angle of attack, adverse slope, and vane configuration. All data resulting from proposed equations were then compared and validated with the experimental data.

This study investigates the geometric parameters of a two-stage stilling basin; 14 sets of tests were carried out in a horizontal flume with a supercritical inflow of relatively low Froude number (Fr₁ = 1.1 ∼ 1.85). The flow pattern, relative amplitude of the tailwater, and energy dissipation ratio were investigated. The two-stage stilling basin led to a hydraulic jump at each stage. Compared to the corresponding classical jump, the energy dissipation ratio in the two-stage stilling basin could be increased by 30%–45%. Herein, a novel method is proposed to calculate the energy dissipation ratio and relative amplitude of the tailwater. The investigation demonstrates the potential of two-stage stilling basin with low-Froude-number flow.

The sediment regime of the Red River system, the second largest in Vietnam, has undergone changes since the implementation of dams and reservoirs, with implications for downstream river processes. We analyzed long-term datasets of daily discharge and suspended sediment concentrations collected at key gauging stations downstream of the three main tributaries: HB on the Da River, YB on the Red River (main channel), VQ on the Lo River, and ST, the outlet of the Red River system. The results indicated a sharp reduction in the annual sediment load transported by the Red River system, as observed at the four stations. For example, at the ST station, there was a dramatic decline of 91% in sediment load, dropping from 117.9 × 10⁶ ton/yr in the period 2009–2021 to 10.5 × 10⁶ ton/yr in the period 1958–1987. The Red River system experienced two notable declines in sediment load. The first decline occurred from 1988 to 2008, which can be attributed to the commencement of Hoa Binh dam's operation in 1988. The second decline has taken place since 2009, coinciding with the utilization of new dam-reservoirs. Meanwhile, an abrupt change in water discharge was observed clearly since the end of 2008 at all four stations. However, the reductions in water discharges were found to be less pronounced when compared to the sediment budget. Based on our analysis, we concluded that the impacts of dam-reservoirs have had a more substantial influence on the system compared to variations in climate, such as air temperature and precipitation.

In 2009, South Korea started a large multi-purpose water project on its four major rivers. The main purposes of the Four Major Rivers Restoration Project (FMRRP), which are directly related to water itself, were: (1) securing water resources to combat water scarcity; (2) reducing flood risks by riverbed dredging and reinforcing levees; and (3) restoring the river's environmental functions. Despite socio-environmental opposition, the project was completed in 2011. This article reviews the sedimentation issues raised during and after the FMRRP regarding technological developments and the lessons learned from the project. A total of five sedimentation issues raised directly from the project are reviewed in this article: (1) riverbed dredging and sediment redeposition; (2) tributary headcut; (3) riverbed scour downstream of the movable weir structures; (4) sedimentation management schemes; and (5) a near-prototype river experiment facility. Each issue is addressed by identifying and analyzing field data, developing new numerical models, and testing at a large-scale experiment facility. From this project, we have found that a comprehensive numerical technique is required to predict the sediment issues as mentioned above in a watershed-scale riverwork.

Accurate streamflow forecasting is very useful in water resources management, design of hydraulic structures, and almost all issues related to the use of water and water resources, especially in arid regions that have increased in recent years. Since water is the source of all life and the most important basic element for humanity to continue its life, streamflow prediction studies increase its importance daily. This research combined the boosted tree (BT) model with robust empirical mode decomposition, empirical mode decomposition, complete ensemble empirical mode decomposition with adaptive noise, empirical wavelet transforms and variational mode decomposition for predicting daily average streamflow data. While historical streamflow data was input in the model's setup, one-day lead-time streamflow data was used as the target. 70% of the data is reserved for training and the rest for testing. 5-fold cross-validation technique was used to solve the over-fitting problem. The coefficient of determination, mean squared error, Nash-Sutcliffe efficiency and percent bias statistical criteria and Taylor diagrams, polar plot, scattering diagram, and violin plot were used to determine the algorithm's success. At the end of the study, it was found that the most successful streamflow predictions were made with the variational mode decomposition-based BT hybrid approach.

Research on water flow resistance characteristics in a vegetation environment is a hotspot in environmental fluid research, which is primarily concentrated on the calculation of the vegetation drag coefficient C_d. At present, relatively few studies exist on the resistance characteristics of vegetation under non-uniform flow conditions, resulting in few general expressions for the research of C_d for this type of condition. In response to these scientific problems, this study selects shrub vegetation as the research object and generalised it as cylinders for the simulation study. This study adopts quadratic and Gaussian functions to change the coordinate expression of cylindrical vegetation C_d and then proposes the drag formulas of cylindrical vegetation in non-uniform flow for non-rainfall and heavy rainfall conditions based on regression analysis. Finally, this study substitutes the proposed C_d formula into the Saint-Venant equation to calculate the depth of channel flow. The newly proposed equations are verified by comparing the measured flow depth data with the calculation results. This study provides technical support for refined hydrodynamic simulations of vegetated flow regions.

Fluvial floods are commonly studied as an occurrence at the level of a specific basin and are speculated to be closely related to the basin's morphometry. It is possible to identify and rank sub-basins based on how susceptible they are to fluvial flooding events using morphometric criteria. However, one of the key causes that triggers fluvial flooding is the increase in precipitation extremes and changes to their patterns. In this study, influence of morphometric factors and extreme precipitation events on the hydrological responses of the Brahmani River, India as well as their sensitivity to fluvial flooding, are investigated to identify the most vulnerable sub-basin in a catchment. The morphometric parameters were calculated from a digital elevation model (DEM), and the change in trend of extreme precipitation indices was detected using precipitation data of period 1991 to 2021. Furthermore, the Standardized Precipitation Index (SPI) was used to determine the frequency of wet cycles on time scale of 1, 3, 12, and 24 months, as well as their link to fluvial flooding. The two sub-basins of the catchment that are most vulnerable to river flooding are recognised as Noamundi and Gomlai based on morphometric criteria. However, analysis of SPI and extreme precipitation indices showed that the Jenapur sub-basin is the most vulnerable to flooding. It is also corroborated with analytic hierarchy process (AHP) based weighted overlay analysis and historical flood records. The outcomes will assist researchers in better understanding the mechanisms causing flooding in the Brahamni River Basin and in developing flood mitigation practices for the most vulnerable Jenapur sub-basin.

Broadcasted fertilization for the reproduction of invertebrates is accomplished through a complicated interaction between spawned gametes and the surrounding flows. Most gametes encounter each other in the vicinity of the sea urchin body where unique flow structures develop, and so analysis of local flow characteristics allows us to better understand the effect of flow on the fertilization process. This study applied a Lagrangian framework based on computational fluid dynamics to estimate the fertilization rate of eggs in a range of flow velocities (0.025–0.2 m/s) and the fertilization rate was the highest at U = 0.1 m/s, which is an intermediate flow speed. Among the four classified sub-zones, such as the aboral surface, wake, substrate, and water column, fertilization occurred most frequently in the wake and substrate regions. The relationship between fertilization rate and flow structures was investigated using three parameters: 1) standardized Morisita index to quantify the pattern of gamete distribution, 2) length of the recirculation zone to specify the areas where the eggs are most frequently fertilized, and 3) integral scale to estimate the dimension of vortex structures downstream. The results of this study show that the fertilization rate is higher inside the recirculation zone, especially when strong vortex structures are observed because the flow provides a favorable condition for the gametes to aggregate and collide with each other.

Extremely high lead level in tap water caused by particulates has attracted increasing attention in recent years. Despite extensive research on the role of particulate Pb in water supply systems with lead service lines, little information is available on the role of particulate Pb in copper (Cu) water distribution systems. In this study, the dissolved, colloidal, and particulate lead and copper concentrations in representative prototype copper pipe water distribution systems with leaded solder joints and brass fixtures are measured. The effects of flow rate and stagnation time on metal fractionation are investigated. For each experimental scenario, all the water that stagnated inside the system is sampled to have a comprehensive understanding of lead contamination. Sampled at flow rates of 200–250 mL/s, the soluble lead and copper make up 60–96 % of the total concentration in the samples after hours of stagnation. More than half of the Pb and Cu particles are larger than 0.8 μm. Higher flow rates result in substantial increases in particulate metal concentrations but have no apparent effect on dissolved metals. The soluble and particulate copper concentrations ($\sim$ 100–250 μg/L) both increase with stagnation time. For the case of Pb, while the particulate concentration increases (up to $\sim$ 40 μg/L after 12 h), the soluble concentration does not change significantly beyond 4 h; this can be attributed to the different solubilities of Pb ($\sim$ 20 μg/L) and Cu ($\sim$ 200 μg/L) in tap water. The results also show that particulates suspended by clean “once through” water (without prior stagnation) can lead to high levels of Pb contamination ($>$ 10 μg/L).

River Thamirabarani sub-basin lies in the southern part of the Western Ghats in the Kanyakumari district of Tamil Nadu, India. The basin’s landforms are formed by swift surficial characteristics with undulated terrains composed of steep-sloped valleys, valley fills, and short-length streams with intensive flows that makes-up site-specific hydro-morphological characteristics. In this study, the GIS-based Natural Resource Conservation Service-Curve Number (NRCS-CN) model is used to assess rainfall-induced runoff by analyzing various hydrological parameters. The curve number (CN) is assigned to each hydrologic soil group (HSGs) based on the measurement of initial abstraction (Ia) and potential maximum retention (S) derived from soils, landuse/ land cover, antecedent soil moisture, etc. The resulting map shows the estimated runoff at the rate of 2.27 – 5.94 mm/m²/yr for the whole study area, whereas the higher runoff rate (4.83 – 5.94 mm/m²/yr) is noted in the upland range of the swift surficial terrains in the north and north-eastern parts that encompasses undulated structural hills, steep-sloped valleys, inselberg, and denudational hills, etc., whereas the work of swift surficial terrains and associated slope gradient of the landforms are considered to be higher runoff rate than the other parts. The moderate runoff rate (2.92 – 3.98 mm/m²/yr) is estimated in the middle parts of pediplains that consist of croplands, plantations, riverbanks, fallows, and built-up areas. Significantly, the lower runoff rate (<2.92 mm/m²/yr) sparsely occurred in the different landforms of the middle and southern parts that include pediplains, riverbanks, natural vegetative covers, valley-filled sediment deposits, etc. Overall results indicate that the higher runoff found over the swift surficial landforms in the north and north-eastern parts due to intensive flow through short-length stream orders. This study is mainly used for understanding hydro-morphological processes and their impacts on basin environments.