Journal of Hydro-environment Research最新文献

In recent years, saltwater intrusion in river estuaries has become more severe and frequent worldwide. The common reasons lie in increasing freshwater withdrawal, river flow regulation and sea level rise due to global warming. In particular, the Red River Delta in northern Vietnam is facing a strong population growth worsening the pressure on freshwater resources for drinking water and irrigation needs. During the dry season, increasing conflicts and constraints in freshwater availability have already been experienced. Adverse combinations of river flow regulations and high sea levels lead to severe upstream propagations of salinity. This study takes advantage of a statistical characterization of discharges released from Hoa Binh reservoir and observed at Son Tay station, the main river flow control upstream of the river delta, along with downscaled and updated sea level rise scenarios to estimate the future extents of saltwater intrusion under different options of water release from reservoirs in the dry season. To do so, a 1D hydraulic model of the river delta network was implemented using MIKE11 software. The hydraulic and the quality modules were calibrated and validated with respect to the present scenario by using water stages and salinity concentrations observed in estuary branches. Sea level rise projections for 2050 and 2100 referred to RCP4.5 and RCP8.5 AR5 emission scenarios were then considered. Results show that river flow regulation can provide an effective mitigation measure. A 20–30% increase in the discharge released from the Son Tay station would be beneficial to push downstream the saltwater intrusion in the main Red River branch during the dry season. For instance, in 2050 the 1‰ salt concentration front is expected to be pushed back at least 6 km when the exceeding probability of the discharge released by Son Tay station decreases from 95% to 25%.

The flow turbulence and Reynolds stress anisotropy in flow over the smooth rigid bed with the emergent rigid vegetation in a straight channel have been experimentally investigated. Higher-order turbulence such as turbulent diffusivity, third-order moments of velocity fluctuation, quadrant analysis and flux of turbulence kinetic energy have been analysed. Reynolds stress anisotropy has been investigated by Anisotropic invariant maps (AIMs) with the use of eigenvalues for both vegetation and non-vegetation condition. In the vegetation zone, more diffusivity occurs and an apparent decrease in velocity causes larger eddies in the outer layer; whereas in the non-vegetation zone, larger eddies formation at near-bed has been found. Quadrant analysis has been done based on relative signs of velocity fluctuation which signifies that Reynolds shear stress is transported from the bed surface to the free surface when flow enters in the vegetation zone from the non-disturbed region. The longitudinal distribution of the anisotropy tensor near the bed surface for the vegetation zone provides the higher anisotropic flow than those of non-vegetation zone. Although, transverse and vertical distributions of the anisotropy tensor in the vicinity of the bed surface for the non-vegetation zone provide a lower anisotropic stream. Flow anisotropy can be understood by AIMs indicating axis-symmetric expansion in a non-vegetation zone whereas axis-symmetric contraction is in the vegetation zone. The outcomes of this study deliver a significant and detailed view of turbulent flow structures in vegetation and non-vegetation zone in an open channel 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.

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.

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.