Journal of Hydro-environment Research最新文献

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.

Water turbidity is a critical index of water quality due to its high correlation with the five main water quality parameters (electrical conductivity, nitrogen, dissolved oxygen, phosphorus, and pH). The exact measurement of water turbidity is a difficult process because many conditions affect the reading of turbidity. Although many researchers applied decomposition-based techniques for preprocessing, it is difficult to use these approaches in real estimation because the newly acquired data greatly affect the initial decomposed subsequent values. In this study, the threshold-based wavelet denoising method, as a data pre-processing, coupled with the deep learning models (i.e., ANN and ANFIS) was employed to enhance the performance of the water turbidity modeling. The results showed that deep learning techniques in temporal modeling of water turbidity have good accuracy and can be used with reasonable confidence. Also, data denoising increases the accuracy of deep learning methods in estimating the amount of water turbidity. ANFIS method is more accurate in both calibration and validation modes as well as in noisy and denoised conditions. Based on the results, data denoising in the ANN method has a more significant impact than in the ANFIS technique. For example, in Comb. 5, which is the best case, the improvement rate of the results in the ANN is 12% and in the ANFIS method is 4%. This could be due to the fuzzy system in handling uncertainties in the model.

Since the Normalized Difference Water Index (NDWI) was proposed, water indices have served as useful tools for surface water detection. However, existing water indices are highly influenced by atmospheric and other environmental conditions and suffer from limited performance, especially in urban areas. At the core of the limitation is the sole dependency on the spectral distribution of reflectance signals. To overcome this, we propose to utilize topographic data as additional information for better water detection. Accordingly, the new index, namely Combined Water Index (CWI), is developed as the product of the topographic index and the reflectance-based index. These two indices excellently compensate each other: the former is free from noise issues but invariant over time while the latter can capture temporal dynamics of waterbody extents. The CWI is applied to four study areas of different development levels (natural, medium-sized cities, and megalopolis) in the Han River basin, South Korea. The water detection results of the CWI is promising, particularly in the heavily developed urban setting, demonstrated through visual images as well as various statistical measures.

The present study was carried out to experimentally investigate the effect of single and double collar on development of local scouring around cylindrical bridge piers under live-bed condition. The single collar with diameter of 3 times the pier diameter placed on the streambed level and double collars one on the streambed level and one on a lower elevation were used. Tests were conducted with different flow intensities equal to 1.4, 2.0, 2.4, 2.8 and 4.0 where flow intensity is defined as the ratio of bed shear velocity to shear velocity of bed material at threshold of motion. One experiment was also carried out with flow intensity of 4.7 at which dunes were washed out and transition flow regime prevailed. The duration of the experiments was long enough to assure complete dune formations and multiple traverses of dunes through the pier location. Results showed that the scour depth fluctuated between a maximum and a minimum value due to the bed features migration. A graph was developed to show the efficiency of single and double collars at different positions and under different flow intensities. With two collars in place, the mean and maximum scour depths at the highest flow intensity, reduced by about 53% and 35% respectively. Efficiency of collar was better in lower flow intensities. Finally, based on the present results, a design table is presented for the elevation of the lower collar based on the flow intensity.

River streams, in general, comprise of two flows: quick flow and baseflow. The baseflow is closely related to geological catchment properties, and understanding the baseflow contribution to stream flow is very important in the planning of water resources management. The baseflow in a sub-catchment of the Red River in Vietnam was quantified using the isotopic technique, and results were compared with Eckhardt’s recursive digital filter (RDF) method. Results of the isotopic approach showed that groundwater is recharged from regions at 300 to 800 m above mean sea level. The upstream baseflow gains from Holocene and Pleistocene aquifers throughout the year, contributing to 65 ± 4 % of the river discharge. On the contrary, the midstream baseflow contributes 44.6 ± 6.5 % of the river’s annual discharge to both Holocene and Pleistocene aquifers. The downstream is more complicated, where the baseflow loses to the Pleistocene aquifer and gains 73 ± 17 % of the river's annual discharge from the Holocene aquifer. The loss of baseflow was attributed to the high rate of groundwater mining.

Maintaining the vegetative cover over the recharge areas is recommended to reduce runoff and increase groundwater potential so that the baseflow could sustain the river stream.

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.