Abstract: Urbanization can alter the hydrogeomorphy of streams and rivers, change stream network structures, and reduce stream network connectivity, which leads to the decrease in the storage capacity of stream network and aggravates flood damages. Therefore, it is of great importance to investigate how stream network connectivity impacts flood storage capacity and flood control in urbanized watersheds. This study proposed a framework to assess stream network connectivity and its impact on flood control. Firstly, a few connectivity indices were adopted to assess longitudinal stream network connectivity. Afterward, the static and dynamic storage capacities of stream network were evaluated using storage capacity indices and a one-dimensional hydrodynamic model. Finally, the impact of stream network connectivity change on flood control was assessed by investigating the changes in stream network connectivity and storage capacity. This framework was applied to the Qinhuai River Basin, China, where intensive urbanization occurred in the last several decades. The results show that stream network storage capacity is affected by stream network connectivity. Increasing stream network connectivity enhances stream network storage capacity.
Abstract: Rivers in arid and semi-arid regions are threatened by droughts and climate change. This study focused on a comparative evaluation of the impacts of climate change and droughts on the vulnerability of river flows in three basins with diverse climates in Iran. The standardized precipitation-evapotranspiration index (SPEI) and precipitation effectiveness variables (PEVs) extracted from the conjunctive precipitation effectiveness index (CPEI) were used to analyze the drought severity. To investigate hydrological droughts in the basins, the normalized difference surface water index (NDSWI) and the streamflow drought index (SDI) were calculated and compared. The effects of droughts were assessed under various representative concentration pathway (RCP) scenarios. Changes in the number of wet days and precipitation depth restricted hydrological droughts, whereas an increasing number of dry days amplified their severity. The projected increases in dry days and precipitation over short durations throughout a year under future climate scenarios would produce changes in drought and flood periods and ultimately impact the frequency and severity of hydrological droughts. Under RCP 4.5, an increase in the frequencies of moderate and severe meteorological/hydrological droughts would further affect the Central Desert Basin. Under RCPs 2.6 and 8.5, the frequencies of severe and extreme droughts would increase, but the drought area would be smaller than that under RCP 4.5, demonstrating less severe drought conditions. Due to the shallow depths of most rivers, SDI was found to be more feasible than NDSWI in detecting hydrological droughts.
Abstract: In this study, a model for the development of the wide floodplain in the lower Yellow River, in China was proposed. This model includes flood control schemes using grading criteria, enables sediment deposition in partitioned zones, and allows free exchange between channel runoff and sediments. The wide floodplain located between the main channel and levees are divided into three typical regions: the tender, low, and high floodplains. Different ecological models should be applied when these floodplains are constructed. This study described the associated research ideas and methodology, and clarified several key issues, such as sediment prediction and regulation, land planning, land use, and multi-dimensional framework of safeguard measures for industries in the lower Yellow River floodplain. A refined ecological development model was proposed for the lower Yellow River floodplain, and future work on ecological and sustainable development of the lower floodplain was suggested. To establish a comprehensive system integrating runoff and sediment resource regulation in the Yellow River Basin, future work should focus on runoff and sediment exchange mechanisms in the wandering lower reach. Furthermore, it is necessary to improve theories on floodplain planning and ecological construction, and these theories should be integrated with the research findings on land development across the lower Yellow River floodplain.
Abstract: This study aimed to synthesize green tea nano zero-valent iron (GT-NZVI) and bentonite-supported green tea nano zero-valent iron (B-GT-NZVI) nanoparticles using green tea extracts in an environmentally sustainable way. Bentonite was used as a support material because it disperses and stabilizes GT-NZVI, and it helps to reduce the cost, increase the adsorption capacity of GT-NZVI, and decrease the optimum amount of GT-NZVI used in Fenton-like oxidation. A scanning electron microscope, atomic force microscopy, and a Fourier transform infrared spectroscope were used to characterize GT-NZVI and B-GT-NZVI, while the zeta potential was measured to evaluate the stability of iron nanoparticles. The decolorization kinetics of reactive blue 238 (RB 238) dye in the aqueous phase in the Fenton-like oxidation process were investigated as well. The effects of various experimental conditions such as reaction time, dosages of catalysts, concentration of H2O2, temperature, addition of inorganic salts, and other parameters were investigated. The results show that the oxidative degradation efficiencies of RB 238 dye catalyzed by GT-NZVI and B-GT-NZVI were 93.5% and 96.2%, respectively, at the optimum reaction conditions as follows: c(H2O2) = 5 mmol/L, ρ(GT-NZVI) or ρ(B-GT-NZVI) = 0.5 g/L, c(RB 238 dye) = 0.05 mmol/L, and pH = 2.5 at 180 min. The best catalytic performance was exhibited when B-GT-NZVI was used. Three kinetic models were employed, and the second-order model was found to be the best model representing the experimental kinetic data of RB 238 dye. The value of activation energy decreased from 38.22 kJ/mol for GT-NZVI to 14.13 kJ/mol for B-GT-NZVI. This indicates that the effect of B-GT-NZVI in decreasing the energy barrier is more pronounced than that of the GT-NZVI catalyst, leading to improved Fenton-like oxidation processes.
Abstract: Oxygen is important in maintaining a clean and reliable water environment. Designing heterojunction photocatalysts that can evolve oxygen from water splitting through an artificial Z-scheme pathway is a promising strategy for solving environmental problems. In this study, flower-like MoS2 nanostructures were fabricated via a simple hydrothermal process, and the electrostatic-based assembly ion-exchange method was used to construct a tandem Ag3PO4/MoS2/g-C3N4 (AMC) heterojunction. The as-synthesized photocatalyst exhibited significant improvements in harvesting visible light and transporting charge carriers. Moreover, the catalyst similar to the Z-scheme with intimate interface contact exhibited high oxygen evolution performance. The oxygen evolution activity of the optimal AMC-10 catalyst was approximately 11 times that of the pristine Ag3PO4. The results indicated that addition of a small amount of the flower-like MoS2 could significantly enhance the efficiency of oxygen evolution by the heterojunction. The findings in this study provide an alternative pathway for rationally designing efficient oxygen-evolving photocatalysts to improve the quality of water and rehabilitate the water environment.
Abstract: Orange peel is a biomass derived from citrus processing with desirable properties for metal sorption. In recent years, orange peel has been used to remove various heavy metals and toxic oxyanions. Selenium (Se) is an essential trace element for mammals. However, when the concentration of selenium exceeds an umbral limit, it becomes toxic. In this study, orange peel was used to treat Se(IV)-contaminated water. A high sorption capacity of 32.5 mg/g was obtained at the temperature of 20ºC and a pH of 2.0. Hydroxyl groups took actions to bind Se(IV) to the surface of the orange peel. The sorption process was spontaneous and endothermic. A chemical sorption mechanism was involved in the removal of Se(IV). The Thomas and modified dose-response models were used to simulate the experimental breakthrough curves. The bed depth service time model was used to calculate the critical bed depth (), and the calculated value was 1.6 cm. This study reveals that orange peel is a useful sorbent for Se(IV), and it is appropriate for the purification of Se(IV)-contaminated water.
Abstract: In this study, field observations were conducted after a heavy rainfall event in the Sumida and Shakujii rivers in Tokyo, Japan. The flow dynamics and fluxes of salt, suspended sediments (SS), and dissolved oxygen (DO) were investigated with the mass balance method. The fractions of freshwater and saltwater in seaward and landward flows were separated. The maximum salt flux in the Shakujii River was 53.8 kg/s during the flood tide, and those in the Sumida River were 680.3 kg/s at the upstream station and 703.7 kg/s at the downstream station. The trends of SS and DO were similar in both rivers. In the Shakujii River, the highest SS (3.1 kg/s) and DO (0.4 kg/s) fluxes appeared during the flood tide after rainfall. In the Sumida River, the maximum SS fluxes (6.1 and 6.3 kg/s at the upstream and downstream stations, respectively) and DO fluxes (1.15 and 1.21 kg/s at the upstream and downstream stations, respectively) appeared during the ebb tide. The mass balance method was used to estimate discharge, salinity, SS concentration, and DO concentration at a station with missing data. The results show that the estimated salinity and SS concentration were in a significant correlation with the on-site observations with correlation coefficients (R) of 0.950 and 0.835, respectively, but not for DO (R = 0.638). The disparity between the computed and measured data may be explained by the differences in velocity, salinity, topography, sedimentation, and the presence of organic matters. The analysis based on the advective salt transport components found a lower salt flux in the Shakujii River (0.36 kg/(m·s)) in comparison with that in the Sumida River (2.88 kg/(m·s)). This indicates a higher probability for salt retention in the Shakujii River.
Abstract: Ship-induced hydrodynamics play an important role in shaping the cross-sectional profile of inland waterways and produce a large amount of pressure on the fluvial environment. This study aimed at quantifying the characteristics of ship-induced waves and currents in a heavy shipping traffic waterway via intensified field measurements conducted in the Changzhou segment of the Grand Canal, in Jiangsu Province, China. Based on the processed hydrodynamic data, waves and currents caused by single ships and multiple ships were investigated. For single ships, the ship-induced wave heights estimated with empirical formulas were not consistent with the observations. Categorized by the loading conditions of barges, the drawdown height was characterized by the ratio of ship speed to its limit speed. The maximum non-dimensional ship-induced wave height was parameterized by a nonlinear combination of the depth Froude number and a blockage coefficient. For multiple ships, when ships closely followed each other or interlaced each other’s paths, it was difficult to characterize the superposition of several ship wakes. The magnitudes of current velocities induced by single ships and multiple ships were respectively nine and six times as large as those of natural flow. This may result in more severe sediment (re)suspension than natural flows.
