Water Science and Engineering - 开云电竞网

Flood disaster monitoring based on Sentinel-1 data: A case study of Sihu Basin and Huaibei Plain, China

Yuan Xu, Zhang Xiao-chun, Wang Xiu-gui, Zhang Yu — 2021-06-01

Yuan Xu, Zhang Xiao-chun, Wang Xiu-gui, Zhang Yu Summer floods occur frequently in many regions of China, affecting economic development and social stability. Remote sensing is a new technique in disaster monitoring. In this study, the Sihu Basin in Hubei Province of China and the Huaibei Plain in Anhui Province of China were selected as the study areas. Thresholds of backscattering coefficients in the decision tree method were calculated with the histogram analysis method, and flood disaster monitoring in the two study areas was conducted with the threshold method using Sentinel-1 satellite images. Through satellite-based flood disaster monitoring, the flooded maps and the areas of expanded water bodies and flooded crops were derived. The satellite-based monitoring maps were derived by comparing the expanded area of images during a flood disaster with that before the disaster. The difference in spatiotemporal distribution of flood disasters in these two regions was analyzed. The results showed that flood disasters in the Sihu Basin occurred frequently in June and July, and flood disasters in the Huaibei Plain mostly occurred in August, with a high interannual variability. Flood disasters in the Sihu Basin were usually widespread, and the affected area was between Changhu and Honghu lakes. The Huaibei Plain was affected by scattered disasters. The annual mean percentages of flooded crop area were 14.91% and 3.74% in the Sihu Basin and Huaibei Plain, respectively. The accuracies of the extracted flooded area in the Sihu Basin in 2016 and 2017 were 96.20% and 95.19%, respectively. Water Science and Engineering. 2021 14(2): 87-96.

Influence of cascade reservoirs on spatiotemporal variations of hydrogeochemistry in Jinsha River

Yuan Qiu-sheng, Wang Pei-fang, Chen Juan, Wang Chao, Liu Sheng, Wang Xun — 2021-06-01

Yuan Qiu-sheng, Wang Pei-fang, Chen Juan, Wang Chao, Liu Sheng, Wang Xun River hydrogeochemistry offers necessary guidance for effective water environmental management. However, the influence of cascade reservoirs on river hydrogeochemistry remains unknown. In this study, the Jinsha River, the headwaters of the Yangtze River of China, was selected to investigate the spatiotemporal variations of hydrogeochemistry after the construction of six cascade reservoirs. Major ions, total dissolved solids, electrical conductivity, and pH values of sampled water in the upper natural reaches and lower reservoir-regulated reaches were analyzed in both flood and dry seasons. The results of Piper diagram and Gibbs plots showed that the hydrogeochemistry of the Jinsha River was naturally controlled by both evaporation-crystallization and carbonate weathering processes, but it was also artificially affected by reservoirs. The impoundment of cascade reservoirs affected the hydrodynamic condition of the river. The river flow in the flood season was reduced by approximately 24.5%, altering the proportions of water sources and leading to notable hydrogeochemical alterations in reservoir-regulated reaches. Conversely, river hydrogeochemistry generally remained unchanged in the dry season, owing to the insignificant effect of cascade reservoirs on river flow. In contrast to what has been observed in previous studies of individual reservoirs, the cumulative influence of cascade reservoirs on the Jinsha River flow regime did not cause abrupt hydrogeochemical changes between the upstream and downstream areas of each reservoir. Moreover, the water quality assessments revealed that the impoundment of cascade reservoirs improved downstream irrigational water quality, with lower Na⁺ ratio values in the flood season. This study provides the earliest evaluation of cascade reservoir influence on the hydrogeochemistry of the Jinsha River. The findings of this study can be used as a reference for scientific guidelines for future environmental management of cascade reservoirs in large rivers. Water Science and Engineering. 2021 14(2): 97-108.

Preparation and characterization of Fe₂O₃/Bi₂WO₆ composite and photocatalytic degradation mechanism of microcystin-LR

Ni Li-xiao, Du Cun-hao, Wu Han-qi, Li Yan, Li Xiang-lan, Xu Chu — 2021-06-01

Ni Li-xiao, Du Cun-hao, Wu Han-qi, Li Yan, Li Xiang-lan, Xu Chu The long-standing popularity of semiconductor photocatalysis, due to its great potential in a variety of applications, has resulted in the creation of numerous semiconductor photocatalysts, and it stimulated the development of various characterization methods. In this study, Fe₂O₃/Bi₂WO₆ composite with a flower-like microsphere and hierarchical structure was synthesized with the facile hydrothermal-impregnation method without any surfactants. X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy, and photoluminescence spectroscopy were used to characterize the structures of the samples. The specific surface area was estimated with the Brunauer-Emmett-Teller (BET) method, and pore size distribution was determined using the Barrett-Joyner-Halenda (BJH) method. The synthesized Fe₂O₃/Bi₂WO₆ composite had an average diameter of approximately 4 nm, with smaller specific surface area and larger pore diameter than those of pristine Bi₂WO₆. The results of XRD and SEM analyses confirmed that the composite was composed of Fe₂O₃ and Bi₂WO₆. The absorption edge of Bi₂WO₆ was at a wavelength of 460 nm. By contrast, the absorption edge of Fe₂O₃/Bi₂WO₆ to visible light was redshifted to 520 nm, with narrower bandgap width and stronger visible light response. It was also found that the main active substances in the degradation of microcystin-LR (MC-LR) were hydroxyl radicals (·OH) and electron holes (h⁺). Consequently, the results further showed that the heterojunction between Fe₂O₃ and Bi₂WO₆ can improve the charge transfer rate and effectively separate the photoinduced electrons and holes. Compared with Bi₂WO₆, Fe₂O₃/Bi₂WO₆ had no significant difference in the adsorption capacity of MC-LR and had more efficient photocatalytic degradation activity of MC-LR. The degradation rates of MC-LR by Fe₂O₃/Bi₂WO₆ and Bi₂WO₆ reached 80% and 56%, respectively. The degradation efficiency of MC-LR was affected by the initial pH value, initial Fe₂O₃/Bi₂WO₆ concentration, and initial MC-LR concentration. Water Science and Engineering. 2021 14(2): 109-118.

Photodegradation of reactive blue 19 dye using magnetic nanophotocatalyst α-Fe₂O₃/WO₃: A comparison study of α-Fe₂O₃/WO₃ and WO₃/NaOH

Delnavaz Mohammad, Farahbakhsh Javad, Mahdian Seyed Sajad — 2021-06-01

Delnavaz Mohammad, Farahbakhsh Javad, Mahdian Seyed Sajad The photocatalytic degradation of reactive blue 19 (RB19) dye was investigated in a slurry system using ultraviolet (UV) and light-emitting diode (LED) lamps as light sources and using magnetic tungsten trioxide nanophotocatalysts (α-Fe₂O₃/WO₃ and WO₃/NaOH) as photocatalysts. The effects of different parameters including irradiation time, initial concentration of RB19, nanophotocatalyst dosage, and pH were examined. The magnetic nanophotocatalysts were also characterized with different methods including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL), differential reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometry (VSM). The XRD and FTIR analyses confirmed the presence of tungsten trioxide on the iron oxide nanoparticles. The VSM analysis confirmed the magnetic ability of the new synthesized nanophotocatalyst α-Fe₂O₃/WO₃ with 39.6 emu/g of saturation magnetization. The reactor performance showed considerable improvement in the α-Fe₂O₃-modified nanophotocatalyst. The impact of visible light was specifically investigated, and it was compared with UV-C light under the same experimental conditions. The reusability of the magnetic nanophotocatalyst α-Fe₂O₃/WO₃ was tested during six cycles, and the magnetic materials showed an excellent removal efficiency after six cycles, with just a 7% decline. Water Science and Engineering. 2021 14(2): 119-128.

Enhancement of removal efficiency of heavy metal ions by polyaniline deposition on electrospun polyacrylonitrile membranes

Mohammad Noor, Atassi Yomen — 2021-06-01

Mohammad Noor, Atassi Yomen This paper describes the preparation of a membrane of polyacrylonitrile (PAN) and its corresponding membrane coated with polyaniline (PANI) for the adsorption of heavy metal ions. Scanning electron microscopy micrographs revealed that all the membranes exhibited nanofibrous morphology. The prepared membranes were characterized by Fourier transform infrared spectroscopy (FTIR). The prepared membranes were used as an adsorbent for hazardous heavy metal ions Pb²⁺ and Cr₂O₇^2-. The adsorption capacity and the removal efficiency of the membranes were examined as function of the initial adsorbate concentration and pH of the medium. Coated membranes with PANI showed better adsorption performance and their direct current (DC) conductivities were correlated to heavy metal ion concentrations. Adsorption isotherms were also performed, and the adsorption process was tested according to the Langmuir and Freundlich models. The regeneration and reuse of the prepared membranes to re-adsorb heavy metal ions were also investigated. The enhancement in adsorption performance and reusability of PANI-coated membranes in comparison with non-coated ones is fully discussed. The results show that the maximum adsorption capacities of lead and chromate ions on the PANI-coated membranes are 290.12 and 1 202.53 mg/g, respectively. Water Science and Engineering. 2021 14(2): 129-138.

Assessment of physicochemical properties of water and their seasonal variation in an urban river in Bangladesh

Rahman Arafat, Jahanara Ishrat, Jolly Yeasmin Nahar — 2021-06-01

Rahman Arafat, Jahanara Ishrat, Jolly Yeasmin Nahar To assess the magnitude of water quality decline in the Turag River of Bangladesh, this study examined the seasonal variation of physicochemical parameters of water, identified potential pollution sources, and clustered the monitoring months with similar characteristics. Water samples were collected in four distinct seasons to evaluate temperature, pH, dissolved oxygen (DO) concentration, five-day biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), electrical conductivity (EC), chloride ion (Cl⁻) concentration, total alkalinity (TA), turbidity, total dissolved solids (TDS) concentration, total suspended solids (TSS) concentration, and total hardness (TH) using standard methods. The analytical results revealed that 40% of water quality indices were within the permissible limits suggested by different agencies, with the exception of EC, Cl⁻ concentration, TA, turbidity, DO concentration, BOD₅, and COD in all seasons. Statistical analyses indicated that 52% of the contrasts were significantly different at a 95% confidence interval. The factor analysis presented the best fit among the parameters, with four factors explaining 94.29% of the total variance. TDS, BOD₅, COD, EC, turbidity, DO, and Cl⁻ were mainly responsible for pollution loading and were caused by the significant amount of industrial discharge and toxicological compounds. The cluster analysis showed the seasonal change in surface water quality, which is usually an indicator of pollution from rainfall or other sources. However, the values of different physicochemical properties varied with seasons, and the highest values of pollutants were recorded in the winter. With the change in seasonal temperature and increase in rainfall, the seasonal Turag River water followed a self-refining trend as follows: rainy season > pre-winter > summer > winter. Water Science and Engineering. 2021 14(2): 139-148.

Estimation of unloading relaxation depth of Baihetan Arch Dam foundation using long-short term memory network

He Ming-jie, Li Hao, Xu Jian-rong, Wang Huan-ling, Xu Wei-ya, Chen Shi-zhuang — 2021-06-01

He Ming-jie, Li Hao, Xu Jian-rong, Wang Huan-ling, Xu Wei-ya, Chen Shi-zhuang The unloading relaxation caused by excavation for construction of high arch dams is an important factor influencing the foundation's integrity and strength. To evaluate the degree of unloading relaxation, the long-short term memory (LSTM) network was used to estimate the depth of unloading relaxation zones on the left bank foundation of the Baihetan Arch Dam. Principal component analysis indicates that rock characteristics, the structural plane, the protection layer, lithology, and time are the main factors. The LSTM network results demonstrate the unloading relaxation characteristics of the left bank, and the relationships with the factors were also analyzed. The structural plane has the most significant influence on the distribution of unloading relaxation zones. Compared with massive basalt, the columnar jointed basalt experiences a more significant unloading relaxation phenomenon with a clear time effect, with the average unloading relaxation period being 50 d. The protection layer can effectively reduce the unloading relaxation depth by approximately 20%. Water Science and Engineering. 2021 14(2): 149-158.

Prediction of boundary shear stress distribution in straight open channels using velocity distribution

Malvandi Behzad, F. Maghrebi Mahmoud — 2021-06-01

Malvandi Behzad, F. Maghrebi Mahmoud Conventional methods for measuring local shear stress on the wetted perimeter of open channels are related to the measurement of the very low velocity close to the boundary. Measuring near-zero velocity values with high fluctuations has always been a difficult task for fluid flow near solid boundaries. To solve the observation problems, a new model was developed to estimate the distribution of boundary shear stress from the velocity distribution in open channels with different cross-sectional shapes. To estimate the shear stress at a point on the wetted perimeter by the model, the velocity must be measured at a point with a known normal distance to the boundary. The experimental work of some other researchers on channels with various cross-sectional shapes, including rectangular, trapezoidal, partially full circular, and compound shapes, was used to evaluate the performance of the proposed model. Optimized exponent coefficients for the model were found using the multivariate Newton method with the minimum of the mean absolute percentage error (MAPE) between the model and experimental data as the objective function. Subsequently, the calculated shear stress distributions along the wetted perimeter were compared with the experimental data. The most important advantage of the proposed model is its inherent simplicity. The mean MAPE value for the seven selected cross-sections was 6.9%. The best results were found in the cross-sections with less discontinuity of the wetted perimeter, including the compound, trapezoidal, and partially full circular pipes. In contrast, for the rectangular cross-section with an angle between the bed and walls of 90°, MAPE increased due to the large discontinuities. Water Science and Engineering. 2021 14(2): 159-166.

Issues influencing accuracy of hydrological modeling in a changing environment

Xu Chong-yu — 2021-06-01

Xu Chong-yu Water Science and Engineering. 2021 14(2): 167-170.