Abstract: Drought is one of the most widespread and devastating extreme climate events when water availability is significantly below normal levels for a long period. In recent years, the Haihe River Basin has been threatened by intensified droughts. Therefore, characterization of droughts in the basin is of great importance for sustainable water resources management. In this study, two multi-scalar drought indices, the standardized precipitation evapotranspiration index (SPEI) with potential evapotranspiration calculated by the Penman–Monteith equation and the standardized precipitation index (SPI), were used to evaluate the spatiotemporal variations of drought characteristics from 1961 to 2017 in the Haihe River Basin. In addition, the large-scale atmospheric circulation patterns were used to further explore the potential links between drought trends and climatic anomalies. An increasing tendency in drought duration was detected over the Haihe River Basin with frequent drought events occurring in the period from 1997 to 2003. The results derived from both SPEI and SPI demonstrated that summer droughts were significantly intensified. The analysis of large-scale atmospheric circulation patterns indicated that the intensified summer droughts could be attributed to the positive geopotential height anomalies in Asian mid-high latitudes and the insufficient water vapor fluxes transported from the south.
Abstract: Climate change might have direct impacts on water quantity in Egypt and lead to indirect effects on Mediterranean saltwater intrusion to groundwater, which exposes agriculture to vulnerability. This study investigated impacts of climate change on agriculture, with particular regard to food security and socioeconomy, and quantified the effectiveness of cropping pattern adaptation measures by integrating three mathematical models. The BlueM model was used for hydrological simulations of Nasser Lake under flooding scenarios to predict the water supply from the High Aswan Dam. The water and salinity balance (WB-SAL) model was adopted to estimate the water salinity in the Nile Delta. The simulated results from the BlueM and WB-SAL models were integrated with the agricultural simulation model for Egypt (ASME) to project cropping patterns, food security, and socioeconomy throughout the country. The results showed that future climate change will directly affect the total crop area; crop areas for 13 crop types; the self-sufficiency of wheat, rice, cereal, and maize supplies; and socioeconomic indicators. The proposed cropping pattern adaptation measures focus on fixing the crop areas of rice and orchards and providing half of the population with lentils, maize, onion, vegetables, milk, and meat. The adaptation measures have the potential to promote food security without causing deterioration of the socioeconomic situation. However, water availability has much more significant effects on food security and socioeconomy than cropping pattern adaptation measures do. Accordingly, the country should rationalize water use efficiency and increase water supply.
Abstract: Drought generally has significant impacts on crops. It is essential to quantitatively evaluate the relationship between crop production and drought degree to provide technical support for drought disaster prevention. In this study, a drought degree index that can reflect the changes in precipitation, evapotranspiration, and soil moisture was developed on the basis of crop yield reduction rate. Four drought scenarios were set up to simulate the effects of meteorological drought on drought degree of crops at different growth stages. A cusp catastrophe model was constructed to analyze the mutation characteristics of the drought degree of maize at different growth stages under different meteorological drought conditions. Xi'an City in China was selected as the study area, and summer maize was selected as the research crop. Precipitation and crop yield data from 1951 to 2010 were used as the fundamental data to investigate drought degree mutation of summer maize. The results show that, under the meteorological drought conditions at the emergence-jointing stage, drought degree may change abruptly, and soil moisture content at the sowing-emergence, jointing-tasseling, and tasseling-mature stages should be kept higher than 39%.
Abstract: In this study, the removal of monovalent and divalent cations, Na+, K+, Mg2+, and Ca2+, in a diluted solution from Chott-El Jerid Lake, Tunisia, was investigated with the electrodialysis technique. The process was tested using two cation-exchange membranes: sulfonated polyether sulfone cross-linked with 10% hexamethylenediamine (HEXCl) and sulfonated polyether sulfone grafted with octylamine (S-PESOS). The commercially available membrane Nafion® was used for comparison. The results showed that Nafion® and S-PESOS membranes had similar removal behaviors, and the investigated cations were ranked in the following descending order in terms of their demineralization rates: Na+ > Ca2+ > Mg2+ > K+. Divalent cations were more effectively removed by HEXCl than by monovalent cations. The plots based on the Weber–Morris model showed a strong linearity. This reveals that intra-particle diffusion was not the removal rate-determining step, and the removal process was controlled by two or more concurrent mechanisms. The Boyd plots did not pass through their origin, and the sole controlling step was determined by film-diffusion resistance, especially after a long period of electrodialysis. Additionally, a semi-empirical model was established to simulate the temporal variation of the treatment process, and the physical significance and values of model parameters were compared for the three membranes. The findings of this study indicate that HEXCl and S-PESOS membranes can be efficiently utilized for water softening, especially when effluents are highly loaded with calcium and magnesium ions.
Abstract: The process of ultrafiltration (UF) of natural seawater often encounters the problems of variation in water quality and coastal blooms. To validate the feasibility of UF in shellfish farms, this study compared the hydraulic performance and pollutant removal efficiency of the UF process with those of the commonly used treatments that combine several filtration steps with ultraviolet (UV) disinfection. The comparison was conducted in the cases of natural seawater and a coastal bloom. Given that the UF process encountered the specific type of pollution, this study evaluated the filtration performance of the UF process and the retention of total suspended solids (TSS), bacteria, phytoplankton, and zooplankton. A real coastal bloom was considered in the case study of an experimental shellfish hatchery/nursery in France. The results show that both treatments were able to eliminate approximately 50% of TSS. However, in contrast with UV treatment combined with filtration, the UF process retained total amounts of phytoplankton, zooplankton, and bacteria in the bloom. Although the hydraulic performance of the UF process was impacted by the coastal bloom, the fouling was eliminated through chemical cleaning conducted at a frequency less than once per 12 h. Despite the severe pollution, this study confirmed the pollution resistance and treatment performance of the UF process, indicating that UF has the potential to enhance the biosecurity level.
Abstract: The mechanical parameters of materials in a dam body and dam foundation tend to change when dams are reinforced in aging processes. It is important to use an early-warning index to reflect the safety status of dams, particularly of heightened projects in the impoundment period. Herein, a new method for monitoring the safety status of heightened dams is proposed based on the deformation monitoring data of a dam structure, a statistical model, and finite-element numerical simulation. First, a fast optimization inversion method for estimation of dam mechanical parameters was developed, which used the water pressure component extracted from a statistical model, an improved inversion objective function, and a genetic optimization iterative algorithm. Then, a finite element model of a heightened concrete gravity dam was established, and the deformation behavior of the dam with rising water levels in the impoundment period was simulated. Subsequently, mechanical parameters of aged dam parts were calculated using the fast optimization inversion method with simulated deformation and the water pressure deformation component obtained by the statistical model under the same conditions of water pressure change. Finally, a new early-warning index of dam deformation was constructed by means of the forward-simulated deformation and other components of the statistical model. The early-warning index is useful for forecasting dam deformation under different water levels, especially high water levels.
Abstract: Ported wall extensions are important hydraulic structures used to reduce crosscurrents in upper approaches to locks. The effect of such extensions located upstream of a solid guard wall on flow characteristics depends on many factors, including geometric and hydraulic parameters. In this study, the hydraulic performance of ported wall extensions was experimentally investigated in terms of the permeability coefficient, expanding angle, extension length, and flow depth. The results demonstrate that the dimensionless maximum transverse velocity is closely related to the permeability coefficient, expanding angle, and flow depth. By contrast, the dimensionless eddy length mainly depends on the permeability coefficient, expanding angle, and extension length. Furthermore, the optimum permeability coefficient increases with the expanding angle or flow depth, and it is approximately constant for different extension lengths. These results have the potential to provide direct guidance for the design of effective ported wall extensions in upper approaches to locks.
Abstract: Strong free-surface water vortices are found throughout industrial hydraulic systems used for water treatment, flow regulation, and energy generation. Previous models using the volumetric flow rate as a model input have generally been semi-empirical, and have tended to have some limitations in terms of the design of practical hydropower systems. In this study, an analytical model of a strong free-surface water vortex was developed. This model only requires the water head and geometric parameters as its inputs and calculates the maximum volumetric flow rate, air-core diameter, and rotational constant. Detailed experimental depth–discharge data from a full-scale gravitational vortex hydropower system, unavailable in the relevant literature, were obtained, and the simulated results showed excellent agreement with the experimental observations. These data could be used to verify similar models using laboratory-scale physical models in order to investigate the scaling effects. In contrast to previous models, this model does not assume a constant average velocity across the vortex radius and allows precise calculation of the resultant velocity vectors. Therefore, this model presents advantages in turbine design for energy generation systems.
Abstract: Supersaturation of dissolved gases in natural water, due to spillage from high dams and other factors, may cause fish mortality. In previous experiments, the dissipation coefficient has been used to denote the degassing process of total dissolved gas (TDG) saturation. These experiments mainly analyzed supersaturated TDG dissipation from a macroscopic view. To precisely clarify the mechanism of supersaturated TDG release, this study investigated bubble adsorption at a wall surface from a microscopic view. The experiment was conducted in a Plexiglas-wall container filled with supersaturated TDG water. A model that calculates the adsorption flux of supersaturated TDG by a solid wall, and helps describe construction for a contact angle at a three-phase intersection, was developed according to Young's equation. This model was used to investigate the formation process of bubbles adsorbed on a solid polymethyl methacrylate (PMMA) surface in supersaturated TDG water. The adsorption effect of a solid wall on TDG release was analyzed based on the experimental data. The modeling results were compared with observations under different wall area conditions, and it was found that TDG release tended to increase with wall area. This study helps improve our understanding of the mechanisms of supersaturated TDG release and provides an important theoretical method for accurate calculation of the release process. The adsorption flux model of the solid wall provides mitigation measures to combat the adverse effects of TDG supersaturation, which will be beneficial to the protection of aquatic organisms in hydropower-regulated rivers.
