Abstract: Variation trends of water resources in the Xiangjiang River Basin over the coming decades have been investigated using the variable infiltration capacity (VIC) model and 14 general circulation models' (GCMs') projections under the representative concentration pathway (RCP4.5) scenario. Results show that the Xiangjiang River Basin will probably experience temperature rises during the period from 2021 to 2050, with precipitation decrease in the 2020s and increase in the 2030s. The VIC model performs well for monthly discharge simulations with better performance for hydrometric stations on the main stream of the Xiangjiang River than for tributary catchments. The simulated annual discharges are significantly correlated to the recorded annual discharges for all the eight selected target stations. The Xiangjiang River Basin may experience water shortages induced by climate change. Annual water resources of the Xiangjiang River Basin over the period from 2021 to 2050 are projected to decrease by 2.76% on average within the range from -7.81% to 7.40%. It is essential to consider the potential impact of climate change on water resources in future planning for sustainable utilization of water resources.
Abstract: In this study, the hydromechanical behavior of a concrete fracture under coupled compressive and shear stresses was investigated. A special experimental device was designed to create a planar fracture in a cylindrical sample and to carry out different kinds of hydromechanical tests on the fracture. Four series of laboratory tests were performed on an ordinary concrete sample. Hydrostatic compression tests were first conducted to characterize the normal compressibility of the fracture. In the second series, direct shear tests were conducted on the fracture under different normal stresses. The maximal shear stress of the fracture was determined as a function of the normal stress. In the third series, fluid flow tests were carried out in view of characterizing the overall hydraulic conductivity of the fracture as a function of its opening and closure. Shear tests with a constant fluid pressure were finally performed to investigate the influence of fluid pressure on the deformation behavior of concrete fractures. Based on the experimental investigation, an elastoplastic model is proposed. This model takes into account the nonlinear elastic behavior of a fracture under normal compression and the plastic deformation and failure due to shear stress. The model was coupled with the classical Darcy’s law to describe the fluid flow along the fracture by considering the variation of permeability with fracture aperture. Numerical results agree with experimental data from various laboratory tests.
Abstract: The embedded water pipe system is often used as a standard cooling technique during the construction of large-scale mass concrete hydrostructures. The prediction of the temperature distribution considering the cooling effects of embedded pipes plays an essential role in the design of the structure and its cooling system. In this study, the singular boundary method, a semi-analytical meshless technique, was employed to analyze the temperature distribution. A numerical algorithm solved the transient temperature field with consideration of the effects of cooling pipe specification, isolation of heat of hydration, and ambient temperature. Numerical results are verified through comparison with those of the finite element method, demonstrating that the proposed approach is accurate in the simulation of the thermal field in concrete structures with a water cooling pipe.
Abstract: Drinking water is supplied through a centralized water supply system and may not be accessed by communities in rural areas of Malaysia. This study investigated the performance of a low-cost, self-prepared integrated activated carbon and sand filtration (CACSF) system for roof-harvested rainwater and lake water for potable use. Activated carbon was self-prepared using locally sourced coconut shell and was activated using commonly available salt rather than a high-tech procedure that requires a chemical reagent. The filtration chamber was comprised of local, readily available sand. The experiments were conducted with varying antecedent dry intervals (ADIs) of up to 15 days and lake water with varying initial chemical oxygen demand (COD) concentration. The CACSF system managed to produce effluents complying with the drinking water standards for the parameters pH, dissolved oxygen (DO), biochemical oxygen demand (BOD5), COD, total suspended solids (TSS), and ammonia nitrogen (NH3-N). The CACSF system successfully decreased the population of Escherichia coli (E. coli) in the influents to less than 30 CFU/mL. Samples with a higher population of E. coli (that is, greater than 30 CFU/mL) did not show 100% removal. The system also showed high potential as an alternative for treated drinking water for roof-harvested rainwater and class II lake water.
Abstract: This study evaluated the performance of rooftop catchment systems in securing non-potable water supply in Birjand, located in an arid area in southeastern Iran. The rooftop catchment systems at seven study sites of different residential buildings were simulated for dry, normal, and wet water years, using 31-year rainfall records. The trial and error approach and mass diagram method were employed to optimize the volume of reservoirs in five different operation scenarios. Results showed that, during the dry water year from 2000 to 2001, for reservoirs with volumes of 200 to 20000 L, the proportion of days that could be secured for non-portable water supply was on average computed to be 16.4%−32.6% across all study sites. During the normal water year from 2009 to 2010 and the wet water year from 1995 to 1996, for reservoirs with volumes of 200 to 20000 L, the proportions were 20.8%−69.6% and 26.8%−80.3%, respectively. Therefore, a rooftop catchment system showed a high potential to meet a significant portion of non-potable water demand in the Birjand climatic region. Reservoir volume optimization using the mass diagram method produced results consistent with those obtained with the trial and error approach, except at sites #1, #2, and #5. At these sites, the trial and error approach performed better than the mass diagram method due to relatively high water consumption. It is concluded that the rooftop catchment system is applicable under the same climatic conditions as the study area, and it can be used as a drought mitigation strategy as well.
Abstract: The estimation of non-point source pollution loads into the Danjiangkou Reservoir is highly significant to environmental protection in the watershed. In order to overcome the drawbacks of traditional watershed numerical models, a base flow separation method was established coupled with a digital filtering method and a flux method. The digital filtering method has been used to separate the base flows of the Hanjiang, Tianhe, Duhe, Danjiang, Laoguan, and Qihe rivers. Based on daily discharge, base flow, and pollutant concentration data, the flux method was used to calculate the point source pollution load and non-point source pollution load. The results show that: (1) In the year 2013, the total inflow of the six rivers mentioned above accounted for 95.9% of the total inflow to the Danjiangkou Reservoir. The total pollution loads of chemical oxygen demand (CODMn) and total phosphorous (TP) from the six rivers were 58.20 × 103 t and 1.863 × 103 t, respectively, and the non-point source pollution loads were 39.82 × 103 t and 1.544 × 103 t, respectively, indicating that the non-point source pollution is a major factor (with a contribution rate of 68.4% for CODMn and 82.9% for TP). (2) The Hanjiang River is the most significant contributor of pollution loads to the Danjiangkou Reservoir, and its CODMn and TP contribution rates reached 79.3% and 83.2%, respectively. The Duhe River took the second place. (3) Non-point source pollution mainly occurred in the wet season in 2013, accounting for 80.8% and 90.9% of the total pollution loads of CODMn and TP, respectively. It is concluded that the emphasis of pollution control should be placed on non-point source pollution.
Abstract: Simulations of two-dimensional (2D) flow past a circular cylinder with the smoothed particle hydrodynamics (SPH) method were conducted in order to accurately determine the drag coefficient. The fluid was modeled as a viscous liquid with weak compressibility. Boundary conditions, such as a no-slip solid wall, inflow and outflow, and periodic boundaries, were employed to resemble the physical problem. A sensitivity analysis, which has been rarely addressed in previous studies, was conducted on several SPH parameters. Hence, the effects of distinct parameters, such as the kernel choices and the domain dimensions, were investigated with the goal of obtaining highly accurate results. A range of Reynolds numbers (1 to 500) was simulated, and the results were compared with existing experimental data. It was observed that the domain dimensions and the resolution of SPH particles, in comparison to the obstacle size, affected the obtained drag coefficient significantly. Other parameters, such as the background pressure, influenced the transient condition, but did not influence the steady state at which the drag coefficient was determined.
Abstract: Numerical experiments were conducted using the Finite Volume Community Ocean Model (FVCOM) to study the impact of the initial density stratification on simulated currents over the Louisiana shelf during Hurricane Katrina. Model results for two simulation scenarios, including an initially stratified shelf and an initially non-stratified shelf, were examined. Comparison of two simulations for two-dimensional (2D) currents, the time series of current speed, and variations of cross-shore currents across different sections showed that the smallest differences between simulated currents for these two scenarios occured over highly mixed regions within 1 radius of maximum wind (RMW) under the hurricane. For areas farther from the mixed zone, differences increased, reaching the maximum values off Terrebonne Bay. These large discrepancies correspond to significant differences between calculated vertical eddy viscosities for the two scenarios. The differences were addressed based on the contradictory behavior of turbulence in a stratified fluid, as compared to a non-stratified fluid. Incorporation of this behavior in the Mellor-Yamada turbulent closure model established a Richardson number-based stability function that was used for estimation of the vertical eddy viscosity from the turbulent energy and macroscale. The results of this study demonstrate the necessity for inclusion of shelf stratification when circulation modeling is conducted using three-dimensional (3D) baroclinic models. To achieve high-accuracy currents, the parameters associated with the turbulence closures should be calibrated with field measurements of currents at different depths.
Abstract: Thermal deformation of a concrete dam changes periodically, and its variation lags behind the air temperature variation. The lag, known as the hysteresis time, is generally attributed to the low velocity of heat conduction in concrete, but this explanation is not entirely sufficient. In this paper, analytical solutions of displacement hysteresis time for a cantilever beam and an arch ring are derived. The influence of different factors on the displacement hysteresis time was examined. A finite element model was used to verify the reliability of the theoretical analytical solutions. The following conclusions are reached: (1) the hysteresis time of the mean temperature is longer than that of the linearly distributed temperature difference; (2) the dam type has a large impact on the displacement hysteresis time, and the hysteresis time of the horizontal displacement of an arch dam is longer than that of a gravity dam; (3) the reservoir water temperature variation lags behind of the air temperature variation, which intensifies the differences in the horizontal displacement hysteresis time between the gravity dam and the arch dam; (4) with a decrease in elevation, the horizontal displacement hysteresis time of a gravity dam tends to increase, whereas the horizontal displacement hysteresis time of an arch dam is likely to increase initially, and then decrease; and (5) along the width of the dam, the horizontal displacement hysteresis time of a gravity dam decreases as a whole, while the horizontal displacement hysteresis time of an arch dam is shorter near the center and longer near dam surfaces.
