Abstract: With a focus on the difficulty of quantitatively describing the degree of nonuniformity of temporal and spatial distributions of water resources, quantitative research was carried out on the temporal and spatial distribution characteristics of water resources in Guangdong Province from 1956 to 2000 based on a cloud model. The spatial variation of the temporal distribution characteristics and the temporal variation of the spatial distribution characteristics were both analyzed. In addition, the relationships between the numerical characteristics of the cloud model of temporal and spatial distributions of water resources and precipitation were also studied. The results show that, using a cloud model, it is possible to intuitively describe the temporal and spatial distribution characteristics of water resources in cloud images. Water resources in Guangdong Province and their temporal and spatial distribution characteristics are differentiated by their geographic locations. Downstream and coastal areas have a larger amount of water resources with greater uniformity and stronger stability in terms of temporal distribution. Regions with more precipitation possess larger amounts of water resources, and years with more precipitation show greater nonuniformity in the spatial distribution of water resources. The correlation between the nonuniformity of the temporal distribution and local precipitation is small, and no correlation is found between the stability of the nonuniformity of the temporal and spatial distributions of water resources and precipitation. The amount of water resources in Guangdong Province shows an increasing trend from 1956 to 2000, the nonuniformity of the spatial distribution of water resources declines, and the stability of the nonuniformity of the spatial distribution of water resources is enhanced.
Abstract: Reference evapotranspiration (ET0) is often used to estimate actual evapotranspiration in water balance studies. In this study, the present and future spatial distributions and temporal trends of in the Xiangjiang River Basin (XJRB) in China were analyzed. during the period from 1961 to 2010 was calculated with historical meteorological data using the FAO Penman-Monteith (FAO P-M) method, while during the period from 2011 to 2100 was downscaled from the Coupled Model Intercomparison Project Phase 5 (CMIP5) outputs under two emission scenarios, representative concentration pathway 4.5 and representative concentration pathway 8.5 (RCP45 and RCP85), using the statistical downscaling model (SDSM). The spatial distribution and temporal trend of were interpreted with the inverse distance weighted (IDW) method and Mann-Kendall test method, respectively. Results show that: (1) the mean annual of the XJRB is 1 006.3 mm during the period from 1961 to 2010, and the lowest and highest values are found in the northeast and northwest parts due to the high latitude and spatial distribution of climatic factors, respectively; (2) the SDSM performs well in simulating the present and can be used to predict the future in the XJRB; and (3) CMIP5 predicts upward trends in annual under the RCP45 and RCP85 scenarios during the period from 2011 to 2100. Compared with the reference period (1961 to 1990), increases by 9.8%, 12.6%, and 15.6% under the RCP45 scenario and 10.2%, 19.1%, and 27.3% under the RCP85 scenario during the periods from 2011 to 2040, from 2041 to 2070, and from 2071 to 2100, respectively. The predicted increasing under the RCP85 scenario is greater than that under the RCP45 scenario during the period from 2011 to 2100.
Abstract: Based on the monthly precipitation and air temperature from 1960 to 1989 in the Luanhe River Basin, the standardized precipitation evapotranspiration index (SPEI) and standardized precipitation index (SPI) at three- and six-month time scales and the self-calibrating Palmer drought severity index (sc-PDSI) were calculated to evaluate droughts in the study area. Temporal variations of the drought severity from 1960 to 1989 were analyzed and compared based on the results of different drought indices, and some typical drought events were identified. Spatial distributions of the drought severity according to the indices were also plotted and investigated. The results reveal the following: the performances of different drought indices are closely associated with the drought duration and the dominant factors of droughts; the SPEI is more accurate than the SPI when both evaporation and precipitation play important roles in drought events; the drought severity shown by the sc-PDSI is generally milder than the actual drought severity from 1960 to 1989; and the evolution of the droughts is usually delayed according to the sc-PDSI. This study provides valuable references for building drought early warning and mitigation systems in the Luanhe River Basin.
Abstract: This study aimed to investigate the effect of temporal variability on the optimization of the Hydrologiska Byråns Vattenbalansavedlning (HBV) model, as well as the calibration performance using manual optimization and average parameter values. By applying the HBV model to the Jiangwan Catchment, whose geological features include lots of cracks and gaps, simulations under various schemes were developed: short, medium-length, and long temporal calibrations. The results show that, with long temporal calibration, the objective function values of the Nash-Sutcliffe efficiency coefficient (NSE), relative error (RE), root mean square error (RMSE), and high flow ratio generally deliver a preferable simulation. Although NSE and RMSE are relatively stable with different temporal scales, significant improvements to RE and the high flow ratio are seen with longer temporal calibration. It is also noted that use of average parameter values does not lead to better simulation results compared with manual optimization. With medium-length temporal calibration, manual optimization delivers the best simulation results, with NSE, RE, RMSE, and the high flow ratio being 0.563 6, 0.122 3, 0.978 8, and 0.854 7, respectively; and calibration using average parameter values delivers NSE, RE, RMSE, and the high flow ratio of 0.481 1, 0.467 6, 1.021 0, and 2.784 0, respectively. Similar behavior is found with long temporal calibration, when NSE, RE, RMSE, and the high flow ratio using manual optimization are 0.525 3, −0.069 2, 1.058 0, and 0.980 0, respectively, as compared with 0.490 3, 0.224 8, 1.096 2, and 0.547 9, respectively, using average parameter values. This study shows that selection of longer periods of temporal calibration in hydrological analysis delivers better simulation in general for water balance analysis.
Abstract: The seasonal variation characteristics of the water quality of the Jinpen Reservoir and the impacts of rainfall runoff on the reservoir were investigated. Water quality monitoring results indicated that, during the stable stratification period, the maximum concentrations of total nitrogen, total phosphorus, ammonia nitrogen, total organic carbon, iron ion, and manganese ion in the water at the reservoir bottom on September 6 reached 2.5 mg/L, 0.12 mg/L, 0.58 mg/L, 3.2 mg/L, 0.97 mg/L, and 0.32 mg/L, respectively. Only heavy storm runoff can affect the main reservoir and cause the water quality to seriously deteriorate. During heavy storms, the stratification of the reservoir was destroyed, and the reservoir water quality consequently deteriorated due to the high-turbidity particulate phosphorus and organic matter in runoff. The turbidity and concentrations of total phosphorus and total organic carbon in the main reservoir increased to 265 NTU, 0.224 mg/L, and 3.9 mg/L, respectively. Potential methods of dealing with the water problems in the Jinpen Reservoir are proposed. Both in stratification and in storm periods, the use of measures such as adjusting intake height, storing clean water, and releasing turbid flow can be helpful to safeguarding the quality of water supplied to the water treatment plants.
Abstract: Solid or liquid waste containing a high concentration of nicotine can pollute sediment in rivers and lakes, and may destroy the ecological balance if it is directly discharged into the environment without any treatment. In this study, the polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) method was used to analyze the variation of the microbial community structure in the control and nicotine-contaminated sediment samples with nicotine concentration and time of exposure. The results demonstrated that the growth of some bacterial species in the nicotine-contaminated sediment samples was inhibited during the exposure. Some bacteria decreased in species diversity and in quantity with the increase of nicotine concentration or time of exposure, while other bacteria were enriched under the effect of nicotine, and their DGGE bands changed from undertones to deep colors. The microbial community structure, however, showed a wide variation in the nicotine-contaminated sediment samples, especially in the sediment samples treated with high-concentration nicotine. The Jaccard index was only 35.1% between the initial sediment sample and the sediment sample with a nicotine concentration of 0.030 μg/g after 28 d of exposure. Diversity indices showed that the contaminated groups had a similar trend over time. The diversity indices of contaminated groups all decreased in the first 7 d after exposure, then increased until day 42. It has been found that nicotine decreased the diversity of the microbial community in the sediment.
Abstract: Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step finite element method at a relatively low Reynolds number of Re = 200 for various dimensionless ratios of and , where D is the cylinder diameter, L is the center-to-center distance between the two cylinders, and G is the gap between the lowest surface of the twin cylinders and the plane wall. The influences of and on the hydrodynamic force coefficients, Strouhal numbers, and vortex shedding modes were examined. Three different vortex shedding modes of the near wake were identified according to the numerical results. It was found that the hydrodynamic force coefficients and vortex shedding modes are quite different with respect to various combinations of and . For very small values of , the vortex shedding is completely suppressed, resulting in the root mean square (RMS) values of drag and lift coefficients of both cylinders and the Strouhal number for the downstream cylinder being almost zero. The mean drag coefficient of the upstream cylinder is larger than that of the downstream cylinder for the same combination of and . It is also observed that change in the vortex shedding modes leads to a significant increase in the RMS values of drag and lift coefficients.
Abstract: This study used the finite element method (FEM) to analyze the stress field and seepage field of a roller-compacted concrete (RCC) dam, with an upstream impervious layer constructed with different types of concrete materials, including three-graded RCC, two-graded RCC, conventional vibrated concrete (CVC), and grout-enriched vibrated RCC (GEVR), corresponding to the design schemes S1 through S4. It also evaluated the anti-seepage performance of the imperious layer in the four design schemes under the normal water level and flood-check level. Stress field analysis of a retaining section and discharge section shows that the maximum tensile stress occurs near the dam heel, the maximum compressive stress occurs near the dam toe, and the stress distributions in the four schemes can satisfy the stress control criteria. Seepage field analysis shows that the uplift pressure heads in schemes S3 and S4 descend rapidly in the anti-seepage region, and that the calculated results of daily seepage flow under the steady seepage condition in these two schemes are about 30% to 50% lower than those in the other two schemes, demonstrating that CVC and GEVR show better anti-seepage performance. The results provide essential parameters such as the uplift pressure head and seepage flow for physical model tests and anti-seepage structure selection in RCC dams.
Abstract: In order to study deposited sediment settlement and consolidation mechanisms, sediment settlement experiments were conducted using a settlement column. Based on the experimental results, sediment settlement stage definition, excessive pore pressure (EPP) dissipation, and consolidation constitutive equations are discussed. Three stages, including the free settlement, hindered settlement, and self-weight consolidation settlement stages, are defined. The results of this study show that sediment settlement is mainly affected by the initial sediment concentration and initial settlement height, and the interface settlement rate is attenuated linearly with time on bilogarithmic scales during the hindered settlement and self-weight consolidation settlement stages. Moreover, the deposited sediment layer in the self-weight consolidation settlement stage experiences large strains, and the settlement amount in this stage is about 32% to 59% of the initial height of deposited sediment. EPP is nonlinearly distributed in the settlement direction, and consolidation settlement is faster than EPP dissipation in the self-weight consolidation settlement stage. Consolidation constitutive equations for the hydraulic conductivity and effective stress, applicable to large-strain consolidation calculation, were also determined and fitted in the power function form.
Abstract: A high-frequency radar system has been deployed in Galway Bay, a semi-enclosed bay on the west coast of Ireland. The system provides surface currents with fine spatial resolution every hour. Prior to its use for model validation, the accuracy of the radar data was verified through comparison with measurements from acoustic Doppler current profilers (ADCPs) and a good correlation between time series of surface current speeds and directions obtained from radar data and ADCP data. Since Galway Bay is located on the coast of the Atlantic Ocean, it is subject to relatively windy conditions, and surface currents are therefore strongly wind-driven. With a view to assimilating the radar data for forecasting purposes, a three-dimensional numerical model of Galway Bay, the Environmental Fluid Dynamics Code (EFDC), was developed based on a terrain-following vertical (sigma) coordinate system. This study shows that the performance and accuracy of the numerical model, particularly with regard to tide- and wind-induced surface currents, are sensitive to the vertical layer structure. Results of five models using different layer structures are presented and compared with radar measurements. A variable vertical structure with thin layers at the bottom and the surface and thicker layers in the middle of the water column was found to be the optimal layer structure for reproduction of tide- and wind-induced surface currents. This structure ensures that wind shear can properly propagate from the surface layer to the sub-surface layers, thereby ensuring that wind forcing is not overdamped by tidal forcing. The vertical layer structure affects not only the velocities at the surface layer but also the velocities further down in the water column.
