Abstract: Grain-size distribution data, as a substitute for measuring hydraulic conductivity (K), has often been used to get K value indirectly. With grain-size distribution data of 150 sets of samples being input data, this study combined the Artificial Neural Network technology (ANN) and Markov Chain Monte Carlo method (MCMC), which replaced the Monte Carlo method (MC) of Generalized Likelihood Uncertainty Estimation (GLUE), to establish the GLUE-ANN model for hydraulic conductivity prediction and uncertainty analysis. By means of applying the GLUE-ANN model to a typical piedmont region and central region of North China Plain, and being compared with actually measured values of hydraulic conductivity, the relative error ranges are between 1.55% and 23.53% and between 14.08% and 27.22% respectively, the accuracy of which can meet the requirements of groundwater resources assessment. The global best parameter gained through posterior distribution test indicates that the GLUE-ANN model, which has satisfying sampling efficiency and optimization capability, is able to reasonably reflect the uncertainty of hydrogeological parameters. Furthermore, the influence of stochastic observation error (SOE) in grain-size analysis upon prediction of hydraulic conductivity was discussed, and it is believed that the influence can not be neglected.
Abstract: The presence of groundwater is strongly related to its geological and geohydrological conditions. It is, however, important to study the groundwater potential in an area before it is utilized to provide clean water. Werner-Schlumberger's method was used to analyze the groundwater potential while hydraulic properties such as soil porosity and hydraulic conductivity were used to determine the quality and ability of the soil to allow water's movement in the aquifer. The results show that the aquifer in the Sekara and Kemuning Muda is at a depth of more than 6 meters below the ground level with moderate groundwater potential. It is also found that the aquifer at depths of over 60 m have high groundwater potential. Moreover, soil porosity in Kemuning is found to be average while the ability to conduct water was moderate. This makes it possible for some surface water to seep into the soil while the remaining flows to the rivers and ditches.
Abstract: The purpose of this paper was to assess the impact of urbanization on the groundwater level (GWL) in aquifers of Binh Duong (BD) Province. The research method is to analyze the trend of GWL, the recharge capacity of surface over time and the relationship between them. The data of the GWL used in the study are the average values in the dry and rainy seasons of 35 observation wells from 2011 to 2018, which are in Pleistocene and Pliocene aquifers. The ability to recharge groundwater from the surface in this study was represented by the curve number (CN), a parameter used in hydrology for calculating direct runoff or infiltration from rainfall. The land use data to identify the CN was analyzed from the Landsat images. The results show that besides over-exploitation, the change of surface characteristic due to the urbanization development process is also the cause of the GWL decline. The analysis of seasonal GWL data shows that the increase in impervious surface area is the cause of GWL decline in the Pleistocene aquifer, which is more evident in the rainy season than in the dry season. The statistical results also show that in the rainy season and in shallow aquifers, a higher CN change can be found with the wells that had a remarkable GWL decline compared to the remaining wells.
Abstract: Engineering Nanoparticles (ENPs)' superior characteristics of adsorption depends on their dispersion in the medium. In this study, multi-walled carbon nanotubes (nonmetal), iron nanoparticles and silver nanoparticles (metallic simple substance), and Nano-TiO2, Nano-Fe2O3 and Nano-ZnO (metal oxide) were selected and respectively added into pure water and aqueous solution with 1% Sodium dodecyl benzene sulfonate (SDBS) surfactant. The dispersion effects were compared by leaving the solutions standing at room temperature under ultrasound. The results show that the dispersion of iron nanoparticles is the lowestamong the six ENPs, and that of multi-walled carbon nanotubes (MWCTS) is the highest. Adding anionic surfactants (SDBS) can obviously improve the dispersion performance of ENPs. The concentration of solution decreases by only 5% in 10 daysafter adding 1% SDBS for ultrasonic dispersion.
Abstract: Sustainable management of groundwater resources has now become an obligation, especially in arid and semi-arid regions given the socio-economic importance of this resource. The optimization in zoning for groundwater exploitation helps in planning and managing groundwater supply works such as boreholes and wells in the catchment. The objective of this study is to use remote sensing and GIS-based Analytical Hierarchy Process (AHP) techniques to evaluate the groundwater potential of Wadi Saida Watershed. Spatial analysis such as geostatistics was also used to validate results and ensure more accuracy. Through the GIS tools and remote sensing technique, earth observation data were converted into thematic layers such as lineament density, geology, drainage density, slope, land use and rainfall, which were combined to delineate groundwater potential zones. Based on their respective impact on groundwater potential, the AHP approach was adopted to assign weights on multi-influencing factors. These results will enable decision-makers to optimize hydrogeological exploration in large-scale catchment areas and map areas. According to the results, the southern part of the Wadi Saida Watershed is characterized as a higher groundwater potential area, where 32% of the total surface area falls in the excellent and good class of groundwater potential. The validation process revealed a 71% agreement between the estimated and actual yield of the existing boreholes in the study area.
Abstract: In order to explore the influence of rainfall on the release of heavy metal Cadmium (Cd) in soil in a coal-mining area,soil column leaching experiments were carried out by simulating 3 types of rainfall (acid rain,normal rainfall,and actual rainfall) with 5 different pH values (4,5,6,6.7,7),and 65 groups of data about leachate pH value and Cd concentration were obtained respectively. The results indicate the general change rule of Cd concentration in leachate: (1) the easiness of Cd release is negatively correlated to the pH value of leaching solution and positively correlated the leaching amount; (2) leaching solution with lower pH values shows more obvious release stages. Leached by solution with different pH values,the release of Cd in soil ranks as follows: Acid rain group > normal rainfall group > actual rainfall group. In the first stage,the acidity of rainfall has a significant impact on the release of Cd in soil,but in the second stage,the release of Cd is alleviated due to the soil buffering. Among the four dynamic equations to simulate the release of Cd in soil,the modified Elovich equation can describe the process most accurately,with the highest coefficient of determination R2 of 0.997 5. These results can serve as a reference for further study on the migration,transformation and enrichment of Cd in soil.
Abstract: When groundwater pollution occurs, to come up with an efficient remediation plan, it is particularly important to collect information of contaminant source (location and source strength) and hydraulic conductivity field of the site accurately and quickly. However, the information can not be obtained by direct observation, and can only be derived from limited measurement data. Data assimilation of observations such as head and concentration is often used to estimate parameters of contaminant source. As for hydraulic conductivity field, especially for complex non-Gaussian field, it can be directly estimated by geostatistics method based on limited hard data, while the accuracy is often not high. Better estimation of hydraulic conductivity can be achieved by solving inverse groundwater problem. Therefore, in this study, the multi-point geostatistics method Quick Sampling (QS) is proposed and introduced for the first time and combined with the iterative local updating ensemble smoother (ILUES) to develop a new data assimilation framework QS-ILUES. It helps to solve the contaminant source parameters and non-Gaussian hydraulic conductivity field simultaneously by assimilating hydraulic head and pollutant concentration data. While the pilot points are utilized to reduce the dimension of hydraulic conductivity field, the influence of pilot points' layout and the ensemble size of ILUES algorithm on the inverse simulation results are further explored.
Abstract: More and more experimental results show that Darcy's law is not fully applicable in low permeability media, and non-Darcy flow has been identified. In this paper we reviewed the research of non-Darcy flow experiments in low-permeability media in recent decades, discuss the existence of non-Darcy flow, and summarize its constitutive equations. The reasons for the threshold gradient were also discussed and summarized for the criterion of the critical point of non-Darcy flow. On this basis, the future development of non-Darcy flow experiments in the rock and clay media were discussed, in order to provide a certain reference for subsequent research on seepage laws in low permeability media.