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The determination of groundwater hydrochemical facies (GHF) is useful for analyzing the chemical composition of groundwater, tracking sources of groundwater recharge and assessing how its chemical composition changes along groundwater flowpaths due to water–rock interactions. This paper proposes a geographical information systems (GIS)-based method for identifying and mapping the spatial distribution of GHF categories in an aquifer. Several procedures including spatial interpolation, raster reclassification, raster-to-vector conversion, spatial union overlay, and generalization methods are coupled in GIS tools to determine the type and distribution of GHF categories. This method was implemented to distinguish shallow GHF categories for a shallow aquifer near Fuyang City in Anhui Province, China. The results obtained from the GIS assessment of water quality data from 30 wells show there were seven types of hydrochemical facies identified in the study area. The major GHFs categories are HCO3–Na + K + Ca + Mg, HCO3–Ca + Mg, HCO3–Na + K + Ca, and HCO3–Na + K, which cover 94% of the total area. The GIS method correctly identified the GHF categories determined in 80% of the wells in the area. The major GHFs categories progressively change in the direction of groundwater flow from HCO3–Ca + Mg to HCO3–Na + K+Ca + Mg, then to HCO3–Na + K + Ca, and then to HCO3–Na + K. The changes in the proportions of major ions in groundwater, coupled with salinity increases in the direction of groundwater flow are due to the combined effects of water–rock interactions in the aquifer and human activities. The method can relatively efficiently identify and map GHF zones for aquifers.

A single fracture is usually idealized theoretically as smooth parallel plates, but the real fractures are rough-walled with points of contact. Though relative roughness is considered in quantifying the flow through a single rough fracture (SRF) previously, additional factors such as the distribution of rough elements and bending degree of streamlines should be considered in order to obtain more accurate results. Semiempirical friction factor (f) and discharge per unit width (q) equations are first deduced taking relative roughness, roughness elements distribution and streamline reattachment length into consideration. A horizontal SRF model was then set up and a series of experiments and simulations were performed. Main conclusions are drawn: Recirculation of streamlines arises in the rough element and the intensity of the recirculation increases with the angle from which the streamlines enter into the rough elements and Reynolds number (Re); streamlines are discontinuously distributed when asperity height is large and nonlinear flow occurs; the nonlinearity of the flow increases with the increasing the asperity height and Re; the critical value of related roughness used to judge whether the influence of roughness on water flow through a SRF can be ignored or not should be much lower than 0.033; the revised f and q equations under laminar flow through a SRF are proved to be better when calculating the f and q values.

Groundwater is often a unique water source for agriculture, industry and domestic use for local inhabitants in semi-arid African continent owing to shortage of surface water and rainfall. It is of significance to quantify and assess the groundwater resources for local sustainable development in order to correctly evaluate groundwater resources of Zinder well field with fractured media in Zinder, Niger. A conceptual model of hydrogeology was set up by a geological and hydrogeological survey. For simulating the real conditions, a large multi-well pumping test with designed pumping rate was conducted. In addition, a two-dimensional finite-element transient flow model was developed to simulate groundwater flow at the site. Results show that generally good agreements have been found between the simulated and observed hydrogeology heads for the test. The hydraulic parameters were obtained from the pumping test. A 11-year prediction of groundwater resources has been made under three exploitation schemes, respectively, and it indicates that the well field can offer 7,000 m3/day when the aquifer remains confined. An optimal scheme of exploitation is provided.

Major ion chemistry of groundwater from main aquifers near the Dingi Coal Mine (Anhui, China) was analyzed with a suite of statistical techniques, in an effort to understand aquifer connectivity and groundwater geochemical evolution. Fifty-seven groundwater samples were analyzed from four aquifers: the Cenozoic top, middle, bottom aquifers and a Permian coal strata aquifer. With increasing depth of the aquifers, groundwater became more mineralized showing greater hardness and salinity. The dissolutions of halite and sylvite, carbonate, sulfate, and silicate minerals were the primary processes controlling groundwater chemical compositions in the Cenozoic bottom and coal strata aquifers, while (K+ + Na+) and HCO3 − originating from silicate mineral weathering were more enriched in the coal strata aquifer. Principal component analysis (PCA) identified two principal components, with the first component representing hardness variation and accounting for 57.5 % of total variance, and the second component (23.5 % of total variance) controlled primarily by salinity and sulfate reduction process. The Cenozoic bottom aquifer had greater hardness than other aquifers whereas the coal strata aquifer was characterized by higher salinity and larger influences of sulfate reduction. Cluster analysis revealed that the coal strata aquifer was largely isolated from the Cenozoic aquifers with possible infiltration at discrete locations, indicating that the high-yield, thick Cenozoic aquifers may serve as a potential additional source for groundwater inrush into coal mines.

Hydrogeochemical characteristic analysis of multiple categorical aquifers, including the delineation of hydrogeochemical spatial distributions, can provide a basic understanding of the groundwater flow system necessary for the prevention and control of groundwater damage associated with coal mines. Nonlinear principal component analysis (PCA) was used to analyse the groundwater chemical characteristics of water samples from five aquifers in Gubei Coal Mine, Anhui Province, China. In particular, Ca2+, Mg2+, Na+ + K+, HCO3 −, Cl−, SO4 2−, and pH were analysed. To analyse the spatial distribution of groundwater chemistry in this Permian fractured aquifer, interpolation of principal component 1 (PC1) scores obtained from the nonlinear PCA was performed using the inverse distance weighting (IDW) method. Additionally, concentrations of the hydrogeochemical variables were plotted against depth. The relationships between water samples, variables, and water samples with variables were simultaneously analysed by nonlinear PCA. The results show: (1) nonlinear PCA explains more variability than standard PCA in the first two principal components (PCs); (2) the Cenozoic top aquifer has low concentrations of Na+ + K+ and Cl−; the Cenozoic middle aquifer and Cenozoic bottom aquifer are characterised by high concentrations of Ca2+ and Mg2+ and low concentrations of HCO3 −; the shallow groundwater of the Permian fractured aquifer is recharged by the Cenozoic bottom aquifer, while other parts have high concentrations of HCO3 − and low concentrations of Ca2+ and Mg2+. The Taiyuan limestone aquifer has similar groundwater chemistry to that of the Cenozoic bottom aquifer, and thus it may be recharged by the Cenozoic bottom aquifer in outcropping Taiyuan Formation strata; (3) the wide south-western and north-western areas of the Permian fractured aquifer may be recharged by the Cenozoic bottom aquifer; and (4) concentrations of Ca2+ and Mg2+ in the Permian fractured aquifer are negatively correlated with sampling depth, while the concentrations of Na+ + K+ and HCO3 − are positively correlated with sampling depth, which verifies that the shallow groundwater of this Permian fractured aquifer is recharged by the Cenozoic bottom aquifer. The findings demonstrate that combining nonlinear PCA with GIS can be a powerful approach for conducting spatial nonlinear analysis of hydrogeochemical characteristics.

Fractal method has been widely applied to many different fields since it can reveal the hidden methodological structures of the sophisticated phenomena in the natural world and obtain more reasonable prediction results. This paper deals with the feasibility of predicting dissolved oxygen (DO) in complex watershed system using fractal method. It adopted sectioned variable dimension fractal model to predict river DO, and yielded satisfactory results with relatively high prediction accuracy. The absolute values of percent relative errors were all less than 6%, most less than 4%. Fractal interpolation method was also employed to simulate river DO by plotting interpolation DO graphs. These findings have important application potential in terms of water DO prediction in complex watershed system.