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The geological cross-section of A-A 0 .

The geological cross-section of A-A 0 .

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The stagnant zones in nested flow systems have been assumed to be critical to accumulation of transported matter, such as metallic ions and hydrocarbons in drainage basins. However, little quantitative research has been devoted to prove this assumption. In this paper, the transport of age mass is used as an example to demonstrate that transported m...

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... Figure 6 shows the stratigraphy and lithology of the cross-section. The basement geometry shows that the basin is an asymmetric syncline. ...
Context 2
... The K 1 l sandstone, with a thickness of about 200 m, is one of the two most important aquifers. Based on poros- ity measurements of rock samples from boreholes B2 and B7 (Figure 6), the mean porosity of fluvial sandstone is 21.1%. Eolian sandstone rock samples from borehole B15 were measured to have a mean porosity of 27.8%. ...

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... On the other hand, a larger watershed can also increase the rainfall contribution to the intermediate flow, which is ultimately discharged to the low-lying streams. Local and intermediate flow systems are characterized by different groundwater residence times (Jiang et al., 2012). The two asynchronous signals in the baseflow can also interfere with each other. ...
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The responses of the nested groundwater flow systems (NGFS) to rainfall fluctuations and the impacts of the NGFS on surface runoff are explored using a fully coupled variably saturated groundwatersurface water model in conjunction with spectral analysis. Numerical experiments are designed to investigate the fractal behaviors of hydraulic head and surface runoff in different scenarios. The results show that the inlets, outlets, and flow patterns of the sub-systems of NGFS can change with rainfall. The scaling-exponent, defined as the slope of the power spectra of the fluctuations of hydraulic head or runoff, is used to depict the fractal behaviors. The scaling-exponent of the hydraulic head is highly variable within the unsaturated zone and local flow systems but remains constant within the intermediate and regional systems. Whether the scaling-exponent of surface runoff exhibits a linear relation with the watershed size depends on the proportion of baseflow in the runoff.
... However, a detailed groundwater head, chemistry, and age profiles, the key information for groundwater flow system identification, are hard to obtain in field conditions because the wells used for head measurements and groundwater sampling always have longer filters and mixed groundwater from different depths. For example, Jiang et al. (2012) highlighted the role of groundwater age profiles but only two 14 C data were available in each wellbore. ...
... Numerical modeling of groundwater age distributions in a basin has indicated that inflection points on depth-dependent dating curves could exist at interfaces between flow systems, especially at stagnation points (Jiang et al., 2012). For example, groundwater age in a regional flow system (RFS) or intermediate flow system (IFS) could be several orders of magnitude higher than that in an overlying local flow system (LFS) and subsequently cause a discontinuity in groundwater age at the interface between these systems. ...
... Hydrogeological conditions in the Ordos Plateau are characterized by shallow groundwater in a thin unconfined Quaternary sandy aquifer and relatively deep groundwater in a thick semi-confined Cretaceous sandstone aquifer. Scattered clayey lenses are present in this bedrock aquifer, causing anisotropic properties but do not break the relatively homogeneous feature of the aquifer media at the regional scale (Hou et al., 2008;Jiang et al., 2012). In the lake basins of the study area, the Quaternary aquifer is generally less than 10 m thick. ...
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Hierarchically nested groundwater flow systems have been widely investigated by numerical modeling and laboratory experiments but seldom recognized from in situ observations and testing. Groundwater age and geochemical profiles were obtained by the authors using a packer system along two wellbores drilled in the Ordos Plateau, China. Groundwater age profiles were constructed from ³H, ⁸⁵Kr, ¹⁴C, and ⁸¹Kr data, with the apparent age generally increasing with depth, while exhibiting several inflection points. These inflection points were compared with geochemical profiles and numerical modeling results to delineate groundwater flow systems. Inflection points with significant increases in the gradients of age and Cl⁻ concentration versus depth may indicate interfaces among flow systems. A concurrent decrease‐increase turning of groundwater age and Cl⁻ concentration is influenced by a stagnation point. The groundwater age profiles are quite different from previous studies, indicating that the method can greatly reduce the uncertainty in model construction.
... The position of the surface that separates local and regional flow is a function of hydrography (drainage density) and climate (recharge) (Goderniaux et al., 2013). The presence of local and regional multi-scale flow systems and their associated stagnation points leads to fractal scaling of RTDs (Cardenas & Jiang, 2010;Jiang et al., 2012;Kollet & Maxwell, 2008). Aquifer geometry as well as spatial variation of recharge have been found to result in complex RTD shapes (C. ...
... This process is a direct consequence of basin asymmetry since waters enter a territory of another flow system due to the differences in driving forces and/or geographic position. At the convergence of opposing flow systems under a discharge area, quasi-stagnant zones and hydraulic traps may develop and support heat and dissolved matter accumulation (Anderson and Munter 1981;Jiang et al. 2012;Jiang et al. 2011;Tóth 1987). ...
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Extensional domain type geothermal plays, as fertile targets for future resource development, consist of an orogen and an adjoining sedimentary basin of asymmetric physiographic and geologic setting. Preliminary geothermal potential, i.e. prospective geothermal regions, basin-scale flow patterns, heat transfer processes, temperature distribution and appearance of thermal springs were analyzed systematically by numerical simulations in groundwater basins with special emphasis on the effects of basin asymmetry. The importance of basin-scale regional groundwater flow studies in preliminary geothermal potential assessment was demonstrated for synthetic and real-life cases. A simulated series of simplified real systems revealed the effects of anisotropy, asymmetry of the topographical driving force for groundwater flow, basin heterogeneity and basal heat flow on heat accumulation, locations of thermal spring discharge and prevailing mechanisms of heat transfer. As a new aspect in basin-scale groundwater and geothermal studies, basin asymmetry was introduced which has a critical role in discharge and accumulation patterns, thus controlling the location of basin parts bearing the highest geothermal potential. During the reconnaissance phase of geothermal exploration, these conceptual, generalized and simplified groundwater flow and heat transport models can support the identification of prospective areas and planning of shallow and deep geothermal energy utilization, also with respect to reinjection possibilities. Finally, the scope of “geothermal hydrogeology” is defined in a scientific manner for the first time.
... In recent years, the hydrogeological communities all over the world have made new contributions to the field practice and mathematical simulation of groundwater flow systems (Doglioni et al. 2010;Vasić et al. 2019;von Asmuth and Knotters 2004;Xu et al. 2013). Chinese hydrogeologists also successively put forward the concept of groundwater flow since the 1980s (Jiang et al. 2012;Liang et al. 2013;Wang et al. 2017). However, compared with the development of numerical simulation, the progress of laboratory experiments is relatively slow, and there are few studies, which is a weak link in the study of groundwater flow system. ...
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Through laboratory data and the analysis of field observation data from the Heihe River Basin in China, groundwater movement (referred to as the groundwater flow) is confirmed, and the groundwater water head value at different vertical depths (in the same aquifer) at any point on the plane differs. When groundwater level rises dynamically, the water head at the lower part of the plane is higher than it is at the head of the upper part; when the groundwater level is dynamically reduced, the upper head is higher than the lower head. That is, the groundwater flow usually moves in an oblique direction, as is the case with the bottom plate. This phenomenon was first observed in laboratory water injection and pumping tests and was verified via the study of water levels at different burial depths for the same aquifer obtained from exploration wells using stratification techniques in the middle reaches of the Heihe River. At the same time, the stratification technology guarantees the practice and field verification of groundwater flow system theory.
... The study area is located in the Ordos Plateau, northwestern China (Fig. 1a,b). The main aquifer of the Ordos Plateau is the thick, poorly consolidated Cretaceous sandstone with sporadic clay lenses, which is an unconfined aquifer with a thickness of around 800-900 m (Hou et al. 2008;Jiang et al. 2012). The Cretaceous sandstone aquifer is overlain extensively by thin, unconsolidated Quaternary sediments, through which rainfall readily infiltrates. ...
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Improved understanding of interactions among the atmosphere, soil water and groundwater can be achieved by observing time-series of soil-water content and water-table fluctuations in a soil profile. Field observations at a site in China show that from mid-June to mid-September, when evapotranspiration is strong, direct groundwater recharge does not occur, and variations in soil-water content in the shallow part of the unsaturated zone are mainly controlled by atmospheric conditions; however, in the deeper part they are controlled by the fluctuating water table. Therefore, a one-dimensional (1D) model with a variable-head lower boundary condition (BC) is built to interpret the responses of soil-water flow to changes in atmospheric and groundwater conditions, and a 1D model with a fixed-head lower BC corresponding to the mean water-table depth is built for comparison. The model with a variable-head lower BC reproduces the observed variations in soil-water content, and results in much smaller groundwater evapotranspiration than the compared model. Moreover, the model with a variable-head lower BC shows a two-sided damping of variations in the soil-water flux from the surface and from the bottom, thus producing a stable middle layer with limited variation in soil-water flux. The limited but stable upward flux in the middle layer indicates restriction of both the direct recharge and evapotranspiration of groundwater. Therefore, this study enhances understanding of interactions between the atmosphere and groundwater in arid regions, and also on the appropriate selection of the lower BC of 1D variably saturated flow models.
... (Bredehoeft, 2018;Tóth, 2005). The spatial distribution of groundwater age in thick 700 unconfined aquifers (Jiang et al., 2010;Jiang et al., 2012) is also more complicated than that in a confined aquifer. Although the transient behavior of groundwater flow to geologically-controlled flowing wells has been studied in the 1950s (Hantush, 1959;Jacob and Lohman, 1952), there is no research on the transient groundwater flow to topographically-controlled flowing wells. ...
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The spewing of groundwater in flowing wells is a phenomenon of interest to the public, but little attention has been paid to the role of flowing wells on the science of groundwater. This study reviews that answering to problems related to flowing wells since the early 19th century led to the birth of many fundamental concepts and principles of groundwater hydrology. The concepts stemmed from flowing wells in confined aquifers include permeability and compressibility, while the principles include Darcy's law, role of aquitards on flowing well conditions and the piston flow pattern, steady-state well hydraulics in confined aquifers, and transient well hydraulics towards constant-head wells in confined or leaky aquifers, all of which are applicable even if flowing well conditions have disappeared. Due to the widespread occurrence of aquitards, there is a long-lasting misconception that flowing wells must be geologically-controlled. The occurrence of flowing wells in topographic lows of unconfined aquifers was anticipated in 1940 and later verified in the 1960s, accompanying with the birth of the theory of topographically-driven groundwater flow, which has been considered as a paradigm shift in groundwater hydrology. Based on studies following this new paradigm, several preconditions of flowing wells given in the 19th century have been found to be not necessary at all. This historical perspective of the causes of flowing well conditions and the role of flowing wells on the science of groundwater could lead to a deeper understanding of the evolution of groundwater hydrology.
... Various studies highlighted that a variation of the positions of SPs greatly influence the vertical HZ extension ( Gomez-Velez J et al., 2014, Marzadri et al., 2016, Singh et al., 2019. Furthermore, the reduced Darcy flux in the vicinity of SPs can lead to accumulation of transported solute and affect groundwater age dating ( Jiang X et al., 2011, Jiang X et al., 2012. ...
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Hyporheic exchange is affected by bedform geometry, which induces complex flow paths within the bedform. Additional factors that influence flow and solute transport in the hyporheic zone are layered profile sediments and density-driven flow. This study explored the combined effects of these factors on hyporheic exchange through laboratory experiments and numerical simulations involving infiltrating solute displacing less-dense resident water in a layered bedform with a low permeability layer (LPL). The bedform consisted of three horizontal layers, in which the hydraulic conductivity of the middle layer (LPL) was less than that of the top (TL) and bottom layers (BL). The results demonstrated that a previously unexplored combination of mechanisms (density effects and layered bedform) produces irregular spatial patterns of solute transport in the hyporheic zone. For instance, the width of solute plume within the bottom layers becomes narrowed compared with tracer transport. With increasing density contrast between infiltrating solute and resident water, the solute plume becomes much narrower, forming fingers. Numerical modeling further shows that the hydraulic conductivity contrast (HCC) and relative thickness (RT) of the hyporheic zone layers also affect the spatial solute transport patterns. As the hydraulic conductivity contrast or relative thickness increases, the plume becomes much narrower. Horizontal ambient flow (HAF) dominated in the bottom layers, and lateral solute spreading and mixing intensified with a higher hydraulic conductivity contrast and relative thickness. Furthermore, the vertical solute plume was detached by the horizontal ambient flow in the bottom layers with a discontinuous low permeability layer, forming a discontinuous zone of vertical solute transport.
... Aquifer parameters, such as hydraulic conductivity and specific storage, are the key parameters that control groundwater flow, subsurface temperature and solute transport (Jiang et al., 2012;Jiang et al., 2009;Manga et al., 2012;Wang et al., 2012). Thus, understanding aquifer hydrological properties is important in evaluating many engineering applications, such as groundwater resource management (Jiang et al., 2009), underground waste storage (Carrigan et al., 1991), slope stability assessment (Sterrett and Edil, 2010), seismic activity monitoring Yan et al., 2016), etc. Traditionally, pumping tests have been the most widely used methods for estimating aquifer properties, such as hydraulic conductivity and specific storage (Hvorslev, 1951;Jacob, 1940). ...
... Goldscheider et al., 2010;Tóth, 1995;Yang et al., 2013). Groundwater circulation in these situations can be described as a regional flow system which is generally gravity-driven by topographic gradients (Jiang et al., 2012;Mádl-Szőnyi and Tóth, 2015;Tóth, 1963;Yang et al., 2017). The precipitation falling in the higher-elevation regions percolates into the aquifer, and is heated to result in deep-seated thermal fluids. ...