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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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... on analytical solutions of hydraulic head and stream function, Jiang et al. [2011] studied the dynamics of groundwater around stagnation points in nested flow systems and found that stagnation points could be divided into three types. A regional convergent stagnation point, which is caused by convergence of two flow systems, is located at the basin bottom ( Figure 1a); a regional divergent stagnation point, which is caused by divergence of two flow systems, is also located at the basin bottom ( Figure 1b); a local stagnation point, is located inside the basin and is caused by diver- gence and convergence of four flow systems ( Figure 1c). ''Local'' is due to the fact that at least one of these four flow systems belongs to a local flow system. ...
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... on analytical solutions of hydraulic head and stream function, Jiang et al. [2011] studied the dynamics of groundwater around stagnation points in nested flow systems and found that stagnation points could be divided into three types. A regional convergent stagnation point, which is caused by convergence of two flow systems, is located at the basin bottom ( Figure 1a); a regional divergent stagnation point, which is caused by divergence of two flow systems, is also located at the basin bottom ( Figure 1b); a local stagnation point, is located inside the basin and is caused by diver- gence and convergence of four flow systems ( Figure 1c). ''Local'' is due to the fact that at least one of these four flow systems belongs to a local flow system. ...
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... on analytical solutions of hydraulic head and stream function, Jiang et al. [2011] studied the dynamics of groundwater around stagnation points in nested flow systems and found that stagnation points could be divided into three types. A regional convergent stagnation point, which is caused by convergence of two flow systems, is located at the basin bottom ( Figure 1a); a regional divergent stagnation point, which is caused by divergence of two flow systems, is also located at the basin bottom ( Figure 1b); a local stagnation point, is located inside the basin and is caused by diver- gence and convergence of four flow systems ( Figure 1c). ''Local'' is due to the fact that at least one of these four flow systems belongs to a local flow system. ...
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... Based on qualitative analysis, Tóth [1980,1999] pro- posed that transported matter such as metallic ions and hydrocarbons could accumulate in stagnant zones. The accu- mulation of metallic ions or petroleum in stagnant zones at the discharge end of a basin where two regional flow systems converge or a regional flow system ascends, i.e., around the regional convergent stagnation points as shown in Figure 1a, has been reported by several researchers [Baskov, 1987;Garven, 1985;Garven and Freeze, 1984;Sanford, 1994;Tóth, 1980, 1988. However, there has been little, if any, quantitative research on the accumulation of transported mat- ter in stagnant zones around regional divergent stagnation points or local stagnation points. ...
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... The measured hydraulic head by packer test and the simulated hydraulic head at different depths of B15 are shown in Figure 10. The absolute values of the differences between measured and simulated hydraulic head range between 0.20 m and 1.51 m, demonstrating that the hetero- geneity and anisotropy of hydraulic conductivity is well characterized. ...
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... to the conceptual model of groundwater flow shown in Figure 8, groundwater mainly flows horizon- tally in the K 1 l sandstone part of B2, and is near a regional divergent stagnation point in the K 1 l sandstone part of B7. The 14 C ages in the K 1 l sandstone part of B2 and B7 are 21,400 years and 19,110 years, respectively (Figure 11c). The simulated age in the K 1 l sandstone part of B2 is around 21,500 year, and is very close to the measured age. ...
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... Groundwater sampled from the K 1 h sandstone part of B7 was measured to be 440 years (Figure 11c), however, the simulated age ranges between 0 and 9000 years from the top to the bottom of the K 1 h sandstone. It is hard to compare these two values because it is difficult to tell which depth groundwater had been sampled at. ...
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... The distributions of hydraulic head, groundwater flow systems and groundwater age of the cross-section obtained from the calibrated model are shown in Figure 11. Hydraulic head is high around the Sishi Ridge, and has a general trend of decreasing toward west and east (Figure 11a). ...
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... The distributions of hydraulic head, groundwater flow systems and groundwater age of the cross-section obtained from the calibrated model are shown in Figure 11. Hydraulic head is high around the Sishi Ridge, and has a general trend of decreasing toward west and east (Figure 11a). Around the Sishi Ridge, which is the regional recharge zone, hydraulic head ranges between 1370 and 1380 m. ...
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... Streamlines help to identify the flowpath of ground- water and the distribution of groundwater flow systems (Figure 11b). The Sishi Ridge is the recharge zone of two regional flow systems, one intermediate flow system and one local flow system. ...
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... Sishi Ridge is the recharge zone of two regional flow systems, one intermediate flow system and one local flow system. Figure 11b also shows the location of two local stagnation points (SP 1 and SP 2) and one re- gional divergent stagnation points (SP 3). SP 1 west of the Dosit River divides four flow systems, including two local flow systems, one intermediate flow system and one re- gional flow system. ...
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... groundwater can reach the Hekou Reservoir through a regional flow system, local flow systems dominate. Due to the large penetration depths of the two local flow systems over SP 2 in Figure 11b, groundwater has its maximum age (larger than 60,000 years but smaller than 120,000 years) around SP 2. This phenomenon is similar to the age distribution around SP 4 in Figure 2c. Sensitivity analysis of dispersivity shows that, smaller dispersivity would lead to an even greater maximum age, while larger dispersivity would result in much younger waters. ...
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... The characteristics of dynamics and age of ground- water around the local stagnation point SP 1 in Figure 11b are discussed below. This point is chosen because borehole B2, where measurements of 14 C age are available, might be within the zone of influence of SP 1. Figure 12 shows the distributions of groundwater age in the western part of the cross-section, as well as four contours of hydraulic head, two dividing streamlines and four schematic streamlines showing the flow direction. ...
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... The characteristics of dynamics and age of ground- water around the local stagnation point SP 1 in Figure 11b are discussed below. This point is chosen because borehole B2, where measurements of 14 C age are available, might be within the zone of influence of SP 1. Figure 12 shows the distributions of groundwater age in the western part of the cross-section, as well as four contours of hydraulic head, two dividing streamlines and four schematic streamlines showing the flow direction. The four contours of hydraulic head of 1220.51 m and 1220.55 m, show the potentiometric minimum around SP 1. ...
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... In Figure 12, it is evident that groundwater below SP 1 is much older than groundwater above SP 1. We plot the vertical distribution of groundwater age through SP 1 under different dispersivities (Figure 13a). ...
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... In Figure 12, it is evident that groundwater below SP 1 is much older than groundwater above SP 1. We plot the vertical distribution of groundwater age through SP 1 under different dispersivities (Figure 13a). Under different longitudinal dispersivities ranging between 30 and 300 m, groundwater age has an abrupt increase near SP 1, and reaches a maximum value below SP 1. ...
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... In B2, the 14 C age in the lower part of K 1 h sand- stone is measured to be 26,060 years, which is several thou- sands years older than groundwater in the K 1 l sandstone (21,400 years). In our calibrated model ( L ¼ 100 m), the maximum age in the lower part of K 1 h sandstone is about 24,260 years, which is almost 3000 years older than the simulated age in the K 1 l sandstone (Figure 13b). If a smaller dispersivity L ¼ 30 m is used, the maximum age in the lower part of K 1 h sandstone is about 7000 years older than the simulated age in the K 1 l sandstone. ...
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... the three available deep wells with age measurements, we found that two of them are located near stagnation points, i.e., B2 is located near a local stagnation point and B7 is located near a regional divergent stagnation point below the divide. Future efforts could be directed to collecting more age data in the area around the Dosit River (Figure 11c) at the elevation of 700$800 m. the maximum groundwater age is located at the stagnation point below basin valley. When regional flow is weak or absent, local stagnation points can be close enough to, or even reach, the basin bottom. ...

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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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... 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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... 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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... 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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... 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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... (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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... 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. ...