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Hydraulic connections between a river and an adjacent aquifer are controlled by the river resistance and aquifer diffusivity. In this paper, we derive a spectral solution linking the power spectrum of river stage fluctuations to that of the hydraulic head of a confined aquifer by means of a physical scaling factor. The physical scaling factor represents an algebraic expression of the river resistance and aquifer diffusivity and is included in an exact spectral solution derived herein. Statistical measures of the aquifer diffusivity and river resistance are provided by fitting the solution versus observed groundwater hydraulic head obtained at several distances and/or frequencies. At a study site in the middle reach of the Yangtze River and downstream of the Three Gorges Dam in China, we find systematic damping of the hydraulic head variations with distance from the river, which follows a fractal pattern driven by the river stage. In general, the estimated parameters are consistent with results reported in the literature, which supports the validity of the proposed spectral approach, although the paper discusses advantages and limitations due to application conditions. Plain Language Summary: The characterization of hydraulic connections between a river and an adjacent aquifer requires knowledge of two critical parameters: the river resistance and the aquifer diffusivity. In this paper, we derive a spectral solution to link the power spectrum of river stage fluctuations to that of the groundwater hydraulic head in a confined aquifer and show how such solutions can be used to simultaneously assess the two critical parameters. Parameters estimated from the field case located in the middle reach of the Yangtze River and downstream of the Three Gorges Dam in China are consistent with results reported in the literature. Application conditions, advantages, and limitations of this spectral approach are also discussed. Key Points: The power spectrum of the hydraulic head is linked to that of the river stage by a scaling factorRiver resistance and aquifer diffusivity are analyzed in spectral formsTheoretical developments are applied to a field case study of the Yangtze River, China [ABSTRACT FROM AUTHOR]

Many deep aquifers overlain by barrier formations in the continental US are used as geological repositories for wastewaters coproduced from hydrocarbon exploration. This practice is to protect shallow groundwater following the US Environmental Protection Agency's regulation. Implicit in such practice is the assumption that deep aquifers overlain by mudstones or shales are confined so that the injected fluids will not migrate upward to contaminate shallow groundwater. However, no systematic test of this hypothesis has been made. Here we invert the groundwater response to both the M2 and the O1 tides and to the barometric pressure across a large (2.046 × 106 km2) geologic regime, the North China Platform, to systematically evaluate the hydraulic parameters as functions of depth and time without a priori assumption. Our result, the first of such inversion, shows no depth dependence of aquifer confinement to a depth of 3,400 m and that deep confined aquifers overlain by barrier formations may become leaky after distant earthquakes. It suggests that monitoring of aquifer confinement may be needed to ensure if the targeted deep aquifer for wastewater injection is really confined. The results may be timely and of global significance because the practice of hydrofracking for natural gas and the deep injection for the disposal of the coproduced wastewaters in the US may soon be adopted by other countries, such as China. Plain Language Summary: A great amount of wastewaters coproduced from hydrocarbon exploration in the mid‐continental US has been injected into deep aquifers. Such practice has been based upon an implicit assumption that deep aquifers confined by aquitards are fully confined so that the injected toxic water will not leak back to contaminate shallow groundwater or the environment. This assumption, however, has never been carefully tested. Here we test this hypothesis using groundwater data from wells over a large geological regime, the North China Platform, as a function of depth and time. Our results show no clear dependence of aquifer confinement on depth, that significant leakage occurs even in the deepest studied aquifer (>3400 m) confined by thick clay/mud aquitards, and that an initially confined aquifer became may leaky after a distant earthquake. Because the practice of hydrofracking for natural gas and deep injection for the disposal of the coproduced wastewaters may soon be adopted by other countries, such as China, our study is timely and may be of global significance. Key Points: Systematic evaluation of the confinement of aquifers in the North China Platform at different depths down to 3.4 kmNovel revealing most of the studied aquifers leak, and has no dependence on aquifer depth or thickness of the overlain geologic barrierBoth the M2 and O1 tidal waves are used in the inversion of aquifer parameters without a prior assumption [ABSTRACT FROM AUTHOR]

Ground rupture due to groundwater pumping is a major environmental hazard accompanying land subsidence in some areas. Ground ruptures usually develop when a significant compaction affects a sedimentary sequence with peculiar geological conditions, for example, the presence of a shallow bedrock with buried ridges. A laboratory test was developed with the aim at improving our understanding of the mechanisms responsible for rupture generation in this particular hydrogeological setting, typical, for instance, of the Guangming village, China. A 0.8‐m high concrete prism, representing a rocky ridge, was placed in a 4.0‐m long, 1.8‐m wide, and 1.4‐m high box and buried by alluvial material. The box was saturated and then drained, with the formation of a main crack above the prism‐shaped ridge. The measured water content, vertical displacements, strains, rupture initiation, and growth are analyzed through an original coupled 3D‐numerical model, simulating the variably saturated groundwater flow in a deformable and fractured porous medium. To our knowledge, this is the first application of such a kind of model to a lab‐scale experiment. Despite the uncertainty on the material parameters, the numerical model allows satisfactorily reproducing the observed groundwater flow, land subsidence, and rupture features (depth and width). The rupture dynamics is captured in part as well, despite the employment of a simple Mohr–Coulomb failure criterion and although other forces (e.g., electrochemical) may likely play a role at the metric scale of the lab test. The modeling outcomes provide a clear view on how the rupture develops from the surface and propagates downward. Key Points: A large lab experiment was carried out to reproduce rupture development due to aquifer exploitation above a bedrock ridgeA novel coupled 3D model of variably saturated flow in deformable and fractured porous media was developed and applied to the lab experimentThe numerical model allows to describe the brittle rupture initiation and growth over time [ABSTRACT FROM AUTHOR]