Conceptual and numerical models of the glacial aquifer system north of Aberdeen, South Dakota

Abstract. Earth fissures accompanying anthropogenic land subsidence due to excessive aquifer exploitation create significant geohazards in China. Numerical models represent a unique scientific approach to predict the generation and development of earth fissures. However, the common geomechanical simulators fail to reproduce fissure development because they cannot be effectively applied in discontinuous mechanics. An innovative modelling approach developed recently is applied to develop a software to simulate fissure development. The pressure changes are used as forcing factors in a 3D geomechanical model, which combines Finite Elements and Interface Elements to simulate the deformation of the continuous aquifer system and the generation and sliding/opening of earth fissures. The approach has been applied to simulate the earth fissures at Guangming Village in Wuxi, China with land subsidence of more than 1 m caused by the overexploitation of the second confined aquifer. The modelling results highlight that the earth fissures at Guangming Village have been caused by tension and shear stresses. Based on the developed modelling approach and the application case study, a software platform is developed to provide a fast preliminary evaluation of the risk of fissure occurrence associated to land subsidence. The software allows for the simulation of a simplified 2D conceptual geologic model of earth fissures, which can be used to investigate how the main factors controlling the geomechanical response of the aquifer system, such as pressure changes, geometry of aquifer system, geomechanical properties, and depth of bedrock/fault etc.

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An analytical study of groundwater fluctuations in unconfined leaky aquifers induced by multiple localized recharge and withdrawal

Global NEST Journal ◽

10.30955/gnj.001037 ◽

2013 ◽

Vol 15 (3) ◽

pp. 394-407 ◽

Cited By ~ 7

Keyword(s):

Groundwater Flow ◽

Numerical Models ◽

Temporal Distribution ◽

Neumann Boundary ◽

Unconfined Aquifer ◽

Flow Equation ◽

Aquifer System ◽

Fourier Cosine ◽

Induced Flow ◽

Vertical Leakage

Commonly used analytical methods for assessing the effects of recharge and withdrawal on the groundwater flow system are based on an idealistic assumption that the aquifer’s base is fully impervious. In reality, the hydrostratigraphic conditions are often complex and involve leakage induced flow between aquifer and the confining layers. In this study, a simple analytical procedure is presented for determining the spatial and temporal distribution of water head in an unconfined aquifer system due to multiple localized recharge and withdrawal at time-varying rates. A new transient function is introduced that can conveniently approximate the rising and recession limbs of any single recharge hydrograph. Solution of linearized two-dimensional groundwater flow equation under Dirichlet and Neumann boundary conditions is obtained using finite Fourier cosine transform with analytic inversion. The study has at least one clear advantage over the existing solutions that it accounts for the vertical leakage in water table buildup and drawdown analysis. A computational example demonstrates that the leakage induced flow plays an important role in recharge and withdrawal processes of unconfined aquifer system. The model results can be used for estimating aquifer’s hydraulic properties and validation of numerical models.

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Conceptualisation of Sea-Water Intrusion in an Island Aquifer System

10.5194/egusphere-egu2020-21336 ◽

2020 ◽

Author(s):

Manuel Sapiano ◽

Leticia Baena-Ruiz ◽

Henry Debattista ◽

David Pulido-Velazquez

Keyword(s):

Sea Water ◽

Numerical Models ◽

Data Availability ◽

Mitigation Measures ◽

Sea Water Intrusion ◽

Aquifer System ◽

Water Intrusion ◽

Aquifer Systems ◽

The Impact ◽

Analytical Approaches

A method to conceptualise the assessment of the impact of sea-water intrusion in island and coastal aquifer systems is being proposed.&#160; The method will enable the undertaking of a first assessment of the sea-water intrusion problem, hence providing an early-stage and simple to apply &#8220;warning system&#8221; enabling the informed and timely application of mitigation measures intended to protect the quantitative and qualitative status of the aquifer system. The method proposes the discretization of the aquifer to enable the correlation of the current aquifer &#8220;freshwater domain&#8221; with reference conditions representing the aquifer system under undisturbed conditions.&#160; The &#8220;freshwater domain&#8221; is defined by the volume of water between the piezometric surface and the seawater interface, and can be obtained from numerical models, where available, or the application of simple analytical approaches such as the Ghyben-Herzberg solution. . The dynamic of the seawater intrusion is defined as the change in natural &#8220;freshwater domain&#8221; and chloride concentrations within it. Therefore, the method is applicable to island and coastal aquifers with low-data availability, and in particular to cases where a numerical-model is not-yet developed. The application of the method will enable the quantification of sea-water intrusion impacts at an aquifer scale, enabling the visual-conceptual representation of the sea-water intrusion affected area, as well as identify the level of intrusion.&#160; The method also enables the temporal assessment of sea-water intrusion, identifying the evolution of intrusion throughout the exploitation period of the aquifer system.&#160; The method has been implemented in a GIS tool, and applied to the Mean Sea Level Aquifer system in Malta.&#160;Aknowledgement: This research has been partially supported by the GeoE.171.008-TACTIC project from GeoERA organization funded by European Union&#8217;s Horizon 2020 research and innovation program and by the SIGLO-AN project (RTI2018-101397-B-I00) from the Spanish Ministry of Science, Innovation and Universities (Programa Estatal de I+D+I orientada a los Retos de la Sociedad)&#160;

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The Significance of Groundwater Flow Modeling Study for Simulation of Opencast Mine Dewatering, Flooding, and the Environmental Impact

Water ◽

10.3390/w11040848 ◽

2019 ◽

Vol 11 (4) ◽

pp. 848 ◽

Cited By ~ 3

Author(s):

Jacek Szczepiński

Keyword(s):

Environmental Impact ◽

Groundwater Flow ◽

Mine Drainage ◽

Numerical Models ◽

Open Pit ◽

Climate Conditions ◽

Aquifer System ◽

Flow Models ◽

Mine Dewatering ◽

Cyclic Changes

Simulations of open pit mines dewatering, their flooding, and environmental impact assessment are performed using groundwater flow models. They must take into consideration both regional groundwater conditions and the specificity of mine dewatering operations. This method has been used to a great extent in Polish opencast mines since the 1970s. However, the use of numerical models in mining hydrogeology has certain limitations resulting from existing uncertainties as to the assumed hydrogeological parameters and boundary conditions. They include shortcomings in the identification of hydrogeological conditions, cyclic changes of precipitation and evaporation, changes resulting from land management due to mining activity, changes in mining work schedules, and post-mining void flooding. Even though groundwater flow models used in mining hydrogeology have numerous limitations, they still provide the most comprehensive information concerning the mine dewatering and flooding processes and their influence on the environment. However, they will always require periodical verification based on new information on the actual response of the aquifer system to the mine drainage and the actual climate conditions, as well as up-to-date schedules of deposit extraction and mine closure.

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