Optimizing Airborne Electromagnetic (AEM) Inversions for Hydrogeological Investigations using a Transdisciplinary Approach
Ken LawrieNiels B. ChristensenRoss BrodieJared D. AbrahamLarysa HalasKokPiang TanRoss C. BrodieJohn Magee
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Abstract:
High-resolution hydrogeophysical data are increasingly acquired as part of investigations to underpin groundwater mapping. However, optimization of AEM data requires careful consideration of AEM system suitability, calibration, validation and inversion methods.In modern laterally-correlated inversions of AEM data, the usefulness of the resulting inversion models depends critically on an optimal choice of the vertical and horizontal regularization of the inversion. Set the constraints too tight, and the resulting models will become overly smooth and potential resolution is lost. Set the constraints too loose, and spurious model details will appear that have no bearing on the hydrogeology. There are several approaches to an automatic choice of the regularization level in AEM inversion based predominantly on obtaining a certain pre-defined data misfit with the smoothest possible model.However, we advocate a pragmatic approach to optimizing the constraints by an iterative procedure involving all available geological, hydrogeological, geochemical, hydraulic and morphological data and understanding. In this approach, in a process of both confirming and negating established interpretations and underlying assumptions, the inversion results are judged by their ability to support a coherent conceptual model based on all available information. This approach has been essential to the identification and assessment of MAR and groundwater extraction options in the Broken Hill Managed Aquifer Recharge project.Keywords:
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Specific storage
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The study examines the hydrogeological conditions and the hydraulic characteristics of the water bearing horizons within the hydrogeologic regime of the study area located west of Iraq to the west of longitude 40°40'. Also the study shed light on the flow behavior regime and its impacts on the groundwater movement, ground water flow velocities (permeability and hydraulic gradients) considering the regional structural phenomena. The Hydrogeological data presented as spatial distribution maps and three dimensional models. The results which were achieved from the field measurements are correlated with the main hydrogeologic control points such as storage and transmissivity coefficients, groundwater depths, aquifers thickness, lateral extensions and groundwater recharge to classify the hydrogeologic districts for development and exploitation. The hydrogeologic regime of the study area is classified and screened into various aquifers, including Ga'ra, Mullusi, Mullusi-Ubaid, Hartha, Tayarat-Digma (Jeed), Muhaywir-Ubaid and Rattga aquifers. The statistical results of the hydraulic and hydrochemical parameters were examined for explaining the spatial distribution of each parameter within the uppermost aquifers and determining the preference hydrogeologic districts for future groundwater exploitation as hereinafter order, Ubaid Mullusi aquifer within district-6, Rattga and Digma-Tayarat aquifer within district-7, Mullusi aquifer within district-2, Hartha aquifer within district-3, Digma-Tayarat aquifer within district-4, Ga'ra aquifer within district-1, Muhaywir-Ubaid aquifer within district-5 and Digma-Tayarat within district-8, respectively.
Aquifer properties
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A study of hydrogeological process involves movement of water beneath the ground surface. Water content in the aquifer influences the quantitative determination of aquifer hydraulic parameters. The limited opportunity to
explore and demonstrate groundwater processes is the reason why students have inappropriate understanding of groundwater concept. The visualisation of groundwater flow is quite difficult as it deals with subsurface condition which cannot be seen. In research, field experiments on groundwater are difficult to carry out because time consuming and involves uncertainty in aquifer conditions. Physical models have been used in classroom as a tool for teaching hydrogeology. Further understanding was developed by demonstration and
observation of groundwater flow using simple sand tank. Previous research implemented sand tank under controlled conditions to investigate the mechanism and flow process of groundwater. A large artificial physical aquifer
model was developed in this study as an alternative to show the students the real aquifer condition and hydrogeology processes. The model consisted of
three different layers of soils, in which water table level was controlled using water tank at both sides of the physical model structure. Hydraulic parameters
of the artificial aquifer and performance of production well were evaluated by pumping tests. The groundwater flow in the artificial aquifer model was simulated accordingly to Darcy‟s law. Analysis of pumping test was computed by an Aquifer Test software. Well performance measurement provided by a step drawdown pumping test estimated the efficiency of well as 99%. The artificial aquifer model was verified by constant rate discharge pumping test and found to be a leaky aquifer. The pumping test analyzed the aquifer with transmissivity of 78.50m2/day and hydraulic conductivity of 7.37m/day while
recovery test analyzed the transmissivity to be 8.22m2/day and hydraulic conductivity of 7.34m/day. Both test analyzed the storage coefficient as 0.5.
This artificial aquifer physical model was designed and developed to enhance student‟s understanding of groundwater theory. Through hands-on pumping test on the aquifer model, students would be able to visualize clearer the groundwater processes.
Aquifer test
Groundwater model
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Declining groundwater levels resulting from groundwater withdrawals in the Santa Fe, New Mexico, area have caused concern about the future availability of water in the Tesuque aquifer system. This report describes the geohydrology of the Tesuque aquifer system in the Santa Fe area and presents a three-dimensional regional groundwater flow model which assesses the effects of existing and possible future groundwater withdrawals on the regional aquifer system. The model was calibrated using simulations of the predevelopment steady-state condition and the 1947-82 historical period. The response of the aquifer to two scenarios of future groundwater withdrawals from 1983 to 2020 was simulated. (USGS)
Groundwater model
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