Clyde Gateway Pilot 3D Geological and Groundwater Model
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This report describes the Clyde Gateway Pilot 3D geological model (superficial deposits, bedrock) and groundwater model (recharge and groundwater flow) which covers 1:10,000 scale Ordnance Survey sheets NS66SW, NS66NW and NS56SE. The groundwater model considers a broader area in general, and also, for practical purposes, a detailed consideration of NS56NE, based on available hydrogeological data. Therefore, the models, and report, address not only the Clyde Gateway area itself, but a larger area which includes for example the alignments of the M74 Extension and East End Regeneration Route.
The report provides background information to the model user including brief geological descriptions, model construction methods, uncertainty factors, limitations and a helpful 3D model user manual.Keywords:
Bedrock
Gateway (web page)
Geological survey
3d model
Groundwater model
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Abstract In three-dimensional (3-D) implicit geological modeling, the bounding surfaces between geological units are automatically constructed from lithological contact data (position and orientation) and the location and orientation of potential faults. This approach was applied to conceptualize a karst aquifer in the Middle Triassic Muschelkalk Formation in southwest Germany, using digital elevation data, geological maps, borehole logs, and geological interpretation. Dip and strike measurements as well as soil-gas surveys of mantel-borne CO 2 were conducted to verify the existence of an unmapped fault. Implicit geological modeling allowed the straightforward assessment of the geological framework and rapid updates with incoming data. Simultaneous 3-D visualizations of the sedimentary units, tectonic features, hydraulic heads, and tracer tests provided insights into the karst-system hydraulics and helped guide the formulation of the conceptual hydrogeological model. The 3-D geological model was automatically translated into a numerical single-continuum steady-state groundwater model that was calibrated to match measured hydraulic heads, spring discharge rates, and flow directions observed in tracer tests. This was possible only by introducing discrete karst conduits, which were implemented as high-conductivity features in the numerical model. The numerical groundwater flow model was applied to initially assess the risk from limestone quarrying to local water supply wells with the help of particle tracking.
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Abstract. Within the scope of climatic change and associated sea level rise, coastal aquifers are endangered and are becoming more a focus of research to ensure the future water supply in coastal areas. For groundwater modelling a good understanding of the geological/hydrogeological situation and the aquifer behavior is necessary. In preparation of groundwater modelling and assessment of climate change impacts on coastal water resources, we setup a geological/hydrogeological model for the North Sea Island of Föhr. Data from different geophysical methods applied from the air, the surface and in boreholes contribute to the 3-D model, e.g. airborne electromagnetics (SkyTEM) for spatial mapping the resistivity of the entire island, seismic reflections for detailed cross-sections in the groundwater catchment area, and geophysical borehole logging for calibration of these measurements. An iterative and integrated evaluation of the results from the different geophysical methods contributes to reliable data as input for the 3-D model covering the whole island and not just the well fields. The complex subsurface structure of the island is revealed. The local waterworks use a freshwater body embedded in saline groundwater. Several glaciations reordered the youngest Tertiary and Quaternary sediments by glaciotectonic thrust faulting, as well as incision and refill of glacial valleys. Both subsurface structures have a strong impact on the distribution of freshwater-bearing aquifers. A digital geological 3-D model reproduces the hydrogeological structure of the island as a base for a groundwater model. In the course of the data interpretation, we deliver a basis for rock identification. We demonstrate that geophysical investigation provide petrophysical parameters and improve the understanding of the subsurface and the groundwater system. The main benefit of our work is that the successful combination of electromagnetic, seismic and borehole data reveals the complex geology of a glacially-affected island. A sound understanding of the subsurface structure and the compilation of a 3-D model is imperative and the basis for a groundwater flow model to predict climate change effects on future water resources.
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Toolbox
Geological survey
Graphical user interface
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In southern Bangladesh excessive levels of As in shallow groundwater have led to deeper groundwater becoming the main alternative source of As-free potable water. Hydrogeological configuration indicates that tube-wells pumping from these depths may be vulnerable to As breakthrough from shallow levels. The thesis explores a range of methods of representing lithological heterogeneity of the Bengal Aquifer System (BAS) in models of groundwater flow and travel time. The aim is to support models of arsenic (As) flux to the deep groundwater flow-system of BAS, and hence to aid assessment of the vulnerability of deep groundwater to invasion by As. The research uses an array of geological information including geophysical logs (n=12), hydrocarbon exploration data (n=11), and drillers' logs (n=589) from a 5000 km2 area to characterise the aquifer heterogeneity as a basis for alternative representations of hydrogeological structure in groundwater flow modelling. Groundwater samples from southern Bangladesh were analysed for 14C in order to determine groundwater age (n=23) and for hydrochemical (n=75) and isotopic (n=50) characterisation. A new hypothesis `SiHA (Silt-clay layers influence Hierarchical groundwater flow systems and Arsenic progression in aquifer)' is presented which integrates sedimentological heterogeneities, groundwater flow, and geochemical processes to explain the distribution and geological evolution of groundwater As in the aquifer. The hypothesis explains the spatio-vertical variability of groundwater As concentration by 'groundwater flow systems and differential flushing' in the aquifer. Groundwater flow models based on eight different yet plausible aquifer representations provide adequate simulations of hydraulic head, but contrasting implications for well catchments and travel times. The better representations are judged by comparing model outcomes of travel time with groundwater age determination using 14C. Comparisons demonstrate the importance of incorporating hydrostratigraphy and spatial heterogeneity in order to optimise model representations, and implications for the security of As-free deep groundwater in the BAS.
Groundwater model
Aquifer test
Groundwater discharge
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