University of Twente Student Theses
Hydro-Geophysical Assessment of Sub Surface to Improve Groundwater Models (Sardon Case Study, Spain)
Mohammed, Abubeker Ali (2010) Hydro-Geophysical Assessment of Sub Surface to Improve Groundwater Models (Sardon Case Study, Spain).
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| Abstract: | The Sardon catchment is characterized by granitic hard rocks. Hard rock aquifers particularly in granitic terrain have extremely different hydraulic parameter than those of porous media as the porosity and permeability are developed due to secondary processes. The secondary porosity in form of fractures and weathering, introduces much more spatial heterogeneity. So it’s difficult to infer the subsurface characteristics based on limited data. The aim of this research was to improve groundwater flow model of Sardon granitic catchment by determining additional model input data using hydrogeophysics. This included: i) Estimation of the spatially distributed water table depth using ground penetrating radar (GPR); ii) Characterizing the hydrostratigraphic layers using electrical resistivity tomography (ERT) in combination with previous VES data; iii) Determining a spatially distributed hydraulic parameters (transmissivity and storativity) using magnetic resonance sounding. To achieve the objective intensive field work of GPR, ERT and MRS was conducted. GPR was implemented for estimation of the water table depths. The survey was conducted with a 200 MHz antenna combined with a differential GPS and a survey wheel for accurate positioning. Measurements were performed following a total of 35 transects (around 22.7km). The interpretation was aided by a forward GPR modelling and measured dielectric permittivity using Hydraprobe. The GPR estimated water table depths ranges from 1.32 to 2.75 m with accuracy of centimetres as compared to the measurements of water table depths in the existing piezometers. The sub surface characterization of the catchment was performed using 13 ERT surveys and previous VES data. Based on this, the hydrostratigaphic layers of the catchment were characterized as a top high resistivity unconsolidated soil layer underlain by a low resistivity weathered and fractured granite which in turn is underlain by high resistivity massive granite. However, the thicknesses of these layers vary from place to place. The thickness of the weathered and fractured granite is higher around the Sardon stream due to the prevailing regional fault. The MRS result also confirms the existence of a high thickness aquifer around the Sardon fault. Finally, the existing steady state groundwater flow model of the Sardon catchment was recalibrated using 22 GPR estimated water table depths, ERT and VES modified hydrostratigraphic layers and MRS derived hydraulic conductivity. The improvement as compared to the previous model was related to additional model constrain by 22 GPR estimated hydraulic heads, to readjustment of hydrostratigraphy based on 80 ERT and VES points and to improvement of the flow domain based on the newly acquired, MRS hydraulic conductivity. |
| Item Type: | Essay (Master) |
| Faculty: | ITC: Faculty of Geo-information Science and Earth Observation |
| Programme: | Geoinformation Science and Earth Observation MSc (75014) |
| Link to this item: | https://purl.utwente.nl/essays/92333 |
| Export this item as: | BibTeX EndNote HTML Citation Reference Manager |
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