University of Twente Student Theses


Numerical Groundwater Flow and Solute Transport Modelling - A Case Study of Sardon Catchment in Spain

Ruwan Rajapakse, R. R. G. (2009) Numerical Groundwater Flow and Solute Transport Modelling - A Case Study of Sardon Catchment in Spain.

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Abstract:The fully transient models are data intensive but more reliable in exploring the groundwater flow regimes than steady state models due to spatio-temporal nature of flux input. However even those models suffer non-uniqueness of solutions due to the several possible combinations between fluxes and system parameters. The coupling of solute transport models with flow models enables to explore the complexity of the flow regime better. This study focused to improve the reliability of the existing fully transient flow model in Sardon catchment through: (i) improvement of the model input data set; (ii) validation of the steady state flow model by solute transport model of chloride considered as natural tracer; (iii) recalibration of the fully transient model using improved input data set (the transient solute transport model could not be performed due to insufficient chloride concentration records). The intensive field tests and processing techniques were used to assess the parameters and fluxes; ADAS data acquisition, borehole drilling , sampling and analysis of chloride in groundwater, forced gradient tracer tests with automated plume monitoring and Electrical Resistivity Tomography (ERT) survey, soil sampling, slug test and differential GPS surveys were performed. The spatio-temporal distribution of groundwater fluxes (recharge and groundwater evapotranspiration) was assessed through pyEARTH-1D model. Chloride Mass Balance (CMB) and well hydrograph analysis were also employed to obtain the recharge. The qualitative zoned maps developed by integration RS-GIS techniques were used to delineate the spatially distributed fluxes in each stress period in the transient model. The largest improvement as compared to the existing model used as starting point of this work was in reformulation of the topological surfaces used in the former model as a consequence of the highprecision differential GPS survey carried over the entire Sardon study area. This survey not only improved the layer boundaries but also the potentiometric surface that was used in the new calibration of the steady state flow MODFLOW model. The local scale dispersivity obtained by numerical model was regionalized and applied in the solute transport MT3D model to validate the steady state flow model using chloride tracer in groundwater. The validation revealed the calibrated steady state flow model was satisfactorily reliable even improvement is still necessary. The solute transport model i.e. chloride concentration distribution in groundwater showed to be insensitive to dispersivity change. The fully transient model was developed for years 2003-2008 and in general its results are in good agreement with previously calibrated model. The average recharge is 0.38 mm/d (24.1 % of annual rainfall) while the groundwater evapotranspiration indicated 0.14 mm/d (8.2 of annual rainfall) in average for the simulated period. The groundwater outflow through the drain along Sardon fault zone is apparently uniform and it is 0.24 mm/d (15.2 % of annual rainfall).
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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