A 3-dimensional, time-variant, numerical groundwater flow model of the Øvre Romerike aquifer, southern Norway
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- Artikler 
Using the U.S.G.S. MODFLOW code, coupled with a Penman-Grindley type recharge model, it has been possible to produce a transient, 3-dimensional groundwater flow model of the Øvre Romerike aquifer. The MODFLOW code was modified to allow the water table to rise across the boundary of aquifer layers, and the recharge model was improved to allow for snow torage effects during winter. 183 groundwater level observation data feom autumn 1975 and flows in ground- water fed springs and streams have been used for calibrating a steady state model. Allowing for the limited resolution attainable using 500 x 500 m grid blocks in areas of high water table gradient, the fit achieved was satisfac- tory. The calibrated distribution of hydraulic conductivity was then used to simulate time-variations in groundwater levels over a period in excess of 30 years. Long-term calibration data at three observation wells showed satis- factory fits with modelled data, again allowing for the limited spatial resolution of the model, and the uncertain elevation of the real data points. A seven-month running average filter was able to simulate the damping effects of the unsaturated zone on recharge maxima and minima, resulting in an impro- ved fit. The modelling work has indicated that hydraulic conductivity values obtained from grain size distributions tend to lead to underestimates of aquifer transmissivity. The model provides a framework for further modelling work on contaminant transport at Trandum landfill, but it is debatable whether the model can be used, unmodified, for contaminant modelling in its present form.