A time-variant numerical groundwater flow model for the Øvre Romerike aquifer, Southern Norway
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Using a modified version of the USGS 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. A steady state model has been calibrated against 183 regional water level observation data from autumm 1975 and against the flows in groundwater-fed springs and streams. The distribution of hydraulic conductivity calibrated using the steady state model was then used to simulate water table variations over a period in excess of 30 years at 3 observation wells. The results show a satisfactory fit with real data, allowing for the limited spatial resolution of the model. A sevenmonth running average filter has been applied to the re- charge data to simulate the damping effects of the unsaturated zone on recharge naxima and minima, resulting in an even better fit. The modelling work has enabled the project's participants to obtain a deeper understanding of the hydraulics of the aquifer, and has also 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 land- fill.