Groundwater modelling for recharge and seepage assessments : case study for the Langbroeker area

This report has been prepared to obtain the MSc degree in Hydrology and Water Resources at IHE and Delft. The title indicates that recharge and seepage assessments were carried out and that the focal area of research has been the Langbroeker area, which is located just south of the 'Utrechtse Heuvelring'. This ice-pushed ridge is protruding in the central part of the Netherlands. Participating in the study were the water board 'Stichtse Rijnlanden', Delft Hydraulics and other local organistaions that delivered data for the study. The recharge assessments were primarily carried out with the unsaturated flow model MUST. Based on the land use in the area, the soil type, the groundwater regime, and naturally the meteorological characteristics, this model has been used to determine both direct recharge and net recharge; the latter as the difference between the direct recharge and capillary rise. The model has been applied for shallow and deep groundwater table areas including the 'Utrechtse Heuvelrug'. For the deep groundwater table areas, a routing procedure was followed to compute the correct recharge at this table. The seepage assessments were done with the saturated groundwater flow model Modflow. The complete model area extended from the 'Gelderse Vallei' up to the Waal River in the Central Betuwe. The geometry of the groundwater system, the conductivities of aquifers and aquitards, recharges, the canal system and the groundwater abstractions were input into the model. The model was calibrated against groundwater levels whereby a target of 0.5 m was set. Based on the calibrated model, seepage rates for the canals and the Kromme Rijn River in the Langbroeker area could be computed