This chapter presents the model development for the case study. The Rijnland SIMGRO model was validated against the main output variable, which is the discharge at the main outlets. A base model, using the data sources normally used for the case study, is developed. The SIMGRO model uses parameter values suggested by experts from the Rijnland Water Board. A DEM derived from Actueel Hoogtebestand Nederland Lidar data was used to define the ground surface elevation of the model. The deep soil data for MODFLOW was obtained from the National Hydrological Instrument data, which is a model; build for the whole country of the Netherlands. The discharge validation was used as the main validation of the SIMGRO model of Rijnland and was conducted for the year 2011. The frequency analysis of summer period shows that the SIMGRO model simulated more cells with lower evapotranspiration than the Earth observation data.