Flow and transport in aquifers of lowland areas are strongly influenced by recharge processes, that is, the downward fluxes of water from surface to groundwater. Precipitation is transferred to aquifers through a complex and interconnected set of processes, including the interactions between vegetation, surface water, vadose zone (soil) and shallow groundwater, which altogether form the so-called critical zone. Groundwater recharge can thus vary significantly over short distances due to spatial variability in soil (type and structure) and land cover (vegetation, buildings…). However, this spatial variability is in general addressed either by applying over-simplistic GIS-based models, or by using more complex, process-based models that are hardly calibrated/validated at the scale of application. The validity of these approaches is highly questionable given the critical zone interaction processes mentioned above. There is thus clearly a need to better characterize and model recharge processes, in order to take into account this spatial variability in an appropriate way in catchment-scale ground water models.
Recharge processes can be monitored and modelled at the soil profile scale, by detailed measurements of important hydrological processes and variables. The research gap identified for the present proposal is to determine how to upscale such point data to the plot and catchment scales at which groundwater models are usually run. In addition, an important question related to the modelling aspect of the research is to assess how the hydrological processes described above are best integrated into one model, coupling all compartments of the critical zone.
A coupled and spatially distributed hydrological model needs to be calibrated and validated for a specific catchment. The aim is to use the Kleine Nete catchment as a case study, since there is quite some hydrological information available. We propose to install a detailed experimental setup, equipped with state-of-the-art instrumentation for monitoring variably-saturated flow processes in selected prototype combinations of land cover, soil type and shallow aquifer (critical zone prototypes).