Towards a holistic approach in characterising the water cycle in the Campine area (NE Belgium) at various temporal and spatial scales

The Neogene aquifer in the Campine area, northeastern Belgium, is a major water resource with many functions. It provides drinking water for the population, irrigation water for agriculture and water for industrial activities and recreational purposes. In addition, owing to its phreatic nature and the shallow groundwater table, it is a water supply for rivers and wetlands as baseflow. The quality and quantity of groundwater, and the geometry of the groundwater body is not only influenced by environmental changes, but also by specific human activities such as groundwater exploitation, polluting industries, deep and shallow geothermal energy, sand extraction etc. It is clear that a proper impact assessment of these activities and changes necessitates the development of well-calibrated and tested coupled hydro(geo)logical models. Here we present the first steps taken into developing an innovative modelling framework to tackle the issue of changes in water cycle under future environmental change in small river catchments draining the Neogene aquifer. The framework includes (i) an integration of different components of the hydrological cycle into a coupled model focusing on unsaturated zone-groundwater-river water interactions at the catchment scale, and, (ii) the use of alternative state variables other than groundwater head, such as hydrochemical and age tracers, temperature, and palaeohydrological proxies. In this presentation we will highlight various measurement techniques that we (plan to) use to quantify the water cycle in this particular setting. Results include: (i) groundwater exfiltration patterns in small creeks from infrared thermometry and 222Rn concentrations (smallest spatial and temporal scale), (ii) deep (a few decameter) temperature profiles from piezometers in discharge and recharge zones, (iii) CFC, 14C and 3H/He-based hydrochronological ages for an individual aquifer covering the last couple of decades and (iv) a catchment wide assessment of long-term hydrological variability deduced from historical maps and soil profile information covering the last few millenia. Combining these physico-chemical state variables obtained from various temporal and spatial scales will allow to calibrate and verify (coupled) hydro(geo)logical models in the most rigorous way.