Assessment of unconventional state variables to constrain groundwater flow models of the Neogene Aquifer in the Campine Basin in Belgium

Numerical models are generally used to represent the physical and/or chemical properties of groundwater systems, and to be implemented in the decision making process from groundwater management supply to safety and feasibility of waste disposal systems. As hydrologic features and hydraulic characteristics are difficult to measure they are generally assumed or inferred by inverse methods. In the general practice, traditional methods only use groundwater hydraulic heads for inverse conditioning. However, the information content therein is limited and, therefore, the complexity of the groundwater system is unsuccessfully captured. Other unconventional types of observations of the state of the aquifer (state variables) can nowadays be measured in more reliable and straightforward ways. In this work, the use of unconventional state variables is explored aiming to improve the current conceptual models and reduce parameter and model outcome uncertainties for groundwater models of the Neogene aquifer, across the Nete Catchment, in the Campine Basin in Belgium. This study shows that the implementation of additional unconventional state variable observations, namely temperature, hydrochemistry and age tracer concentrations, exhibit strong potential for conditioning groundwater flow models. Depending on the application (e.g. shallow areas or deep into the aquifer) these state variables present robust solutions to reduce model parameter and derived flux uncertainties.