When is a groundwater model considered calibrated?

A groundwater model is considered calibrated when hydraulic heads and fluxes reproduce the system being modeled within an acceptable tolerance. Calibration is a process that involves adjusting model parameters so that the model outputs—such as hydraulic heads (the height of the water table or potentiometric surface) and fluxes (the flow of water through the soil or rock)—align closely with observed data from the actual groundwater system.

This process seeks to ensure that the model accurately represents the behavior of the groundwater system under various conditions. Acceptable tolerance indicates that while a perfect match may not always be achievable, the differences between the model outputs and the observed data are small enough to be considered reliable for the purposes of analysis and decision-making.

The importance of this calibration process lies in its ability to create a predictive model that can be used for future scenarios, water resource management, or understanding the impact of different variables on the groundwater system. While accurately predicting future water levels and reflecting seasonal variations can be objectives of a groundwater model, they are not the criteria for calibration. Additionally, matching historical data perfectly is not always realistic nor necessary, as models can still be effective with slight discrepancies, as long as the outputs remain within acceptable limits.