Realistic forecasting of groundwater level, based on the eigenstructure of aquifer dynamics

Short-term management of groundwater resources, especially during droughts, can be assisted by forecasts of groundwater levels. Such forecasts need to account for the dynamic response of the aquifer to likely recharge scenarios and recent but unknown abstractions. This paper describes a method for formulating ARMAX forecast equations from a linear system description based on the eigenvalues and eigenvectors (eigenstructure) of aquifer dynamics. For the piezometric response of a heterogeneous aquifer to a fixed spatial distribution of land surface recharge, with time-varying magnitude, only a few eigenvalues are significant. The resulting model is demonstrated with monthly values of land surface recharge and groundwater level data from a 2000 km2 alluvial aquifer in Canterbury, New Zealand.