PHASE-DOMAIN MODELING IN HYDROGEOLOGY: AN UNDER-USED AND UNDER-APPRECIATED TOOL

The vast majority of groundwater modeling efforts focus on two main approaches: “steady state” modeling, in which it is assumed that groundwater discharge is steady everywhere within a modeled domain; and “transient” modeling, in which temporal changes in groundwater heads and discharges are modeled based on time-varying forcing. A less common approach is to perform “phase domain” simulation of groundwater, in which aquifers are impacted by periodic forcings at one or more frequencies. While this approach has been implemented occasionally in modeling efforts (for example, in studying coastal aquifers), I believe it presents a valuable approximation for modeling aquifers subjected to many more periodic or pseudo-periodic real-world forcings, including tides, pumping schedules, evapotranspiration, hyporheic exchange, and rainfall-driven recharge. In addition, phase domain modeling provides a practical and efficient method for understanding complex variability in groundwater flowpaths, which may significantly alter transport and reactions in the environment.

In this presentation, I will briefly introduce the theory and approximations used to implement phase domain groundwater flow simulations. I will then discuss the use of phase domain groundwater models in applications such as flow path delineation and aquifer characterization. Finally, I will discuss modeling trade-offs between the three approaches in terms of data requirements, modeling errors, and physical approximation reliability.