When Do Complex Transport Dynamics Arise in Natural Groundwater Systems?

TL;DR

This study investigates the conditions under which complex transport dynamics occur in natural groundwater systems, revealing that heterogeneity and tidal forces can produce diverse and long-lasting solute transport behaviors in aquifers.

Contribution

It provides a parametric analysis showing how aquifer properties and tidal influences lead to complex transport structures, expanding understanding of natural groundwater dynamics.

Findings

Complex transport can arise in heterogeneous aquifers due to transient Darcy flows.

Such dynamics can trap solutes for extended periods, affecting mixing.

Widespread potential for complex transport exists in coastal groundwater systems.

Abstract

In a recent paper (Trefry et al., 2019) we showed that the interplay of aquifer heterogeneity and poroelasticity can produce complex transport in tidally forced aquifers, with significant implications for solute transport, mixing and reaction. However, what was unknown was how broadly these transport dynamics can arise in natural groundwater systems, and how these dynamics depend upon the aquifer properties, tidal and regional flow characteristics. In this study we answer these questions through parametric studies of these governing properties. We uncover the mechanisms that govern complex transport dynamics and the bifurcations between transport structures with changes in the governing parameters, and we determine the propensity for complex dynamics to occur in natural aquifer systems. These results clearly demonstrate that complex transport structures and dynamics may arise in natural tidally forced aquifers around the world, producing solute transport and mixing behaviour that is very different to that of the conventional Darcy flow picture. Key Points: * Transient Darcy flows can generate complex transport dynamics in heterogeneous compressible aquifers. * This complex transport can trap dispersing solutes for many years. * Global tidal maps indicate widespread potential for complex transport dynamics in coastal zones.