ESR N°1 : Mixing and chemical reaction hotspots in saline-freshwater mixing zones

Research objectives

The main objectives are to identify and quantify the structural and hydraulic controls of mixing and evaluate the influence of fluctuations in recharge and temperature. The idea is that fluid deformation in heterogeneous media together with local dispersion lead to a strong localization of enhanced mixing and reaction efficiency, which is amplified by density variations.

Numerical simulations of variable density flow in heterogeneous aquifer coupled to geochemical reactions will give new insight into these processes, which will be contrasted to data from geophysical monitoring and experimentation.

Collaboration on the development and use of novel techniques for the characterization of transport and flow heterogeneity as well as reaction monitoring will be done with ESRs 9 and 12.

Project description

Mixing across the SW-FW (saltwater-freshwater) interface is a key process that affects karst development, exchange reactions and biochemical processes. The evolution of the SW-FW interface is strongly influenced by the density difference between salt and freshwater as well as temporal flow fluctuations induced for example by sea level fluctuations, and ever present spatial heterogeneity in the hydraulic and chemical medium properties.

The mixing processes across the interface may furthermore be affected by inland recharge and temperature variations. Monitoring these influences, coupled with field experiments and numerical modeling, will hopefully provide new insights into mixing and freshwater displacement in coastal aquifers and subsequent geochemical reactions.

Tasks and methodology

• Quantification of flow heterogeneity and fluid deformation

• Identification of flow strain and stress centers, which drive concentration gradients and mixing

• Development of mixing and reaction diagnostics to explain and predict observed reaction patterns

Data & Datasets

Datasets produced during the research project are accessible on Zenodo: https://zenodo.org/record/4005971

Dissemination & Communications

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2020

K. de Vriendt, M. Pool, M. Dentz (2020)
Heterogeneity-Induced Mixing and Reaction Hot Spots Facilitate Karst Propagation in Coastal Aquifers. Geophysical Research Letters
https://doi.org/10.1029/2020GL087529
Abstract

2018

Saltwater intrusion meeting conference (Gdansk, Poland)
Mixing and calcite dissolution in heterogeneous coastal aquifers abstract

4th Cargèse Summer School – ENIGMA Summer School
Mixing and calcite dissolution in heterogeneous coastal aquifers | A numerical 2D study poster