Groundwater salinity mapping of the Belgian coastal zone to improve local freshwater storage availability

Abstract

In the European TOPSOIL project, countries around the North Sea are searching for solutions for climate related threats. They explore the possibilities of using the topsoil layer to solve current and future water challenges. The main objective is to improve the climate resilience of the water management of the topsoil and shallow aquifers in the North Sea region. TOPSOIL is supported by the Interreg VB North Sea Region program in line with priority 3 of the program: ‘Sustainable North Sea Region, protecting against climate change and preserving the environment’. The Belgian part of this project, called FRESHEM for GO-FRESH Vlaanderen (‘FREsh Salt groundwater distribution by Helicopter ElectroMagnetic survey for Geohydrological Opportunities FRESH water supply’), focuses on mapping the salinity distribution of groundwater using airborne electromagnetics and aims to look into a number of measures that could increase the availability of freshwater for agriculture in the polder area. Two pilot projects will evaluate the possibilities for freshwater storage and aims to specify what measures can be taken to achieve this. Together with the other water users and water managers, The Flanders Environment Agency wants to prepare a plan for the realization of one or more pilot projects that can improve the availability of freshwater.

Airborne electromagnetic mapping of coastal groundwater salinity

“…The effect that different data densities and types have on regional saline groundwater mapping using AEM was quantitatively examined using highly detailed 3D synthetic models. Increasing interest in the field of hydrogeophysics (Binley et al, 2015) has highlighted the potential of using AEM to map groundwater salinity quantitatively in 3D (e.g., Delsman et al, 2018;Faneca Sànchez et al, 2012;Vandevelde et al, 2018). As geophysical inversions -a necessary part of AEM data processing -are most commonly delivered as 1D vertical measurements, a considerable amount of further processing is required to recover a fully 3D, quantitative groundwater salinity model in practical units (such as chloride in g/l).…”

“…Relatively few AEM studies have attempted to quantify regional groundwater salinity in 3D using FFs (e.g. Faneca Sànchez et al, 2012, Vandevelde et al, 2018. However, the recent success of hydrogeophysical groundwater investigations have resulted in increased attention to the method (Binley et al, 2015).…”

“…Auken et al, 2008;Gunnink et al, 2012) alongside groundwater salinity distributions (e.g. Delsman et al, 2018;Vandevelde et al, 2018). A comparison of available AEM methods for groundwater mapping purposes is described in Steuer et al (2009).…”

“…In more saline environments however, mapping structure (which can relate to parameters such as hydraulic conductivity) is more challenging because signals are dominated by the strong EC contrasts found at freshsaline interfaces (King et al, 2020b). Naturally, this makes it highly suitable for mapping salinity instead, where in these environments the method has seen continued success for decades (Delsman et al, 2018;Faneca Sànchez et al, 2012;Fitterman and Deszcz-Pan, 2001;Jørgensen et al, 2012;Rahman et al, 2021;Vandevelde et al, 2018).…”