The 3D groundwater salinity distribution and fresh groundwater volumes in the Mekong Delta, Vietnam, inferred from geostatistical analyses

Abstract. Over the last decades, economic developments in the Vietnamese Mekong delta have led to a sharp increase in groundwater pumping for domestic, agricultural and industrial use. This has resulted in alarming rates of land subsidence and groundwater salinization. Effective groundwater management, including strategies to work towards sustainable groundwater use, requires knowledge about the current groundwater salinity distribution, in particular the available volumes of fresh groundwater. At the moment, no comprehensive dataset of the spatial distribution of fresh groundwater is available. To create a 3D model of Total Dissolved Solids (TDS), an existing geological model of the spatial distribution and thickness of the aquifers and aquitards is updated. Next, based on the sedimentological description of the borehole data, maps of drainable porosity for each aquifer are interpolated. Measured TDS in groundwater, inferred TDS from resistivity measurements in boreholes and soft incomplete data from domestic wells are combined in an indicator kriging routine to obtain the full probability distribution of TDS for each (x,y,z) location. This statistical distribution of TDS combined with drainable porosity yields estimates of the volume of fresh groundwater (TDS  https://doi.org/10.5281/zenodo.4441776 (Gunnink et al, 2021).