Abstract
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, maps of drainable porosity for each aquifer are interpolated based on the sedimentological description of the borehole data. Measured TDS in groundwater, inferred TDS from resistivity measurements in boreholes and soft incomplete data (derived from measurements in boreholes and 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 < 1 g L−1) in each aquifer. Uncertainty estimates of these volumes follow from a Monte Carlo analysis (sequential indicator simulation). Results yield an estimated fresh groundwater volume for the Mekong Delta of 867 billion cubic metres with an uncertainty range of 830–900 billion cubic metres, which is somewhat higher than previous assessments of fresh groundwater volumes. The resulting dataset can for instance be used in groundwater flow and salt transport modelling as well as aquifer storage and recovery projects to support informed groundwater management decisions, e.g. to prevent further salinization of the Mekong Delta groundwater system and land subsidence, and is available at https://doi.org/10.5281/zenodo.4441776 (Gunnink et al., 2021).
Highlights
A large part of the world’s population lives in deltas, many of which are located in developing countries
In Vietnam, there is a rapidly growing awareness that the interrelated issues of depletion of water resources and salt water intrusion will negatively affect the potential for economic development of the country, including the Mekong Delta (Renaud and Kuenzer, 2012; Nguyen and Gupta, 2001; Tam et al, 2014; Tran et al, 2012)
The objective of this research is to use state-of-the-art geostatistical methods to create a dataset of the 3D groundwater salinity distribution in the aquifers of the MKD (TDS in g L−1, as a measure of groundwater salinity) to provide water managers and policymakers with an accurate assessment of the spatially varying fresh groundwater volumes, including their uncertainties
Summary
A large part of the world’s population lives in deltas, many of which are located in developing countries In these areas, there is a great demand for fresh water for domestic, agricultural and industrial use (Wada et al, 2011; Gioasan et al, 2014; Tessler et al, 2015; Syvitski et al, 2009; Van Engelen et al, 2019). Bui et al (2013) estimated that approximately 600 billion cubic metres fresh groundwater is available in the aquifers of the Mekong Delta Notwithstanding this apparent large volume, over-exploitation of fresh groundwater resources occurs, causing lateral salt water intrusion into the groundwater system, upconing of brackish to saline groundwater under extraction wells and land subsidence (Bui et al, 2013; Erban et al, 2014b; Minderhoud et al, 2017; Rahman et al, 2019). This might impose additional risk to groundwater quality in the long term
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