Charles Robin Gruel, Edward Park, Loc Huu Ho , Sameh Kantoush, Lian Feng, Binh Van Doan, Adam D. Switzer

The river beds of the Mekong Delta are some of the most intensively sand mined places in the world, however sand mining budgets are limited to rough and indirect estimates. Here, we provide a systematic, semi-physically based estimation of the Mekong Delta’s sand mining budget. We provide a quantified budget that overcomes limitations resulting from previous reliance on officially declared statistics and bathymetric surveys of short channel reaches. We apply Sentinel-1 radar imagery to monitor the distribution of sand mining activities using boat metrics-driven mining intensity maps correlated with a field-based bathymetry difference map derived from two extensive bathymetric surveys of ~100 km reaches in the Tiền River conducted in 2014 and 2017 that cover ~15% of the Mekong Delta. We then extrapolate the Tiền River findings to the broader Vietnamese Mekong Delta from 2015 to 2020 and measure a continuous increase of the extraction budget by ~25% between 2015 (38 Mm3/yr) and 2020 (47 Mm3/yr). We estimate a total sand mining budget of 254 Mm3 during the 6-year study period with an average annual rate of ~42 Mm3. Our semi-physically based annual rate differs from both official declarations provided and estimates from previous studies implying that a substantial portion of sand mining budget remains unaccounted for. Riverbed sand mining remains key threat to the Mekong Delta as it exacerbates or contributes to a multitude of other threats including dam construction effects on sedimentation, ongoing subsidence, sea level rise and recurring salt intrusion. This integrated study offers a new method that is readily implementable elsewhere to allow for extensive monitoring and quantification of sand mining activities that are vital for assessing future projections on environmental impacts.