Counterfactual modeling isolates sand mining impacts, revealing it as a key driver of Mekong Delta destabilization.

Sand mining is a poorly quantified threat to river deltas because its impacts are often confounded with those of dams and climate change. Here, we isolate its effects in the Vietnamese Mekong Delta, a global sand mining hot spot, using a long-term numerical model and observed mining data. Results show that mining exceeds natural sediment supply by 6 to 15 times, causing riverbed erosion across ~65% of channels, with mean incision rates of ~0.10 meters per year (~25 to 30% of total incision driven by all drivers). This channel deepening alters flow, reduces sediment transport, and enhances saltwater intrusion. Sand mining alone contributes ~16 to 30% of the annual salinity increase, extending intrusion up to ~1.5 kilometers further inland during the dry season. These changes demonstrate that sand mining is a major, previously underquantified driver of delta instability, affecting river morphology, flow, sediment, and salinity. This study provides a framework to quantify these impacts and support better management of sand extraction in vulnerable deltas worldwide.