Erosion

The Mekong Delta coastline has experienced accelerating erosion since the late 1990s, driven by a fundamental sediment budget deficit. Under natural conditions, the delta built itself seaward at ~10–16 m/year — the rate at which upstream sediment supply matched wave and tidal reworking. Since the cascade of upstream hydropower dams (particularly in China and Laos) cut sediment loads by an estimated 50–70%, the coastline has shifted from accretion to erosion.

Satellite monitoring shows that between 2005 and 2020 the delta lost approximately 500 km² of land, concentrated on the western coast (Cà Mau peninsula, Kiên Giang) and the Cửu Long estuary mouths. Erosion rates of 40–60 m/year have been recorded on exposed headlands. The consequences compound the other forces: as the coastline retreats and mangrove buffer zones disappear, tidal intrusion reaches further inland, storm energy penetrates unimpeded, and the sediment that once built natural levees is no longer replenished. Sand mining in the delta channels has further stripped in-channel sediment reserves, accelerating bed incision and salinity propagation along the bottom.