Riverbed incision and salinity

July 12, 2021

What's causing the salinity problems in the Mekong Delta? International attention has often focused on the impacts of upstream dams, but researchers from Viet Nam and the region have recently shown that sand mining is also an important local driver of salinity intrusion. 

Their research analyzed seasonal tide patterns and water levels at 11 stations across the delta. They found that dry-season discharge of water had increased over a 20-year period even before the big drought years of 2016 and 2020. Yet, this had been insufficient to counter the ongoing rise in salinity intrusion. 

Rice field at Soc Tran in the Mekong Delta, Viet Nam. Credit: Giau Tran / Unsplash

Meanwhile, as much as 15 cm of riverbed has been cut away yearly to meet demand for river sand and gravel used in construction. This increases the extent and velocity of tidewater as it surges inland. The researchers link the rise in salinity intrusion with sand mining activities at many environmental hotspots in the Mekong Delta.

Salinity intrusion is ultimately the outcome of many long-term, interacting factors, including climate change, hydropower development, and land subsidence due to groundwater pumping. But sand mining is causing rapid, visible consequences in the short-term. With the increasing impacts of salinity placing two million hectares of the region's "food basket" at risk every year, its impacts should not be underestimated.

Sand dredge on the Tien River in the Mekong Delta, Viet Nam, December 2020. Credit: Edward Park

Source: Ho Huu Loc, Doan Van Binh, Edward Park, Sangam Shrestha, Tran Duc Dung, Vu Hai Son, Nguyen Hoang Thu Truc, Nguyen Phuong Mai, and Chris Seijger. ‘Intensifying saline water intrusion and drought in the Mekong Delta: From physical evidence to policy outlooks.’ Science of The Total Environment, Vol. 757, 2021, 143919, ISSN 0048-9697. https://doi.org/10.1016/j.scitotenv.2020.143919

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