Intensifying saline water intrusion and drought in the Mekong Delta: From physical evidence to policy outlooks

Ho Huu Loc; Doan Van Binh; Edward Park; Sangam Shrestha; Tran Duc Dung; Vu Hai Son; Nguyen Hoang Thu Truc; Nguyen Phuong Mai; Chris Seijger

doi:10.1016/j.scitotenv.2020.143919

Intensifying saline water intrusion and drought in the Mekong Delta: From physical evidence to policy outlooks

Sci Total Environ. 2021 Feb 25:757:143919. doi: 10.1016/j.scitotenv.2020.143919. Epub 2020 Dec 3.

Authors

Ho Huu Loc¹, Doan Van Binh², Edward Park³, Sangam Shrestha¹, Tran Duc Dung⁴, Vu Hai Son⁵, Nguyen Hoang Thu Truc⁶, Nguyen Phuong Mai⁷, Chris Seijger⁸

Affiliations

¹ Water Engineering and Management, School of Engineering and Technology, Asian Institute of Technology, Pathum Thani, Thailand.
² Department of Water Resource Engineering, Thuyloi University, Hanoi, Viet Nam; Water Resources Center, Disaster Prevention Research Institute, Kyoto University, Uji City, Japan.
³ National Institute of Education, Nanyang Technological University, Singapore; Asian School of the Environment, Nanyang Technological University, Singapore. Electronic address: edward.park@nie.edu.sg.
⁴ Center of Water Management and Climate Change, Institute for Environment and Resources, Vietnam National University, Ho Chi Minh City, Viet Nam.
⁵ Viet Nam Disaster Management Authority, Department of Safety Control for Natural Disaster, Ministry of Agriculture and Rural Development, Viet Nam.
⁶ Department of Water Resource Engineering, Thuyloi University, Hanoi, Viet Nam.
⁷ Department of Civil Engineering, Thuyloi University, Hanoi, Viet Nam.
⁸ Water Resources Management Group, Wageningen University, Netherlands.

PMID: 33316509
DOI: 10.1016/j.scitotenv.2020.143919

Abstract

This paper assesses the recently intensified saline water intrusion (SI) and drought in the Vietnamese Mekong Delta (VMD). While the existing literature predominantly points the cause of drought to the hydropower dams in the upstream of the Mekong Basin, we contribute new physical evidence of the intensification of saline water intrusion (through backwater effect) in the VMD caused by three anthropogenic drivers: riverbed incision (due to both riverbed mining and dam construction), sea level rise and land subsidence. Thereupon, we highlight that it is critical to not underestimate the impacts from the localized factors, especially the riverbed-mining which can incise the channel by up to 15 cm/year and amplify the salinity intrusion. Our analysis is based on the extensive sets of hourly-to-daily hydrological time series from 11 gauge stations across the VMD. First, several signs of significantly increased tidal amplification (up to 66%) were revealed through the spectral analysis of the hourly water level data. This trend was further validated through the changes in slopes of the rating curves at the tidal zones, implying the relationships between the shift of the backwater effects on the rivers in VMD and the lowered water levels caused by the riverbed incision. Finally, we introduce a novel approach using the annual incision rates of the riverbed to compare four SI driving factors in terms of their relative contributions to the balance between fresh and saline water in the VMD.

Keywords: Backwater effect; Dam construction; Riverbed mining; Salinity intrusion; Sea level rise; Vietnamese Mekong Delta (VMD).