Author(s): Doan Van Binh; Sameh Kantoush; Tetsuya Sumi; Nguyen Phuong Mai; La Vinh Trung
Linked Author(s): Tetsuya Sumi
Keywords: Riverbed incision; Vietnamese Mekong Delta; Mekong River; Sediment load; Dam
Abstract: Sediment load of Mekong River (MR) is of crucial importance for the sustainability and survivability of the Vietnamese Mekong Delta (VMD) in the context of sea level rise induced by climate change. The VMD is sinking due to rapidly morphological degradation caused by altered flow regime and reduced sediment supply from the MR as the result of upstream hydropower dam development. To clarify, we conducted a boat -based bathymetric field survey in August-September 2017 to measure the riverbed elevations along approximately 570 km of the Tien and Hau rivers and the Vam Nao channel in the VMD, which was compared to the river bathymetric data measured in 2014. We estimated that riverbed incision in the Tien river from Tan Chau to My Thuan from 2014 to 2017 (-52.5 Mm3/yr) was at least three times greater than that in the past 10-20 years. We revealed that rapid riverbed incision in the VMD was consistent with significant decrease in the sediment load, from 166.7 Mt/yr in 1980-1992 (predam) to 44.2 Mt/yr in the 2014-2017 (postdam) when 64 hydropower dams completed in the MR basin. Moreover, reduced flood discharges from the MR due to dam operation, (i.e., resulting in the reduction in the flow power necessary to transport the sediment), sand mining, dyke systems, and channelization are more likely the considerable drivers of riverbed incision in the VMD. Therefore, collaboratively integrated management of the MR among riparian coun tries is important for the sustainability and survivability of the VMD.