The Impact of Sediment Deficiency on Riverbed Evolution in Major Mekong Delta Rivers
Tra Nguyen Quynh Nga, Tran Thi Kim, Huynh Cong Hoai, Nguyen Thi Bay
Abstract
The bed change in the Vietnamese Mekong Delta has been increasingly altered caused by natural processes and anthropogenic activities, and it becomes even more complicated under the influence of rising sea levels. At the Tan Chau and Chau Doc stations, the water volume entering the Mekong Delta did not change between 2008 and 2017, but the sediment load decreased by one-third, which caused a significant bed change in the river. This study evaluates riverbed evolution in the Mekong Delta under sediment deficiency and forecasts erosion dynamics until 2030 due to sea-level rise. Results indicate that increased riverbed erosion in 2017 is linked to a 30% drop in sediment supply compared to 2008. Simulations for 2017 indicate a 0.15% decrease in accretion rate—measured as the change in bed elevation—in the upper Tien River compared to 2008, and a 0.5% decrease in the lower reaches. Erosion rates nearly doubled in the upper reaches from Tan Chau to My Thuan, while the lower reaches showed minimal change (0.33%). By 2030, erosion will intensify, especially along the Tien River from Tan Chau to Hong Ngu, reaching 1.6 m/year. Accretion will decrease sharply, with the highest rate at 0.1 m/year near Long Khanh islet