Author(s): Menna Allah Ahmed; Sameh Kantoush; Tetsuya Sumi; Doan Van Binh; Nguyen Mai; Binh Nguyen; Nguyen Doan; Luc Tuan; Nguyen Vuong; Huong Vu; Le Quyen; Ha Thang

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Keywords: Estuarine circulation; Riverbed incision; Riverbank erosion; Mekong delt

Abstract: Estuarine circulation is a fundamental characteristic in shaping estuarine dynamics, yet the interrelation between estuarine circulation and morphological alterations in tropical river systems such as the Vietnamese Mekong Delta (VMD) remains insufficiently investigated. Our study aims to address this gap by assessing short-term spatial variations in estuarine circulations within Dinh An and Co Chien distributaries during the 2016 dry season, a year marked by one of the worst droughts in the region. A one-dimensional hydrodynamic and advection-dispersion model (MIKE 11) was employed to analyze circulation variations based on nondimensional parameter space. Additionally, bathymetric datasets from 2017 and 2020 coupled with remote sensing techniques were utilized to scrutinize the relevance between estuarine circulation and morphological changes in the VMD. The analysis revealed that the semidiurnal tidal cycle significantly impacted the circulation patterns of both distributaries. Spatially, the circulation at 0 km and 25 km from the river mouth displayed distinct behavior: Co Chien’s circulation pattern was influenced by severe morphological alterations in the riverbed elevations whereas, Dinh An maintained a relatively stable circulation pattern due to a stabilized riverbed. Moreover, during this dry season, Dinh An was classified as a salt wedge estuary, experiencing localized riverbank erosion intensified around the wedge areas where the suspended sediment concentration (SSC) was substantially lower than that in the freshwater zone. In contrast, Co Chien, classified as a strongly stratified estuary, exhibited more widespread riverbank erosion because of the shear stresses caused by stratified water layers across that segment. This study provides crucial insights into the interplay between circulation mechanisms and morphological evolution in the VMD, offering a deeper understanding of morphological alterations and their broader implications for delta sustainability amidst changing environmental conditions

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P2030-cd

Year: 2025