Intensified susceptibility to riverbed incisions under sand mining impacts in the Vietnamese Mekong Delta: A long-term spatiotemporal analysis

Abstract

The Vietnamese Mekong Delta (VMD) has experienced severe morphological changes for decades, resulting in serious social, economic, and environmental consequences. Several natural and anthropogenic factors have contributed to the increasing rate of riverbed incision along the VMD. While previous studies have assessed riverbed incisions in specific affected regions or within limited timeframes, a comprehensive analysis of long-term spatiotemporal variations in incised sediment volumes across the entire delta has been lacking. This study quantitatively evaluated the spatial and temporal morphological changes in the VMD utilizing bathymetric data from 1998 to 2020. Additionally, susceptibility zones, categorized into seven classes for incised and accreted sediment volumes, were delineated considering the influence of sand mining activities. Furthermore, this study pioneers the quantification of sand mining contributions to riverbed incisions along the VMD. The analysis revealed pronounced and irregular morphological alterations in the delta channels over the 22 years of the study. The estimated net annual incision volumes for the entire region were -119 Mm³/year, −69 Mm³/year, and -66 Mm³/year for the 1998–2005, 2005–2017, and 2017–2020 time intervals, respectively. Between 2017 and 2020, the dynamic processes intensified notably, with some areas experiencing either high incision (up to −13 m/year) or high accretion (up to 11 m/year). Intriguingly, most incise-prone areas were partly situated within regions associated with sand mining. The contribution of licensed sand mining to annual net riverbed incisions increased from 27.7 % in 2005–2017 to 35.3 % in 2017–2020. This study highlights the influence of sand mining on exacerbating the vulnerability of different areas within the VMD and provides valuable insights for effective sediment management strategies.