An assessment of uncontrolled human interventions on the contemporary sediment budget and morphological alterations of the Vu Gia Thu Bon River basin, central Vietnam.

The Vu Gia Thu Bon (VGTB) River basin is critical for regional development and prosperity in water resources. However, human interventions (e.g., dam construction and sand mining) have significantly affected this basin's sediment budget and morphological alterations over recent decades. Such humane actions drive an imbalance in water resources in the basin from upstream to downstream. Therefore, this study investigated spatiotemporal changes in sediment budget and morphology alterations using long-term data and bathymetric surveys; from these data, dams and sand mining contributions were quantified and differentiated. Based on field survey data and interviews, we estimated the sand-mining volume by incorporating reported and a newly proposed empirical formula. The results show that the total riverbed incision volume from 2010 to 2021 was 63.30 Mm, with an incision rate of 0.14 m/yr. The officially reported sand-mining rate was 1.12 Mm/yr, while the newly proposed empirical formula estimated 4.4 Mm/yr. According to the developed empirical formula, the percentage reductions in the sediment budget due to sand mining and upstream dams were 69.7 % and 30.3 %, respectively, according to reports, and 17.8 % and 82.2 %. The statistical method was thus likely too conservative compared to the developed empirical formula. We found that the natural sediment supplies sourced from upstream were insufficient to compensate for the mined bed material. Therefore, our combination of different datasets permitted the assessment of future geomorphological developments within the VGTB River basin under the ongoing sediment deficits. The results of this study provide valuable insights into the impacts of human interventions, specifically sand mining, on the sediment budget, morphological alterations, and riverbed incision. The developed assessment forms the foundation for developing and expanding the region's water/sediment resource management strategies.