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

Abstract

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 Mm³, with an incision rate of 0.14 m/yr. The officially reported sand-mining rate was 1.12 Mm³/yr, while the newly proposed empirical formula estimated 4.4 Mm³/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.

Keywords: Dam construction; Morphological alterations; Newly proposed empirical formula; Sand mining; Sediment budget; Vu Gia Thu Bon River basin.

Fig. 1

(a) Location of the VGTB River basin, including river systems and dam locations. The full names of the labeled dams are shown in Table A.1. (b) The VGTB River network, hydrological stations, and sand-mining sites on the VGTB River from 2008 to 2017 [32] and in 2021 from a field survey of authors. (c) The amount of sand mined from 2008 to 2017 and the accumulated mined volume from 1990 to 2017. (d) The relationships between the reduction in the sediment budget in the Thu Bon River and the coastal erosion area and between the sediment budget and the coastal retreat rate from 2010 to 2021.

Fig. 2

Framework of the current study.

Fig. 3

Map of cross-sectional locations surveyed.

Fig. 4

(a), (b) Annual flow discharge and sediment load data recorded at the Thanh My and Nong Son stations from 1996 to 2020. (c), (d) Relationships between the discharge and sediment amounts in the predam and postdam periods.

Fig. 5

Violin plots representing the kernel densities of the (a) daily suspended sediment concentrations and (b) annual sediment loads at the Thanh My and Nong Son stations in the predam (1996–2010) and postdam (2011–2020) periods.

Fig. 6

Relationships between the depth of the main channel and the annual moving-average flow discharge and between the channel depth and SSC at Thanh My and Nong Son stations from 1996 to 2020.

Fig. 7

Sand-mining activity in the VGTB River basin (the author took photos during the field surveys).

Fig. 8

(a) Riverbed elevation in 2010, (b) riverbed elevation in 2021 in 3 subregions: A - the Vu Gia River, B - the Quang Hue Channel, part of the Vu Gia and Thu Bon Rivers, and C - the Thu Bon River, and (c)–(d) riverbed elevations at the Thanh My and Nong Son stations in 1996, 2010, and 2021.

Fig. 9

(a) The riverbank of the VGTB River system in 1973, 1979, 1990, 1996, 2010, and 2021. (b) The mean and trend of river width from 2001 to 2020 at sub_A Analytical techniques are inherited from the research results of Yang et al. on the GEE platform. (c) The riverbed elevation in 2010 and 2021 at sub_B.

Fig. 10

The centrelines of the VGTB River system in 1973, 1979, 1990, 1996, 2000, 2005, 2010, 2015, and 2021.

Fig. 11

Shoreline variations at the Cua Dai estuary in 1973, 1979, 1990, 1996, 2000, 2005, 2010, 2015, and 2021 as obtained by analysis of remote sensing images. An image of erosion on the left bank in 2016, taken from the author's field survey, is shown. The shoreline data were extracted from historical Landsat-5, Landsat-7, and Landsat-8 imagery. Landsat images courtesy of the USGS were downloaded from the USGS EROS Center.

Fig. 12

(a)–(b) The sediment budget changes in 2010 and 2021 in the Vu Gia and Thu Bon Rivers. (c)–(e) The sediment budget changes in the Vu Gia River, Thu Bon River, and the entire VGTB River system during 2010–2021.