Detail Abstract

Impacts of dams and sand mining on flow regime and sediment morphology changes in the Vu Gia Thu Bon River basin

Abstract

The Vu Gia Thu Bon (VGTB) River basin plays an important role in water resources in the Central region of Vietnam. However, over the recent decades, dam construction and other anthropogenic activities have increasingly profound effects on the flow regime and sediment budget. Understanding these impacts is critical for the foundation of sustainable hydrogeomorphology management. In this study, the long-term discharge and sediment load were spatiotemporally assessed from 1996 to 2020. The river bathymetric data (in 2010 and 2021) were also analyzed to further clarify the effects of upstream sediment changes and sand mining on morphological evolution. The mean annual sediment in Vu Gia and Thu Bon Rivers decreased by 36% and 47.2%, respectively, in the post-dam period compared with the pre-dam period. The volume of sand mining is approximately 453 Mm³ from 1990 to 2018. Comparison of the effect of dam construction and sand mining shows that sand mining has the most influence on the reduction in sediment.  The total incision volume during the period of 2010–2021 in our concerned river sector (-63.25 Mm³, averaging at -5.27 Mm³/yr) with a rate of incision depth of -0.14 m/yr. Results of the study provided useful insights into the effects of anthropogenic activities on the sediment budget. These changes of riverbed incision on hydrological processes invested to better understand water level changes and saline intrusion.