Quantifying the impacts of hydraulic infrastructure on tropical streamflows

Abstract

Hydraulic infrastructures, such as reservoirs and water diversion channels, cause altered streamflow worldwide. Therefore, this study aimed to assess the coupled impacts of reservoir operations and water transfer on downstream streamflow over 42 years for a tropical river in Vietnam, the Vu Gia Thu Bon (VGTB).We also quantified variations in the multi-sub-basin contributions to the water budget associated with hydraulic structure development. Therefore, a semi-distributed hydrological model, SWAT (Soil and Water Assessment Tool), was developed for the entire VGTB basin considering two plausible scenarios: with a dam and without a dam. In this study, reservoirs substantially affected the streamflow during the 2011-2020 period when 12 cascading hydropower dams were constructed in the Vu Gia sub-basins. The cascading reservoirs across the Vu Gia River reduced the annual average streamflow by 28.1% during this period, whereas their influence was augmented by 13.9% at reaches further downstream. In contrast, the local reservoir and flow diversions created on the Thu Bon River resulted in a 6.5% increase in streamflow. The upstream reservoir operation significantly increased streamflow at the midstream stations by 27.8% compared to the no-dam period. The streamflow decreased in the dry season by 5.6% in the Vu Gia sub-basins and increased by 61.7% in the Thu Bon sub-basins. However, the impacts decreased in the wet season by 41.3% due to the operation of reservoirs, in which Dak Mi 4 had the most significant influence. It was found that the water diverted to the Thu Bon River was governed and reduced by the cascading hydropower dams. Therefore, the operation of 11 reservoirs has partially compensated for the lost water in the Vu Gia sub-basins, to which the Dak Mi 4 plant has transferred 19.7 m 3 /s (14%). Our findings classify the impact of cascading dams and diversion structures and their interaction with climate change.

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 study area has a unique topography with mountain ranges running from west to east. The basin's geography is primarily mountainous, with an average slope of 25 %, accounting for 60 % of the entire catchment area, and the slope varies from 0 to 70° [ [30] , [43] ]. The lithology in the basin is mainly sedimentary, igneous, and metamorphic rocks.…”

“…The distribution of rainfall is temporally and spatially uneven, varying significantly between seasons and the geographical terrain of the region. From 1980 to 2020, the basin received yearly rainfall varying from 2184 mm to 4188 mm [ 44 ]. The region experiences a distinct rainy season (September–December), with peak rainfall from October to December, elevating the flood risk.…”

“…The intensive development of dams and reservoirs in the last two decades has changed the flow regime and reduced the sediment load of this river, consequently damaging the coastline ( Fig. 1 b) [ [29] , [30] , [31] ]. Ha [ 31 ] indicated that the sediment flow from the Thu Bon River was reduced by half compared to the period before the construction of the upstream reservoir.…”

Preface special issue: “Processes and patterns in tropical hydrology”

“…The impact of hydraulic structures on the river hydrology of a larger humid tropical catchment in Vietnam is assessed by Nguyen et al (2023). The varied impacts on streamflow dynamics because of reservoir operation and water transfers are most notable in the midcatchment with reduced streamflow (30%) but mostly increased streamflow during the dry season.…”

“…The authors find a moderate increase in soil water availability in treated rice plots, suggesting that biochar could be used as a potential soil moisture retention technique but not likely as a replacement for other water management strategies in croplands across the seasonally‐dry Tropics. The impact of hydraulic structures on the river hydrology of a larger humid tropical catchment in Vietnam is assessed by Nguyen et al (2023). The varied impacts on streamflow dynamics because of reservoir operation and water transfers are most notable in the mid‐catchment with reduced streamflow (~30%) but mostly increased streamflow during the dry season.…”