Abstract
The Mekong Delta constitutes a complicated multi-channel estuarine system, exchanging water with a delta-wide irrigation system. A 1D–2DH coupled numerical domain is calibrated and validated for water level and discharge during the dry season. This approach benefits from the simplicity of a 1D network within the estuarine and irrigation systems, while maintaining the interaction with the spatial tidal dynamics of the 2DH coastal domain. First, the role of the irrigation system on tidal dynamics is quantified; then, tidal propagation, freshwater budget, and the effect of offshore subtidal water level on discharge division are investigated. The results show that the complex irrigation system, in a friction-like manner, reduces the tidal amplitude up to 25%. The channels aggregate to 1% of the total water volume in the delta, while accommodating up to 10% of the tidal prism. Tidal amplitude reduces upstream, while subtidal water level is highly sensitive to upstream discharge, spring–neap cycles, and wind-generated offshore surge. Although cumulative discharge division within the estuarine network is consistent, temporal discharge division can be significantly sensitive to offshore wind-surge. During the dry season, it can reverse the expected subtidal discharge division within the time-scale of a few days and potentially influence salt intrusion.
Highlights
The Vietnamese Mekong Delta (VMD) covers approximately 60,000 km2 of land [1], is home to 18 million people, contributes to 26% of Vietnam’s national GDP [2], and provides half of the nation’s food supply [3,4]
Spatial and temporal variability of tidal amplitude, and the interaction of water level emphasizes the importance of a coastal model domain to capture the interactive nature of upstream discharge and downstream subtidal water level emphasizes the importance of a coastal the multi-channel estuarine system with the coastal sea
We have shown that subtidal water level variations can influence and occasionally reverse temporal discharge division within the multi-channel estuarine system, especially during the low flow regime
Summary
The Vietnamese Mekong Delta (VMD) covers approximately 60,000 km of land [1], is home to 18 million people, contributes to 26% of Vietnam’s national GDP [2], and provides half of the nation’s food supply [3,4]. The delta drains the Mekong catchment of approximately 760,000 km , along. 4910 km of the Mekong River [5,6]. The Mekong River within the VMD transforms to a multi-channel estuarine system draining to the coastal waters. A distinct feature of the Mekong estuarine system is the presence of thousands of man-made small irrigation/navigation channels, exchanging water with the main rivers.
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