Flow division dynamics in the Mekong Delta: application of a 1d-2d coupled model

S. Eslami Arab, M. van der Vegt, P. Hoekstra, Herman W.J. Kernkamp, Nam Nguyen Trung, Dung Do Duc, Tho Tran Quang, Febru Mochamed Februarianto, A. van Dam, Tho Tran Quang

Research output: Working paperAcademic

Abstract

The low-lying and rapidly urbanizing Mekong Delta, constitutes a complicated multi-channel estuarine system exchanging water and substances with a delta-wide irrigation system. A 1D-2D numerical model domain of the Mekong Delta (including rivers and canals) is calibrated and validated for water level and discharge during the dry season. The numerical model consists of the 1D domain of the rivers and delta-wide irrigation system coupled with the 2D domains of the continental shelf and the Tonle Sap Lake. Using the coupled domain keeps the simplicity of a 1D network within the deltas estuarine and irrigation systems, while maintaining the interaction with the spatial tidal dynamics of the 2D coastal domain. Using this numerical model, 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 suggest that the complex irrigation system has a friction-like effect on tidal propagation, reducing tidal amplitude to maximum 25%. The channels aggregate to only 1% of the total volume in the delta, but they accommodate up to 10% of the tidal prism. Tidal amplitude, except in some of the channels, generally reduces upstream, while subtidal water level is highly sensitive to spring-neap cycle and wind generated offshore surge. Cumulative discharge division between various estuarine channels is calculated and compared to the previously provided estimates. Although the cumulative discharge division is consistent over longer periods, temporal discharge division can be significantly sensitive to wind-induced offshore subtidal water level variations. This sensitivity increases towards end of the dry season and can completely reverse the known subtidal discharge division within a timescale of few days, perhaps strongly impacting salt intrusion and water quality dynamics.
Original languageEnglish
PublisherCopernicus Publications
Publication statusPublished - 1 Apr 2019

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