Hydraulic Structures & Flood Control: A Case Study of the Red River, Vietnam
Introduction
Hanoi, Vietnam’s second-largest city, lies in the Red River Delta, a region prone to heavy rainfall and flooding, with risks exacerbated by climate change. The Red River, flowing through Hanoi, faces significant flood and drought challenges, particularly during the May–September flood season. Major floods in 1945, 1969, and 1971 caused severe damage, underscoring the area’s vulnerability.
Hanoi is safeguarded by the Red River dike system. In emergencies, floodwater is discharged into Van Coc Lake, a regulating reservoir 30 km from the city center, via the Van Coc Gate and an overflow point, then drained through the Day Weir. The primary aim of this blog is to introduce the study area and scenarios that demonstrate the effectiveness of various hydraulic structures using the EEMS model.
Study Area
The location and elevation map of the research area are shown in Figures 1 and 2. The area includes part of the Red River region flowing through Hanoi, from Son Tay Station to the downstream of Long Bien Station, as well as the Van Coc Lake area. The riverbed elevation is varied, ranging from −9 m to 17 m.
To protect Hanoi from flooding the Red River dike system was constructed centuries ago, and an emergency flood control solution has been in place since 1937. This solution involves discharging floodwater into Van Coc Lake, which serves as a regulating reservoir, through the Van Coc Gate and an overflow point located on the Red River bank. The water then drains into the Day River via the Day Weir. Photographs of the upstream and downstream of the Day Weir and Van Coc Gate are shown in Figure 3.
EEMS Model and Boundary conditions
EFDC+ is particularly effective in simulating hydrodynamic and ecological processes in large and complex environments, such as river systems and floodplain areas. It is capable of providing accurate, detailed forecasts of water flow and sediment transport. Moreover, hydraulic structures like sluice gates and weirs function effectively within EEMS, offering many valuable and flexible options for real-world scenarios. Therefore, EEMS is an ideal choice for this study.
The research area covers 241 km² and consists of 9,033 grid cells, with 216 rows and 123 columns, which were used in the EEMS model as shown in Figure 4.
The outflow boundary conditions are located at points 1, 2, and 3, as shown in Figures 5.
Water level data from the study by Anh et al. (2020), which has been calibrated, are shown in Figures 6, 7, 8, and 9. The hydrodynamic model parameters used in the model are shown in Table 1.
Table 1. Hydrodynamic model parameters.
Parameter | Value |
Horizontal Eddy Viscosity Multiplier | 0.0002 |
Horizontal Momentum Diffusivity | 0.1 |
Average Roughness (m) | 0.01 |
Dry Depth (m) | 0.05 |
To demonstrate the effectiveness of these hydraulic structures, two scenarios, listed in Table 2, were set up. in scenario 1, Van Coc Lake is not utilised as a regulating reservoir. In scenario 2, Van Coc Gate, Day Weir, and overflow point are operated together.
Table 2. Two scenarios for operating procedure of the Van Coc Gate, Day Weir, and overflow point.
Scenario | Van Coc gate | Day Weir | Overflow point |
1 (Non-Operational – Base model) | Close | Close | Close |
2 (Operational) | Open | Open | Open |
In both scenarios, observed discharge data from the 11-day period of the 1971 catastrophic flood were used as the upstream inflow boundary conditions at Son Tay Station.
Conclusion
This blog has presented the study area and outlined the scenarios used to evaluate the effectiveness of hydraulic structures in flood control. The results will be discussed in an upcoming blog post.
References
Anh, S. H., T. Tabata, K. Hiramatsu, M. Harada and L.N. Chung (2020). An optimal scenario for the emergency solution to protect the Hanoi Capital from flood disaster of the Red River by using the Van Coc Lake, J. Flood Risk Manag, 1–20. https://doi.org/10.1111/jfr3.12661.
