Flood hazard assessment of residential areas inside the Van Coc Lake, Hanoi, in an emergency situation

The Van Coc Lake is a regulating reservoir located in the Dan Phuong and Phuc Tho Districts (30 km from the center of the Hanoi Capital). It is usually dry and includes arable land and residential areas. To protect the Hanoi Capital from flood disasters in emergency situations, floodwater is received from the Red River through the Van Coc Gate and the overflow point, and the floodwater drains downstream through the Day Weir. The authors have proposed the effective operating procedure in the emergency situations by optimizing the inflow discharge at the Van Coc Gate and the overflow point, and the outflow discharge at the Day Weir for ensuring the flood mitigation effect of the lake and the safety of the operating system. However, risk-reduction strategies based on a flood hazard assessment for the residential areas located inside the lake have not been adequately resolved. In this study, the inundation situations inside the lake area were identified with a two-dimensional depth-integrated hydrodynamic model in high resolution. The results indicated that the residential areas were highly vulnerable to floods. When the water depth in front of the Day Weir reached 1.0 m, 3.0 m, and its peak at 4.9 m, 57.13%, 85.52%, and 99.76% of the total residential areas (6.33 km²) were inundated respectively. The highest velocity was primarily focused around the Van Coc Gate, overflow point, and Day Weir with velocities of 0.6 - 2.0 m/s.