Despite huge amounts of financial investment and efforts in improving the drainage system in Hanoi, flooding still happens often when there is heavy rain in Hanoi.
In recent years, Hanoi City has invested more than 15,000 billion VND to build drainage systems, pumping stations, renovating water reservoirs in the inner city districts and the western region. In order to prevent the inner city from being flooded when it rains heavily, over the years, Hanoi has spent thousands of billions of dong on renovating and upgrading drainage projects. By 2016, Hanoi had completed drainage projects for the inner city, with a total investment of more than 8,000 billion VND (~$336,700,000). For the flooding prevention in the west of the capital, Hanoi had also invested VND 7,400 billion to build the Yen Nghia pumping station projec with a capacity of 120m3/s pumps water from Nhue river basin to Day river, reducing flooding in Ha Dong, Thanh Xuan, Nam Tu Liem districts. Furthermore, up to now, the Hanoi drainage system has been fully invested and built according to the planning for the area of To Lich river, Lu river, Set river and Kim Nguu river with an area of 77.5km2 in the area of 8 Ba Dinh districts, Hoan Kiem, Dong Da, Hai Ba Trung, Hoang Mai, Tay Ho. Typically, Yen So key project cluster includes Yen So pumping station 90m3/s along with a system of canals and lakes, with a rain intensity design of 310mm/2d for the whole system and 70mm/h for the sewer system.
However, until now, Hanoi is still suffering from flooding, affecting the lives of thousands of people. One main reason is that over the years, while the city has spent a lot of resources investing in drainage projects, some projects have not been completed on time. For example, Thuy Khue Street (La Pho slope, Tay Ho district) drains water depends on the Thuy Khue ditch system, however, after 10 years of construction, the project to renovate Thuy Khue canal with a length of 1.8 km is still in the process of site clearance. The project of Yen Nghia drainage pumping station with the goal of preventing waterlogging for districts, Ha Dong, Hoai Duc and Thang Long boulevards was completed in 2020, but has not been able to operate yet because the canals leading water from Nhue River have not been completed.
Furthermore, as the city is carrying out a number of large-scale construction works, some of which have affected the drainage system. For example, at the intersection of Phan Boi Chau - Ly Thuong Kiet, the slow implementation of the S12 metro station (Non metro project - Hanoi station) has caused the drainage system in the area to be affected. The construction unit has directed the common drainage of the route into a separate pipeline running close to the construction site, which has not met the demand, slowing down the ability to drain water.
Another reason is the decreasing level of water and trees area in Hanoi. As the rate of concreting is increasing, the water that cannot penetrate into the ground must be poured into the depression, forming a waterlogged point. Hanoi has no statistics on the status of ponds and lakes being filled, however, a report by the Center for Environmental and Community Research (CECR) of the Vietnam Union of Science and Technology Associations shows that 17 lakes in Hanoi are completely levelled, while only 7 new lakes were added. The water surface area from 2,100 ha before 2010 has decreased to 1,165 ha in 2015.
According to Prof. Vu Trong Hong, the former Deputy Minister of Agriculture and Rural Development, the drainage system in the inner city of Hanoi can now meet the rainfall of 100mm/2h, so if the rainfall is over 100mm/2h, there will be overload, leading to flooding. However, due to climate change becoming more and more complicated, with heavy rainfall in a short period of time, the actual rainfall exceeded the calculation.
Still, there have been some significant improvements compared to years before thanks to the recent pumping project development. By 2022, Hanoi had solved 5/16 flooding points on main streets, and the remaining 11 points the city had had received effective solutions. Other small flooded points with quick water withdrawal time have also been arranged to be on standby, minimising the time and depth of inundation.
Source: the Internet