Urban Flooding and Its “Intractable” Causes

Urban flooding is an increasingly concerning issue, particularly in recent days, as prolonged rainfall in major cities across Vietnam has severely affected production, daily activities, and people’s lives; caused significant damage to construction projects, destroyed technical infrastructure, disrupted traffic, and contributed to environmental pollution…

Flooding is occurring not only in lowland and coastal urban areas but also in urban areas in midland, mountainous, and highland regions. So, what are the fundamental causes of urban flooding? Let’s take a look at some of these causes with LPC.

1. Urban Flooding Due to Natural, Meteorological, and Hydrological Conditions

The first causes of urban flooding are natural conditions, terrain, tides, upstream floods, and, in particular, the impacts of climate change. These natural conditions contribute to various types of flooding:

• Tidal flooding: Caused by the influence of tides from the East Sea or West Sea during high tide or spring tide periods. Rising water levels in rivers and canals make drainage difficult in low-lying areas, resulting in flooding.
• Rainfall flooding: This is one of the most common causes across all regions. As rainfall increases, heavy and prolonged rainfall over large areas can exceed the design capacity of drainage systems.
• Flooding caused by river floods: Floods directly from upstream rivers, as well as water released from irrigation and hydropower reservoirs upstream, can cause flooding and become even more dangerous when occurring simultaneously with heavy rainfall and high tides.

2. Urban Flooding Due to the Drainage Capacity of the Drainage System

The heavy rainfall on May 29 caused 35 flooded locations in Hanoi, concentrated in several districts such as Thanh Xuan, Cau Giay, Hoan Kiem, Hai Ba Trung, and Thanh Tri District…

The drainage systems in cities, most of which were built on the foundations of older urban areas, remain incomplete and have many limitations. Cities and urban areas have developed through different stages, with different planning horizons and levels of investment. As a result, urban infrastructure in general, and drainage systems in particular, have not yet met current requirements.

3. Urban Flooding Due to Urban Planning and Development Management

During the development process, inadequate management of construction planning and insufficient control over ground elevations have resulted in encroachment on planned drainage systems, a significant reduction in water retention areas, and a lack of integrated connections between drainage systems in new and existing areas, all of which negatively affect drainage capacity.

• The increasing area of concrete surfaces in urban areas reduces groundwater recharge and creates the urban heat island effect.
• Excessive construction of high-rise buildings can contribute to land subsidence.
• Scattered construction materials reduce the effective cross-section of waterways and obstruct water flow.

4. Urban Organization and Management Capacity of Local Authorities

The maintenance and upkeep of drainage systems have not been sufficiently effective. The dredging of sediment from rivers, canals, and drainage networks remains limited. Budgets allocated to these activities are also constrained.

Funding for the construction, renovation, and upgrading of drainage systems needs to be invested in a coordinated manner. However, in reality, funding remains very limited and relies largely on ODA loans. Coordination between investment in technical infrastructure and drainage infrastructure has also been inadequate.

5. Due to Community Awareness

Illegal construction; filling in and encroaching on rivers, canals, streams, ponds, and lakes; excessive groundwater extraction; and indiscriminate disposal of waste into manholes, canals, drains, and onto roads can block drainage pipes, making water drainage increasingly difficult.