Flood control looked at from urbanization

 VietNamNet Bridge – The funding for anti-flood projects is said to be incommensurate with the effectiveness from these.

Professor Le Huy Ba, Director of the Institute of Science, Technology and Environmental Management, talks with VietNamNet about flooding and flood control in Ho Chi Minh City.

Professor Le Huy Ba says that HCM City should not construct
 more buildings in the downtown area.

How do you assess the flooding situation in HCM City at present?

The flooded areas in the downtown area include the districts 1, 3, 4, 5, 7, 10, 11, Phu Nhuan and part of Binh Chanh, Binh Thanh, Tan Binh districts. The flooded areas along main canals, including Nhieu Loc - Thi Nghe, Tan Hoa - Lo Gom, Tau Hu - Ben Nghe, Doi, Te, Tham Luong, on an area of 140km2.

Due to the geological position of Ho Chi Minh City, the city is categorized as "semi- flooding tide city." The city's main drainage direction is North, North West, North East to South, Southeast. Therefore, the more we expand the modern urban area in the South, East of Saigon like Binh Chanh, District 7, Nha Be and Can Gio, the more we prevent the drainage of the city.

You mean that urbanization is probably the culprit, how about the consequences of climate change?

When considering the cause of flooding in Ho Chi Minh City, we need to consider a combination of rain, tide and the urbanization process. In particular, the element that enhances rain and tide, making more severe impacts on urban flooding is climate change. Climate change makes the earth warming, the sea level rise, especially when the tide has increased and will rise by 1 m by the end of this century.

All temperature measure stations confirm the evidence of climate change. Currently, the average temperature has increased by 0.3 to 0.4 degrees Celsius over the past decades and it tends to further increase. The model studies show that in the 21st century, the Earth's average temperature could increase from 1.1 to 6 degrees Celsius.

As the sea level rises by 1 meter, 14 million people in the Mekong Delta will be affected, 40,000 km2 of the delta will be flooded and 1,700 km2 of coast will be submerged. Ho Chi Minh City (Can Gio, Nha Be, District 2, District 8, District 7, Thu Thiem, part of Binh Thanh, Binh Chanh) will be encroached by salt water.

So HCM City has gone astray when it started urbanization?

So far, according to the studies, the sea level rises caused by climate change does not make a significant impact on urban flood in HCM City. Therefore, the current flooding is mainly caused by humans, particularly due to unscientific urbanization combined with rain, including urban rain. Wastewater can cause flooding but it is not significant at all, only in terms of water pollution.

Could you go into detail?

Mistakes in the process of urbanization, especially the leveling of depressed areas, ponds, lakes and canals to build houses and roads, have resulted in flooding.

Residential areas, urban areas, industrial zones have grown massively, while the drainage system has not been given due attention, so whenever it rains roads are flooded. If roads are raised, houses are flooded. If houses are raised, roads are flooded.

Specifically, if flooding is controlled in one area, new flooded sites appear. Many places are deeply submerged in the water for 3-4 days after downpours. Recently, old apartment blocks were demolished to build new buildings, which are much higher than the old ones (10-15 floors). Actually, it is a big mistake: on the same area, with the same facilities, the population will increase, the number of vehicles will also increase, and traffic congestion and flood will inevitably rise.

Because of these factors lead, flooding in Ho Chi Minh City comes to a deadlock. No project brings about viable results.

Everyone knows clearly that climate change will cause the sea level rise but they still planned to develop and expand urbanization to the low areas such as District 7, the South East and South West of the city, along with the massive works and sea encroaching works.

In your viewpoint, what ground does the city’s anti-flooding effort should start from?

We have to make drainage based on the natural basin, on the basis of correctly identifying each small basin, combining small basins into large basins, to calculate the water balance for that basin itself.

Reservoirs must be built. The peripheral areas, including the regions with enough land (1 ha or more) need to have reservoirs. HCM City has little reservoirs; the construction of reservoirs is essential and urgent.

The city should not build high-rise buildings in low, sunken areas in the south, southwest of the city. District 8 and District 4 are more and more flooded, because they are low-lying areas, now they are more flooded because the surrounding low-lying areas have been urbanized already.

If construction must be implemented in the low-lying regions, because of special reasons, what should we do?

We should avoid putting the length of the buildings perpendicularly to the direction of drainage, not building roads hindering the flow. It is necessary to take into account the sea level rise due to global warming, at least 20cm, highest 70cm, within 15-20 year. It is a necessity that we cannot resist. So, no matter what, in construction planning, especially in the lowlands that are affected by the tide, we need to take into account the sea level rise.

Minh Dung