Experience against flooding in Asian cities

Many Asian countries such as Japan, Thailand, and Cambodia have suffered great damage from floods and storms in the past.

Experience against flooding in countries around the world

However, these countries have come up with effective long-term solutions.

Experience against flooding in Tokyo

In September 1958, Typhoon Kanogawa caused heavy damage in the area around the Kanda River Basin (Japan) with 38,356 houses submerged in water, causing great loss of life and property.

Under this situation, the Tokyo city government decided to build a floodwater regulating tank underground with two phases with a total construction period of 20 years and construction cost of 101 billion yen (about 839 million USD).

This work was named Kanda River / water tank regulating underground 7 , including an 4.5km underground pipeline with an internal diameter of 12.5m.

It has the capacity to store up to 540,000m3 of floodwater from three major rivers in Tokyo city during the flood season including Kanda, Myoshoji and Zenpukuji rivers.

The first of the 2km long pipes began operation in April 1997, and the second pipe (connected to the first pipe) was 2.5 km long operating in September 2005. This work plays a very important role in preventing flood damage in Tokyo city.

At the end of August, ASEAN journalists were able to visit this project. From the construction office No. 3 of the Tokyo Metropolitan Government in Nakano Prefecture, our journalist delegation was led down the tunnel about 100m away.

It took only a minute by the elevator, we reached the main location of the tunnel about 43m from the ground. These are giant, humid pipes.

The representative of the project management board said that the temperature in the tunnel is always kept at 18 ^o C regardless of the weather outside and the amount of oxygen is always guaranteed to be sufficient for employees or visitors.

The representative said the regulating tank system ensures flood water does not overflow the river.

Diagram to regulate water from rivers to prevent flooding for Tokyo City - (Graphic: Tan Dat).

During the flood season, the water intake system on the three rivers Kanda, Myoshoji and Zenpukuji opened to receive a huge amount of water when the water level on the rivers reached an alarming level.

After the water recedes and the river level returns to normal, the water pumping system of this project will automatically bring the water back to the river.

These underground structures are designed to resist earthquakes and are periodically maintained. This system runs automatically so it saves manpower costs. Often employees come to check this system once or twice a week. During the rainy season, there will be staff available here.

The project management board said that in the past, flooding caused flooding in large areas and large losses of people and property. For example, before this underground pipeline, the 1993 tropical storm (288mm of rainfall) caused heavy damage in the middle of the Kanda River when it flooded more than 85 hectares and 3,117 houses.

However, after the project was put into use, the tropical storm in October 2004 had similar rainfall (284mm) but the damage decreased significantly and only 4ha of land and 46 houses were flooded.

According to the project management, this underground water tank operates mainly in the rainy season. In the dry season, staff will clean up the sediment in the pipe. Pipe maintenance costs range from 100-200 million yen per year, including utilities and staff.

The representative added that the project management occasionally invites children to go to the tunnel to paint to raise awareness of environmental protection for Japanese children.

After the historic flood in Thailand and Cambodia

Immediately after the historic flood in Bangkok in 2011, 675 people died, millions of people were affected and losses of up to 15 billion USD, Thai Prime Minister Yingluck Shinawatra at that time announced a treatment plan. $ 9.4 billion to implement flood management and control projects to prevent damage caused by flooding in the future.

According to Aljazeera, these projects include planting trees and building dams along the upstream branches of the Chao Praya River, including the construction of reservoirs in river basins where floods are formed, construction of flood discharge channels in an area of ​​323,749ha of agricultural land plus irrigation systems, projects to clean up canals and build a water management data system .

Also in 2011, according to adpc.net, 17,787 families in 12 districts and 66 communes of Siem Reap Province (Cambodia) were affected by floods, 5,339 people were moved to avoid floods.

Siem Reap is mostly affected by floods every year, both in urban and rural areas. But with the determination of the authorities and the people, the damage caused by the flood has been significantly reduced.

The Phnom Penh Post newspaper quoted the director of Noun Krisna Department of Meteorology and Water Management as saying that there are no floods in Siem Reap at present as the government has improved the water treatment system to prevent floods, especially in the temples.

A strategy to build dams was made by the provincial government in 2012 after Siem Reap, Angkor Thom and Banteay Srei submerged in flood waters in November 2011.

Meanwhile, the people of Siem Reap countryside built a higher foundation, built small dams to prevent floods and rebuild roads in the village to prevent floods.