Chinese dams prevent flood in Vietnam’s southwestern region?

VietNamNet 15 November 2010

VietNamNet Bridge – “Vietnam’s Mekong Delta or the southwestern region needs floods and develops thanks to floods,” the acting director of the Southern Institute for Irrigation Planning Nguyen Ngoc Anh told VietNamNet in a recent interview about the abnormal flood season in the Mekong Delta this year.

This year the early flood in May was very low and the flood peak came late. The flood season 2010 is abnormal compared to other years. Compared to 2002, the flood peak in the upstream of the Mekong Delta was 2m lower than that of 2000. The total amount of water is equivalent to 60-70 percent of the average in previous years. The Mekong Delta has suffered great losses due to the late and small flood.

VietNamNet talks with Nguyen Ngoc Anh about this phenomenon.

The Mekong Delta is divided into three flood regions:

The hollow-flooded region includes Can Tho, Hau Giang, Kien Giang, Tien Giang and a part of Vinh Long and Long An provinces. This region needs a dike system to protect the densely populated areas, which have good infrastructure facilities, and orchards.

The mean-flooded region consists of Dong Thap, An Giang and a part of Long An and Kien Giang provinces. This region needs to control flood from August to December.

The deeply-flooded region comprises Long An, Dong Thap and An Giang (the areas along the Vietnam-Cambodia border). This region doesn’t need to prevent flood strictly.

Ngoc Anh said that the Mekong Delta residents are aware of the advantage of living together with flood and benefit from floods.

What is the reason for this to happen in Vietnam’s southwestern region

I can confirm that natural reasons play a major role. Due to droughts, the flood in the Mekong River upstream is small, resulting in low water inCambodia’s Tonle Sap lake. The flood in Vietnam’s Mekong Delta is small, too.

In addition, Chinese reservoirs in the Mekong River upstream, Lao and Thai reservoirs in the Mekong River downstream kept water earlier this year, which made early floods small. Reservoirs in Vietnam’s Central Highlandshave not stored up a sufficient amount of water, partly causing the water shortage in the Mekong Delta.

Many scientists said that the building of hydro-power dams in the MekongRiver upstream (in China) is the major reason for low and late floods inVietnam’s Mekong Delta. What do you think about this?

I know that the water flow of the Mekong River passing through Chinaaccounts for 10 percent of the river’s total water output. China has many big reservoirs, including one which contains more than 10 billion cubic meters of water, and these reservoirs will certainly make impacts on the downstream.

However, Laos, Thailand and Cambodia will suffer impacts from Chinese dams first, before Vietnam.

But technically speaking, the construction of hydro-power dams in the upstream will certainly influence the flow and water output in the upstream. Moreover, dams will also cause the decrease of alluvial material in the Mekong Delta. Is that correct?

Certainly! In theory, hydro-power plants have to store up water and this will affect the water and alluvial material volumes in the Mekong Delta.

Big hydro-power reservoirs in the upstream reduce the amount of alluvial material in the downstream by 30-40 percent. Moreover, they reduce the volume of sand in the river bed, which is very dangerous. It can cause landslide along the riverbank if sand exploration is not controlled.

However, the impact can only be measured accurately based on the information on operating procedures of hydro-power dams in the upstream. But we currently don’t have enough information about this.

What do you think about the operation of dams on the Mekong River and their influences on Vietnam’s Mekong Delta?

This issue was discussed at a recent meeting about the Mekong River. Many international experts said reservoirs in the upstream can help reduce harmful? Large? Overflooding? floods in the Mekong Delta.

But I think that this opinion is inaccurate because reservoirs can only help reduce medium floods, not strong floods like those in 1991 and 2000. When medium floods are futher diminished and become small floods, this has negative effects on the Mekong Delta, because it is the region that needs floods and develops thanks to floods.

What are the consequences of low floods in the Mekong River?

This year’s late and low flood has caused many difficulties for people in the Mekong Delta. The great difference between water levels in different flood seasons has caused serious land erosion.

on average, the Mekong Delta receives around 150 million tons of alluvia in a flood season. It is around 100 million tons in small flood season and up to 60-70 million tons in August and September.

This year the volume of alluvial material for the Mekong Delta will be very low because the flood is very low, and this will in turn affect the Winter Spring rice crop. Salt water encroachment will increase.

The seafood output will be very low, especially the output of linh fish.