Will hydro-power plants cause more floods in Vietnam?

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21/10/2020    15:00 GMT+7 vietnamnet

If there were no hydroelectric dams, floods would still occur, even at a higher level. In many cases, without hydropower reservoirs, floods would be more serious.

VietNamNet introduces an article by Assoc. Prof. Dr. Vu Thanh Ca, lecturer at the Hanoi University of Natural Resources and Environment, and former Director of the Institute for Marine and Island Studies under the Vietnam Administration of Sea and Islands.

Thủy điện có gây thêm lũ?
Half of a landslide hill buries the operating office of Rao Trang 3 hydropower plant in the central province of Thua Thien – Hue.

I taught river environmental engineering at Saitama University in Japan for six years. In 1995, Mr. Phan Van Khai (Deputy Prime Minister at that time) visited Japan and he was impressed by anti-landslide works in Japan.

You should go to Japan to see the dykes, the concrete-made slopes to block landslides to understand how they have modernized. Yet Japan still has deaths by mountain landslides, floods and flash floods, which proves how devastating the floods are.

Heavy rains, dike broking, landslides, flash floods regularly occur in Japan, and in many cases, the incidents exceeded all procedures, so they cannot blame anyone.

Flood discharge process

Recently, every rainy season, there are many opinions about building hydroelectric reservoirs and flood discharge in Vietnam. How should we look at this issue?

The current flood discharge process of hydroelectric dams is as follows:

When the rain comes, the reservoir reaches the level of “catching the flood”. Recently, the “flood catching” level has been reduced, depending on whether the reservoir has the flood regulating function.

The rain is still heavy, the amount of water running to the reservoir is quite large; The water in the lake rises above a certain level (the first threshold is called the discharge threshold), the reservoir begins to release water to reduce the water rise. The discharge volume increases along with the water level in the reservoir.

When the water level in the reservoir reaches the second threshold, the reservoir discharges a flow that is equal to the coming flow to the reservoir. At that time the amount of water downstream is still the same with or without a hydropower reservoir. A hydropower reservoir does not discharge too much water because it still needs to store water for electricity generation. The water in the lake is its property.

If there were no hydroelectric dams, floods would be still the same, or even higher.

However, many people still believe that floods in downstream is due to water discharged by hydropower plants.

So do hydropower plants increase flooding?

Thủy điện có gây thêm lũ?
To access Rao Trang 3 and Rao Trang 4 hydropower plants, the rescue team had to move by canoe.

We can just do an experiment: Take a pot with a little water, put a tap in it and let water run into the pot. Initially, the water is kept inside the pot. Then the water level in the pot rises, until it spills. This is flood discharge. At this time, the amount of water from the tap to the pot is equal to the water discharged and the water level in the pot remains the same. The reservoir is that pot. That pot holds a little extra water, but does not produce more water to spill. If there is a hole at the back of the yard, it is clear that the water flowing through the pot will cause less flooding there.

Many people believe that hydroelectricity has a lots of implications for the environment, ecology and increasing coastal erosion by blocking the flow of mud and sand. Hydropower also poses a huge risk of flash flooding if the dam fails. But there is no scientific basis to say that hydroelectricity increases floods. If there were no hydroelectric dams, floods would still the same, or even higher. In many cases, without a hydropower reservoir, floods would be much higher.

There was a time when I lived with my uncle’s family on the bank of the Red River (Hanoi). My family had a boat to use during the flood season. Every year, the water flooded our house and my family had to evacuate, leaving only 1 person in the boat to watch the house.

Since the Hoa Binh hydropower dam was built, there have been no floods. We moved off the riverbank a long time ago, but my wife’s uncle and cousin-in-law still live outside the Red River dike. Since the Hoa Binh hydroelectric dam was built, especially in the last 15 years, their home has never been flooded.

Usually, depending on the soil conditions (with or without rain before so the soil is wet or not), soil, holes and leaves, branches can only hold a small amount of water, let’s say about 20cm or 200mm. So the remaining water will flow downstream, causing floods. If the rainfall is 700mm, the downward flow is 500mm.

When the water in the hydropower reservoir rises to the level of “flood catching”, the reservoir begins to discharge water but the discharge flow is required to be much smaller than the coming flow. When the water level in the reservoir increases, they increase the discharge amount and when the maximum water level is reached, the reservoir is allowed to discharge with a volume equal to the coming flow. At that time, it is not important if there is a reservoir.

So the reservoir can store 4m of water and the ground can store 0.2m of water. Many large reservoirs, like A Vuong hydropower plant, hold 14m of water. Do reservoirs cause flooding? Of course not!

I do not support hydroelectricity

Water is money so hydropower managers do not want to discharge water. Furthermore, small hydroelectric plants do not have a flood regulation function so they discharge as much as the volume of water running into the reservoir. There is absolutely no reason for extra discharge. However, in any case, the amount of discharged water is always less than or equal to the amount of inflow water, ie hydroelectricity does not create more floods.

Hydropower reservoirs in Vietnam, especially Hoa Binh, are all operating according to international standards. After the dam was built, there was almost no flooding in Hanoi.

Hydropower dams indeed cause a huge environmental impact, but do not increase flood risks.

I am not in favor of hydropower and if I have the right to choose, I would follow the American model, destroying old hydropower plants, not building new ones, and only developing thermal and other forms of energy.

Vu Thanh Ca

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