Deforestation, khlongs, reservoirs and the floods of 2011
'The center of Bangkok will certainly flood, that is inevitable. In a week the water will slosh over the big bag wall and put the center under 1 to 2 meters of water.'
Graham Catterwell in The Nation, Nov. 9, 2011.
Short timeline
- First floods at the beginning of August, especially in the North, Isan and the north of the central plain. 13 deaths have already been reported.
- In early/mid September, almost all provinces in the central plain were flooded.
- At the end of September/beginning of October, the dams are forced to discharge more and more water, Ayuttaya and the industrial areas there are flooded. The graphic shows the situation on October 1.
- In mid-October, Bangkok is under threat for the first time. Chaotic times are coming. Residents who can afford to flee flee.
- The battle to keep at least the business district of Bangkok flood-free will really start in mid/late October. Experts and politicians are at each other's throats with contradictory predictions and advice. It is decided that an attempt will be made to protect the center of Bangkok from water.
- On November 5, the 6 kilometer long sandbag dike (big bag wall) to protect the business center of Bangkok ready. Fighting breaks out with suburb residents who now have to deal with much more water for a longer period of time.
- At the end of November, the city center of Bangkok was saved, but riots around the dike remain.
- Only at the end of December/beginning of January did the high water disappear everywhere.
The 2011 floods were the worst in living memory
Thailand's 2011 floods were the worst in living memory, killing nearly 900 people, causing $46 billion in damage and disrupting the lives of millions. No wonder that much attention has been paid to the cause of this disaster and ways to avoid such a thing in the future.
It was often said that this one man made disaster was mainly referring to the deforestation, the policy regarding the reservoirs and the lack of maintenance of the canals, especially around Bangkok. I dispute that view and see the exceptional precipitation in 2011 as by far the main culprit.
My story is about the possible causes mentioned above and I focus on Bangkok and the surrounding area, which is the heart of Thailand, but let's not forget that there were also floods in the North, Northeast and South, although much less.
Rainfall
There is no doubt that the rainfall in 2011 was exceptionally high. The KNMI calculated that precipitation in the North was 60 percent more than average and the highest since 1901. In the rest of the country it was around 50 percent more. In March 2011, there was already 350 percent more rain than normal.
On July 31, the remnants of a tropical depression, Nockten, Thailand. It already caused non-threatening flooding in the central plain in August. From late September to late October, three other tropical depressions (Haitang, Nesat, Nalgae) water above especially the North. (In the months of July, August and September, Thailand receives an average of five times as much water as in the Netherlands during the same period.)
In October, water poured into Bangkok over a broad front 40 times greater than the Chao Phraya can drain in one day.
deforestation
I am a great walker in the woods and deeply regret the deforestation. But is it a cause of the 2011 disaster? Deforestation is certainly responsible for local, temporary flash flood but almost certainly not before this disaster. Firstly, not because 100 years ago, when Thailand was still covered with 80 percent forest, there were already serious floods. Secondly, because in August the forest floor is already saturated with water and the precipitation simply flows off afterwards, trees or not.
Reservoirs
Five rivers flow south to form the Chao Phraya somewhere near Nakhorn Sawan. They are the Wang, Ping, Yom, Nan and the Pasak. In the Ping lies the Bhumiphon Dam (Trat) and in the Nan the Sirikit Dam (Uttaradit). There are some smaller dams, but they are nothing compared to the two large dams in terms of water storage capacity.
Irrigation and power generation
The main function of the two large dams has always been irrigation and power generation. Flood prevention came second, if at all. It is important to emphasize this because these two functions (1 irrigation and power generation and 2 water collection to prevent flooding) conflict with each other.
For irrigation and power generation, the reservoirs must be as full as possible by the end of the rainy season, and the reverse is true for flood prevention. All protocols (until then) focused on the former, filling reservoirs by the end of September to ensure sufficient water in the cool and dry season. In addition, in 2010, a dry year, there was not enough water behind the dams and that was again criticized. A diabolical dilemma.
Effect of dams on flood prevention is disappointing
Then another important point. The two large dams, Bhumiphon and Sirikit, collect only 25 percent of all the water coming from the North, the rest flows outside these dams to the South, into the central plain. Even with a perfect flood prevention policy around the dams, you would only reduce the amount of water to the south by 25 percent.
Why was a lot of water discharged from the dams only in September/October?
The large volumes of water that had to be discharged from the dams in September and October to prevent dam failure certainly contributed to the severity and duration of the flooding. Could that have been prevented? Opinions are divided on that.
There are those who say that water should have flowed off in June/July (which did happen, but in small amounts), but in those months the water level in the reservoirs was completely according to plan, between 50 and 60 percent filled, so no reason at all for care. In August, the water level increased rapidly, but certainly not very exceptionally. Moreover, there was already flooding in the central plain at that time and people were hesitant to make it worse.
It was only after the heavy rainfall in September/October that the water level became critical and discharges had to be made. It is, I think, unreasonable to assume that in June/July it could be foreseen that there would still be a lot of rain in September/October, as the long-term forecasts of the weather are not that good.
The khlongs
The poor state of repair of the khlongs, the system of canals in and around Bangkok, is also often cited as a contributing factor to the severity of the flooding. This is not entirely correct for the following reason.
The canal system was largely designed by a Dutchman, Homan van der Heide, at the beginning of the last century, and was and is exclusively intended for irrigation. They have not been constructed nor are they suitable for draining excess water from the central plain around Bangkok to the sea, at least not in sufficient quantities (they are currently being worked on).
Conclusion
I believe that by far the main cause of the floods in 2011 was the exceptional rainfall that year, with other factors perhaps contributing in a small way. It was only for a small part man-made. I would also like to note that in all monsoon countries, from Pakistan to the Philippines, this kind of flooding occurs regularly, with no one pointing to anything other than heavy rainfall as the culprit.
I did not go into, and do not want to go into, the policy once the floods were a fact, that is a subject in itself.
You have to weigh up many interests
With regard to the prevention of such flood disasters in the future, I will only say that it is an immensely difficult task; especially since you have to balance so many interests (farmers-other residents; Bangkok-countryside; environmental-economic development; etc.). It takes time. There is no such thing as a perfect solution, it is almost always a choice between two evils, with all that entails in consultation, bickering, quarrels and revolts.
Several hearings have already been held on the construction of excess water storage areas (a quick, cheap but partial solution), the so-called monkey cheeks, in the north of the central plain. That doesn't really help because the residents are not really enthusiastic about the idea that they have to stand in 1 to 2 meters of water for months so that the Bangkokians can keep their feet dry.
I suspect it will always be a very partial solution with some minor or major improvements here and there. Preparing well for the next flood is therefore equally important.
Positive and a story that makes it clearer than all that shouting and bleating of the EXPERTS. Thanks for the information Tino.
A nice story indeed, I don't know if it is positive, Tino knows a lot about it, but is he now an expert? It's a pity that if one gives a response to a subject like this, given entirely and based on his own experience, this what he hears and sees, is immediately portrayed as the bleating of a Connoisseur.
And why is it that everything floods again in the normal years after 2011? Like, for example, Ayuttaya being flooded again? While a concrete wall had still been placed on the dike at the weak spot identified in 2011? People had forgotten to look at the condition of the dike, so that in 2012 the water flowed under (!) the concrete wall...
From the - analytically - clear story of Tino you taste the final conclusion "nothing can be done about it" and therefore also "do nothing about it".
And that seems to me to be a somewhat too fatalistic approach. But that will be judged by Gerrie as "bleating of EXPERTS".
Nicely written, but I was in Rangsit just before the flood in September 2011 and a canal there was completely full of plants and the lock gates could no longer be opened, later at the end of October during the flood the houses of the family had about 80 cm of water and on the news I saw that citizens with picks and bats dug a hole in the dike at a sluice, to protect the wealthy homeowners who only had 30 cm at the time, and because of the large hole the low area filled up, resulting in 1.80 in the house that about 60 cm higher than the road, my house had 14 extra people to eat and sleep, still cozy thanks to such people and irresponsible drivers.
In a forest of factors, it is not easy, if not impossible (even for water experts) to determine exactly the causes of floods in this country (such as that of 2011) and their mutual coherence and individual importance.
More important is the question of how we can reduce the damage caused by such floods and which issues are given priority. For example, keeping the center of Bangkok dry seems to be (or has become) priority number 1. Older Thais and expats can still remember flooding in Silom and Sukhumvit. I can still remember that during the floods in 2011 it was suggested to open all dams, to remove all dikes so that the water could find its natural way (also through the city) to the sea. The expectation was that the center of Bangkok would be below 4 centimeters for a maximum of 30 days. For top decision-making politicians in this country, this was absolutely unacceptable. No one else was asked for an opinion, not even parliament.
Indeed Chris. I walked through water up to my knees on Sukhumvit. Huge rain, very true, but the water hyacinths were also to blame for the severity and the deforested slopes also contributed. I will leave open whether and to what extent one factor contributed more to the floods than the other, as I am not an expert {at least not of flood causes}.
We were under 1.50 water at Laksi for two months, just to spare the center. Our flood, and its extra-long duration, was certainly manmade.
I also cannot share Tino's conclusions. What about those extra rice harvests, for which they held water for longer than justifiable? And the fact that all dams had too high a level at about the same time and then let God's water flow over God's field?
In addition, a conspiracy theory is doing the rounds whereby owners of higher lands could suddenly sell them as floodfree at high prices. So flood to lend a hand to land speculators.
Everything is possible in Thailand, except looking ahead
Dear Tino, I believe that the effect of deforestation is greater than you would like to believe. If you mention the situation 100 years ago, you indicate that the land was 80% forested. I can assure you that this was certainly not the case in Bangkok's river delta, which had long been known for its fertile soil. So in this area 100 years ago the tree population must not have been much different than it is today.
Tino just felt like a nice story on Thailandblog, he made it pretty long and beautifully written himself, but I have to agree with people like Dr. Tim.
The effect of deforestation is a huge problem all over the world and certainly also in Thailand. Years ago they started to drive the farmers crazy to grow rice and for the convenience of this they dig the ground 50 cm to create a depth to to be able to retain water for growing the rice, which is actually not necessary at all.
In addition, most forests have simply disappeared, what remains when you drive through Thailand with your four-wheeler are only standing trees that usually do not have much left because there is no ground around them.
I'm really excited to keep going now. I take a triangle with Nakhon Sawan as the top and the line between Nakhon Pathom and Prachin Buri as the base. Count me in because I'm not very good at that. I think it's about roughly 17.500 square kilometers. I'm going to reforest this imaginary. I put 100 trees on every hectare. So they are 10 meters apart. Trees are usually closer together in forests, but I don't want to exaggerate because you can't plant trees everywhere. For the same reason, I also rounded down the land area. One hundred trees per hectare, there will be 10.000 per square kilometer. On that much land I can plant 17.500x 10.000 trees. That's 175 million trees. What's the effect? These trees evaporate at least 250 liters of water per day. That is at least 450 million tons of water that does not have to go through the rivers every day. I assume that at least 3 cubic meters of water per tree can be stored in the ground. that is more than 500 million tons of water that does not enter the rivers either. Moreover, the rivers are twice as deep because 'deforested' rivers take huge masses of sand with them and deposit them along the way.
The rainwater from 2011 is no problem at all for the system I am describing here. Sincerely, Tim
Nature was indeed fierce that year.
I am not an expert, but I do see consequences of human actions.
All year round one sees brown-colored rivers, which wash tons and tons of fertile soil to the sea. Jungle, also on protected mountain slopes, is being cut down to make way for agriculture and/or livestock farming. In the area where I live, 50 years ago there were monkeys, even tigers. Now one only sees corn and sugar cane.
No more trees and roots that can collect and absorb a lot of water. The earth is washed away until a stone slope remains, from which the water races towards streams and rivers. What remains is unusable soil, almost nothing grows on it. Man is an important factor in my opinion.