ResX

If I can recall conversion factor correctly 2million Rai is equal to 3200km2 of land. If this is required for temporary measure only then I have nothing to say. But if they want to make the area permanent, something is terribly wrong. I don't know what is it. But it isn't about the flood control.

You don't need 3.2billion m2 of land to deal with 17billion cubic meter of waters. Even if Thailand has decided to take 34billion m3 of flood water that area is pretty to big. Bhumibol dam required 0nly 0.3billion m2 of land to keep at least 7billion m3 of water to stay calm.

Is my conversion factor correct? Or did I miss something?

oilreg, read up on it. The dams were full. They had to open the dams, that's what caused the flooding. But there was no way for them to deal with the water by the time it got full. It was too late.

Or, they let the dams to be fully filled due to some reasons best known to them.

am i the only one believing at all that the floods where caused by opening the dams?

seriously guys, i live in ChiangMai, a few days before we had the floods in CNX they opened the dam to release the water

a few days before the BKK flooding happened they opened the big dam_n down there,

anyone saying this is coinicidence has a slight tendency of being ignorance

No. You are not the only one. Let me in the team. Even the last year's floods. Uncoordinated dam water released was a part of the equation.

I think I know what was going here. Somebody went to one of the water resources conferences. One of the papers presented was about dam break study. He picked up the new terminology which is called Probable Maximum Flood (PMF). For this nature of dam break analysis researchers always use PMF as one of the dam break scenarios to be studied. PMF for Chao Pharaya based on my estimate is about 60billion cubic meters of waters that fall in less than 14 days.

The bad news is that PMF is possible to happen. Good news is it is less probable. The odd is smaller than 1/10,000.

My suggestion about PMF is that don't be scared by it more than anybody else in the world. It is not a bad idea to get the nation to be prepared to deal with it. Especially true if the nation has at least one major dam. Obviously, it shall not be done the way that the minister was trying to do.

That is pretty too high. The odd is less than 1/10000. Think about dealing with 15-20 billions of water that might fall in 7-14 days effectively, assuming they come towards the end of the monsoon. Then 99.5% chance that you are in control over the floods.

As I say, I'm guessing because the details are not clear. But Logically the tunnel should enable them to keep the dam half full, then is there is a sudden farming demand for water they can supplement the dam water with the tunnel water.

The problems have been that the dam has been TOO full. There shouldn't be a need to bring water in from elsewhere.

The problem with this plan is that it would be quite expensive for occasional use.

Yes the dam has been too full because of pressure from the rice growers. They feared there would not be enough water for their needs.

I agree it would be quite expensive for occasional use, the real question then is are we seeing a climate change which will convert "occasional" into "regular" or "frequent".?Put another way, are you a believer or a skeptic on global warming?

Correct. To be precise the dams were kept full at the wrong time and they used the "wrong" definition for "fully filled reservoir". They should have not allowed systematically any flood control dam in Thailand without 20% reserve margin before the middle of October every year. This figure is derived by assuming the total storage from all flood dams within Chao Pharaya catchment is 75billion cubic meters.

During run up to flood period last year there was no serious initiative to curb raising dams levels so that 20% reserve margin could have been preserved by 1st October. The way the the dams were operated appeared as if there was systematic attempt to completely fill up the dams as early as August.

The "Water Mismanagement" during the last year's floods valued about 10-12 billion cubic meters. They have to know that 2million rai additional area for flood storage alone is not sufficient no ensure the flood of the size as big as the last year can be regulated safely. The dams operational strategy particularly when dealing with raising water levels have to be improved. This is the part that the dam operations last year was badly done.

Bringing 3000m3/s of water to Bhumibol. dam, I think it is well to ambitious. Annual average discharge for the entire Chao Pharaya catchment is just slightly over 2000m3/s. if you add these two figures then then they become 5000m3/s. During the last year's floods, Chao Pharaya peak discharge was just over 4700m3/s.

I thought they have exhausted of ideas and resources to deal with floods. Surprisingly, they still dare to import "floods" from other nation.

I generally enjoy your posts but I think I should point out the error in your last post. You posted as if this was about floods and dams and tunnels and irrigation and reservoirs and hydro power. It isn't about any of those things. It's about looting the country as swiftly and as greatly as possible. I hope that explanation lends some insight.

Thank you for your remark and your additional information looking from the other perspective.

I am not sure because the press releases are not clear, but I think the idea is that with an input from a river as back up the dams won't need to be kept at such a high level. I assume the input from the river can be turned off if the dams hold enough water.

Even cleverer would be to fit reversible turbines in the tunnel, so the dam can send water back into the river if the level rises too much. Rather like Dinorwig http://en.wikipedia....g_Power_Station

Bhumibol dam has reversible turbine as you mentioned. Very big one. If you trace where the waters that flooded BKK last year came from, most likely part of them came from this turbine. The ethic to operate this kind of turbine, given 24 hours period it shall not increase nor decrease total discharge from the dam at least when the downstream is going to be flooded. That is why reversible turbine is there in the first placed. Looking the way they managed the floods last year, with due respect, I don't think they bother to comply with this ethic.

The implication of your comment, as I read it, it that the tunnel will have no control gear to regulate or stop the flow. I think even a Thai engineer would realise the need for this.

I think what ResX is suggesting that the flow would need to be stopped basically all the time.

Close to that rate. Almost all the time. To be honest, once in every 4-5 years it definitely helps Thailand to deal with drought. If at this rate of utilization is economically feasible, then go for it. The chance is when Thailand gets drought Burma may not have a lot of water to send to Thailand. I don't know that river is super big and you can take for granted at least 1,500m3/s will always be there to serve the purpose.

Remember that average flow dominates at least 50% of the time. For the Chao Pharaya its value is about 2,300m3/s. So you can't take 3,000m3/s, >50% of the time. When Chao Pharaya river flow is running low below 1,500m3/s, says 20% of the time you may or may not require additional water from Salween river. It depends on how much water inside all the dams in Thailand. If you need to draw down you dams for flood control it doesn't make sense to pump water into the dams.

The good news is it works somehow. But the utilization factor could be around 10%. This is calculated by assuming when the time you need it Salween river has what you want.

I get your point clearly. If you want to regulate you must have mean to regulate. If Chao Pharaya river can take up to 3,500m3/s before "hurting" somebody, you can't regulate average flow of 4,500m3/s without violating 3,500m3/s limit.

What I was trying to say is there is no feasible mean as far as I can see to do so. There are two things that you have to have to make the vision works, namely to build another reservoir in Burma and to build another "river" the size of Chao Pharaya. Otherwise you can't channel 3,000 m3/s from Burma safely and economically. Wuth these two things in place then I can assure you that it works. The only problem, as I can clearly see right now the utilization factor is going to be very low. Most of the time whether you don't need that imported water or you can't import it since you have flood problem on you own. Obviously you don't want to import the water just for a sake of channeling it to the second Chao Pharaya.

I am not sure because the press releases are not clear, but I think the idea is that with an input from a river as back up the dams won't need to be kept at such a high level. I assume the input from the river can be turned off if the dams hold enough water.

Even cleverer would be to fit reversible turbines in the tunnel, so the dam can send water back into the river if the level rises too much. Rather like Dinorwig http://en.wikipedia....g_Power_Station

Where they are going to put that 3,000m3/s? They can't discharge it since the Chao Pharaya river cannot take additional more than 1,500m3/s most of the time? Even they can find good time to discharge 1,500m3/s taken from Salween river so that they don't have to keep the water in any reservoir, this will make Chao Pharaya river discharge to be at 3,500m3/s 50% of the time. How about if moderate to heavy off season storms strike near BKK and they carry another 1,500m3/s (one third of the last year's discharge)? That makes total discharge through BKK to be at 5,000m3/s. Remember 2011? This is about peak discharge that passed through BKK last year.

Say they are very smart about managing the water (I doubt) and they really can ensure they know how to import the right amount at the right time, how they are going to be sure that Salween river has the quantity that they want?

Basically it is a good deal to buy water from other nations if we really don't have enough. But the decision has to take into account issues that have to be dealt with.

Bringing 3000m3/s of water to Bhumibol. dam, I think it is well to ambitious. Annual average discharge for the entire Chao Pharaya catchment is just slightly over 2000m3/s. if you add these two figures then then they become 5000m3/s. During the last year's floods, Chao Pharaya peak discharge was just over 4700m3/s.

I thought they have exhausted of ideas and resources to deal with floods. Surprisingly, they still dare to import "floods" from other nation.

ResX

You seem to be a rare breed on TV...someone who knows what he is talking about!

If that is the case, could you enlighten me as to the causes of the flooding that hit Thailand's lower Chao Phraya Basin last year at a cost of some $40billion.

Just a case of input overload, human error or a cocktail of the two?

Thanks

To summarize, two things that contributed to the floods: (1) The authorities were indecisive about the intensity of floods they wished to deal with.... How did they know everything work according to the plan if didn't even know what to expect? (2) They didn't really clear about when to declare that they have won against the floods... Last year they celebrated their "appear to be a success" two months before the game was over. Some say most of the dams had 100% filled as early as August. They had two months to go through the monsoon! This is like armies going to war without enough fire powers. You can expect they can win the war if only their enemy retreats due to some reasons.

This is Sirkit dam right? Anybody has the idea whether this is the recent photo?

From Water Management point of view, it is okay to do that provided the host country agrees with the proposal. Wait a minute. You see. Thailand has major problem to deal with 90-100 billion cubic meters of water per annum. Now it is talking about to raise the amount of water to be managed by the order of 25-75%.

It is a very narrow line can be drawn between "wise move" and "greed".

Fair enough, since the amount of rainfall will have a direct bearing on the degree of flooding.

So do the amount of ranfall waters that dams can hold and rainfall duration.

ResX's note has lots of numbers and measurements. However, all the calculations of a hundred experts can't negate the fact that Bangkok is built in a flood-plain. It's a mudflat that is sinking an average of 10 cm per year in places. Seas are rising. No amount of calculations or expenditues or reservoirs or massive pumps or splillways, or monkey-cheeks, or walled rivers, are going to significantly counter the forces of mother nature. Tides will continue. Water seeks its level.

A trillion trillion baht of concrete and sub-standard re-bar and disfunctional pumps aren't going to change the force of gravity.

Noted. But then they should try to do what best for time being until they can resolve BKK sinking problem and rising sea level. As far as " flood plain" issue is concern, flood plain cannot be defined in isolation with peak river discharge. They must come together. So we can make a natural flood plain for 1000 years to become dry if we can lower peak discharge of the river! Netherland is good example to illustrate the point. To certain extent BKK also can be a good example too to illustrate how flood plain can be made dry 95% of the times. Thanks to your 75billion cubic meters storage reservoirs. Without them BKK is a gone case as what you have seen last year.

What Thailand needs to do is to increase 95% reliability to make BKK dry to 99.5% level. This figure was reccommended by the Dutch experts too. What I'm trying to share is it can be done by improving dams operations, and obviously a little bit designs improvements for its flood control structures here and there. I don't think TBH 350billion is required to achieve this objective.

Let's look at this by shifting to comparing the Titanic with the Thaitanic. The Titanic was a relatively well-made iron ship. In hindsight, engineers would have recommended many technical improvements, such as thicker sides, and additional ballast chambers which would not overflow when filled - one to another, and so on. However, the Titanic was cruising in icy waters and mother nature prevailed to sink it.

Similarly, the Bangkok region has many engineers looking at why it flooded in 2011 and what improvements could be done to try and allay future wet years (btw, all years have monsoons, and 2011 was not the wettest in recent times. Similarly, ice forms in the North Atlantic each year). Mother nature does not respect man's best efforts at trying to restrict it.

ResX suggests, "they should try to do what best for time being until they can resolve BKK sinking problem."

Maidu responds: No group of geniuses nor a bazillion dollars can resolve Bkk's sinking problem. Maybe ResX meant to say, "....until they can decide what region of higher ground to move to." That would make more sense. However, Bkk's and Thailand's leaders aren't seriously looking at the option of relocating to higher ground. Instead, they will be spending tens of trillions of baht over the next 15 years, trying to keep the Thaitanic from sinking. Their childrens' or grandchildren's generation might have the intelligence to start making the move, but by then, their elders will have poured tens of trillions down the drain (and in to well-connected and unscrupulous contractors' pockets).

Thank you maidu. Points well understood. We are not in argument right from the start. After all we just talk about two separate issues. My issue is about how to protect BKK from floods as long as time permits. Your issue is to have the permanent solution.

Like it or not BKK will be there the way it did at least over the next 15 years. This is the reality that everybody have to accept at the moment. What I'm trying to say, even this is the case, the situation is not entirely hopeless as many people try to paint the scenario. I'm not trying to provide words of comfort. I really beleive with what I say. My belive is guide by my expertise in this area.

You said that many engineers were looking about the flood problem in 2011. Maybe you are right but I know for sure all of them failed to look at the most crucial issue, i.e. by hook or by crook all flood control dams in Thailand should have to have stroge margin at least 17 billion cubic meters by 1 st October every year. They should try to optimize this margin at least until november end. This can be done fairly easy if they develop mathematical models for the entire Chao Pharaya catchment. In 2011, it seemed to me the persons in charge in dams operations cheered when all dams levels approaching 100% storage capacity some claimed as early as August. They should by that time, or if not by now that allowing the dams to achieve 100% filled before the monsoon is over is a fatal error.

You also mentioned that 2011 flood is not the biggest so far. But then why then it was big then? Don't tell me BKK has sunk by 1m over the last 50 years! Actually, I was trying to provide the answer to your observation many times in my previous posts. I have gone through deliberate study before I can make the claim that, there was no valid Standard Operating Procedure (SOP) about dams operations that I can see over the last 8 years. The operations of the dams were so random that BKK saved from floods many times in the past because of marely good lucks. Actually, by having reservoirs with the size of 75 billion cubic meters, 95% chances is already in favor of no flood scenario. You don't need any SOP to secure this odd. But to raise the odd from 95 to 99.5% is entirely another type of game plan.

Even until today, I have no clue to suggest water management authorities in Thailand know precisely "the enemy" that they have to face. Try ask them what intensity of flood thta they are currently trying to deal with and what is its return probability. I would say you don't find the valid answers. They have to define these two things clearly before anything else. If they don't they can spend TBH 350billions but nothing is going to chance.....

I give three important tips for Thailand to face the coming floods. They are for free. That doesn't mean they are useless.

1. 17 billion cubic meters of flood waters can come over the duration of 60 days. But the flood control strategy has to be prepared as if they come in at most in two weeks.

2. It is true that 1 in 50 years flood return has Average Recurrence Frequency 20 times in 1000 years, but the strategy has to be implemented as if it comes overy year over the next 50 years.

3. If nobody cruch the numbers to come with accurate dams releases and when to release before and during flood periods using many equtaions that can be 15 times more complex than what I have illustrated, then it can be sure that they will never get the right result that they want. This simply means dams releases are not coordinated. The decisions about when to release and by how much have become the operational objectives for each dam. If this is the case, you cannot expect other scenario then chaos. This is like a country that has to leader. Remember 2011 floods?

ResX's note has lots of numbers and measurements. However, all the calculations of a hundred experts can't negate the fact that Bangkok is built in a flood-plain. It's a mudflat that is sinking an average of 10 cm per year in places. Seas are rising. No amount of calculations or expenditues or reservoirs or massive pumps or splillways, or monkey-cheeks, or walled rivers, are going to significantly counter the forces of mother nature. Tides will continue. Water seeks its level.

A trillion trillion baht of concrete and sub-standard re-bar and disfunctional pumps aren't going to change the force of gravity.

Noted. But then they should try to do what best for time being until they can resolve BKK sinking problem and rising sea level. As far as " flood plain" issue is concern, flood plain cannot be defined in isolation with peak river discharge. They must come together. So we can make a natural flood plain for 1000 years to become dry if we can lower peak discharge of the river! Netherland is good example to illustrate the point. To certain extent BKK also can be a good example too to illustrate how flood plain can be made dry 95% of the times. Thanks to your 75billion cubic meters storage reservoirs. Without them BKK is a gone case as what you have seen last year.

What Thailand needs to do is to increase 95% reliability to make BKK dry to 99.5% level. This figure was reccommended by the Dutch experts too. What I'm trying to share is it can be done by improving dams operations, and obviously a little bit designs improvements for its flood control structures here and there. I don't think TBH 350billion is required to achieve this objective.

Let me share how we did it without a need for additional tunnel. We have a power generation & flood control reservoir, and probably rank second of third the largest in SEA in term of total storage volume.

Name of the reservoir : We name it R

Total storage = 15billion cubic meter (Greater than Bhumibol & Sirkit)

Regulated strorage = 7.5 billion cubic meter (Bigger than Sirkit but smaller than Bhumibol)

Water surface area = 350km2 at Full Supply Level (FSL)

FSL at = EL 165 m (from Sea Level)

Average annual rainfall = 5.5 billion cubic meters

25-year maximum = 7.9 billion cubic meters per annum

Type of spillway = Non regulated gate (Free surface flow) Its bottom crest is at FSL (Bhumibol doens't have this type of gate. Therefore as you can learn later Bhumibol will work for the flood if water level yend to violate its FSL). For Sirikit, I'm not sure. If Sirkit has this type of spillway gate then the way they operated the reservoir during last year's flood was flaw.

Flood retention volume = 3billion cubic meters (From EL 165m - EL 172m)

Reservoir flood design = 7000m3/s.

Design flood return freuency = 1 in 1000 years.

* Note the design engineers of the dam were very confident that the dam does not require any sluice gate. I share that sentiment. So we can't draw down our reservoir level by other mean rather than via power generation. Maximum daily discharge is 30 million cubic meters (~1 billion cubic meters per month). Beware ! Many sluice gates you have the higher tendency for dam operators to make mistake!

Intensity of flood to be captured by the reservoir = 3billion cubic meters in 7 days (This one was determined by me, 8 years ago to optimize power generation while keeping flood risk below 2.5%)

Flood return frequency : 1 in 40 years.

Monsoon season : Nov - Mid January (Once it extended to Feb)

The strategy-

You see the underlying problem to deal with flood. The expected flood intensity is 3 billion cubic meters that might fall in 7 days. Whilst our discharge capacity is only 210 million cubic meters in 7 days. We can't race with the expected flood flow when it strikes. So we have to deal with it before. Given as short as two months period the reservoir discharge is almost always greater than accumulated rainfalls for the same period. This enables us to drawdown our reservoir water level about 8 meters below the FSL so that we have about 3 billion cubic meters of margin. We need more than 7 months every year to achieve this objective. We will ensure this margin will be made available by 1st Nov every year. We don't need weather forecast to come with this strategy. I would say statistical method is still the best for this purpose!

I think you should able to see that if 3 billion cubic meters of flood waters that fall in 7 days our reservoir can take it all even if we keep outgoing discharge at minimum says 10 million cubic meters per day. Since the flood of this intensity has return probability 2.5% therefore, for any year 97.5% chances we are going to beat the flood completely without losing a drop of water. This is the very straigh forward scenario.

How about if the reservoir has to face the biggest flood in 1600 years or two 1 in 40 year flood frequency that strike 14 days? So we will be facing 6 billion cubic meters of flood waters. What happens next? Answer: We take the 7 days and the remaining 7 days will be placed inside the flood retention storage above FSL. The non regulated spillway will ensure that 3 billion cubic meters of flood water will be discharge out naturally by gravity for longer than 3 months. Therefore the peak flood flow in 7 days will be made smaller by 4 folds as it appears at the dowstreams . Although the flood at dowstreams cannot be prevented but the reservoir + our flood control strategy will able to reduce 1 in 1600 years flood as small as 1 in 20 years flood!

Bhumibol dam does not have flood retention storge as ours. How it is going to deal with the flood with intesity greater than it can handle? If 3 billion cubic meters of flood waters try to violate its FSL the dam operators will open the sluice gates. They will keep the opening wider until the water level cease to increase. What does it mean? The dam will no longer hold any additional flood water since it has no more space to store the water. So the operators try to balance between incoming flood flow with total discharge of the dam. This will make flood at down stream even worse when compared to as if the dam is not there in the first place.....

So the question is... How long does the water released up north take to get to Ayudhya? If the 48 hour forecast says it's going to rain in Ayudhya, is that too late to reduce the flow from the dams destined to arrive in Ayudhya coinciding with the rain?

Short term weather forecast for about 3 days lead time has greater than 80% reliability to predict rainfall scenario. Even 10 days lead time forecast using an outdated forecasting system can score 60% reliability. This was said by one of the ministers. The important question have they tried to do it this way? This is not the only way to deal with discharge coordination problem such as this one.

Last year, the floods covered about 100 km square to a depth of a metre (on average). Now they want to build flood walls along the river to contain the floods.

The flood walls will need to be a hundred metres high.

Posted with Thaivisa App http://apps.thaivisa.com

There is something about flood flows that an ordinary man cannot see. While a 1in 50 years flood flow for the entire chao Pharaya catchment is about 17billion cubic meter of flood flow that falls in 7 days or 28,100m3/s (Average =2,200m3/s), there are instances that the instantenous flood flows could be as high as 130,000 to 150,000 m3/s! They could last for 8 hours. How big the tunnel size to deal with 28,100 m3/s, 130,000 m3/s? Let me try to estimate. For the same depth, they are about 15 and 75 folds wider than Chao Pharaya river respectively. Taking average wide of the Chao Pharaya is 500m to transport average flow 2200m3/s for 300km, then total water surface requires is 150km2. For 15 folds higher flow Thailand needs 2250km2 of water surface area. To me it looks more like a reservoir than a tunnel.

Whatever option Thailand is going to implement I wish to remind that the critical succes factor is centered around the dams operations.

Embankments are pointless, unless there are areas for the excess water to go.

The only real solution is a diversion channel large enough to take all the excess water, that starts above Ayutthaya and takes water all the way to the sea. I saw plans like that on tv a few times during the floods.

Ideally, it would be combined with a London style barrier to divert the water into the channel.

Also, all the klongs in Thonburi should lead into an overflow channel that also takes water direct to the sea, which would prevent river levels rising too high through Bkk.

However, should they build a barrier through Bkk, I hope they combine it with a highway that will allow traffic from the north to easily pass through Bkk without having to enter the usual jams. The roadway could be in a waterproof tunnel and a pedestrian walkway could be constructed above it- nice for tourism with potential for outdoor restaurants etc.

If you can keep the flood water without additional cost why you additional diversion tunnel? Chao Pharaya river is the most efficient and "natural diversion tunnel". Here is the overall scenario that I think I get it very close to the reality. All major and medium size dams in Thailand can store up to the maximum of 75billion cubic meters of water. This is about the same size as the average annual rainfall for the entire Chao Pharaya catchment. The flood that hit Thailand last year is estimated to be "17billion cubic meters of water that flew in 7 days" (It was said the flood is the biggest flood in 50 years). It is obvious that the dams in Thailand can store water 4 times higher than the "1 in 50 years flood return".

Thailand needs water management tools more than anything else.....

Didn't work very well last year! Climate change means that all previous weather patterns are irrelevant. Just because the dams can hold enough water this year doesn't mean they can hold them in the future. Besides, it's irrelevant how much water can be held if it's controlled by politicians, as polies will always stuff things up.

A diversion channel will always save Ayutthaya and downstream communities, and let's not forget Bkk is sinking, so a diversion or higher barriers are going to be necessary anyway.

Perhaps re look the strategy that had been used. How come the the total 75 billion cubic meters of storage capacity reservoirs could have been beaten so easily by the 17 billion cubic meters of flood water? Some of the reservoirs even contributed to that 17 billion cubic meters of flood water.

Here is the real problem so that you can see how badly Bhumibol dam went wrong. During floods based on my conservative estimate the dam shall hold at least 4 billion cubic meters of flood waters. How Bhumibol had performed? Close to the opposite. It was not holding 4 billion cubic meters. Worse still it discharged about 1 billion cubic meters of water. So flood control effectivenes, if you want to measure is -25%. Sirkit dam didn't impressed either. I didn't think the remaining 200++ medium size dams were better since Bhumibol and Sirkit dams were very good indicative to see how efficient flood control operation was executed.

It is the type of BS that the Government puts out more lies, who can believe them.

This was posted today at around 9 A.M.;

Posted Today, 09:00

Chao Phraya River overflows, inundating Ayutthaya's Sena District, officials say unseasonal rain caused high water level, not water discharged from dams /MCOT

and at 16:08 this afternoon MCOT posted this so I guess the lies are stil comming and no-one takes responsibilty.

Here's this month's rainfall from the Thai Met Dept:

This map shows the departure from normal:

It does show about 5cm of rain above average, most of which will drain out the Tha Chin River, not the Chao Phraya. It just so happens that the Sena district in Ayutthaya is to the west, near the Tha Chin rather than the Chao Phraya.

In this case, the officials may be right, it is unseasonable rain, not dam discharge causing this flood.

Average rainfall for Bhumibol catchment is roughly about 9billion cubic meters per 12 months (286m3/s). What happens if they opt to release 7billion cubic meter of water in 3 months from Bhumibol? Yes, the average discharge will be 900m3/s, or more than 3 folds higher than average! In our country, normally 4 folds discharge above the average is not enough to start floods for most of our rivers. I don't know about Thailand. But then the river downstream to the dam has lost its natural retention capacity. The dam discharge has used it. The water level can be very close to its banks. What happens when its rain? Any average rainfall could mean at least 2 folds higher than average flow. If you add dam water release and average rainfall what do you get? It is 3+2 =5 folds above average. I'm almost certain that some areas down stream will be inundated.

Taking the rainfall alone it was unlikely Ayuthia would be flooded. Taking the dam water release alone you may find similar outcome. But when you add up together what will you get? Yes. River flow is 5fold higher than average. Just see water level for any river close to you. Just imagine if the level increases by 4 folds. Do you think it may not reach the top of the river banks?

FYI, During BKK flooding last year river discharge near river mouth was said to be 4,700m3/s. Average flow of the Chao Pharaya is about 2,200m3/s. It was only three folds higher than the average. I think you know better how much damage 3 folds higher than average flow could inflict.

They need to release the water. But this 'flooding' seems like a strong over-reaction. How many households are flooded? How many businesses closed? How extensive is the damage?

I was caught in a sudden downpour the other day, and it sounds like the water I drove through was about the same as this 'flood'. It was isolated flooding and several kilometers away it was dry. Part of the problem is the panic that I felt. The big floods left me very wary of any water.

I hope the damage was minimal and further incidents can be averted.

As long as they think that they don't know how worse the future flood is going to be you are going to see this kind of probably trial and error mitigation measure. Too bad if the water management authorities have yet to know what size of flood in future they are going to deal with. The rule is that if they cannot define the flood they are going to deal with, they cannot be wrong. The only problem is they cannot be right either.

They have to know without any doubt the maximum size of floods they want to deal with. Comprehensive flood control procedure starts from there on.