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Monday, October 17, 2011

Thai flood an opinion from Isaan

In Ubol Ratana Reservoir
I recently started a discussion on twitter relative to data? being bandied about the capacity of reservoirs in Thailand. Figures are posted such as 105%, 107%, 115%, but what, if anything do these numbers mean and what relevance do they have.
In the way most things, such as buildings, roads, airplanes, cars etc are designed is, with what we technically call a "fudge factor". In other words if it is calculated that a building needs to withstand 100k winds, you build it to withstand 125k winds, so on and so forth.
Now folks were kind enough to send articles from the US and elsewhere, but are they relevant in Thailand.
40 years ago in the US where I went to University to become an engineer we could calculate the amount of water that would come from any catchment area depending on rainfall. 40 years on methods and equipment are many times more sophisticated. These methods and equipment obviously have not found their way to Thailand.
Now about reservoirs to calculate the volume in cubic meters you need to know the area times the depth (HxD=V). The area grows as the place gets deeper. But at the end of the day even if you disregard silting and other variables it is impossible to figure out volume without Precise elevation data.
As an aside, I have not seen with somewhat careful research, any precise measurement of inflows or outflows at any moving body of water in Isaan.
If a reservoir is about 180k in circumference it is easy to figure the difference 1mm of elevation would make in volume.
Anyhow I nor anyone else as far as I know still has a clue as to what they mean by x% of capacity.
It is simple to say a reservoir is full at x meters above sea level and it is easy to mark. People near a reservoir should know the elevation of their property and this should be announced as levels rise, as elevation has significance while volume of water does not.
It is all moot since from what I have seen of government data for isaan it is more than 90% incorrect. I was taught that there can only be 2 reasons for errors of this magnitude.

I do not have my contour maps with me, but will post some at a later date to help understand.

anyhow thanks to everyone for their input.
also i am doing this on a netbook with 64 year ol eyes, so spelling and grammer might be even more twisted than usual.