Severe floods are relatively common in Thailand, but this years’ are the “worst in modern history.” 250 deaths are reported already, with flooding expected for at least another month. Economic damages will be several billions of dollars. Our house is safe and dry, but some nearby towns are severely flooded. An American retired to a beautiful 3-story house on a nearby river, his 2nd-story floor already near the height of nearby roofs. Several days ago, he was stranded on his 3rd floor and rescued by boat.
Several regions, drained by different rivers, are affected but chief focus is on the center: Chiang Mai and most of Northern and Central Thailand drain through the Chao Phya River to the Gulf of Thailand. Nakhon Sawan, the large city where four rivers from the north merge together to become the Chao Phya River, has been kept relatively dry by levees built in response to previous floods, but upriver reservoirs filled to capacity release water and those levees may be topped tonight or tomorrow. Yesterday, we traveled to Nakhon Sawan. The detour we used to drive to that city was already closed by evening and a return trip which usually takes 1 hour took over 4 hours with traffic jam and detouring. Conditions change fast. Isolated areas cannot be supplied with drinking water so filtering devices are boated in and stranded people drink filtered flood water. Thai government has asked citizens to “think for themselves.”
The megastere may be a useful measure to quantize the water; this is the volume of water in a cube 100 meters to a side, and weighs 1 million metric tons. Average flow in the Chao Phya River is 2 or 3 megasteres per hour but with the upriver dam release is now about 20 megasteres per hour. A day’s flow at that rate, spread evenly across Bangkok Province, would put that metropolis under a foot of water, if my arithmetic is correct. Instead, of course, much of the water is diverted to the towns and farmlands of Central Thailand, with local gangs fighting for control of floodgates. A big (and bitter) news story is that Suphanburi, controlled by notorious ex-Premier and “Influential Person” Banharn, has been kept relatively dry. 
The Bhumipol and Sirikit reservoirs have a combined capacity of 23,000 megasteres, which would be 48 days of river flow even at the maximum rate. Not all that capacity is “usable” but had those reservoirs been gradually emptied before the flooding season, it might seem that this problem could have been avoided. But that would have been disastrous if the weather had turned instead to drought. Instead the major reservoirs have been near capacity for weeks, rendering them useless for flood control. It would be interesting to understand whether a mistake was made but I wouldn’t know where to start.
AFAIK, Bangkok is still relatively dry; I hope Siam Sam will give us a report on what’s expected there. And I hope he gives thanks to us up here as, without the damming, Bangkok would be under water and conditions would be more normal here. :dubious: :rolleyes:
The helicopter clip made it look like Nakhon Sawan had been devastated, but in fact it was a clip of the riverside market running in a loop: “zooming out” would have been more informative if less sensational.