Get In More Sand Bags

[Rinrada]

Couple of things on C.M.(wife on torasap)

Red Lion now back to normal.....no more river water in beer..

Highland Golf course should open in Oct.......torai-krup

and Surveys to start next week on NEW Chiang Mai International Airport on the San K Rd.....

also interesting bit of infom from unknown source on Dams/Water /Rivers in CM...the future looks WET....

Dams

There are no dams on the Ping River north of Chiang Mai.

(Contrary to popular misconception.)

The Ping River rises at the Burmese border north of Chiang Dao, which is itself due north of Chiang Mai.

The source is about 120 km from Chiang Mai, maybe about 160 km measured along the river.

The river flows past Chiang Dao, Mae Taeng and Mae Rim, before reaching Chiang Mai. Many streams and small rivers join it en route.

Opposite Mae Taeng the Ping River is joined from the East by the Ngat River. This river drains the Phrao valley. This river has a dam, just above where it joins the Ping River.

The dam is known as Mae Ngat Dam. It is an earth fill dam, about 59 m high, and includes a 9 MW power station, commissioned in 1985 and operated by EGAT. The dam is reported as being 100% full in 2001 and 2002.

Rumours that the structure of the Mae Ngat dam is structurally suspect may be based on misconceptions. It is possible that those responsible for the dam wish to prevent it being over-topped. If this were to happen, the down stream face could be damaged by water flowing down it. So it is possible that water is released from the dam, not because of doubts about the strength of the dam itself, but simply to prevent it from being over-topped.

Just north of the town of Mae Taeng the Ping River is joined by the Mae Taeng River. This is a large river; its source is also near the Burmese border, north of Wieng Haeng. The Mae Taeng and its tributaries drain the large area on the west side of Chiang Dao Mountain. This area stretches to the border with Mae Hong Son province.

There is a small dam on the Mae Taeng River. This is used to bleed water off into the irrigation canal which runs down the West side of the Chiang Mai flood plain, past the 700 year stadium and southwards to Hang Dong.

The only other significant dam north of Chiang Mai is the Mae Kuang dam, just north of Doi Saket. This dam is older than the Mae Ngat Dam. It has never been full. The in-flow during the wet season cannot keep up with the draw off for irrigation during the dry season. The dam serves the irrigation canals which run on the east and central areas of the Chiang Mai flood plain. There are plans to build a pipeline for the Mae Ngat dam to help fill the Mae Kuang Dam. Water from the Mae Kuang Dam eventually reaches the Ping River south of Chiang Mai.

Ping River Gradients

The gradient of the Ping River between Chiang Dao and Mae Taeng is about 2 metres per kilometre, from Mae Taeng to Mae Rim it is about 1 metre per kilometre and from Mae Rim to Chiang Mai it is only 4 metres in 20 kilometres, which is on a par with the Mississippi. So water flows over this stretch are slow. If the river is obliged to carry more water than normal it can only do this by increasing its height. The laws of hydraulics dictate that this will increase the speed of flow, but not by much.

Land Levels

The walled centre of Chiang Mai is at about 310 metres asl (above sea level). The 310 m contour runs from Tapae Gate to the south west corner. The north west corner is about 312 m. asl, the South East corner is about 309 m. asl. The riverbank along the Ping River close to Chiang Mai town is about 306 m asl. (Which explains why the flood water last weekend reached about half way along Loi Kroh.)

The 310 m. contour crosses the Ping River opposite Mae Rim.

To the east of Chiang Mai, land levels fall! Bo Sang is about 295 m. asl. San Kamphaeng is about 300 m asl. So, land levels in the centre of the flood plain are lower than land levels immediately adjacent to the Ping River. How can this be?Flood Plains

Chiang Mai is in a flood plain. A characteristic of flood plains is that they flood periodically. Otherwise they wouldn’t be there in the first place. This will have been happening in the Chiang Mai flood plain over the past 50 million years or so. When the river in a flood plain overflows its banks, sediment is deposited on the adjacent land, causing its level to rise. (Up to 200 years ago there were no gangs of labourers available to wash the mud away.) The land close to the Ping River has probably been increasing in height by about 1 metre every 200 years.

Recognising that the land around Bo Sang is 10 metres lower than the banks of the Ping River near Chiang Mai, it may well be that, at some time in the future, the Ping River will decide to abandon its present route close to Chiang Mai town and take the easier option of flowing down the centre of the flood plain and through Bo Sang. This will take some of the charm away from the Riverside Restaurant - which will need a new name. Man-made measures to prevent this happening could well be very expensive.

Inhabitation of Flood Plains

Flood plains are fertile and therefore attract human settlement. Early inhabitants may well have been more ready to recognise the risks from floods than their modern successors. Their houses are likely to have been built on stilts or on locally raised ground - and they won’t have had basements or underground car parks.

Insurance companies seem to be well aware of the risks to property in flood plains and exclude flooding from their property policies.

What can be done?

More dams up-stream would certainly help by holding back storm water and allowing its later controlled release. But dams are unpopular with environmentalists and, understandably, with the people who would be displaced by their construction and impounding.

Maybe one could be hidden on the Mae Taeng River in the valley to the West of Chiang Dao.

Otherwise, not a lot! At least, not a lot without damaging the charms of the river outside the wet season. If the river is extensively dredged it would be able to carry more water without flooding after heavy rains up-stream but the water level would be pretty low for most of the dry season. Frequent mini-barrages would avoid this but these can cause problems when flows are high.

The riverbanks could be built up, aka the Mississippi levees, at substantial cost and with the destruction of much present riverside property and with the end result that the river would be difficult to see, except from bridges.

In the short term, owners or occupiers of property near the Ping River should hold a good stock of sand bags and mops.

The August 2005 floods are unlikely to be the last.

[jomama]

I don't know all the technical terms, so please bear with me.

The Mae Ngat Dam did overflow in 1994. I saw it a few days after the flood that year and part of the outside spillway at the top was washed away and the drainage area below had "ravines" that were cut by fast flowing water. The surrounding village area had been flooded and damaged.

[chownah]

Rinrada, Thanks for a very interesting post. I would like to add one additional strategy to reduce flooding; replant the trees that have been removed over the last 200 years.

[softy]

Sounds to me like you had better stock up on some of these - http://www.wwtsasia.com/sandbags.htm. At least you would have something on hand incase it flooded again... good luck.

[Ricardo]

We do also have a small-ish dam, in the mountains about 4 miles east of Mae-Jo, which must eventually flow into the main river. It looks to be earth-construction, feeds at least one pipe-line down to Mae-Jo, and may also be used to supply some of the other local irrigation-needs.

It makes a nice place for a run out by car/bicycle - esp. if you like fishing.

Sorry I don't have the name, ? does anyone have a good (say 1" to 1 mile) map of this area ? ! , we're still new to the area.

Chang

[zxray]

How did the Riverside resturant fare after the recent flood? Is it cleaned up and open for buisness?

Thanks Ray

[Rinrada]

Seem to remember from another post that is OK and up and running.

Hope to ceck it out next month sometime.....as well as red lion,,,omallys...spotlight...bears den..happy bar...pub..un.bar..mango...and others ...got 2 days