HEADLINES [click on headline to view story]:

Flood mitigation for Chiang Mai - is it a possibility?

China’s march into SE Asia

Leap of faith required for Macau Tower jump

Flood mitigation for Chiang Mai - is it a possibility?

A retired Civil Engineer

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.

China’s march into SE Asia

Reinhard Hohler

According to People’s Daily Online on August 17, Yunnan Province will build or extend three traffic and transport lines to connect China with South Asia and Southeast Asia.

This was revealed at the 20th session of the economic coordination conference of Southwest China’s six provinces and autonomous regions (Sichuan, Yunnan, Guizhou, Tibet, Guangxi and Guangdong) held in Guiyang, capital city of Guizhou Province on August 17.

The three lines are as follows:

The western line runs along Yunan-Myanmar (Kunming-Wanding Town) Highway and continues as China-India (Stilwell) Highway. Also, there is the Guangdong-Dali Railway to Myanmar, India and Bangladesh.

The central line is the Lancang-Mekong River shipping line together with the Kunming-Daluo Highway and via Monglar and Kyaingtong in Myanmar to Chiang Rai and Chiang Mai in the northern part of Thailand. The new Xishuangbanna International Airport connects to Laos, Myanmar, Thailand and further to Singapore.

The eastern line runs along Yunnan-Vietnam (Kunming-Hekou Town) Highway and is based on the direction of the Yunnan-Viet Nam Railway, connecting to the Honghe (Red River) shipping line, which will to be developed accordingly to reach Hanoi, the bustling capital of Vietnam.

All three lines will bring a mass of goods and people from China to the countries of Southeast Asia and from there further to the Indian Sub-continent via the Asian Highway.

Leap of faith required for Macau Tower jump

TTG Asia
Photo: Marion Vogt

Bungee jumping exponent, AJ Hackett, has opened the world’s highest sky jump, offering a plunge off the 233m outer rim of the Macau Tower.

Thanks to AJ Hackett, you, too, can now jump off the Macau Tower – if that is something that you would want to do.

A hybrid of bungee jump and skydiving, the sky jump is a controlled aerial journey involving no rebound or hanging upside down. It ends with a gentle landing at the base of the tower. The system is regulated by a cable brake and the fall takes 14 seconds.

The Macau Tower jump is 41 m higher than the existing sky jump site at Sky Tower Auckland. The thrill is now on sale to all comers at USD 60, which includes video evidence of the controlled 14 second fall and a certificate upon completion.

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