As the northeastern areas are elevated plain and basin-shaped areas, the edge of the region is a plateau that slopes to the middle, which is the lowest point or the Mun and Chi River. It slopes from the west to the east. Both rivers meet at the borderline of Kanthararom District, Si Sa Ket Province, Mueang District, Ubon Ratchathani Province and Warin Chamrap Distrit, Ubon Ratchathani Province. Then, they flow passing Sawang Wirawong, Don Mot Daeng, Tan Sum and Phibun Mangsahan districts and eventually flow into the Mekong River in Khong Chiam District.
Ubon Ratchathani is the Chi River’s destination to meet the Mun River. The Chi River Basin’s area is 49,130 km2, while the Mun River Basin’s area is 69,700 km2. The average annual runoff is over 30,000 MCM.

There was no direct rain in Ubon Ratchathani. Why was it flooded?

At the end of August, tropical storms Podul and Kajiki moved across the upper and central northeastern parts, so there was much rainfall in the watershed areas of the Chi tributary. A massive volume of water from Khon Kaen, Mahasarakham, Roi Et, Yasothon, and Amnat Charoen provinces flowed to the Chi River, which flowed into the Mun River and finally to Ubon Ratchathani City.

In the past, severe floods occurred in Ubon Ratchathani in 1978 and 2002. But the flood in September 2019 is more severe than that in 2002. A massive surge of water from Yasothon, Roi Et and Amnat Charoen provinces flowed into Ubon Ratchathani on September 12. Thus, inner economic areas were at risk of inundation. Currently, water from the Mun River is retarded by Rasi Salai and Hua Na dams to avoid reaching of the two rivers at the same time. The flood situation in the central part is still critical and being drained. Eight regulators at Pak Mun Dam have been opened. Additional water-pushing machines have been installed in Phibun Mangsahan District to speed up drainage into the Mekong River. At present, waterlogged fields amount to about 500,000 rai, assessed by the Department of Disaster Prevention and Mitigation (DDPM).
If waterlogged fields of 500,000 rai assessed by the DDPM are 1 m deep, the volume will be 800 MCM. If they are 2 m deep, the volume will be 1,600 MCM that must be urgently drained into the Mekong River.
Systematic water management requires a wide variety tools as follows:
1. Allocation of retarding areas or “monkey cheek” to retain and release water gradually. When large- and medium-scale dams cannot be constructed, monkey cheek is an alternative to store water to be used for agriculture in the dry season.
2. Ubon Ratchathani diversion canal is constructed like a bypass road to cut the excess water of the Mun River passing Ubon Ratchathani so that it flows to bypass the city to the end of Ubon Ratchathani and flows into the Mekong River faster.
3. Flood prevention dikes to prevent flooding in inner economic and significant areas
4. River improvement, such as dike construction and river dredging
5. Drainage system and river obstruction improvement
6. Bank erosion protection

However, overall water management is necessary, not only in Ubon Ratchathani Province but other provinces from upstream to downstream of the Chi and Mun rivers must be taken into consideration to seek proper solutions through a discussion with the people sector, village philosophers and experts. At present, the agency in charge of the country’s water management and integration with other agencies to manage water and solve problems systematically is the Office of the National Water Resources.

 Pictures of flooded areas from: Thai geo-academic http://www.geothai.net

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