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  A Summary Report: Conceptual Study Report on Laos-Thai Friendship Water Development for Sustainable Agriculture in Savannakhet Province of Lao P.D.R. and Lower Chi Basin of Thailand, June 1998

Conducted by Sanyu Consultants Inc.  

Prepared by Southeast Asia Rivers Network-Thailand Chapter, June 20, 2002

Purpose of Agreement

This cooperative agreement on water development between Lao PDR and Thailand would seek “inundation protection in the Xonburi and Champhon Districts of the Savannakhet Province”, “irrigation of farm lands in the main and tributary basins of the Xe Banghiang river” and the lower Chi basin of Northeast Thailand, and water storage in the Xe Banghiang reservoir during the dry season for both countries (1)

Project Background

Originating in the mountainous areas, the Xe Banghiang river forms the border between the Savannakhet Province, Lao PDR and the Quang Tri Province,Vietnam.  It continues to run across the Savannakhet Province and empties into the Mekong river.  It is one of the largest rivers in Lao PDR with a catchment area of 19,400 sq.km and average annual runoff of 16,000 MCM. 


The Savannakhet Province supports the nation's food security with more than 110,000 ha of farmland and 680,000 in population.  In particular, the lowland area between the Xe Xangxay and Xe Champhon tributaries is particularly important since it holds about 50,000 ha of fertile farm area.  This lowland area suffers annually from flooding damage from the Xe Banghiang river discharge during August to September.  Every year about 10,000-20,000 ha out of the 50,000 is damaged by floods. 

A dam has been proposed for “the regulation of flood discharge as well as irrigation of the downstream reach of the Xe Banghiang river” (1).


The lower Chi basin in the northeast of Thailand has an agricultural area of about 300,00 ha. This area employs rain-fed cultivation because of very scarce water resources in the area. 

Flood Protection

The inundation protection plan proposes two dams, Xe Banghiang Dam no. 1. and 2.  These dams would cut flood discharge by 2,000-3,000 cu.m/sec and store the discharge in the reservoir.  



The irrigation and agridevelopment plans would benefit the lower Xe Banghiang River basin Laos and the lower Chi basin in the Northeast region of Thailand.  The Xe Banghiang River basin encompasses the lowland area along the Xe Xangxay and Xe Champhon tributaries and the plateau areas surrounding the reservoir and a number of small tributaries which empty into the reservoir. The area to benefit from irrigation includes 50,000 ha in the low land and 30,000 ha in the plateau area. The low land area to benefit from flood control includes an additional 20,000 ha.  The estimated available irrigation water per year is 950 MCM.

The lower Chi basin consists of a number of tributary basins of the Mun River including, Lam Sebai, Lam Sebok, Huai Siao Yai, Huiasiao Noi etc.  The 300,000 ha in this area would be irrigated by surplus water from irrigation facilities in Laos.  The estimated available irrigation water per year is 3,270 MCM. 

Total irrigation requirement- estimation on monthly basis (unit: MCM) (3.3- subsection 3b)


Wet Season

Dry Season

Whole year

Lao side




Thai side










The total unit water cost to the Laos side is around US $ 0.011 per cu.m or equivalent to 0.44 Baht.  This estimate includes water source facilities and irrigation system costs.  The unit investment cost will be US $1,400/ha.


The total unit water cost to the Thai side is US $25.7 per 1,000 m3 or equivalent to about 0.1 Baht per cu.m.  The unit investment cost will be US $2,650/ha.

The Thai side will pay for their share of the cost of  water source facilities, the exclusive use of facilities on the Thai side, and water royalties.  The cost per annum for water source facilities which the Thai side will share is US $8.5 million.  Water royalties must be paid to the Laos side “for allocation of the Xe Banghiang river water to the lower Chi basin” (8.2). The amount of the royalties will determined by discussion and agreement between both countries.  “However if it is the same as the water sources cost, the unit water cost of the Thai side to share will be 1.10 Baht per cu.m of water inclusive of water sources cost, water royalty cost and cost for exclusive use facilities of the Thai side” (8.2).

Unit Water Cost in Laos and Thai Side (8.2)


Laos Side

Thai Side

Xe Banghiang Dam (Water Source)



Laos-Thai Diversion Canal (Water Diversion)



Irrigation System in Laos



Irrigation System in Thai



Total Water Cost/1,000 m3


25.7 (=0.1 Baht/ m3)

Water Cost/ m3

(Unit Water Cost)

US $0.011/ m3 (=0.44 Baht)

US $0.026/ m3 (=1.0 Baht)

Project Facility Plan

The project facility plan proposes two dams, a water diversion facility, and irrigation systems for the Laos and Thai sides. 

Irrigation facilities for the low land area on the Laos side consists of a canal system from the Xe Banghiang reservoir with canals on the right and left bank.  The 30,000 ha in the plateau areas are at an elevation less than 170MSL which is higher than the water level in the reservoir.  Therefore, the following facilities are required: a small scale reservoir, a small scale weir with gate facilities, and a small scale pumping station.  The lowland areas, however, are at an elevation below 140 m MSL which allows for 50,000 ha to be irrigated by gravity via the canal system.  This system will require canals on the right and left bank of the Xe Banghiang river. 

On the Thai side, facilities consist of the Bang Koi pumping station and an irrigation canal. The lower Chi basin is at an elevation of 120-150 m MSL which engenders the need for the pumping station.  The main irrigation canal has a length of 200 km with 190 km running through flat plains and 10 km through highland at an elevation of 160-170 m.  Secondary canals will expand irrigation to farmland in Amnat Charoen, Yatsothorn, the northern part of Ubon Ratchathani and a part of the Tung Kula Ronghai area.  These canals measure 550 km in length.

Dam specifications (5.2-4)


Xe Banghiang dam no.1

Xe  Banghiang dam no. 2

Bang Koi regulating reservoir







23 m


Full water level in reservoir

155m (for no. 1 and no.2)



Effective reservoir capacity

2,500 MCM (for no. 1 and no. 2)


Regulating capacity: 15 MCM

Dam type

Rock fill with center core

Rock fill with center core

Earth fill

The proposed benefits of the no. 1 and 2. dams are irrigation and a flood discharge control rate of 6,000-8,000 cu.m/sec during flood season. 

The Laos-Thai water diversion facility is made up of the Laos diversion canal, Mekong siphon, Thai diversion canal, and the Bang Koi regulating reservoir. The Laos diversion canal starts from the no. 2 dam and ends at the Mekong siphon.  This 20 km open canal passes through flat plateau land at an elevation of 140 m-150 m. The Mekong siphon is located at the Ban Khilek site where the river is the narrowest and the riverbed is covered with a hard sand stone rock layer.  Three tunnels have been proposed; two for the two 3 km siphons and one for a 1000 m road tunnel. The Mekong siphon would bring water at a rate of 250 cu.m/sec from the Laos diversion canal to the Thai side.  Located at the end of the Thai diversion canal, the Bang Koi regulating reservoir would regulate this diverted water.

The Thai diversion canal is “located at the outlet of the Mekong siphon runs along the Mekong river at right bank ends at Bang Koi regulating reservoir” (5.2). It's 5 km long and has a discharge capacity of 250 km.

Environmental Impacts

The study reports that there are no special wild animals or reserved forest area in the Xe Banghiang basin that would be impacted by the project.  However, the project would require the resettlement of 20-30 small villages whose land would be submerged.  There would be no serious impact to the downstream of the Mekong River.


The estimated total cost of the project is US $908,000.

The estimated cost of the irrigation project on the Thai side is US $536 million.


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