Changes in Mekong River’s Water Level from Pak Beng Dam[1]
The Pak Beng Dam project will build a hydropower dam that blocks the Mekong River in Laos. It is only 90 kilometers from Kaeng Pha Dai, Wiang Kaen district, Chiang Rai province. Currently, this project only anticipates its last step, the signing of the power purchase agreement (PPA) with EGAT from Thailand. After that, its construction will begin. However, until now, there has yet to be any study from relevant agencies on the flooding level at 340 meters above sea level (m.s.l.), the backwater level, how Pak Beng Dam will affect the Mekong water level in Thailand, and how border marks in Mekong River will changes. These changes are only for the power purchase of 897 MW from Pak Beng Dam, while the power reserve margin is over 50% at present. This document will discuss changes from and impacts of the Pak Bang Dam at 340 m.s.l.
From a survey of the contour line from the 1:50000 map, the 340-m.s.l. will transverse the Mekong riverbank and to tributaries, e.g., Nam Ngao (which was not shown in the contour line in the map) and Nam Ing (the contour line recurved at Ban Thung Aang). The contour line in the Mekong River will end at the fringe between Ban Joko and Ban Donchai. Therefore, the Pak Beng Dam will infringe inland for approximately 24 kilometers, which does not include the backwater level yet (villagers call this “Hua Nam” (water head).
The study of information from the hydropower dam project owner and the report of technical evaluation from the Mekong River Commissioner (MRC) found that at the flooding 340-meter level, Kaeng Phadai will be inundated throughout the year and will appear amidst the river only in the dry season (Figure 4). The backwater level in Kaeng Pha Dai will be 3 meters tall when the water flow of the Mekong River decreases to 2,200 cubic meters per second or lower and will overflow into Nam Ngao or Nam Ing tributaries.
The fieldwork surveying the water level posts of the Water Resource Department showed the flooding level of 340 m.s.l. in many locations clearly: Ing River’s mouth, Ban Jaem Pong, and Ngao River. Even though villages along the Mekong River will not be inundated, communities will lose their 5-to-300-Rai arable plots in lowland areas of the Ngao River. There is also a risk of a backwater (villagers call this “Hua Nam” (water head) in the rainy season for agricultural and community settlements in the Ngao River Basin in Wiang Kaen district. Moreover, the river ecosystem will change from flowing to stagnant water flow because of hydropower dams. This change means communities could not use fishing gears specific to flowing rivers, e.g., “Lai Mong” (flowing fishing nets). There will be impacts on aquatic life species, “Gai” (freshwater algae), resident and migratory bird habitats, and destruction of the flowing river chain of the ecosystem.
The survey of Mekong River changes is summarized below.
- Mekong River water level changes at Kaeng Pha Dai, Wiang Kaen district, Chiang Rai province.
Pak Beng Dam’s water reserve level at 340 m.s.l. will overflow into the Thai border, especially in Kaeng Pha Dai. It will be inundated and cut off from the Mekong riverbank on the Thai side and become rock rapids inside the river forever. That estimation is from the cross-section of the Mekong River at Kaeng Pha Dai and backwater levels in various flow rates from the Technical Review Report on Prior Consultation for the Proposed Pak Beng Hydropower Project in Figure 1 and the backwater level in Figure 2.
Figure 1 Cross-section of Mekong River at Kaeng Pa Dai, showing the flooding level of Pak Beng Dam at 340 m.s.l. and the backwater level at the flowrate of (1) 2,200, (2) 3,000, (3) 6,000, and (4) 10,000 cubic meters per second.
Figure 2 Backwater Level from Technical Review Report on Prior Consultation for the Proposed Pak Beng Hydropower Project[2]
Figure 2 compares the backwater level in different water flows at Kaeng Pha Dai. It shows that the backwater level will rise at a lower flow rate. The highest backwater level is at 3 meters with a flow rate of 2,200 cubic meters per second, and the backwater level will decrease to 1.4 meters with a flow rate of 10,000 cubic meters per second. However, the Mekong River flow rate can be compared to the water level at Chiang Saen (approximately) at 3.28 and 7.95 meters, as shown in Figure 1.
This model indicates that in the flow rate below 2,200 cubic meters per second, the backwater level at Kaeng Pha Dai will be more than 3 meters. Even when the average flow rate of the Mekong River at Chiang Saen station from January to April for four years (2020 – 2023) was below 2,200 cubic meters per second, which means that Kaeng Pha Dai will be inundated and could not be a tourist attraction anymore. It will also lead to conflict over the borders in the Mekong River between Thailand and Laos, as shown in Figure 3 and Figure 4.
Table 1
| Flow rate (cubic meters per second) | Compared to the Mekong River Water Level at Chiang Saen station (meters) | The usual water level at Kaeng Pha Dai (m.s.l.) | Backwater level at Kaeng Pha Dai (m.s.l.) | Approximate water increase level (meters) |
| 2,200 | 3.28[3] | 338.2 | 341.2 | 3 |
| 3,000 | 3.97[4] | 339.8 | 342 | 2.2 |
| 6,000 | 6.66[5] | 343.2 | 345 | 1.8 |
| 10,000 | 7.95[6] | 347.4 | 348.8 | 1.4 |
Figure 3 Kaeng Pha Dai, during low water level season, will connect to the Thai riverbank and is Thailand’s territory.
Figure 4 Kaeng Pha Dai with the inundation level as in the flow rate model will split Kaeng Pha Dai from Thailand to be only rapids in the Mekong River.
- Upstream Mekong Water Level Changes (from Pak Beng Dam)
The upstream water level change from Pak Beng Dam will occur in Kaeng Pha Dai and its upstream for approximately 24 kilometers. The end of the dam will be at the fringe between Ban Joko and Ban Donchai, Chiang Khong district, Chiang Rai province. Rak Chiang Khong group, Living River Association (LRA), International Rivers, and Mekong Butterfly conducted field surveys on February 28, 2023, to study and compare findings with primary water level posts which were installed by the Water Resource Department in 2018 in Ing River’s mouth, Ban Jam Pong, and Ngao River’s mouth. The study results are shown below.
- The Mekong River Water Level Changes in Ngao River and its River Mouth
The 340-meters level in Ngao River’s mouth will be higher than the water level on the survey date by 2.70-3.00 meters, which will impact Ngao River inland riparian plots for vegetation like maize or other crops. The exact impacted areas could not be confirmed yet, but it was estimated at 3-to-500 Rai. Besides, the higher water level from Pak Beng Dam in the Ngao River will flood inland villages that grow rice and pomelos as the water cannot flow or drain normally. There has yet to be a thorough damage study for this case. The Ngao River water level changes are shown in Figure 5 and Figure 6.
Figure 5 An image of Ngao River’s mouth to the Mekong River at Ban Jampong, Wiang Kaen district, Chaing Rai province on February 28, 2023.
Figure 6 Inland Ngao River Basin and Low Land Areas for Agriculture on February 28, 2023
2.2 Mekong River Water Level Changes in Ban Jam Pong, Wiang Kaen district, Chiang Rai province
The flooding level at 340 m.s.l. will create dam-like conditions and stagnant water throughout the year from the Ngao River to Ban Jam Pong. The water level will be higher than in the picture (February 28, 2023) by 2.70 – 3.00 meters. Villagers will not be able to fish in the flowing water ecosystem, e.g., “Lai Mong” (flowing fishing nets) and “Jan” (fishing traps). Aquatic species in flowing ecosystems will gradually go extinct. All aquatic plants below 340 m.s.l. will go extinct. Figure 7 and Figure 8 shows the flooding level.
Figure 7 Water Level Posts by the Water Resource Department at Ban Jam Pong Pier in Chiang Rai on February 28, 2023
Figure 8 The flooding level at 340 m.s.l. at Ban Jam Pong Pier in Wiang Kaen district, Chiang Rai province on February 28, 2023
2.3 The Mekong River Water Level Changes in Ing River’s Mouth, Ban Pak Ing Tai, Chiang Rai province, February 28, 2023
The flooding level at 340 m.s.l. will create a dam-like condition and stagnant water throughout the year. At Ing River’s mouth, the Mekong River water level will be higher than the level in the picture by 1 meter and overflow into Ing River and Ban Thung Ang. Villagers will not be able to fish in flowing water, e.g., using “Lai Mong” (flowing fishing nets) and “Jan” (fishing traps). The aquatic species in flowing water will gradually disappear and become extinct, affecting fish species in the Ing River, as shown in Figure 9.
Figure 9 Ing River’s mouth, Ban Pak Ing Tai, Chiang Khong district, Chiang Rai province on February 28, 2023
2.5 Changes in Water Currents at the End of Pak Beng Dam
At 340 m.s.l., Pak Beng Dam will end in the fringe between Ban Joko and Ban Donchai. The ecosystem and natural food chain from Kaeng Pha Dai to this area will be affected, namely, feeding and nesting areas for migratory and resident birds, future “Gai” freshwater algae growth which is also a crucial income for local communities in Chiang Khong district, see Figure 10 and Figure 11.
Figure 10
Figure 11
————————————–
[1] Compiled by Montree Chantawong, the Mekong Butterfly, April 5, 2023
[2] Technical Review Report on Prior Consultation for the Proposed Pak Beng Hydropower Project in the process of Procedures for Notification, Prior Consultation and Agreement (PNPCA) by the Mekong River Commission Secretariat in June 2017 in an theme of“Backwater effects into Thailand” pages 63-64.
[3] Reference: Flow rate at 2,250 cubic meters per second on April 11, 2021.
[4] Reference: Flow rate at 3,010 cubic meters per second on July 27, 2021.
[5] Reference: Flow rate at 5,980 cubic meters per second on July 5, 2001.
[6] Reference: Flow rate at 11,000 cubic meters per second on July 29, 1990.
themekongbutterfly.wordpress.com 