(PDF) Mekong River Dry Season Changes Due to Hydropower Dams and Extractive Processes: Making Sense of Contradictory Community Observations in Thailand, Laos and Cambodia
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Mekong River Dry Season Changes Due to Hydropower Dams and Extractive Processes: Making Sense of Contradictory Community Observations in Thailand, Laos and Cambodia
Ian G Baird
2025, Water Alternatives
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Abstract
The Mekong is amongst the most important rivers in the world with regard to biodiversity and livelihood. Over the last few decades, however, the river has experienced dramatic hydrological changes, mainly due to the construction of large hydropower dams on the mainstream Mekong and its tributaries. Other potentially crucial factors include sand mining, erosion, embankment construction, and water extraction. In March and early April of 2024, we organised focus group interviews to discuss the changes that have occurred during the dry season with local people living in different communities along the mainstream Mekong River: 32 villages in eight provinces in northern and northeastern Thailand, 9 villages in Champassak Province, southern Laos, and 3 villages in Stung Treng Province, northeastern Cambodia. In this paper, we present some of the results of this research, particularly focusing on water level and suspended sediment discharge changes, as local people along the Mekong River have varied understandings regarding whether there is more or less water in the Mekong River during the dry season. We argue that riverbed incision resulting largely from hydropower dam development and sand mining have, in particular, led many people living along the Mekong between northeastern Thailand and central Laos to incorrectly believe that there is less water in the Mekong River during the dry season compared to the past, while dry season water releases from upriver hydropower dams have led those in northern Thailand, lower northeastern Thailand, southern Laos, and northeastern Cambodia to assess that there is now more water in the Mekong River.
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www.water-alternatives.org
Volume 18 | Issue 3
Baird, I.G.; Thorne, M.A.S. and Gaja-Svasti, S. 2025. Mekong River dry season
changes due to hydropower dams and extractive processes: Making sense of
contradictory community observations in Thailand, Laos, and Cambodia.
Water Alternatives 18(3): 521-545
Mekong River dry season changes due to hydropower dams and
extractive processes: Making sense of contradictory community
observations in Thailand, Laos and Cambodia
Ian G. Baird
Department of Geography, University of Wisconsin-Madison, Madison, WI, USA;
[email protected]
Michael A.S. Thorne
British Antarctic Survey, Cambridge, UK;
[email protected]
Sirasak Gaja-Svasti
Ubon Ratchathani University, Warin Chamrap, Ubon Ratchathani, Thailand;
[email protected]
ABSTRACT: The Mekong is amongst the most important rivers in the world with regard to biodiversity and livelihood.
Over the last few decades, however, the river has experienced dramatic hydrological changes, mainly due to the
construction of large hydropower dams on the mainstream Mekong and its tributaries. Other potentially crucial
factors include sand mining, erosion, embankment construction, and water extraction. In March and early April of
2024, we organised focus group interviews to discuss the changes that have occurred during the dry season with
local people living in different communities along the mainstream Mekong River: 32 villages in eight provinces in
northern and northeastern Thailand, 9 villages in Champassak Province, southern Laos, and 3 villages in Stung Treng
Province, northeastern Cambodia. In this paper, we present some of the results of this research, particularly
focusing on water level and suspended sediment discharge changes, as local people along the Mekong River have
varied understandings regarding whether there is more or less water in the Mekong River during the dry season.
We argue that riverbed incision resulting largely from hydropower dam development and sand mining have, in
particular, led many people living along the Mekong between northeastern Thailand and central Laos to incorrectly
believe that there is less water in the Mekong River during the dry season compared to the past, while dry season
water releases from upriver hydropower dams have led those in northern Thailand, lower northeastern Thailand,
southern Laos, and northeastern Cambodia to assess that there is now more water in the Mekong River.
KEYWORDS: Hydrology, sediment, local knowledge, water level, Mekong River, Thailand, Laos, Cambodia
INTRODUCTION
Everyone seems to agree that the Mekong River has undergone significant changes over the last few of
decades (MRC, 2021; Eyler et al., 2024); indeed, hundreds of dams of various sizes have been built on the
mainstream Mekong River and its tributaries (Eyler et al., 2024). But while such dams are bound to lead
to some changes, there is a lack of consensus amongst the people living along the river regarding the
changes that have occurred. Illustrative of this, one community leader living in a village adjacent to the
mainstream Mekong River in Ubon Ratchathani Province, Thailand, told us in March 2024 that there had
been significant disagreements and debate amongst villagers living along different stretches of the river
regarding whether there was more or less water in the Mekong River during the dry season when
compared to decades ago. This debate especially intensified when villagers from different locations along
the Mekong River in Thailand attended networking meetings regarding the river. For example, those from
Baird et al.: Mekong River dry season changes due to hydropower dams and extractive processes
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Nong Khai Province insisted that there was less water in the Mekong compared to decades earlier, while
those from Ubon Ratchathani mostly believed that there was more water in the Mekong during the dry
season. While this debate has been ongoing along the Mekong River in Thailand for some time, it has not
yet been discussed in the literature. This paper is intended to fill that gap, including a consideration of
the changes that have actually occurred and their causes.
The perceptions of different people regarding environmental change are crucial, and not just because
such perceptions influence what people think the problems are and what causes them; they also
determine what policies and policy changes are advocated for by different people and groups. Thus,
public understandings of environmental policy need to be given sufficient consideration, even when
those perceptions are inaccurate and not based on credible evidence (see Forsyth and Walker, 2008).
Whether there is actually more or less water in the Mekong mainstream during the dry season is
crucial, as increased water can negatively impact various important habitats, such as flooded forests, and
the many species that depend on these habitats, including various fish species and others (Baird and
Thorne, 2023). Too little water can also have negative environmental and social impacts. These negative
impacts can in turn adversely affect local livelihoods. Changes in water levels in the Mekong River also
has important implications for the Mekong Delta in Vietnam, especially due to related changes in saltwater intrusion and erosion there.
The objective of this paper is to consider why villagers who all have close and long-term livelihood
connections to the Mekong River differ in their understandings of whether there is more or less water
flowing down the river during the dry season, depending where along it they live. We also consider how
hydrological and sediment flow data can help to better understand these discrepancies. This question is
justified because local people themselves are debating the status of dry season water levels. We argue
that sediment transport changes along the mainstream Mekong River, combined with geological factors
and sand mining, have resulted in people living at various locations along the river coming to contrasting
conclusions regarding the dry season hydrological changes that have occurred, despite the upstream
dams having measurable effects everywhere downstream along the mainstream Mekong River.
The paper proceeds as follows: In the next section we explain our methods. We then present the
results of our focus group interviews with local people living along the Mekong River. Next, we present
other hydrological, water extraction and suspended sediment discharge data. We then consider erosion
and riverbank embankments, hydropower development impacts, and sand mining impacts before finally
discussing how local understandings of water levels during the dry season might be explained and what
the implications of our findings are, both in terms of local perceptions and environmental changes along
the Mekong.
METHODS
In recent years, remote sensing has become a powerful way to monitor changes to the environment.
Indeed, it is now possible to track water surface area in reservoirs along the river using satellite imagery
(see, for example, Vu et al., 2022; Eyler et al., 2024; Mahto et al., 2024). It can also be used to assess
riverbank erosion (Kummu et al., 2008; Tha et al., 2022) and even to estimate numbers of sand mining
operators on parts of the Mekong River (Hackney et al., 2021). But while satellite technology has
immense value, it can also lead to erroneous assumptions, because while it allows us to observe changes,
it cannot necessarily explain the reasons for many of those changes.
At the same time, because it has become much easier to gather data about hydrological changes in
the Mekong from physical gauges and remote sensing technology, the views of people living along the
river have not been sufficiently considered, leading to local conditions and explanations generally being
overlooked. This study, therefore, is focused on how local people who live along the Mekong River
perceive the changes the river has undergone over the last few decades, with an emphasis on the dry
Baird et al.: Mekong River dry season changes due to hydropower dams and extractive processes
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season. However, we also rely on other expert and government interview data, as well as quantitative
data.
Our methods are partially based on previous research that we conducted along the Mekong River in
Stung Treng Province, northeastern Cambodia in June 2022 (Baird & Thorne, 2023). At that time, we
interviewed local people living along the Mekong and made use of national hydrological data to
understand how the river has changed during the dry season, and particularly why much of the seasonally
inundated forests located within the Mekong riverbed and along its banks have died in recent years. This
research was inspired by that previous work, with the idea of scaling up the study to learn from local
people living along a much greater length of the river about how the Mekong River is changing and how
such changes are affecting them. We come from a position of strongly agreeing with various other
researchers who have pointed to the great value of local knowledge regarding various kinds of aquatic
ecosystems (Haggan et al., 2007; Silvano et al., 2023; Hamelin et al., 2024), especially for complex tropical
ecosystems where much less research has been conducted than in environments proximal to more
industrialised parts of the world (Johannes et al., 2000). This is especially the case for people who spend
large amounts of time interacting with and observing rivers and aquatic life as part of their everyday
livelihood activities (Baird, 2006, 2007; Baird and Manorom, 2019). We wanted to take advantage of
these people’s deep local knowledge, and we tried to engage with them in a manner that was most
conducive to obtaining accurate information (see Baird, 2006).
Our focus was on changes during the dry season, between February and April, when Mekong River
waters are typically at their lowest. Historically reduced water levels during this season are especially
important for the survival of flooded forests and other types of riverine vegetation. Carrying out the
interviews during the dry season was advantageous, since when we spoke with villagers, often near the
river, they could more easily show us what they were talking about. In addition, less agricultural activity
occurs during this season, which made it easier for local people – most of whom are farmers and fishers
– to participate in discussions without it interfering with their work.
Thus, we set out a plan to visit villages along the Mekong River in Thailand, Laos, and Cambodia during
March and April. We decided to visit villages along the river at intervals; we did not choose exact distances
between villages but hoped to visit communities at intervals of less than 50 km away from each other.
We visited two contiguous regions. One where the Mekong acts as the border of Northern Thailand and
Laos; the other where the Mekong flows down from Laos to form the border with Thailand all the way to
Stung Treng in Northern Cambodia. Villages were often chosen based on factors such as distance from
each other, but some were chosen because we already had contacts there, or because of information
that had been provided by non-government organisations (NGOs) and their allies working along the
Mekong River. This meant that some residents were active members of NGO networks. However, in many
villages we visited, we had no contacts.
During our community visits, groups of villagers, both men and women, mostly between their 40s and
70s, met us informally at different locations, ranging from open air structures adjacent to the Mekong to
individual homes. The interviews were semi-structured, in that we had a pre-determined list of topics
and general questions regarding dry season Mekong River changes in the area that we intended to ask in
each community we visited. These focus group interviews were sometimes conducted in Central Thai,
but were mainly done using various dialects of Lao, including Northern Lao, Isan Lao, Southern Lao, and
Northeastern Cambodian Lao. The first author, who is fluent in all of these languages and dialects, led
the interview and discussion process in the villages, with each group interview and discussion taking
between one and two hours. In addition, we sometimes combined interviews with short walks, drives, or
boat trips to observe aspects of the Mekong River, often accompanied by the villagers we were
interviewing.
Interviews with locals were conducted in 32 villages in eight provinces (Chiang Rai, Loei, Nong Khai,
Bueng Kan, Nakorn Phanom, Mukdahan, Amnat Charoen and Ubon Ratchathani) in northern and
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northeastern Thailand, 9 villages in Champassak Province, southern Laos, and 3 villages in Stung Treng
Province, northeastern Cambodia (Figure 1). (We decided not to interview people in northern and central
Laos due to logistical limitations.) The village interviews were all done between March 1 and April 3, 2024.
We started at the village farthest upstream (in Chiang Saen District) and gradually travelled downstream
through Thailand before crossing into southern Laos and northern Cambodia, conducting the final
interview just north of Stung Treng Town.
Figure 1. Map of the villages where focus group discussions were conducted along the mainstream
Mekong River in March and April 2024.
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Given that the villagers’ responses were subjective, we did not expect them all to align with each other
or to be necessarily factual. However, the people we interviewed were almost all rural farmers who have
interacted with the river for livelihood reasons for most of their lives, especially for daily fishing activities
and also when cultivating crops on islands and riverbanks along the river, so they have accumulated
considerable in-depth knowledge about the river over time. What is particularly striking about the
information we received from them is that people from multiple communities in the uppermost and
lowermost parts of our study area reported higher water levels during the dry season, while many
communities in the middle section of the study area reported lower water levels during the dry season.
This consistency across multiple groups of people living along specific sections of the river increased our
confidence in their reports, even if what was reported was initially contradictory.
While the foundations of this research were the village focus group interviews, we did not constrain
ourselves to a single method. Apart from making observations and taking measurements in the field, we
also interviewed local government officials during the same time period, particularly in Thailand. In
addition, after the main fieldwork was completed, we conducted follow-up research. Information was
collected about sand mining through interviews in Laos and Thailand, suspended sediment discharge and
other data such as water extraction statistics were collected from authorities in Thailand, and hydrology
data was obtained from the Mekong River Commission (MRC) via the Stimson Center (see below). In
particular, we looked at water gauge levels during the dry season months of February, March, and April
at Chiang Saen (1960-2023), Nakhon Phanom (1924-2023), and Pakse (1923-2023). We examined the
monthly average water levels for all the years of data available at each location (see Figures 2-4). Finally,
we conducted a number of interviews with various Mekong hydrology experts to discuss our findings.
Ultimately, while our starting point was to utilise the local knowledge of people who have lived along
the Mekong for most or all of their lives, we tried to make use of whatever information could contribute
to answering our questions, so our research can best be described as applying mixed methods.
VILLAGER RESPONSES
The people we interviewed along the Mekong River provided a great deal of interesting and useful
information regarding Mekong River changes. However, this paper is especially focused on their
responses to a standard question that we asked in every community we visited: "Do you think that dry
season water levels in the Mekong River Basin over the last few decades have increased or declined?"
Crucially, during the interviews, we assumed that water levels and water discharge were correlated, and
the interviewees also made the same assumption.
In 2022, when we conducted similar research along the Mekong River in Stung Treng Province,
northeastern Cambodia, all the people we spoke with were certain that water levels had increased during
the dry season in recent decades. Moreover, hydrological data from the Pakse station in southern Laos,
the closest hydrological gauge upriver from Stung Treng, confirmed villager reports that water levels
during the dry season had increased significantly over the previous 15-20 years or so, due to hydropower
dam water releases upriver (Baird and Thorne, 2023). So we expected that local people living upstream
in Laos and Thailand would also report increased water levels during the dry season.
Our 20 or so interviewees from Chiang Rai Province in northern Thailand did all report that dry season
water levels have increased dramatically, sometimes as much as two to three meters higher. (It should
be noted that the Xayaburi Dam in Laos is too far downstream to affect northern Thailand via the
backwater effect.) Villagers in Loei Province, in northeastern Thailand, also reported higher water levels
during the dry season. However, beginning in Tat Suem Village, Sangkhom District, Nong Khai Province,
villagers began to report that there is now less water in the Mekong River during the dry season. This
response surprised us, as it contradicted reports from the villagers upriver of Tat Suem and also seemed
to contradict official hydrological data. However, we found that villagers from communities downstream
from Tat Suem also reported that there is less water during the dry season than before. In fact, this was
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consistently reported in 17 villages between Tat Suem Village and Pong Kham Village in Wan Yai District,
Mukdahan Province, including villages in Nong Khai, Bueng Kan, and Nakorn Phanom Provinces, and part
of Mukdahan Province. However, from Na Pho Village, Ton Tan District, in southern Mukdahan Province,
down past Amnat Charoen and Ubon Ratchathani Provinces in northeastern Thailand, villagers once again
reported that there is more water in the Mekong during the dry season compared to a few decades
earlier. Locals in Champasak Province, southern Laos, and Stung Treng Province, northeastern Cambodia,
also consistently reported more water in the Mekong during the dry season.
Villagers often justified their observations by basing them on riverine landmarks, such as particular
large rocks or riverbank characteristics. By observing these locations year after year, they had developed
relative understandings of annual changes in water levels.
We were initially perplexed. How could it be that people from the first six villages that we visited in
Chiang Rai and Loei Provinces reported that there is more water during the dry season compared to the
past, followed by the next 17 villages reporting that there is less water during the dry season, and then
the last 21 villages downstream again reporting that there is more water during the dry season? We could
not initially imagine how these findings could be correct; this would imply the presence of more water
upstream, less water in the middle stretch of the river, and then more water again downstream in the
same river. But neither could we simply dismiss these findings, as the reporting was consistent over many
villages and different but adjacent geographical areas.
Crucially, these findings encouraged us to look for additional evidence that could help us understand
what the villagers had reported to us. The following sections of the paper are devoted to making sense
of the above-outlined puzzle, and we think that the findings are quite useful for understanding how the
Mekong River has changed over the last few decades and why local people have reported particular
changes.
MEKONG RIVER HYDROLOGICAL CHANGES DUE TO HYDROPOWER DAM DEVELOPMENT
The hydrological data for the Mekong River during the dry season within our study area indicate that the
mainstream Mekong River south of China, at gauge stations located at Chiang Saen, Nakorn Phanom, or
Pakse, has more water flowing down it during the dry season (specifically for the months of February,
March, and April) than was the case before the Mekong dams in China began being built in the 1990s.
Unfortunately, however, the exact amounts of water released downstream since the dams in China were
constructed are not publicly available, so we only have the MRC hydrological data from the lower Mekong
countries to work with.
Water levels at the three stations for February, March and April are shown in Figures 2-4. These figures
also indicate when four of the key dams on the Lancang/Mekong River in China were commissioned: the
Manwan Dam (1995), the Jinghong Dam (2008), the Xiaowan Dam (2010), and the Nuozhadu Dam (2012).
For a detailed history of hydropower dam development in the Mekong River Basin, see Sneddon (2015),
Soukhaphon et al. (2021), and Middleton (2022).
Figures 2-4 clearly indicate that the volume of water in the mainstream Mekong River during the
height of the dry season, whether at Chiang Saen, Nakorn Phanom, or Pakse, has significantly increased
since the early 1990s, and especially since the 2010s. Water volumes have decreased somewhat from
their highest dry season levels over the last couple of years, although they are still higher than historical
levels. The most recent change has been reported to be at least partially due to a lack of rain in the upper
basin (Eyler et al., 2024).
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Figure 2. Mekong River water volumes at Chiang Saen during the months of February, March, and April
between 1960 and 2023. Commission dates of four of the main upstream dams are indicated
(M = Manwan Dam [1995]; J = Jinghong Dam [2008]; X = Xiaowan Dam [2010]; N = Nuozhadu
Dam [2012]).
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Figure 3. Mekong River water volumes at Nakorn Phanom during the months of February, March, and
April between 1924 and 2023. Commission dates of four of the main upstream dams are
indicated (M = Manwan Dam [1995]; J = Jinghong Dam [2008]; X = Xiaowan Dam [2010]; N =
Nuozhadu Dam [2012]).
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Figure 4. Mekong River water volumes at Pakse during the months of February, March, and April between
1923 and 2023. Commission dates of four of the main upstream dams are indicated (M =
Manwan Dam [1995]; J = Jinghong Dam [2008]; X = Xiaowan Dam [2010]; N = Nuozhadu Dam
[2012]).
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Hydropower dams can cause considerable daily fluctuations to downstream water flows (Wyatt and
Baird, 2007; Morovati et al., 2024), something that local people widely reported during our fieldwork.
However, other dams, including the Xiaowan and Nuozhadu Dams in China and some of the larger
tributary dams in Laos, have large enough reservoirs to store water during the rainy season and gradually
release it to produce electricity throughout the year, including during the dry season, resulting in overall
increases in dry season flows (Eyler et al., 2024). This commonly occurs downstream of hydropower dams
with large reservoirs (McCully, 2001).
There is compelling evidence that the construction and operation of large mainstream and tributary
dams in China are the main cause of increased downstream flows during the dry season. Räsänen et al.
(2012) reported that over a decade ago at Chiang Saen, in 2011, dry season water discharge had already
increased from between 34 and 155% between December and May, and this was before all the present
dams along the Lancang (Mekong) River in China had been built. These changes became even more
pronounced by 2014, after more dams in China had been built, with water discharge at Chiang Saen
between March and May increasing by between 121% and 187% (Räsänen et al., 2017). However, there
has been significant tributary dam construction in Laos over the last couple of decades, with a large
number still being built at present, and those dams are likely to be causing significant changes, although
detailed research on this aspect has so far not been conducted. Dams have also caused serious
downstream impacts along the tributaries (Claassen, 2004; Wyatt and Baird, 2007; Lacombe et al., 2014;
Baird et al., 2015; Hecht et al., 2019; Middleton, 2022; RFA, 2024).
With all these changes occurring to the Mekong and its tributaries, one has to wonder about the
accuracy of the water level calculations along the Mekong. That is beyond the scope of this study, but
according to the head of the Thai Meteorological Department in Mukdahan, which monitors 25 gauges
in Mukdahan and Nakhon Phanom Province, the gauges are frequently recalibrated for accuracy and are
therefore believed to be fairly accurate.1 We were not, however, in a position to verify this claim.
The hydrological data presented above is revealing, but it did not resolve the discrepancy between
the villager reports about dry season water levels.
WATER EXTRACTION
Following the village-level fieldwork, we considered whether water extraction might help explain the
different responses we received from villagers about dry season water levels.
First, there are large numbers of small and medium-sized pumps located on the Mekong River along
the Thailand-Laos border, with water being pumped mainly for agricultural purposes but also for
providing domestic water to many villages, towns, and cities located along the Mekong River. Crucially,
according to the water utilisation rules agreed upon by member countries of the MRC, it is permitted to
pump water from the Mekong River for agricultural and domestic purposes during the dry season, but
only for use by communities located directly adjacent to the Mekong River. This rule is in place to prevent
the over-extraction of water during the dry season. Projects designed to transfer water longer distances
from the river must pass through the MRC public consultation process and international agreement in
certain cases; up to now, no such projects have been officially proposed through the MRC process.
We were able to obtain some data about major Mekong water extraction on the Thai side of the
border. Most of the total pumping capacity of 166 m3/second reported involves two projects in Nong
Khai Province: the Huai Luang Project in Phon Phisai District, which has the capacity to pump 150
m3/second (90% of the total capacity), and the Huai Mong Project in Tha Bo District, which has a pumping
capacity of 13.4 m3/second (less than 8% of the total capacity). Thus, the remaining pumping capacity of
all the other locations is just over 2% of the total (Government of Thailand, no date).
Usap Phaensaen, Director of the Thai Meteorological Department, Mukdahan Province, March 18, 2024.
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We were also able to obtain the 2013 data for domestic water supply pumping in Laos, although these
data are imperfect because they do not cover water extraction from the Mekong River only but also from
other bodies of water in Laos. Unlike the Thai data, which include information about pumping capacity
per hour, the data from Laos do not include pumping capacity but only the actual amounts of water
extracted. It was reported that in 2013, a total of 148 Mm 3 of water was pumped for domestic water
usage. A significant amount of that total came from the Mekong. It is noticeable that 65 Mm 3 of that
water, or 44% of the total, was extracted in Vientiane Prefecture. Savannakhet was second, at 53 Mm 3
extracted, which amounted to 36% of the total amount extracted nationally. Luang Prabang extracted
the third most, at 6 Mm3, amounting to just 4% of the total, and Champasak Province extracted the fourth
most at 5 Mm3, just 3%. All the other provinces in Laos combined only accounted for 13% of the total
amount of water extracted in Laos (Lao PDR Government, 2013).
Considering that Mekong River’s dry season flow is typically between 1000 m3 and 5000 m3 per
second, and that the average extraction rate for domestic consumption throughout the region is less than
5 m3 per second, which is only 0.5% of the 1000 m3 per second flow at the river’s lowest point, it seems
likely that water extraction at present is not significantly affecting the dry season flow of the river. This is
also the opinion of hydrologists who have worked on the Mekong River in recent years.2
MEKONG RIVER SUSPENDED SEDIMENT DISCHARGE CHANGES
We now consider whether changes to sediment flow along the Mekong River can help explain the
conflicting accounts by villagers about dry season water levels.
Historically, the Mekong River and its tributaries transported over 160 million metric tons of sediment
to the South China Sea annually (Wild et al., 2015). About half of this was believed to have originated in
China, although sediment fluxes in the Mekong River Basin are complex, with sediment sizes and types
varying across the basin (Bravard et al., 2013). The literature on sediment flows along the Mekong River
strongly indicates that sediment plays an important role in its productivity and ecosystem health (Bravard
et al., 2014; Baran et al., 2015). Unfortunately, as the data below clearly show, the amount of sediment
flowing down the Mekong River has dramatically declined since the early 1990s, largely due to sediment
being trapped behind upriver dams (Kummu and Varis, 2007; Kummu et al., 2010; Sarkkula et al., 2010;
Xue et al., 2011; Bravard et al., 2013; Wild et al., 2015; Binh et al., 2020a, 2020b; MRC, 2021; Chuenchom
et al., 2023), combined with sand mining and other causes such as land-use changes and climate change
(Bravard et al., 2013; Pokhrel et al., 2018). Increased deforestation in the upper basin has resulted in
increased erosion (Lacombe et al., 2018), but there is very little rain during the dry season, so upland
erosion at this time tends to be minimal. And even with this increased erosion taken over the course of
the year, the VietNamNet Bridge (2015) reported that the amount of sediment flowing into the South
China Sea had declined from 160 million tons historically to just 75 million tons in 2014. The amount of
sediment flowing down the Mekong can only have been reduced further since then, as even more dams
have been built. Efforts have been made to develop low sediment-trapping dams, but they have not been
as successful at solving the problem as initially hoped (Schmitt et al., 2019).
We were able to obtain suspended sediment discharge data for the 1990s and 2020s from Chiang
Saen, Nong Khai, and Khong Chiam (Figures 5-7) from the Office of National Water Resources (ONWR) in
Thailand. For each location, we graphed three years of suspended sediment discharge data from the early
1990s and three from the early 2020s, in order to compare suspended sediment discharge levels from
before mainstream Mekong hydropower dams were constructed with the most recent period for which
data were available, after many dams had been constructed. We chose three years for each period to
average out any individual year exceptions that might have occurred.
Timo Räsänen, pers. comm., March 11, 2024.
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Figure 5. Suspended sediment discharge data from Chiang Saen, Chiang Rai Province, northern Thailand.
Figure 6. Suspended sediment discharge data from Nong Khai, Nong Khai Province, northeastern
Thailand.
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Figure 7. Suspended sediment discharge data from Khong Chiam, Ubon Ratchathani Province,
northeastern Thailand.
The Mekong River suspended sediment discharge data presented in Figures 5-7 indicate that between
the 1990s and the 2020s there has been a dramatic decline in the amount of sediment flowing through
the Mekong River system. It appears to have been particularly significant at Chiang Saen (Figure 5), which
makes sense, because Chiang Saen is just ~350 kilometers downstream from the Jinghong Dam, the
closest dam to Thailand on the Lancang/Mekong mainstream Mekong River in China. There were no other
large dams built on Mekong tributaries upriver from Chiang Saen prior to the construction of the Jinghong
Dam.3 Recently, the MRC Secretariat’s CEO, Dr. Anoulak Kittikhoun, expressed serious concerns about
the decline of the Mekong River’s sediment load (Vongphachanh, 2023).
It is well known from other river basins around the world that the primary productivity of rivers
declines significantly when dam construction deprives those rivers of sediment (Sarkkula et al., 2010). In
some parts of the world, such as for the Rhine River in Europe, artificially produced sediment is being
added to the river for the benefit of the river’s ecology (Chardon et al., 2021; Mörtl and De Cesare, 2021;
Krapesch et al., 2024). However, for the Mekong, there are no plausible ways of compensating for such
a dramatic reduction in sediment (Sarkkula et al., 2010). There has not been much research done on the
exact impacts of suspended sediment discharge changes on aquatic life and livelihoods along the
Mekong, but there is no doubt that the so-called "sandscape" of the Mekong River Basin is crucial
(Rousseau and Marschke, 2023) to its ecosystem and plays an important role in the high productivity of
the river. Baran et al. (2015) have reported that diminished sediment in the Mekong River is negatively
impacting primary productivity, including fish stocks, respiration, nutrition, reproduction, and migration,
as well as reshaping their habitats.
While there have been dramatic declines of sediment along the Mekong River in Nong Khai and Khong
Chiam as well, it is noteworthy that there has been less of a decline in Nong Khai compared to Khong
However, sediment is trapped not only by the Jinghong Dam but by all the dams in the cascade along the Lancang River and its
tributaries in China.
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Chiam, something that warrants further research. In summary, however, these data indicate that there
has been a dramatic overall decline in sediment flowing down the Mekong River since hydropower dams
in China started being constructed the 1990s. This is something that others have also reported (Kallio and
Kummu, 2021).
RIVERBANK EROSION AND EMBANKMENT
The Mekong River hydrology literature clearly indicates that water flows have changed significantly over
the last few decades. In particular, there is now more water flowing down the mainstream Mekong River
during the low-flow part of the year (February, March, and April), and there is less water flowing down
the Mekong during the rainy season (Eyler et al., 2024). Moreover, it is widely recognised that these
changes have been due to hydropower development upriver, especially on the Lancang (Mekong) upper
basin in China (Kummu and Sarkkula, 2008; Richter et al., 2010; Lauri et al., 2012; Räsänen et al., 2012,
2017; Li et al., 2017; Sabo et al., 2017; Arias et al., 2019; Hoang et al., 2019; Binh et al., 2020a, b; Eyler
and Weatherby, 2020; Baird et al., 2021; Kallio and Kummu, 2021; Lu et al., 2021; RFA, 2022;
Keithmaleesatti et al., 2022; Chen et al., 2024).
Riverbank erosion along the Mekong River has historically been much less than along many other large
rivers in the world (Kummu et al., 2008), although some parts of the Mekong are more prone to erosion
than others (Miyazawa et al., 2008). Over the last few decades, however, riverbank erosion has become
a well-known negative impact of hydropower dam development (Darby et al., 2013; Hackney et al., 2020),
whether in Thailand (Pattanamongkol, 2023), Cambodia (Tha et al., 2022, 2024), or in Vietnam (Tran et
al., 2023; Hackney et al., 2020). Indeed, the rate of riverbank erosion on the Mekong along the ThailandLaos border was much slower between 1961 and 1992, before any dams were built on the Mekong River,
when compared to the period between 1992 and 2005, after dam construction began (Kummu et al.,
2008). When sediment is trapped by dams, it commonly occurs that erosion downstream is increased
due to what is known as the 'hungry water' phenomenon, when the capacity for erosion increases due
to the sediment-depleted nature of the river (McCully, 2001; RFA, 2022). Our field interviews and
observations along the Mekong River also indicate that there has been significant riverbank erosion along
the Mekong River in Thailand, Laos, and Cambodia since the 1990s. Other researchers have also reported
on this trend (Darby et al., 2013; Hackney et al., 2020; Tha et al., 2022, 2024; Tran et al., 2023), as have
journalists in Vietnam (Tuyển, 2022), Cambodia (Flynn and Srey, 2022) and Thailand (Rujivanarom, 2023).
Riverbank erosion has, in turn, led to a substantial portion of the Mekong mainstream that serves as
a border between Thailand and Laos being embanked by government agencies, especially on the Thai
side of the border but also along parts of the Mekong River in Laos. A senior Lao PDR government official
who works for the Ministry of Public Works and Transport reported, in June 2024, that 83% of the Mekong
on the Thai side of the river has already been embanked, compared to only 12-13% on the Lao side.4
There has been less in Laos due to river embankment being quite costly (Miyazawa et al., 2008;
Rujivanarom, 2023).
Villagers who live along the Thai side of the river recognise that embanking the river has had some
negative impacts on the environment by damaging riverbank vegetation and habitat. However, they
generally feel that embankment has been necessary to prevent erosion, which has led to the loss of quite
large amounts of land (Pattanamongkol, 2023). The Office of National Water Resources (ONWR) in
Thailand reported that in 2012-2013, 44 km2 of land was lost on the Thai side of the Mekong due to
riverbank erosion. Since then, embankment construction has reduced erosion in some areas, but 46 km2
of land was still lost between 2014 and 2018, presumably mainly in areas without embankments. Most
recently, between 2018 and 2020, another 18-24 km2 of land was eroded (Rujivanarom, 2023). Villagers
Senior Government Official, Waterway Impact and Management Division, Ministry of Public Works and Transport, Lao PDR,
pers. comm., Vientiane, June 7, 2024.
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on the Thai side report that riverbank erosion on the Lao side of the river is much worse than on the Thai
side, since there are much fewer river embankments there.
So, while sediment trapping by dams and sand and gravel mining are removing sediment from the
river, riverbank erosion would normally add more sediment to the river. However, it appears that thanks
to the widespread embankments, much more sediment is being removed than is being added through
erosion, thus leading to the lowering of the riverbed. This, in turn, could be what has led many along the
middle stretch of the study area, where the substrate is much sandier than along other stretches of the
river, to believe that there is less water in the Mekong River during the dry season than in the past, even
if there is significant evidence to suggest that this is not the case.
HYDROPOWER DAMS AND SEDIMENT
Globally, the downstream impacts of hydropower dams are generally not taken as seriously as the
impacts that occur in reservoir areas (Baird et al., 2021). Where they are, some have called for
implementing environmental flow regimes, in which water is released from dams in such a way as to
partially replicate natural flows (Dyson et al., 2003; Richter and Thomas, 2007; Baird and Quastel, 2015;
Sabo et al., 2017). But it is well known that the construction of dams can dramatically alter the amount
of sediment also flowing down rivers, leading to serious delta erosion (Goldsmith and Hilyard, 1984;
McCully, 2001). This is a major concern in the Mekong Delta of Vietnam (Vietnam News Service, 2012;
VietNamNet Bridge, 2015; Tuyển, 2022; Park, 2024). Lu et al. (2014) have confirmed that sediment
transport is being obstructed more in the upper Mekong (Lancang) River in China than along any other
sections of the Mekong River and that the obstruction began in 1993 during the construction of the
Manwan Dam, the first Mekong mainstream dam built in China (see also Fu et al., 2008).
Recently, Chuenchom et al. (2023) have reported that existing dams (as of 2018) in the Mekong River
Basin have the potential to trap around 61% of its sediment, and that the amount could expand to 69%
of the sediment load if more dams included in government development plans are constructed. Chua and
Xi (2022) have documented even more serious declines, reporting that the amount of sediment flowing
down the Mekong River at Chiang Saen in northern Thailand has declined by 84% when comparing
sediment levels recorded between 1965 and 1991 with those recorded between 2010 and 2019. In line
with these and other previous findings (cf. Baird and Thorne, 2023), Binh et al. (2020b) have reported
that between 2012 and 2015, sediment flow to the Mekong Delta in Vietnam declined by 74.1%, of which
40.2% was believed to be attributable to the six dams that had been constructed on the Lancang
(mainstream Mekong) River in China at the time. Binh et al. (2020b) attributed 14.8% of the effect to
sand mining.
In summary, there seems little doubt that the major reduction in recorded sediment in the Mekong
since the 1990s is strongly related to the construction of many large dams along the mainstream Mekong
and its tributaries. The MRC (2018) has predicted that if all the dams in the Mekong River Basin are
constructed as planned, by 2040 there will be a reduction of over 96% in the amount of sediment entering
the Mekong Delta. This will not only negatively impact the Mekong Delta ecosystem and the enormous
numbers of people who depend on it; water and nutrients that enter the South China Sea from the
Mekong River have historically contributed to the primary productivity of the coastal ecosystem and its
large variety of fish species and other aquatic life (Rainboth et al., 2012). These findings are considered
further below.
HYDROPOWER DAMS AND INCISION
'Incision' is a natural riverbed erosion process that frequently becomes accentuated due to human
activities. Dam-induced incision has long been recognised, from the Colorado River in the United States
(Grams et al., 2007) to the Yellow River in China (Li et al., 2021). In the case of the Mekong, the reduction
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in sediment is contributing to incision; various hydrologists who have conducted related research in the
Mekong region, including Christopher Hackney (cf. Wetzel, 2020),5 Chris Darby (cf. Timmins, 2019), Timo
Räsänen,6 and Doan Van Binh7 believe that the Mekong’s riverbed has lowered due to erosion or incision.
The Mekong Delta is sinking with it (Binh et al., 2021; Chua et al., 2024), making the Delta more vulnerable
to sea level rise caused by human-induced climate change (Allison et al., 2017).
This incision, like the erosion already discussed, is likely to be a result of the "hungry water" effect,
which often occurs when sediment-depleted water flows downstream and erodes more than it did
previously in order to add sediment to its sediment-depleted water (McCully, 2001). In this case, the river
has been depleted of sediment and as a result has caused increased downstream erosion and incision.
However, it is also important to consider the impacts of sand mining, as we do below.
SAND MINING
Sand, gravel, and pebbles are extracted from rivers in various parts of the world for different reasons but
especially for land reclamation and for producing concrete for construction. More development in the
Mekong region has increased the demand for river sand and gravel, leading to the mining of the river’s
sediment and thus the reduction of the river’s sediment load (Bravard et al., 2013).8 The extraction of
sediment in upstream areas results in less sediment in the river downstream.
The negative environmental impacts of 'sand mining', which is the extraction of sand or other
sediment from rivers, has been known in Europe since the 1950s; also in the case of the Pearl River in
China, the riverbed has been severely lowered due to sand mining (Bravard et al., 2013). Along the
Mekong River, impacts have become evident in some areas since the 1990s (Bravard et al., 2013).
However, sand mining has become increasingly controversial, both globally (Bendixen et al., 2019a,
2019b, 2021; Wetzel, 2020; Rentier and Cammeraat, 2022) and more recently in the Mekong River Basin,
including in Thailand (Piman and Shrestha, 2017), Cambodia (Flynn and Srey, 2022; Rousseau and
Marschke, 2023), Vietnam (Timmins, 2019; Hackney et al., 2020; Tuyển, 2022; Tran et al., 2023), and the
Mekong more generally (Sarkkula et al., 2010; Bravard et al., 2013, 2014; Kondolf et al., 2014, 2018; Chua
and Xi, 2022; Park, 2024).
Sand, gravel and pebble mining along the Mekong River is now widely recognised as being detrimental
both to the environment and the livelihoods of those who depend on the river having a healthy
ecosystem (Bravard et al., 2013; Kondolf et al., 2014; Hackney et al., 2020; Tran et al., 2023). Hackney et
al. (2020), for example, have written about increased riverbank instability along the Mekong River due to
sand mining, and Flynn and Srey (2022), like Asif and van Arragon (2024), have reported serious tensions
between those who make their living from sand mining and fisheries along the Mekong River in
Cambodia.
The Joint Committee for Management on the Mekong River and Heung River (JCMH) was coestablished by the governments of Thailand and Lao PDR in order to regulate natural resource extraction,
including sand mining, along the river border between the two countries (Rujivanarom, 2023). Incision
and riverbed erosion are recognised as problems along the Mekong River in Laos and Thailand, and this
is the main reason rules have been adopted prohibiting sand mining within 1000 m of the tips of islands
Chris Hackney, pers. comm., April 18, 2024.
Timo Räsänen, pers. comm., March 11, 2024.
Doan Van Binh, pers. comm., April 10, 2024.
Villagers living along the Mekong River in Thailand and Laos are quite aware that sand mining can lead to increased riverbank
erosion. This may differ considerably from Vietnam, where Tran et al. report that many people living in the Mekong Delta are
aware that sand mining has detrimental environmental impacts but are generally not aware that it increases riverbank erosion
(2023). However, Tuyển (2022) reports that at least in some parts of the Mekong Delta, local people are quite aware of the
impacts that sand mining is having on riverbank erosion.
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and at least 100 m from the middle of islands, riverbanks, and sand bars. Sand extraction over two metres
deep is also prohibited, while mining for pebbles is not supposed to go deeper than ten metres (Ministry
of Public Works and Transport, Lao PDR, 2010). Moreover, the Thailand and Lao PDR governments (2006)
have also prohibited sand mining within 1000 m of river embankments, due to concerns that incision and
related riverbank erosion could damage this valuable infrastructure (Thailand and Lao PDR Governments,
2006; Rujivanarom, 2023).
Since the river is often less than two kilometres wide, this has made sand mining impossible along
many parts of the Thai side of the Mekong River where river embankments have been constructed. This
in turn has led to an increased amount of illegal sand mining along the Mekong River, at least in Thailand,9
although to what degree remains uncertain. As a result of these tensions and the increase in illegal sand
mining, the Thai National Committee on Sand Mining released a resolution allowing provincial
administrations to revise sand mining zoning rules to fit local environmental and economic
circumstances. However, illegal sand mining still persists (Rujivanarom, 2023).
There seems to be little doubt that parts of the Mekong riverbed are significantly lower than in the
past, and that this is due to incision. However, the degree to which sand mining is responsible for this
incision, compared to hydropower dam development and other causes, remains uncertain. Some
villagers in Chiang Rai Province have reported that groundwater levels adjacent to the river have also
declined, based on the depth of water in wells, but they attributed this to river embankment construction
rather than riverbed lowering. Kondolf et al. (2018) believe that hydropower dam development is the
main cause of changes in Mekong River sediment transport. However, they point out that it is not the
only cause, and that sand mining, climate change, diking and water infrastructure development, and
accelerated subsidence water pumping were also partially responsible. We would add that land-use
change is another factor.
While it is widely recognised that large amounts of sand and gravel has been extracted from the
Mekong River over the last few decades, one serious challenge is knowing the exact volume of extracted
material. In Thailand, for example, the government gives out legal sand and gravel mining concessions to
companies operating in different provinces, and the Department of Industry claims that there are about
140 sand mining companies registered in Thai provinces adjacent to the Mekong River (Rujivanarom,
2023). However, they do not collect data on the exact amounts of gravel and sand extracted.10 In Lao
PDR, sand and gravel concessions are approved by the government, and before concessions are granted,
companies need to prepare management plans that include the estimated amount of sand and gravel
that they will harvest annually. However, the government does not collect data on the actual amount of
sand and gravel extracted in Laos either.11
In some areas, the number of sand mining operations on the Thai side of the Mekong has increased
considerably in recent years, along with an increase in demand for sand. Some Thai sand miners are
supposedly registered in Laos but operate near the Thai side of the border. One official has claimed that
80% of the sand extracted from the Mekong by these Thai operators is illegally exported back to Thailand
(Rujivanarom, 2023). While Lao government officials in Vientiane stress that it is illegal to export sand
Article 9 of The Thai Land Code Act stipulates that illegal sand mining can be punished by up to five years’ imprisonment and a
20,000 baht fine (Rujivanarom, 2023).
10
Official from the Public Land Management Sub-Bureau, Public Land Management Bureau, Department of Land, Thailand, pers.
comm., Bangkok, June 11, 2024.
11
Senior Government Official, Waterway Impact and Management Division, Ministry of Public Works and Transport, Lao PDR,
pers. comm., Vientiane, June 7, 2024.
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and gravel from Laos and that no exceptions have been granted by the central government, 12 our
fieldwork indicates that it is nonetheless taking place.
Villagers living along the Mekong River in northeastern Thailand have been reporting illegal Thai
mining operations to Thai government officials for years, but not much has been done to combat it.
Reportedly, illegal sand miners are frequently tipped off in advance about visits by government officials,
giving them chances to evade apprehension. Local "influential people" also often protect illegal sand
miners (Rujivanarom, 2023).
Bravard et al. (2013: 6) reported that 55.2 metric tons of sediment was extracted from the Mekong
mainstream River in Laos, Thailand, Cambodia and Vietnam in 2011-2012. Of this, they reported that 90%
was sand, 8% was gravel, 13 and 1% was pebbles. 14 Ultimately, Bravard et al. (2013: 6) found that
Cambodia extracted 60% of the sediment, while Vietnam extracted 22%, Thailand extracted 13%, and
Laos extracted 4%. These statistics were based on interviews with operators, and it was recognised that,
as extraction companies, they may have underestimated the actual amounts. In Laos, for example, sand
miners are supposed to pay a 10% tax to the government based on amounts extracted (President’s Office,
Lao PDR, 2005), which encourages underreporting.
Because of the sensitivity of the sand mining issues in the Mekong region (see also Bravard et al.,
2013), none of the member governments of the MRC provide sand mining data to the MRC,15 thus making
regionally relevant research on sand mining difficult to conduct. Bravard et al. (2013: 5) also reported
that, at the time of their study, "Official statistics from national agencies and the MRC were not readily
available". Still, over the last few decades, there appears to have been an increase in the amount of sand
and gravel being extracted from the Mekong River and its tributaries (Rujivanarom, 2023). Illustrative of
this, MME, NERI, and ICMM (2011) reported that the amount of sand extracted in Laos increased from
less than 300,000 m3 per year in 2001 to over 1,000,000 m3 in 2008, and interviews of sand miners on
the Thai side of the Mekong in May-June 2025 clearly indicated that they were increasingly granted
permission to extract sand and gravel on the Lao side of the river.16 All of this indicates overall increases
in extraction in recent years.
While many owners and managers of sand mining companies in various parts of the world are believed
to rely on high-level political connections and sometimes exhibit degrees of organised criminal behaviour
(Rentier and Cammeraat, 2022; Park, 2024), including in Cambodia (Global Witness, 2009; Flynn and Srey,
2022) and Thailand (Rujivanarom, 2023), many sand mining company owners and managers have worked
in the industry for decades and have considerable knowledge about sediment flows and changes in river
flows over time.
In June 2024, we interviewed someone who had been a manager of a sand mining company north of
Vientiane for over thirty years. The results were useful for corroborating the hydrological and sediment
data already presented here. He reported that when he started operating in the area during the early
1990s, after he had to move his operations from the Done Chanh area near Vientiane, there was typically
six metres of sand build-up along the riverbed of the Mekong River at the end of the rainy season in front
12
Senior Government Official, Waterway Impact and Management Division, Ministry of Public Works and Transport, Lao PDR,
pers. comm., Vientiane, June 7, 2024.
13
No gravel extraction was reported in Vietnam, and only 10,000 m3 of gravel was reported to have been extracted in Laos. It
was reported that 857,740 m3 of gravel was extracted in Thailand and 2,044,940 m3 in Cambodia (Bravard et al., 2013: 6).
14 Pebbles were reportedly only extracted in Laos, with no extraction being recorded for Thailand, Cambodia, or Vietnam
(Bravard et al., 2013: 6). Pebbles are generally more rounded by hydrological erosion than gravel, although the terms are
sometimes used interchangeably.
15
Official at Mekong River Commission, pers. comm., Vientiane, May 29, 2024.
16
Interviews with sand miners in Ubon Ratchathani, Amnat Charoen, Mukdahan, and Nakorn Phanom Provinces, May-June 2025.
Baird et al.: Mekong River dry season changes due to hydropower dams and extractive processes
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of his operation. However, by the 2000s, after the Chinese had completed dams in the upper Mekong,
only three metres of sand remained. Then, when the Xayaburi Dam was built, the amount of sand
accumulation downstream declined even further. At present there is reportedly only 80 cm remaining at
the end of each rainy season.17 This is despite the Xayaburi dam – unlike many other dams – having the
ability to occasionally flush sediments, which improves the operating capacity of the dam (see Glijnis,
2022).
Recent developments in the creation of sand and gravel from crushed rock, called 'm-sand', may
lessen levels of sand and gravel extraction in the future, but it is unclear how rapidly the transition to msand is occurring, and the cost of Mekong sand and gravel is still generally the cheapest option for
builders.
In summary, sand mining is likely to be playing an important role in Mekong River changes, but it is
difficult to assess its relative impact compared to sediment trapping behind dams.
CONCLUSION
A few important findings emerge from this study. First, as stated above, Mekong River villagers in the
upper stretches of the study area, as well as the most downstream parts of the study area, believe that
there is more water in the Mekong during the dry season, and people living along the middle stretch
believe there is less water during the dry season. This odd situation can be explained by the hydrological
and sediment flow changes caused by upriver dams and downstream incision, especially in areas with
less bedrock, but we needed both local knowledge and the available associated data to reach this
explanation. The additional data we collected indicate that there is a considerable lowering of the
Mekong riverbed, likely due to a combination of river incision and sand and gravel mining – along the
northern northeast Thai section of the of the river in particular, due to the sandier nature of the riverbed
in this area. Incision certainly occurs within bedrock, but it obviously happens much more quickly with
sand. Sand mining’s importance relative to incision is hard to assess; more research is needed to quantify
these changes and determine the exact cause.
Thus, while there is more water released during the dry season from the active storage of hydropower
dams upstream, incision and sediment removal in the sandy areas of the Mekong have led many people
living along these stretches of the River, in Nong Khai, Bueng Kan, Nakorn Phanom, and much of
Mukdahan province, to believe that dry season levels have declined. Upstream and downstream from
this section, villagers report that there is more water in the river during the dry season. We have
considered whether changes along the Mekong tributaries in Laos might explain the circumstances, but
even if that were the case, it would not get us closer to explaining why villagers perceive the situation
differently along different stretches of the mainstream Mekong River. Moreover, most of the tributaries
that have experienced major hydropower dam construction in recent years are in Laos and flow into the
middle section of our study area (i.e. Theun/Kading, Hinboun, etc) – the area where dry season water
levels were reported to be lower than those reported on paper. Since these dams would presumably add
more water in the dry season, not less, they cannot explain what local people have reported.
Sediment transport along the mainstream Mekong River has dramatically declined since the 1990s,
when hydropower dams on the Mekong River in China and elsewhere in the basin began being
developed. This has led to serious downstream riverbed incision and riverbank erosion, leading to the
lowering of the riverbed and encouraging riverbank embankment in order to reduce land loss. While
some of these processes are likely to have counteracting effects, it appears that riverbed erosion,
sediment extraction, and riverbed incision have been particularly impactful along the section of the river
where the substrate is sandy.
17 Sand
mining company manager, Vientiane Prefecture, pers comm., June 2, 2024.
Baird et al.: Mekong River dry season changes due to hydropower dams and extractive processes
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Apart from providing important new information about hydrological changes and sediment flows
along the Mekong River, this study addresses why people living along different stretches of the river have
different perceptions about the hydrological changes that have taken place there. While the use of new
technologies to better understand the Mekong is exciting, care needs to be taken to consider such
information alongside local understandings of river changes. Ultimately, this study indicates that more
efforts should be put into studying incision extent and impacts, especially along the Thailand-Laos border,
and we contend that local knowledge, whether held by villagers or sand mine operators, can help, along
with other methods, to better understand riverine changes. Furthermore, more regular, detailed
bathymetric surveys along the Mekong will be particularly useful for ascertaining the state of the incision
and the effects of the changes that have been wrought on the river through dam construction and other
human activities. We tried to obtain such data from various sources, but we were not able to find
anything that could be easily used to assess changes to the riverbed. In any case, there is still compelling
evidence that in the middle part of our study area, the riverbed is sinking, resulting in the perception that
there is now less water in the river during the dry season even though there is actually more.
ACKNOWLEDGEMENTS
Thank you to all the people living along the Mekong River in Thailand, Laos, and Cambodia who provided
information to us during our research. Without them, this study would not have been possible. Various
academics interested in the Mekong River also contributed useful information. Thanks to the Office of
the National Water Resources (ONWR) of Thailand for providing the suspended sediment discharge data
used in this paper and to the Waterways Impacts and Management Division of the Ministry of Public
Works and Transport of the Lao PDR for providing information about sand mining regulations in Laos. We
are thankful for the financial and other support provided by the Stimson Center in Washington, DC; and
the Chino Cienega Foundation. In particular, thanks to Brian Eyler, Courtney Weatherby, and Regan Kwan
from the Stimson Center. The Cartography Lab of the Department of Geography at the University of
Wisconsin-Madison prepared the map.
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Vu, D.T.; Thanh, D.D.; Galelli, S. and Hossain, F. 2022. Satellite observations reveal 13 years of reservoir filling strategies, operating rules, and hydrological alterations in the Upper Mekong River Basin. Hydrology and Earth System Sciences 26: 2345-2364, https://doi.org/10.5194/hess-26-2345-2022
Wetzel, C. 2020. The covert industry that is destroying the world's rivers. Scienceline, July 30.
Wild, T.B.; Loucks, D.P.; Annandale G.W. and Kaini, P. 2015. Maintaining sediment flows through hydropower dams in the Mekong River Basin. Journal of Water Resources Planning and Management 142(1), https://doi.org/10.1061/(ASCE)WR.1943-5452.000056
Wyatt, A.B. and Baird, I.G. 2007. Transboundary Impact Assessment in the Sesan River Basin: The Case of the Yali Falls Dam. International Journal of Water Resources Development 23(3): 427-442, https://doi.org/10.1080/07900620701400443
Xue, Z.; Liu, J.P. and Ge, Q. 2011. Changes in hydrology and sediment delivery of the Mekong River in the last 50 years: Connection to damming, monsoon, and Enso. Earth Surface Processes and Landforms 36: 296-308, https://doi.org/10.1002/esp.2036
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Ian G Baird
University of Wisconsin-Madison, Faculty Member
Most of my research is focused on mainland Southeast Asia, especially Laos, Cambodia and Thailand, and the peoples who come from there. My interests are varied and include: political ecology, social and spatial (re)organization, upland-lowland relations in mainland Southeast Asia, Indigenous studies, large hydroelectric dams, large-scale economic land concessions, land and resource tenure, protected areas, Hmong studies, Lao studies, Brao studies, 19th and 20th history in mainland Southeast Asia, border and boundaries studies, insurgencies and counter-insurgencies in mainland Southeast Asia, qualitative methods, Champassak, Mekong fish and fisheries, development studies, non-government organizations (NGOs), internal resettlement, Buddhism, Animism, identities and post-colonial studies.
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Ecogeographical Diversity and Dry Season Changes along the Mainstream Mekong River in Thailand, Laos and Cambodia
Michael A.S. Thorne
Ian G Baird
Natural History Bulletin of the Siam Society, 2025
The Mekong River is experiencing dramatic hydrological and sediment transport changes, largely due to the development of hydropower dams, both on its mainstream and tributaries. We ask, "how well do local people with a lifetime of experience living along and interacting with the Mekong River on a daily basis understand the changes that are occurring?" In this article, we present the results of research conducted with groups of villagers living in 44 communities located along the mainstream Mekong River from Chiang Saen District, Chiang Rai Province, in northern Thailand, downstream to Stung Treng Town in Stung Treng Province, northeastern Cambodia. Local people are well aware that changes are occurring and causing various types of negative environmental and social impacts, such as to seasonally inundated forests and vegetation along the river, sandbars, birds, algae, fish, mollusks, crabs and shrimps, semi-aquatic earthworms, and insects. Mitigation measures, such as the construction of river embankments, are causing their own adverse environmental impacts. Here, we argue that local knowledge related to the ecogeographical diversity of the Mekong River has been underappreciated, particularly as a result of increased reliance on remote sensing to understand environmental changes along the Mekong, and that local ecological knowledge can help us better understand Mekong River changes.
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Transboundary Water Governance: The Impacts of Upstream Dams on the Mekong River in Cambodia
Steve Chan
GMSARN International Journal, 2023
Hydroelectric dams block rivers at their upstream and control the water flow to downstream users. Existing watershed communities, irrigation and fishery are usually sacrificed to pave the way for development. The Lancang-Mekong River originates in the Tibet Plateau of China with Himalayan glaciers being the main sources of the headwaters. Taking advantage of its high altitude, China has constructed dam cascades upstream which block the water flowing towards the Mekong River. Downstream communities in Thailand, Cambodia, and Vietnam are suffering as a result. Extreme weather is usual in recent years in the Mekong Basin. Flood and drought come almost annually to the watersheds of the Mekong River. Qualitative methods including archive research and unstructured interviews were used. Four informants as well as twenty-two farmers, fishermen and migrant workers were interviewed in Phnom Penh and Kampong Cham of Cambodia. The findings showed that farming and fishing yield was reduced as the Tonlé Sap system had been disrupted by dams on the Mekong River. Existing ways of Mekong River governance are ineffective in protecting the river ecosystem and livelihood of the basin communities downstream.
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A synthesis of hydroclimatic, ecological, and socioeconomic data for transdisciplinary research in the Mekong
Jiaguo Qi
Scientific Data
The Mekong River basin (MRB) is a transboundary basin that supports livelihoods of over 70 million inhabitants and diverse terrestrial-aquatic ecosystems. This critical lifeline for people and ecosystems is under transformation due to climatic stressors and human activities (e.g., land use change and dam construction). Thus, there is an urgent need to better understand the changing hydrological and ecological systems in the MRB and develop improved adaptation strategies. This, however, is hampered partly by lack of sufficient, reliable, and accessible observational data across the basin. Here, we fill this long-standing gap for MRB by synthesizing climate, hydrological, ecological, and socioeconomic data from various disparate sources. The data— including groundwater records digitized from the literature—provide crucial insights into surface water systems, groundwater dynamics, land use patterns, and socioeconomic changes. The analyses presented also shed light on uncertainties asso...
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The Downstream Impacts of Dams on the Seasonally Flooded Riverine Forests of the Mekong River in Northeastern Cambodia
Ian G Baird
South East Asia Research, 2023
On the Mekong River, north of Stung Treng town in northeastern Cambodia, and below the border with Laos, lies an area of riverine seasonally flooded forest designated as an internationally significant Ramsar wetland site because of its exceptional biodiversity and importance to livelihoods. This article reports on the cumulative and cascading impacts of numerous upstream hydropower dams in China and Laos on this vital ecosystem due to the release of water during the dry season, which prevents the flooded forest from undergoing its critically important drying out period. In particular, we investigate the damage being wrought on these flooded forests and on the various species dependent on them. Different species have been variously affected, but some have been largely destroyed. Others are being increasingly impacted. This habitat loss is negatively affecting fisheries, especially for a number of Pangasiidae catfish and Cyprinid carps, which is having an adverse effect on local livelihoods. New dams upriver, and continued high dry-season water from existing dams, are likely to lead eventually to the increased degradation and possibly the eradication of the flooded forests along the mainstream Mekong River, unless measures are taken to address the problem.
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Perceptions, data, and river management: Lessons from the Mekong River
Ian Campbell
Water resources research, 2007
Workshops to identify transboundary and basin-wide environmental issues and a diagnostic study by consultants identified priority environmental concerns of resource managers in the lower Mekong River basin. The issues identified, in priority order, were water quality, reduction in dry season flows, sedimentation, fisheries decline, wetland degradation, and flooding. An analysis of the available data found no evidence that water quality was poor except in the delta, where nutrient levels were high and increasing. Dry season flows have not decreased, and in the immediate future they are more likely to increase. Suspended sediment levels in the river are not high, and there is no indication that sediment loads are substantially increasing. Fish catch per unit effort has declined over the past decades, as have catches of large fish, but total fish catch has increased. Flooding does not appear to have increased in frequency or extent. There is no reliable quantitative information available on changes in wetland extent or condition, although it is reasonable to assume that both have declined. Reasons for the mismatch between perceptions and the data may include a failure by management agencies to analyze and publish data and provide adequate responses to issues raised in the popular press. This results from a lack of capacity in many government agencies and the Mekong River Commission, where there are high staff turnover rates and a dependence on short-term experts with limited experience in the basin.
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The contentious politics of hydropower dam impact assessments in the Mekong River basin
W. Nathan Green
Ian G Baird
Political Geography, 2020
Since the 1990s, many large hydropower dams have been built in the Mekong River Basin. There has been considerable concern about resettlement and compensation linked to reservoir flooding, as well as the impacts of dams on wild-capture fisheries, riparian livelihoods, and aquatic biodiversity and ecosystems. Anti-dam activists in the Mekong Basin have contested these impacts by claiming that dam impact assessments limit the spatial scale of recognized impact areas in order to reduce both the political backlash against projects and the costs of dam development. In this article, we consider the contentious politics of hydropower dam impact assessments in order to understand how the spatial strategies of anti-dam activists influence the recognized scale of dam impacts. We analyze three of the most contested hydropower projects in the Mekong River Basin: the operational Pak Mun dam in northeastern Thailand, the recently completed Lower Sesan 2 dam in northeastern Cambodia, and the planned Sambor dam on the mainstream Mekong River in Cambodia. We argue that the recognized scale of impacts is in part an outcome of anti-dam activists’ different spatial imaginaries and associated scale frames—along with those of state actors, business interests, and project consultants—that inform activist strategies for mobilizing geographically dispersed people to make claims about dam impacts. Although activists have sometimes challenged the spatial extent of project impact assessments, they have also sometimes inadvertently adopted strategies to contest dams that have reproduced project scale frames favorable to dam proponents.
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Social impact monitoring and vulnerability assessment 2014 Report on Baseline Survey 2014 of the Lower Mekong Mainstream and Flood Plain Areas Report prepared by Mekong River Commission
Jens Sjørslev
SIMVA 2014. Social Impact monitoring and vulnerability assessment 2014, 2018
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Change in land and water use: Micro and macro perspectives from the Mekong River Delta
François Molle
2000
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Laos (Lao PDR)
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