| Survey & investigation
process makes the Mekong Basin account for 20% of the world’s freshwater fish catch. The fish catch in Cambodia alone is responsible for 60-70% of the national population’s animal protein intake. Data in this MDM report shows that the Tonle Sap Expansion has varied significantly between 2018- 2022, with the timing of peak expansion shifting from September to October. During 2019, 2020, and 2021, the expansion reached sub-normal levels with the weakest expansion occurring in 2019 at around 58% of normal. The Mekong Data Monitor says that this highlights a need to prioritise the conservation about the Tonle Sap Watershed. More study is needed to determine the importance of Tonle Sap tributary contributions to the wet season expansion process, particularly during wet seasons with low flow in the mainstream. There is also concern that the Tonle Sap tributaries are both understudied and being exploited at an alarming rate by the construction of small and medium-sized dams and irrigation canals.
Data
In an effort to improve utilisation of water resources across a shared vision for the Mekong River, and helping to avoid or mitigate environmental and social impacts, the MDM report says that as a best practice, all countries with dams in the Mekong Basin should publish and share daily or hourly dam operation data. Ideally this will be via an information portal available to the public, but at minimum to the Mekong River Commission. While higher resolution satellite data from more sophisticated remote sensing instruments can also reduce potential bias and improve accuracy. Thailand, Vietnam, and Laos already publicly
share relevant information on some of their dams in the Mekong Basin. Notable developments achieved over the course of 2022 and 2023 include improved data sharing from China. China now sends data updates to governments party to the 1995 Mekong Agreement (Thailand, Laos, Cambodia, Vietnam) and the Mekong River Commission Secretariat on river levels at the Jinghong and Man’an gauge at 12-hour intervals. Previously China had only updated its hourly data once every 24 hours. Providing data at 12-hour intervals improves the ability to monitor sudden releases and restrictions from dams upstream of these river gauges and provides vulnerable communities with more time to adapt to sudden changes. China has also pledged to share dam operations data and the MDM team says that while improvements in data-sharing are welcome, details of what data would be included in this pledge are scarce, and it will continue to follow these developments closely.
3S Basin report The Mekong Data Monitor team has also carried out
groundbreaking research into how the operation of previously unstudied dams were impacting the Sekong, Sesan, and Srepok Rivers – three transboundary river basins running through Laos, Vietnam, and Cambodia collectively known as the 3S Basin. This basin provides the Mekong with around 20% of its annual flow, and its relative
proximity to the Tonle Sap Lake means alterations to hydrological flow and fish migration patterns in the 3S can have a potentially outsized impact on the Mekong fishery. In June 2023, the team published a technical
report which shows how 20 dams in Vietnam, Laos, and Cambodia are changing the hydrological flows of the 3S Basin and the Mekong River, and focused on changes from 2016 to 2022. The reported concluded that operations of seasonal and hydropeaking dams are determined with little to no consideration of downstream ecosystem impacts or early warning for sudden releases of water which can cause flash floods. Giving these findings, some of its recommendations include that.
Authorities in Cambodia and the Mekong River Commission should restore physical gauge reporting at the Siempang gauge on the Sekong River. No daily discharge data is available for this gauge after 2012. The Sekong River is responsible for approximately 10% of total Mekong. The use of dams for hydropeaking purposes is damaging to communities and ecosystems downstream. Effective early warning systems are needed at the transboundary scale to communicate when hydropeaking operations or sudden reservoir drawdowns due to emergency management procedures at the dam site release water that can cause a flash flood in communities downstream. This is necessary in all 3S Basins as well as on their tributary rivers which have communities living below and between dams. To maximise downstream fishery productivity and agricultural production, minimum and maximum flow thresholds for seasonal storage dams should be determined in order to reduce the impacts dams deliver to seasonal flow regimes
What’s Next for MDM? The Mekong Dam Monitor team wants to engage
local institutions and organisations with capacity building programmes to teach people in the Mekong how to produce similar analysis and satellite derived products. MDM says it is actively looking for new partners for new studies and/or the production of new products and services at varying scales, and is specifically interested in identifying dam impacts on the Tonle Sap Expansion (among other factors), gaining a better understanding the relationship between dam impacts and the Tonle Sap fishery, and conducting an analysis of climate trends in the basin. The Mekong Dam Monitor Project is an online
platform which uses remote sensing, satellite imagery, and GIS analysis to provide near-real time reporting and data downloads across numerous previously unreported indicators in the Mekong Basin. The platform is freely available for public use and all research inputs are public-access resources. This project is a collaborative partnership formed by the Stimson Centre’s Southeast Asia Programme and Eyes on Earth, Inc with funding support from the Mekong-US Partnership, the Chino Cienega Foundation, and individual donors.
Mekong Mainstream Dam Monitor (
stimson.org)
Above: The Nam Ngum Dam is a hydroelectric dam on the Nam Ngum River, a major tributary of the Mekong River in Laos. It was the first hydropower dam built in the Lao PDR
Above: Aerial view of the dry Mekong River. Climate interactions with dam impacts and river flow are described as being complex, and much is unknown about such effects on the Mekong’s ecology
References
Brian Eyler, Alan Basist, Regan Kwan, Courtney Weatherby, Claude Williams, 2024, Mekong Dam Monitor Annual Report: 2022–2023. The Stimson Centre, Washington D.C, USA.
https://www.stimson. org/2023/mekong- dam-monitor-annual- report-2022-2023/
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