Using information derived from satellite observations with data provided by the Mekong River Commission, the Mekong Dam Monitor’s annual report for 2022-23 provides an insight into dam operations and Mekong River flows during the 2022 wet season to the 2023 dry season.
As the report states: “So much of what makes the Mekong unique, from being the world’s largest freshwater fishery to its robust agricultural production to its incredible biodiversity, relies on the extreme highs and lows of its annual flood pulse.” However, the Mekong Dam Monitor (MDM) says evidence shows that the operations of the largest storage dams in the Mekong Basin are leading to a reduction of the benefits provided by the flood pulse.
Over time, MDM states, especially with the impact of new climate patterns, this flattening of the flood pulse will significantly reduce the Mekong’s fish population and the opportunity for floodplain agriculture, particularly in Cambodia and Vietnam. Improved basin-wide seasonal and monthly weather forecasting and better communication between upstream and downstream countries could mitigate the impacts of dams during times of crisis, helping to avoid exacerbating an already bad situation, it adds.
To reduce the impacts that dams deliver to seasonal flow regimes and thus maximise downstream fishery productivity and agricultural production, minimum and maximum flow thresholds for existing and planned seasonal storage dams on the mainstream and tributaries should be determined. Furthermore as climate interactions with dam impacts and river flow are complex, and much is unknown about the interaction of these effects on the Mekong’s ecology and socio-economic outcomes, the MDM says more study is required to provide greater understanding and improved evaluation.
Hydropeaking
Between June 2022 and May 2023, the MDM team issued 20 alerts when China’s upstream dams released or restricted enough water to cause a 0.5m or higher rise or fall in river levels within a 24-hour period at Chiang Saen, Thailand. Alerts are issued to national governments, the Mekong River Commission, and the tens of thousands of people living in affected communities via social media. Local community people in Chiang Saen who received the alerts confirmed they helped protect their assets, namely boats which had previously been washed away during sudden releases of water.
MDM says that smarter dam management is needed and dam operators throughout the basin should avoid sudden flow releases or restrictions which cause severe downstream fluctuations, while reducing hydropeaking practices can avoid these impacts. In cases where sudden releases and restrictions are necessary for dam safety or other reasons, dam operators should provide early warning days in advance to relevant authorities and communities downstream so that vulnerable people have time to prepare. In addition, local authorities should create clear processes for notification and require compliance by dam operators.
Tonle Sap
The Tonle Sap Lake is often called the beating heart of the Mekong Basin. During normal wet season conditions, it expands to five times its dry season area and sixty times its dry season volume of water. This expansion is mostly driven by the Mekong flood pulse bringing higher river levels throughout the Mekong mainstream, causing the famous “Tonle Sap Reversal” where the river which traditionally flows out of the Tonle Sap reverses direction. This reversal sends water from the Mekong into the Tonle Sap, and transported with that water are fish eggs and larvae which find a rich habitat inside the Tonle Sap Lake where fish feed and grow.
As the lake contracts in the dry season and drains back into the Mekong system, migratory fish move upstream into tributaries in Cambodia, Laos, Vietnam, and Thailand and water and sediment flow downstream to nourish the Mekong Delta. This 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 on the Mekong River
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.
As a best practice, MDM recommends that all countries with dams in the Mekong Basin should publish and share daily or hourly dam operation data—ideally via an information portal available to the public, but at minimum to the Mekong River Commission. This data and information will provide more awareness around reservoir and river conditions, leading to ways to avoid or mitigate environmental and social impacts.
3S Basin report
The Mekong Dam 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 the Mekong Dam Monitor
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.
