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The Mekong River, flowing across South East Asia, is one of the World’s largest rivers. It’s delta in Viet Nam is home to more than 17 million people and is some of SE Asia’s most fertile and productive land, thanks to the large sediment and nutrient supply originating from its 795,000 km2 basin. In global terms it is also relatively un-modified, with few man made alterations and obstructions along its 4,350 km route from the Himalaya to the South China Sea. However, the pressure to start harvesting the Mekong’s natural resources has slowly begun to increase, and it seems that in the coming years the river and the communities it supports are likely to experience vast changes.
It is estimated that the Mekong could provide ~59,000 MW in hydropower  (more than the total electrical generation capacity of Australia  ). Currently there are 4 existing hydropower dams in operation on the main stem of the Mekong in China (with one currently under construction), and a further 26 operating on tributaries of the Mekong in Laos PDR, Viet Nam and Thailand . Unsurprisingly, with the enormous potential the Mekong offers, there are also currently 11 more dams being proposed along the mainstem of the river (9 in Laos PDR and 2 in Cambodia) [4,5]. If these projects are to go ahead, it is highly likely that major impacts on ecology, hydrology and sediment transport will be felt across the whole of the Mekong basin and particularly at the delta.
Of the proposed dams, perhaps the most controversial is the Xayaburi dam in Laos PDR. Originally proposed by in 2010, the dam received a critical appraisal by the Mekong River Commission (MRC), an inter-governmental agency that works directly with the governments of Cambodia, Lao PDR, Thailand and Viet Nam to jointly manage shared water resources and promote the sustainable development of the Mekong River. This report recommended that construction of the dam was put on hold for 10 years whilst scientific studies into the ecological and hydrological effects of the dam were undertaken. However, in November 2012 Laos PDR officially began construction of the £2.2bn dam. This has caused tension and anger within the region, with Cambodia and Viet Nam calling for an immediate halt to construction as the potential effects of the construction downstream are as yet unknown. Internationally there has been widespread condemnation of the decision, with NGOs and scientists warning against the potential disruption to fish stocks, sediment delivery and livelihoods the dam may cause in downstream countries .
Although the scientific reasons for delaying the construction of the dam are numerous, and undoubtedly more detailed consultation is needed to reduce the ecological and environmental impacts of the dam, for Laos PDR the decision to go ahead with the construction process is less clear cut. Laos PDR is ranked 136 out of 229 of countries in the world by GDP (approximately $8.3bn), with 26% of its population below the poverty line . For such a country, it is unsurprising that it wishes to make the most of its natural resources. Hydropower development is its best bet for independent economic development, with trade deals with Thailand already arranged. The income and trade that such development may bring is surely of great benefit to Laos PDR, for who can blame a country for trying to improve and further develop its economy?
That argument would be OK if all the other effects of the construction had been considered and, perhaps more importantly, Laos was to be the main benefactor of the development. In fact, the dam is being built by a Thai construction company with Thailand purchasing 95% of the electricity for 25 years, at which point Laos PDR will finally get to enjoy the full benefits of the electricity it produces. However, given the dynamic nature of the Mekong, in 25 years it is highly likely the dam will have silted up and will be highly inefficient and expensive to run (a similar story to the Sanmenxia dam in China), stifling the economic benefit Laos PDR may expect to receive. Furthermore, the scientific arguments remain unaddressed. Phillip Hirsch of the University of Sydney predicts that the dam may result in a drop in fish stock larger than the entire freshwater catch of Europe and West Africa combined . In addition, sediment starvation downstream will have serious implications for the productivity and stability of the delta in Viet Nam. Deltas rely on a constant supply of sediment to continue aggrading in the presence of enhanced sea-level rise. By curtailing the sediment supply to these regions, there is a risk that land will be lost, productivity will decrease and the 17 million people living on the Mekong delta will need to relocate. With millions of people relying on the supply of sediment, nutrients and fish downstream, it seems somewhat irresponsible of the Laotian government to not even consider the environmental impacts of the Xayaburi dam.
Given that hydropower appears to be the best route to economic development for the countries along the course of the Mekong, and given the environmental and ecological impacts of dam construction, it appears that this part of South East Asia is facing a crucial period in time. This was one of the key issues discussed at the recent Mekong Environmental Symposium (my experience of which is detailed here) where scientists and policy makers from the Mekong region and around the globe met to discuss the pressing issues for the Mekong countries. There was agreement that any future dam construction along the mainstem of the Mekong, and its tributaries, needs to be carefully assessed if livelihoods and ecosystems are to be maintained downstream. Of particular concern was the proposed constructions in Cambodia and Laos PDR, as well as the construction of a cascade of three-dams on the 3S basins of tributaries (the Se Kong, Se San and Se Pok rivers). This is where the project I’m currently working on (STELAR-S2S) may be able to provide some help. This project is looking into sediment transport and erosion along the Mekong, and aims to quantify sediment delivery to the deltaic regions under sceanrios of future climate. These projections could be highly beneficial in understanding the impact of any dam construction which may occur over the coming years.
It appears that the future the Mekong is highly uncertain. For a sustainable future, more studies need to be conducted and dam construction needs to be managed, however with the pressure on national governments to increase economies and develop, are the Mekong countries likely to push on regardless?
Mekong River Commission (2010). “State of the Basin Report, 2010” (PDF). MRC, Vientiane, Laos
 P. King, J. Bird & L. Haas (2007). “The current status of environmental criteria for hydropower development in the Mekong Region: a literature compilation”. WWF-Living Mekong Program.
 “ICEM, 2009. Inception Report, Vol. 2: Mainstream Project Profile Summaries. MRC SEA for Hydropower on the Mekong Mainstream. Hanoi, International Center for Environmental Management.”. Mekong River Commission.
 Lanza, G.R. (2012) “Dam Threatens Mekong Ecology”, Science, 338, 1537.
 CIA world fact book https://www.cia.gov/library/publications/the-world-factbook/rankorder/2001rank.html?countryName=Laos&countryCode=la®ionCode=eas&rank=136#la
 “Laos admits work is going ahead on controversial dam”, The Economist, http://www.economist.com/news/asia/21565676-laos-admits-work-going-ahead-controversial-dam-river-elegy
It takes a couple of days, but once your body has acclimatised to the 25°C rise in temperature, the jet lag and the continuous presence of the sun, Cambodia is a great place to do fieldwork. It’s only been a few days since the STELAR-S2S advanced party arrived in Phnom Penh for the inaugural fieldwork camp and you can tell we’re all still struggling with the change from the British winter. Waking up and going down for breakfast in the hotel to be greeted by the zombie-like forms of Steve, Jules and Dan huddling around the table tells you we’ve not quite adjusted yet. Hopefully by the end of the 20 days we’ll be fully acclimatised.
Just experiencing the sheer scale of the Mekong river and understanding its importance to the Cambodian people is again something that takes a while to adjust t; not only is it the main source of food and water, but also the main transport network and a lot of peoples back gardens. It’s a beast (not a technical term, but aptly descriptive none the less). Just as an example, we visited an island in the middle of the river 10 km long and 2.5 km wide (a size big enough to hold a mid-size town). So coming from a background of gullies a few hundred meters long has required quite a recalibration of the senses.
The first few days of the fieldwork have mainly been focused on getting everything sorted for the crux of the fieldwork to come later on. Having found a boat to get us up and down the river, RV STELAR (left) and a willing driver, we set off out of Phonm Pehn looking for sites at which we can sampleriver bed, and bank material, whilst also keeping an eye out for unforeseen factors we may have to deal with over the next couple of years.
We’ve been making quite a few measurements since we’ve been here, stopping approximately every 5 km along the river. We’ve been sampling the river bed sediment using a grab sampler which is dropped off the side off the boat in and allowed to sink to the bed. A grabbing mechanism is then activated which clasps shut the container on the sampler, (hopefully) trapping a sample of the bed sediment inside. This has proved a bit hit and miss: with the strong current meaning the sampler drifts downstream without hitting the bed and the occasional failure of the grabbing mechanism.
On top of this, we’ve been taking bank material samples and floodplain cores to look at quantifying the grain size of the river banks and rates of flood inundation (and sediment deposition) on the floodplains, respectively. After sitting on the boat (which gets a nice breeze blowing in off of the river), taking a 5ft sediment core during the dry season is extremely exhausting: not only is the ground almost concrete, it’s pushing 30°C. After various trials, we’ve perfected the optimal technique (right); it has definitely brought the team closer together! The final part of the work we’re doing out here is trying to quantify the resisting properties of the river bank. This is needed to inform the river bank erosion model if we are to get an accurate representation of rates of erosion later on. To do this we use a Cohesive Strength Meter (CSM) which quantifies the threshold stress at which bank material is detached (below).
The next couple of days are taken up by meetings in Phnom Penh, set up to smooth the progress of the project over the coming years. They’ll make a nice change from being out in the mid-day sun (typical Englishmen!). After that it’s up to Kratie, 300 km north of Phomn Pehn, where we start the fieldwork proper. We’ll be making our way back down river to Phnom Pehn, covering the 300 km reach in detail and so will be doiing a lot more sampling in the mid day sun. It’s exhausting, but it’s great fun and I’m looking forward to the rest of our time out here. I expect it will look completely different when we come back out during the monsoon in August!