In Southern Vietnam The Mekong River’s natural dispersion of sediment over thousands of years has lead to the creation of the world’s third largest river delta, a triangular area of land that has amassed a shocking 700 km of coastline (Li, Liu, Saito, & Nguyen, 2017). Despite its massive size, this vast coastline is retreating at a shocking rate detrimental to the people, and and animals that call it home. Paul Liu, an Assistant Professor at N.C. State’s college of Marine, Earth and Atmospheric Sciences, and his colleagues Xing Li, Yoshiki Saito, and Van Lap Nguyen set out to determine the culprit of the shrinking delta. When trying to determine the cause of this retreating coastline the conductors of the studies specifically looked into if the excessive daming of the the Mekong River and its distributaries. The Mekong River flows through six countries in Southeast Asia on its way to the delta making it a critical resource to the communities it comes through. Traditionally the rivers main gifts to the area have been its agricultural benefits and the fisheries it supports. Recently though, a new benefit has emerged from the vast expanse of rivers created by the Mekong River. Many countries have utilized the river and its distributaries as a way to create power for their communities with hydropower dams. But are these dams destroying the land that so many call home?
The Mekong River Delta is currently home to roughly 17.5 million people and that population is expected to continue to grow over the next couple years (Li, Liu, Saito, & Nguyen, 2017). Making up that population is a mixture of life styles from the large, urban center of Ho Chi Minh City to the many rural communities that dot the landscape. The Mekong River Delta isn’t just land that people call home it is also a crucial agricultural hub for Vietnam and beyond. The low lying fertile land with ample access to the many freshwater tributaries flowing from the Mekong River has long made this a hotspot for agriculture. This fertile soil has allowed the delta to move up to fifth on the list of world rice exporters, and also it is home of the world’s richest inland fishery (Li, Liu, Saito, & Nguyen, 2017). This fishery is spurred on by the river being home to the second highest rate of fish biodiversity, which only trails the Amazon River (Li, Liu, Saito, & Nguyen, 2017). The threatening changes of decreased sediment accretion, erosion, and sea level change is putting all these fragile systems in jeopardy going forward.
The accretion and erosion of soil on the Mekong River Delta has been a known, and natural occurence for thousands of years. Coastlines are constantly shifting and morphing but the common trend is that the land area gradually increases on the delta as time passes. This explains the concern when it started to appear that the natural erosion on the coast of delta was not being replenished. The common belief was that this change could be attributed to the large increase of dams being placed on the Mekong River and its tributaries starting in the 1990’s (Li, Liu, Saito, & Nguyen, 2017). As water flows through these dams it has a tendency to pile soil on one side and prevent it from flowing through and further down the river. This disruption when carried out over many dams can have catastrophic effects on sediment movement. More dams are on the horizon as well, China, the leader in dam construction on the river now has competition from Laos, Cambodia, Thailand, and Vietnam, who all have projects in the works (Khadka, 2016). The sediment retention not only takes away from the landmass of the delta, but sediment also carries vital nutrients that aquatic life relies on (Khadka, 2016). When those crucial nutrients are retained it can have a huge effect on fish populations down stream. All these effects can become even more drastic when it comes to how climate change is also affecting coastlines worldwide. The melting of polar ice caps has continued to cause sea levels to rise. Studies have concluded that a sea level rise of close to six feet is not only very feasible, but should be expected by the end of the century (Dennis & Mooney, 2016). The negative effects of this eroding shoreline compiled with sea level rise could change the area forever.
So, Paul Liu and his team of scientists set out to study how a delta so essential to so many was being washed away in front of our very eyes. The team decided to use Landsat Images, a set of images gathered from various satellites, that spanned 43 years (1973-2015) to compare coastline changes and shifts (Li, Liu, Saito, & Nguyen, 2017). These Landsat images had been used multiple times before when studying similar coast line changes around the world, for example at the Nile Delta, the Yellow River Delta, and others (Li, Liu, Saito, & Nguyen, 2017). Using the Landsat Images allowed the team to take advantage of the Digital Shoreline Analysis System (DSAS) (Li, Liu, Saito, & Nguyen, 2017). The DSAS allowed the team to calculate the shore change rate by casting transect lines that can be used to track the retreat of the shoreline over time (Li, Liu, Saito, & Nguyen, 2017). These transect lines allowed for area to be calculated and recorded in various tables organizing segments of the coast. This hard data allowed for the comparison of the deltas size from year to year in a purely quantitative way.
The results obtained from the study confirmed what was feared that the delta was drastically shrinking in areas due to erosion. The coastline was divided into four segments to more specifically pinpoint the effects of erosion, but erosion was observed across all segments (Li, Liu, Saito, & Nguyen, 2017). The greatest rate of erosion was in segment 2 where 95% of the coastline was suffering from significant erosion (Li, Liu, Saito, & Nguyen, 2017). Segment 3 was the only coast that could qualify as being an accretion segment, but still there was erosion present in over 10% of the coast, the study also unveiled that despite there being accretion in the section the rate was decreasing (Li, Liu, Saito, & Nguyen, 2017). It was determined that the delta as a whole can now be classified as a eroding delta, instead of one that is experiencing accretion (Li, Liu, Saito, & Nguyen, 2017). Being able to quantify the area exactly through the studied led the team to determine that the delta was losing an average of half a football of land each year over the last ten years that the images were used (2005-2015) (Li, Liu, Saito, & Nguyen, 2017). Specifically the data showed that 2005 was a turning point for the delta in which erosion began to become severely detrimental for the area (Li, Liu, Saito, & Nguyen, 2017). The rising sea levels also increase problems for the freshwater tributaries of the Mekong River that flow into the ocean. The sea waters rising has increased the salinity in the freshwater inland causing rice farmers to change away from the crop (Khadka, 2015). Lost land to both erosion, rising sea levels, and increased salinity of water poses great threats for the agricultural communities in the lower Mekong Delta. These changes to the environment directly affect the poor rural farmers that rely on the rice crop to provide for there families. Also, any threat to these agricultural communities then directly affects the urban communities that rely on there resources to function.
It is noted in the study that dams may not be the sole cause of this decreasing of land area on the delta. Sediment mining in the area is believed to extract a great amount of sediment from the river and its tributaries estimated at 56-57 million tons yearly (Li, Liu, Saito, & Nguyen, 2017). Projects have also been started to change the landscape surrounding the Mekong river. The most notable has been China’s Grain for Green Project that went into effect in 1999. The Grain for Green Project’s aim is to convert farmland which can often produce excess sediment and cause floods into land that will more likely retain sediment (Li, Liu, Saito, & Nguyen, 2017). The wide adoption of this Project in the area has likely attributed to less sediment flow on the river. The burden of the shrinking delta does not sit completely on the shoulders of the dams but they are surely the main contributor to the lack of sediment that reaches the Delta. Continued research that targets the dams exactly and how effectively they retain sediment would be a useful piece to quantify the exact impact of each dam.
So going forward the question becomes what can the countries that rely on the flow of the Mekong River do to preserve the sustainability of the Delta. The design of dams makes it very hard to allow sediment to roll through them, specifically the large dams that frequent the Mekong River. A study done on the same river by researchers out of Cornell University may have found an interesting alternative to the large sediment blocking dams. The studied showed that by using multiple smaller dams they could obtain similar energy output with far less sediment retention (Wild, Loucks, Annandale, & Kaini, 2016). They were able to produce a system with smaller dams that allowed about three to four times the amount of sediment flow through then the already proposed large dam they were studying in Cambodia (Wild, Loucks, Annandale, & Kaini, 2016). Problems arise from trying to reverse the effects of the already over 100 dams that are present on the river and its tributaries. With that being said, there may be another interesting alternative that has emerged which seems to have struck a creative alternative to helping making the existing dams more environmentally conscious. These “floating solar panels” would mean attaching solar panels to the already existing dams (Cronin, 2018). This would allow the solar panels to work during the day and the dams work at night, roughly cutting the time of dam operation in half (Cronin, 2018). This would allow for natural movement of sediment, nutrients, and fish during daylight. This would have a huge effect on health of the delta and those who rely on it.
In the end the Mekong Delta isn’t the only delta in the world that is experiencing severe erosion. The Mekong Delta stands out because of the sheer numbers of dams on the river but its not alone. Delta’s at the end of the Nile, Yellow, and even the Mississippi are suffering from a lack of sediment accretion due to the retention of dams (Dankedar & Bosshard, 2014). As hydropower dams gain steam as a more environmentally friendly alternative than traditional sources of energy, it’s important to bring forward the truth about hydropower dams and how they disrupt the environment around them. Dams not only prevent sediment flow but also stop natural migrations of fish, variant levels of flow cause havoc to fragile shoreline ecosystems, and in some cases a breach can cause catastrophic flooding. Continued innovation in the hydropower field is required if we are going to continue to expand on it as an energy source and if we are going to save the world’s deltas.