Posted on July, 05 2017

Lately a lot of attention was directed to the negative impacts upstream development are causing to the Mekong delta, but Vietnam is not the only one to suffer: the ecosystems of the Mekong River in Laos and Cambodia are also deteriorating rapidly, threatening the economy and peoples’ well-being across the region, writes Marc Goichot, WWF Freshwater Lead, Greater Mekong Region.
 
Water quality is degrading quickly, floods and droughts are happening more often and are becoming more intense, fisheries are declining, river erosion is increasing at an alarming rate – and climate change is aggravating everything. Many things are contributing to these problems, including land use change, intensifying agriculture and industry, overfishing, and sand and gravel mining in the river, but large dams are the prime suspects.
 
Large dams have two key sets of environmental impacts, which in turn affect socio-economics. First, they regulate water and therefore affect the natural water flows. Large reservoirs store water in the wet season and release it in the dry season, but smaller dams, including the so-called run-of-the-river dams, also affect hydrology on shorter time cycles.
 
Second, dams and their reservoirs fragment rivers. They block the movement of fish, and keep larvae and eggs from moving downstream, affecting the life cycle of many species of fish, leading to reduction of fish stocks and sometimes species extinction.
 
The dams and associated reservoirs also reduce the sediment flows and associated nutrients from upstream to downstream. Nutrients are the first step of the aquatic food chain, thus if you reduce them you affect the entire ecosystem. Nutrients also fertilize floodplains so reducing them can have impacts on fisheries and agriculture productivity.
 
The crucial part of the fragmentation impacts is the blockage of sediment. An important portion of fine sediments (silt and clays) is trapped in reservoirs (trapping nutrients with them). While some fine sediment may still transit through reservoirs suspended in water, it is clear that coarser sediments cannot; pebbles, gravels and most of the sand are trapped and are no longer available to maintain ecosystems downstream.
 
This is a major problem as those are the grain-sizes that play the most important role in maintaining the stability of the riverbed. If they are reduced, the riverbed will become deeper; the water table follows becoming deeper as well and making access to water more difficult and aggravating drought. This also affects fisheries and the self-cleansing capacity of the river.
 
The deepening of the riverbed affects agriculture, fisheries, water quality, and also infrastructure; bridges over the Mekong River in Laos and Cambodia are at risk if their pillars are exposed by riverbed scouring. Reduction of sand and gravel also causes river bank erosion, which translates into loss of agriculture land as well as the loss of private property (e.g. houses) and infrastructures (e.g. roads).
 
Many of those impacts are already being felt, but rarely are they attributed to dams. In large rivers the impact of dams on the shape of the riverbed can take a long time to occur – up to 30-50 years – but there is no doubt it will happen as these processes are very well understood by scientists.
 
Both Laos and Cambodia are very vulnerable to all these impacts, as is Thailand. The section of the river from Vientiane to Pakse is particularly vulnerable to erosion, affecting Laos on the left bank, and Thailand on the right bank. In Cambodia, the entire river downstream of Kratie, including the city of Phnom Penh, are at risk of increased erosion with many costly associated impacts. 
 
The dangers of river fragmentation are often underestimated when the environmental impacts of dams are discussed. Proponents of run-of-the-river dams argue that these dams’ limited impacts on water regulation make them more environmentally friendly, but they do not sufficiently address their fragmentation impacts. In my view, the later are the most concerning.
 
But are these environmental impacts offset by hydropower’s benefits to the economy? Recent research has challenged the prevailing estimates of hydropower’s contribution to the economy as a whole by attempting to compare the estimated revenue generated by hydropower to the costs of hydropower’s unintended impacts. When these externalities are taken into account, hydropower turns from a net positive to a net negative for the economy.
 
It’s time to shift the paradigm and look at all the ways a healthy Mekong River can support the economy.
 
All economic sectors – including agriculture, fisheries, food and beverage, tourism, energy, construction, mining, and manufacturing from textile to electronics – depend somehow on the river. It provides affordable clean water and sand for construction (both concrete and glass are primarily sand), while cheap protein from wild fisheries is a key component in the region’s competitively low wages. Preserving the Mekong’s natural flows of water and sediment protects the infrastructure, such as roads and bridges, that all economic sectors rely upon and helps prevent flood and drought. All of this contributes to making Laos and Cambodia attractive investment destinations for a wide range of industry players.
 
When comparing all of these economic benefits to the limited revenue from hydropower generation, the true costs of unsustainable hydropower development to the wider economy for all Mekong countries become clear.
 
The way forward is to understand economic development in a much more comprehensive way. In a large river basin like the Mekong, everything is linked. What is done to advance one economic sector in one place in the basin will have consequences for the other sectors across the region. If developing one sector is done at the expense of many others, then one should question the sustainability of the development model.

The short and simple definition of a sustainable project is that everyone is better off after the project is developed – or at minimum, no one is worse off – and that no irreplaceable assets are lost, whether those be cultural (e.g. a building with high historical or spiritual value for a community) or natural (an endemic species of fish). In that frame, the siting of hydropower is key and should be considered very carefully.

The future of all Mekong river countries is at stake, yet solutions exist to ensure nobody loses.

This opinion was originally published in Thanh Nien