Dam construction impacts biodiversity, fishery resilience, forests, and natural water flows. In addition, International Rivers estimates that dams contribute to 4% of global warming due to the production of greenhouse gases from rotting vegetation in reservoirs.
Several dams planned in Burma are located in areas with biodversity of global value and which have not yet been properly surveyed. Dam reservoirs will inundate these biologically rich areas while the resulting human displacement will impact remaining habitats. The rivers themselves are also repositories of immense biodiversity; for example the Salween River has 143 fish species, 47 of them endemic.
The flood areas of the Weigyi, Hatgyi, and Dagwin dams lie fully within the Kayah-Karen Montane Rainforest ecoregion, globally recognized as an area of outstanding biodiversity. A 2008 study of the Khoe Kay bend in the Salween River near the Weigyi dam site documented 194 plant species and 200 animals, 42 of which are considered endangered and including unknown and endemic species.
The Tamanthi dam will inundate vital habitats of globally endangered large mammals like tiger Panthera tigris, elephant Elephus maximus, and the endemic Myanmar’s Roofed Turtle Kachuga travittata will become globally extinct as no other site is for this species is currently known.
Large dams destroy ecosystem integrity, fragment riverine ecosystems, isolate populations of species living up and downstream of the dam, cutting off migrations which can contribute to inbreeding from smaller genetic pools. Dams inundate riverine habitats upstream and alter seasonal flow regimes and natural sedimentation processes downstream. In addition, dams can have direct impacts on fish migration routes and access to spawning grounds.
Dams in Burma threaten to flood some of the world’s last remaining rainforests. Between 1990-2005, Burma lost 18% of its forest cover, one of the highest rates of deforestation in the world. In addition to inundation, the road building and displacement put further pressures on forests by increasing logging activity and human habitation in previously untouched forest areas.
In addition to blocking migration routes so that fish cannot reach upstream areas to spawn, the downstream impacts of dams on fisheries are also severe. The number of fish species decline due to dams: for instance, according to the Southeast Asia Rivers Network, 50 of 100 species disappeared and the remaining species dropped in numbers after the Thai government built the Pak Mun dam in the country’s northeast.
Altered water flows
Dams alter natural flooding cycles, disrupting the replenishment of water and nutrients to wetlands and floodplain areas downstream, impacting agricultural productivity and fish catches. Especially during the filling of reservoirs upstream, the flow of fresh water downstream may be reduced. In delta areas, this may cause salt water intrusion, altering estuarial ecosystems and potentially devastating agricultural crops. Unnatural changes in water levels can also disorient migratory species, impacting fish populations and ultimately affecting species survival.