Dams! Bad for us and the environment!

The latest dam tragedy in Brazil involved the rupture of a mine tailings dam in Brumadinho, in Minas Gerais (MG) state. Another such dam burst in 2015 in Mariana, also in MG. The loss of life, livelihoods and the environmental damage are overwhelming. Yet mining operations continue with outdated models for tailings containment dams, many of which are decades old, their monitoring flawed or their problems just ignored.

During my Freshwater Biology classes in November 2018, I reminded my students of the tragedy in Mariana three years ago and of the human and environmental costs that are still being counted ’till today. Whether large or small, and regardless of their purpose, dams will always have negative impacts. These may be socio-economic, cultural, environmental, architectural and geomorphological, occurring on large or small scales depending on the size of the dam.


The Pimentel dam (Belo Monte project) under construction in 2014, on the Xingu river, Brazil.

There is growing support for abandoning dam models for hydropower, due to the much greater social and environmental costs relative to the benefits of the dam. There is much information detailing the personal suffering, hardship and environmental damage created by dams in Brazil, especially in the Amazon region. Yet dam planning and building continue and even so-called sustainable dams generate impacts, and opposition to their construction.


Comparison of the Volta Grande, on the Xingu river, Brazil in 2000 (left) and 2017 (right). Image credits: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. See here for more information on these images.

On a much smaller scale, my PhD candidate Lenita Sousa da Silva looked at the impact of small reservoirs for agricultural use on water quality and macroinvertebrate diversity. Although small in size, these reservoirs are numerous and are often created on headwater streams, which are important for biodiversity and as sources feeding larger rivers. Lenita found large reductions in macroinvertebrate diversity, especially of sensitive insect taxa in the dammed streams in comparison to streams without dams. In the reservoirs, there were declines in dissolved oxygen and pH, and increases in conductivity, temperature and turbidity, along with increasing dominance of Diptera and Annelida.


Well conserved riparian habitat in a low order stream near Bragança, Pará, Brazil.

Currently over 60% of Brazil’s energy comes from large hydropower plants. As climate change takes its toll on rainfall and river discharge, new thinking is required globally to diversify energy sources and integrate hydropower with other renewable energy sources. Agricultural practices need to take into account aquatic habitat conservation. It makes perfect sense to protect water sources on farmland! The mining sector needs to rethink its policy on tailings disposal and better develop safe storage and sustainable reuse. The tragedies of Mariana and Brumadinho must not be allowed to happen again.

Update: The NY Times published an editorial on the Brumadinho dam tragedy on 31 Jan 2019, which provides supporting details for much of the above.

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