By Alan Hewett, Trust For Nature Covenanter
The recent debate about increasing the size of the Buffalo River dam brings into question whether there is a future for any new dams. In recent years the negative impact of dams has become well known. Numerous publications in global scientific literature document the adverse effects of dams on river and estuarine ecosystems. Most countries have stopped building dams, decommissioned existing ones, while others have been forced to divert valuable resources into fixing problems caused by them.
Rivers are a vibrant source of energy but dams stop this. They trap silt and sediment at rates of between 0.5% and 1% of a dam’s storage capacity. By restraining sediment upstream dams accelerate erosion downstream. Dams starve the current of a river and disrupted and altered water flow causes riverbed deepening and soil is scoured from river banks. Riverbed deepening or incising also lowers water tables.
Radiant heat from the sun evaporates water at a huge rate. Annually, heat consumes between 5 and 15% of earths stored freshwater. Of course climate change is exacerbating this problem.
Dams can alter the chemistry and biology of rivers. Warm water and lower oxygen content boosts invasive species and algae blooms. They also block fish migrations and kill native aquatic life. We have seen the disappearance of birds in floodplains and huge losses of forest, wetland and farmland.
Dams are supposed to mitigate flooding but they dramatically affect floodplains by reducing the capacity of upstream watersheds to absorb and control the sudden impact of extreme weather events.
There is even evidence that because of the shift of water from oceans to reservoirs the earth’s daily rotation has increased. This is because there are over fifty thousand large dams in the world today.
The construction of the Three Gorges dam in China demonstrates the problems associated with huge dams. Hailed as a magnificent engineering feat this project has been beset with difficulties. The cost has been $37 billion and rising. It has caused landslides, damaged infrastructure, created ecological destruction, failed to mitigate flooding, affected water tables and displaced over a million people.
Dams are built for the wrong reasons. They are often constructed for political and economical purposes with little regard for the environmental damage they cause and the long term effects on the lives of people.