Do dams help – or damn – Mother Nature?

But dams affect many ecological aspects of a river. Rivers depend on the constant disturbance of a certain tolerance. Dams slow the river and this disturbance may damage or destroy this pattern of ecology. Temperature is also another problem that dams create. Rivers tend to have fairly homogeneous temperatures. Organisms depending upon a regular cycle […]

But dams affect many ecological aspects of a river. Rivers depend on the constant disturbance of a certain tolerance. Dams slow the river and this disturbance may damage or destroy this pattern of ecology. Temperature is also another problem that dams create. Rivers tend to have fairly homogeneous temperatures. Organisms depending upon a regular cycle of temperatures may be unable to adapt; the balance of other fauna (especially plant life and microscopic fauna) may be affected by the change of oxygen content.

Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks and sand bar erosion, among other problems. Experts say a large dam can cause the loss of entire ecospheres, including endangered and undiscovered species in the area, and the replacement of the original environment by a new inland lake.

Depending upon the circumstances, a dam can either reduce or increase the net production of greenhouse gases. An increase can occur if the reservoir created by the dam itself acts as a source of substantial amounts of potent greenhouse gases (methane and carbon dioxide) due to plant material in flooded areas decaying in an anaerobic environment. Large lakes formed behind dams have been indicated as contributing to earthquakes, due to changes in loading and/or the height of the water table.

The impact of dams on human society is also significant. For example, the Three Gorges Dam on the Yangtze River in China, is more than five times the size of the Hoover Dam (U.S.) will create a reservoir 600 km long, to be used for hydro-power generation. Its construction required the loss of over a million people’s homes and their mass relocation, the loss of many valuable archaeological and cultural sites, as well as significant ecological change.It is estimated that to date, 40-80 million people worldwide have been physically displaced from their homes as a result of dam construction.

The Kafin-Zaki dam project (see main story) has been a controversial one as well, with Yobe State government kicking against it for a number of reasons. A recent report in the Guardian UK credited to the Worldwide Fund (WWF) says dams are destroying important sources of water and causing economic disruption, despite having been designed to provide cheaper power and support irrigation systems. It reads in part: “Part of the problem is that dams can destroy wetlands, which hold water like sponges and cannot be replicated by manmade storage facilities.”

“The world’s ailing rivers and the communities that depend on them face a bleak future without prompt action,” the WWF also said in a 15-page report, which assessed the environmental impact of six dam projects around the world. As well as flooding valleys, dams destroy fisheries and threaten endangered species. “Bad dams and bad economics are apparently still alive and kicking,” said Ute Collier, the author of the report. “As the energy and water crisis tightens, we need to ensure that we choose the solutions with the least environmental damage and the greatest social benefits.” A £17m dam in Belize was designed to reduce electricity imports, but local people have seen prices rise since its completion, the report said. It also has flooded 1,000 hectares (2,500 acres) of pristine rainforest.

Globally, there are 400 large dams under construction and hundreds more planned. According to the WWF report 60% of major rivers have already been fragmented and up to 80 million people displaced. Alarming information, indeed.