Dams disrupt this ecology.
Share by Email We remain desperately dependent on water for our survival. With seven billion of us now needing water, agriculture, industry and to generate power, the human demand on global water supplies has never been greater.
And much of this is at the expense of the other water users on this planet — all species need water, and ecosystems around the world are suffering from the decline in supply.
An even tinier proportion hangs in the atmosphere as clouds and rain. Since ancient times people have found many ways to store water — from trapping roof run-off to underground monsoon storage. But over the past two centurieshumans have carried out The effects of river damming on the planet earth on an increasingly grander scale.
Dams are a great way to store water for release during drought, to modulate damaging floods, and to provide electricity by passing falling water through turbines. In the US, there are more than 85, damsstoppering large and small rivers, and in most cases utterly transforming natural flow.
The most famous of these, the Hoover Damconstructed in the s, is largely responsible for the fact that the mighty Colorado River no longer reaches the ocean. Dams, for all their attractive benefits, are saddled with an overflow of negative impacts. Creating a reservoir means a large area must be flooded — often prime riverside land.
Communities may lose their land, houses and culturally important sites such as ancestral burial grounds, or a landscape that carries strong meaning for them. Environmentally, the new reservoir can be a haven for wildlife, especially birds; however, inappropriate flooding of vegetation can cause greenhouse gas emissions and poison the water for fish.
Also, the dramatic rise and fall of water levels during dam releases — sometimes of several metres — is too extreme for plants and animals to cope with, resulting in dead zones around the shores of reservoirs. Fish that lay their eggs in the shallows among submerged tree roots, for example, may find a few hours later that those sites are high and dry with the eggs desiccated.
Downstream of a dam, the seasonal floods that revitalize wetlands and fertilise paddy fields cease. The flow may be so reduced that farmers cannot irrigate their fields and streams are no longer navigable.
In many cases the upstream-downstream demands straddle national borders leading to conflict over precious water, disputes have been ongoing between India and Pakistanand Turkey, Syria and Iraqfor example.
They also prevent fish migrations up- and downstream, and dams are a barrier to sediment flows. Instead of being flushed downriver, sediments get backed up against the dam walls, which damages turbines and causes the reservoir level to increase over time.
Downstream, though, the effects of losing nutrient-rich sediments is far more problematic. The fertility of the entire system can be affected, with soils lost during seasonal rains not being replaced.
Perhaps the most problematic result of this loss of sediment replenishment can be seen in deltas, often host to large cities, which are literally sinking into the oceans.
Groundwater is being extracted to feed the city — in part because the river volume is no longer adequate to meet the need — causing the urban weight to sink, and sediments washed away by the ocean are no longer being replaced.
The result is sea level rise in cities from Shanghai to Alexandria. Some countries, such as Chile, which is planning to dam Patagonian rivers, and Laos, which plans to dam the Mekong, rely on energy imports and so hydro is a very attractive domestic option.
The economic benefits can be huge. The dam has been an outstanding economic success, bringing improved harvests from better irrigation despite drought conditions, hydropower and flood protection worth billions of dollars. So if we accept that many controversial dams are going to be built, how can we limit their damage?
Jamie Skinnerwho was senior advisor to the World Commission on Dams, and now heads the Water division at the International Institute for Environment and Development, suggests the answer might be to issue dam builders with limited-length licences.
The reason many dams are being removed there now, is that their licences have expired and the dams would no longer pass the more stringent environmental planning regulations," he says. Acceptable impact Removing the permanency of dams would make them more palatable to environmentalists, especially if licences were only granted with the proviso that the firm could afford to remove it in 30 years.
The problem is that in many countries, poor governance and corruption mean that such agreements could be worthless. Even in the US, where companies are legally obliged to put aside funds for environmental clean-ups, it is often the state that ends up paying.
Limited lifespans are sensible for another reason too — climate change is altering rainfall patterns around the world, leaving many dams economically worthless.
Essentially, Skinner says, dam planning needs to be a participatory process. The scientists can analyse the different engineering options and their power and environmental outcomes, but it is down to society to decide what constitutes an acceptable impact.
Putting in gated spillways makes for a more regular flow that is less damaging to ecosystems, for example, but reduces power output, so the dam managers will make less money.
Equally, if we, as an international community, decide that some environments are simply too precious to dam, then we must offer compensation to those countries for their loss of potential power generation, and provide realistic alternatives for economic development.
If you would like to comment on this story or anything else you have seen on Future, head over to our Facebook page or message us on Twitter.The Amazon River Basin, which contains 20% of the world’s freshwater and covers more than million square kilometers, is being threatened by hydroelectric dams.
As every river is unique in terms of its flow patterns, the landscapes it flows through and the species it supports, so the design and operating pattern of every dam is unique, as are the effects the dam has on the river and its associated ecosystems.
Three Gorges Dam crosses the Yangtze River in Hubei province, China. It is the world’s largest hydroelectric power station by total capacity, which will be 22, MW when completed.
During the waning days of August , workers in northwestern Washington State finished dismantling the Glines Canyon Dam on the Elwha River; the largest dam removal project in U.S. history. Mar 03, · These effects are several hundred times smaller than natural variations in Earth's motion, Dr.
Chao said in an interview, and they pose no danger to people or the global environment. Avatar and the Damming of Planet Earth. Kayapó warriors, Xingu River, Brazil. Terence Turner. The Belo Monte Dam on the Xingu River in the Amazon would flood about square kilometers of land belonging to the Kayapó Indians and other indigenous peoples.
Belo Monte is just one of more than dams planned in the Amazon region.