The reason is that they migrate up and down rivers. Salmon are famous for their long journey. They travel hundreds of kilometers from the sea up the rivers to reach spawning grounds, where they lay their eggs. Freshwater eels also travel a long way to reproduce. And a lot of other fish species migrate just to search for food. Migration ends as soon as something like this shows up: a dam. Without help, fish are unable to reach the upper level. And they might not survive being washed down with the rushing water from the upper to the lower level.
Conservationists might come up with a solution like gathering fish on one level of a dam and transporting them to the other level - by monorail. This is what actually happens at the Hwacheon Dam in South Korea. The dam interrupted an important fish migration route when it was built in Fish ladders are more natural. They offer an alternative route from the upper to the lower level and vice versa, allowing fish to overcome the man-made obstacle themselves.
Though manmade, fish ladders don't have to be elaborate, expensive constructions - they can be small and simple, like this one. When the weir, dam or lock is economically important and quite big, the fish ladder will look very impressive. This one in Geesthacht near Hamburg, Germany, on the river Elbe, is meters 1, feet long. It is the biggest fish ladder in Europe, consisting of 45 interconnected pools that the fish have to pass through. Fish ladders can take the form of spiral staircases.
Fish work their way up from one pool to the other. This construction, though, needs less space than the usual kind of fish ladder. An added benefit: the roundish pools prevent the fish from hurting themselves in the course of their journey. One of these spiral staircases for fish is to be found at a hydropower station near Kiel in northern Germany. Looking like some futuristic industrialstructure, it is meters feet long, consists of 36 pools and covers an incline of 3 percent.
Eels are weak swimmers, they just slither up- and downstream. They need special eel ladders: watery, ascending ramps with brush-like structures on the ground. Special rest areas allow them to have a break during their climb. Eels' ladders are often built alongside ordinary fish ladders. Climate change and rapid population growth are among the reasons for rising water insecurity.
Mini hydropower plants are springing up all over the small Balkan state of Montenegro. The government says it's part of a renewables drive but activists and locals argue the plants are destroying their "lifeline. Displacement and extinctions have sparked fury at large dams, but many see them as vital for clean energy and water. Visit the new DW website Take a look at the beta version of dw. Go to the new dw. More info OK. Wrong language?
Change it here DW. COM has chosen English as your language setting. COM in 30 languages. Deutsche Welle. Audiotrainer Deutschtrainer Die Bienenretter. Environment Five ways mega-dams harm the environment As the reservoir behind a new dam on the Nile River fills up, DW examines the ways such mega-dams hurt the environment, and looks at a few alternatives. Dams alter ecosystems Water is life — and since dams block water, that impacts life downstream, both for ecosystems and people.
Although sturgeon survived the dinosaur age, they may be wiped out by humans. The rare Tapanuli orangutan is threatened by a dam in Sumatra. Living Planet: Water — a limited resource. Tackling the growing threat of water conflict Climate change and rapid population growth are among the reasons for rising water insecurity. In the Balkans, locals fight to save their wild flowing rivers from hydropower Mini hydropower plants are springing up all over the small Balkan state of Montenegro.
Dams: Clean power, sullied legacy Displacement and extinctions have sparked fury at large dams, but many see them as vital for clean energy and water. Video explainer: Blue gold — the dwindling resource of water. A visit to Ethiopia's controversial Nile dam.
Mekong River threatened by dams and climate change. Impressive though it may be, Paradise, like other large dams, is a mix of good points and bad. For some people, the bad prevail.
High among the complaints has been that the rationale behind it was political. In the s, the idea of a dam on the Burnett River was dismissed as uneconomic, but former Queensland Premier Peter Beattie made it an election promise in But nothing has galvanised public opinion more than the plight of the endangered Australian, or Queensland, lungfish. Among the last of a group that lived million years ago, this once-abundant fish is restricted mostly to the Burnett and Mary rivers.
Biologists believe Paradise Dam has had, and will have, serious consequences for it. Declining water consumption in most of Australia has stalled dam-building in recent years.
But not in south-east Queensland. There, the population is set to soar from 2. South-east Queensland consumes about , ML a year. The Queensland Government says that by t he region will need , , ML more, even with water restrictions. Prodded by drought but committed to economic growth, the government has assembled a mix of measures to provide the extra water. Among them are recycling, desalination, raising some existing dams and building two new ones — Traveston Crossing on the Mary River, and Wyaralong nearer to Brisbane.
Peter Beattie said new dams were unavoidable and his successor, Anna Bligh, concurs: the dam at Traveston Crossing looks likely to go ahead. Dave seems to delight in such engineering challenges. With a sweep of his arm, he shows where the dam would sit, stretching 1. QWI would build the dam in two stages. The dam wall would be RCC, Dave says, and at its western end it would merge with an earth-and-rock embankment.
Since one aim of the dam is to limit flooding in Gympie, 20 km to the north, the spillway would have six floodgates. QWI aims to build the dam to Stage 2 height immediately so that the only extra work needed later to raise the water level by another 8.
As with Paradise, there was talk of political expediency, but the government insisted the looming water crisis allowed no choice. As in the Burnett, the lungfish is central here. A decision based on the final Environmental Impact Statement is due in mid Assuming all the initiatives to mitigate environmental impacts eventuate, the future may indeed be rosy after Stage 1. The EIS deals only with Stage 1.
About Stage 2 — odd years down the track on current plans — it says little. So Stage 2 remains an unknown: deepening the reservoir by 8. QWI acknowledges that stress, depression, social withdrawal, community disintegration and deep mistrust have resulted but says not everyone has suffered.
By late , QWI had reached sale agreements for 65 per cent of the land it needs. Many people who sold have leased back their former properties and may continue to live on them for a time. Glenda breeds cattle on 68 ha beside the Mary about 1 km upstream of the proposed dam site.
Her house and land would vanish under water at Stage 1. She grew up in the area and as a child fantasised about living beside the Mary. Then I bought it off him and it was only last year that I finally paid everything off. And sadness and tears and frustration because I believed the process of water resources planning should have involved the community and some warning.
Other anti-dam protest signs dot the Mary Valley. Amazon Prime uses similar tools to make sure your order gets to you within the promised two days. Airlines use similar algorithms to gauge how much they can overbook and still have enough seats on their planes for all the passengers that show up. However, we are applying these methods in new ways to optimize our use of natural resources while minimizing our harm to the environment.
No amount of clever design will eliminate the impact that dams have on freshwater ecosystems. Fine-tuning the flow of water downstream, as we propose, will not single-handedly address how dams block fish movement, create reservoirs that emit striking amounts of methane into our atmosphere , and promote invasive species that thrive in altered freshwater environments.
But we and other scientists are working to minimize the harmful environmental impacts of large dams while recognizing that modern society relies on these structures. The views expressed are those of the author s and are not necessarily those of Scientific American. William Chen is a mathematician, ecologist, and environmental writer based in Seattle.
Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital.
Credit: timthefinn Wikimedia We wanted to know: Is it possible to have a triple-win of meeting agricultural water needs, benefiting native fish species, and deterring invasive fish species? Perhaps we can have our water and drink it, too. Get smart.
0コメント