When China is building DAMS, began in the history of the United States the largest dam removal project.

Across the United States have dismantled DAMS, restore natural state to rivers. But scientists point out that dismantling the intercept the Banks of the river is just the first step to restore river health.

Rogge River in the Jackson county of southwest Oregon, 126 miles from the Pacific Ocean, there is the beautiful natural scenery, just as its name suggests, rogge River, English Rogue River, Rogue has the meaning of the wild -). Prompt, cold water lightly leaped over stones, sweeping down the tree, and to move on. In the south bank of the river, Craig figure, stop, take a closer look at a gravel CongJi willow waist high. He is very satisfied. Stand three years ago, this was the Gold Ray dam (Gold) Ray Cam place like a bog draining, now it has been long out of the willow tree, whether it is planted, or natural born, all of this is a good thing. Off the coast of willow and cottonwood native species make some invasive species can only stop at the water bay. These new vegetation can cling sediment in flood season to slow the water, provide habitats for birds and insects. Walk up along the Banks of the river, but also can see small clump of cypress like green flag rooted in steep slope.

Figure, said: "we must determine which parts of the world will be the river, which is high. I think we are doing pretty well."

Mr Tusks work in a government committee Jacques rogge river valley. The committee is responsible for the dam site of a comprehensive repair and surveillance program. Since 2008, the three DAMS are removed Jacques rogge river basin, the gold ray dam is the last one. In 1904, has just set up gold LeiBa was a paling type construction; Reconstruction in 1941, the dam reach 38 feet high and 360 feet long (about 12 meters high, 110 meters long), is used to generate electricity. In 1972, Jackson county government to take over the dam and then shut down the turbine for electricity generation. Since then, the dam is only used to a small lake water, river became residents of the leisure entertainment places. But for the salmon, the dam is their another obstacle to upstream to spawn.

Demolition of a dam is very easy. Just remove the obstacle, fish can swim freely along the river, sediment can be down the river, river can restore lines in the past. Scott is white river restoration consulting company "river planning group" in the field of civil engineer, he says, despite the resilience of river is very strong, but the demolition of the dam are only the first step to repair the ecological system, there are a lot of subsequent problems, such as: the lack of vegetation, without increasing the complexity of habitat wood residues, gravel, and flood plain, grazing without barriers around the river, some will attract young fish tributary channel lack of shelter.

River planning group is responsible for the gold ray dam site of planting trees and bank slope reinforcement project. Staff should pay in addition to accumulate for nearly 100 years of garbage, including tires, trains, cars and farm machinery. Then the local original vegetation in this area, to stop the alien species invasion. For a period of time, shrub and grass will fill up the space. Now standing here, you wouldnt think had longer than a football field concrete buildings across the river.

On the list of the Banks of the army corps of engineers, more than six feet (1.83 meters) high of more than 79000, and thousands of smaller, which prevents the free flow of the river. Thomas ardito in Massachusetts, belonging to "earth island", the director of the institute of ecosystem repair center, he said: "almost all river to build the dam in the United States, I think most countries will experience a stage of development." The dam can be used to control flood, for farmland and urban water supply, power generation or entertainment. The dam is very important in the past, but now some dam has lost its function.

In recent decades, due to some dam maintenance has more than its benefits, calling for demolition of the dams voice more and more. Dismantled DAMS have different purpose: restoring waterways for fish and other wildlife, restore natural sedimentation process and the flow of nutrients, reduce the security hidden danger. Many DAMS built in the fifties and sixties of the 20th century has reached the life, this situation is particularly common in the northeast region. Overage dam pose a safety hazard, the U.S. has more than 4000 DAMS are at risk of collapse, and some now is not in conformity with the federal or state law about the provisions of the fishway.

Under normal circumstances, the demolition of the dam is lower than the cost of construction of fish ladder or to meet the requirements of the law for the maintenance. , according to environmental groups "American rivers" in the past 100 years, the United States has dismantled more than 1100 DAMS, with nearly 800 are of dismantling in recent 20 years, there are 2012 in 2012 alone.

DAMS successively removed, like domino. The United States the largest dam in the history of demolition project is underway - Washingtons Olympic national park YiErHua two DAMS on the river. Californias biggest dam removal project is in carmel river, more than SAN clemente, use fixed number of year of the dam will pass for rainbow trout laying eggs. Maines noble Scott river two DAMS is also facing demolition, the two on the chattahoochee Georgia has been removed. The klamath river flows through the Oregon and Californias four DAMS is also included in the demolition.

However, demolished almost always controversial dam plan. Local community focused on dams entertainment purposes, reservoir of beautiful scenery, but also the dam itself as a heritage; Scientists, environmentalists, indigenous tribes will recover river hydrology situation, ecosystems and fish migration channels in the first place. Rogge riverside of some of the farmers, for example, against the demolition of the dam. Is the 81 - year - old Dalton strauss said: "we lobbied hard, dont dismantle the dam, but I also try to keep the attitude of a citizen should have."

But that does not see more. Compromise is always hard to achieve, to retain or remove means a complete failure. "The river", Dennis, deputy director of the environmental restoration of huo, felt the sea, said: "in general, always solve technical problems, the biggest challenge is social problems."

At the federal, state, and local government approval dismantle dam plan before, the influence of the comprehensive evaluation. Ardito said: "in the end we always done too much research, however, after long-term demolition impact studies are few and far between. Huo, felt the sea, said: "there are two areas of lack of funds, namely after the start and end. It did not work after the demolition of the dam as part of the environment restoration."

Monitoring project spending very little compared with the demolition of the dam itself, but can help scientists to study the demolition of the short-term and long-term effects of the dam. Ardito said: "to understand the whole process of river and wetland restoration, you need to about 10 years of monitoring data, but this kind of work is very difficult to find."

"American rivers" environmental restoration, head of serena said McClane, comprehensive monitoring of dam site can be used as sample, and provide a reference for future dam removal project data. Long-term research reveals dismantled DAMS on regional ecological system and economic benefits, thus reducing the demolition of the issues raised by the project.

Sometimes some support for the demolition of the dam will also worry about dam from road-related: the sediment will damage downstream of the habitat, the threat of infrastructure, affect water quality, or release of heavy metal pollutants such as? Biological and ecological engineering professor at the university of Oregon state, darcy figure luo studied gold LeiBa river shape and the change of water level, dismantled and track the movement of sediment. She found that near the dam upstream from road-related decline, downstream increased; Upper reaches of river bank erosion occurs near the dam, deposition in the downstream of the dam is more than 2800 meters of less than.

Figure luo also studied the demolition of the dam a year or two fish and aquatic insects of geology and physical change feedback. She said: "I concern is whether ecological system will remove the dam as a disturbance factors?" according to the results, she believe the answer is no.

"American rivers," Mr Hay, felt, said although figure luo warning not according to the situation of the dam is dismantled the Pacific northwest coast to make general conclusions, but her research can still demolition some inspirations for the future. "Many people are worried about her study show that the effects of the dam, such as a large number of sediment release impact on downstream, didnt happen."

But there are still some problems, the gold ray dam swim a few Wells dry, dozen the owner of the downstream river water inlet were choked up with silt. The Jackson county is digging new Wells for water inlet blocked the landlord will provide the funding and technical support, and trucked water during the transition.

Social and economic aspects, research center of the southern Oregon Eva scilla aboutthis and Dr Has begun investigating gold LeiBa is dismantled, the influence of her query the southern Oregons visitor Numbers change, interviews with tourists and fishing, drifting wizard. Drift is a large local business. Scilla aboutthis and found that the dam site of figure 11 miles upstream fleur state park is more popular. Several companies have introduced a one-day Tours, including the original water OuDeJing downstream water rafting and exciting level 3 and level 4 white-water rafting, or impossible a few years ago such travel.

She said: "overall, and downstream of the dam site using has changed." Along the river much entertainment, including fishing, rafting, swimming, picnic, etc., especially in figure fleur region. Some fishing guide complained more turbid water after dam removal, according to the report, however, they present a tendency of increasing overall revenue. Scilla aboutthis and pointed out that the economic and health also improves fish migration channels. Most wizards have expanded the tour area, also referred to a rise in the quality of fish. Scilla aboutthis and said, "because we dont see how much negative change, (the study) can relieve people concern about other demolition project in the future."

The northwestern region of many people, rogge river dam dismantling the mean the same thing: more of the salmon. Through the 157 - mile - long river of five in rogge river and its tributaries is spawning fish is very good, namely spring Chinook salmon, autumn Chinook salmon, rainbow trout and steelhead in winter and summer across the country are increasingly rare silver salmon.

Dam block movement of local fish. Sometimes some fish can leap hurdles, but this extra cost their valuable energy. For example, savage rapids on the fish ladder is very long, there are multiple entries. Salmon often avoid it in vain to get over the dam. Seasonal water reservoir will bring to the downstream small floods, often after stranded fish.

After dam removal, every autumn, Oregon, the fish and wildlife department ichthyology Dan niek van dijk accounting Numbers as gold bay fish spawning area number. Chinook salmon soon began to lay their eggs in the new environment. Niek van dijk, said: "we are almost countless." There are often reported more healthy, migratory fish time earlier, but very careful not to make fish populations niek van dijk rich conclusion. He said: "since the dam removal, migratory fish populations has increased, but has also increased the amount of Marine fishing."

Niek van dijk said: "the greatest benefit of the project or will still water recovery for the local fish that free flow of rivers in the process of evolution." Reservoir will make fish gathered themselves together, and make them more likely to be predators or fishermen hunt. Dam caused by environment beneficial to the fish is more like deep water, still water, especially the introduction of alien species such as big black bass. "Fish agglomeration phenomenon" study investigated local and exotic species number and proportion, preliminary results showed that the gold LeiBa near the salmon and ratio are increased.

This autumn, after the dam dismantling of the birth of the first generation of salmon will return to their waters. They will be back from the sea to swim and go up, and the river is more than a century ago. Here there is no obstacle, no fish ladder. Only river, only gradually on repair of rivers.