How many dams have there been

In most cases, the dam owner itself is the decision-maker, often deciding that the costs of continuing to operate and maintain the dam are more than removing the dam. State dam safety offices can sometimes order a dam to be removed if there are major safety concerns. State fish and wildlife offices are also often involved in the decision-making, particularly when the goals of the project include restoration of habitat for migratory and resident aquatic species.

If the dam in question is a hydropower facility, the Federal Energy Regulatory Commission can order a hydropower dam under their jurisdiction to be removed for both environmental and safety reasons. Although most rivers cannot be completely restored to historic conditions — simply because of the amount of development that has occurred on and along them — dam removal can often recreate conditions that move the river towards those historic conditions.

For example, fish are returning to historic stretches of river that had been previously obstructed on Butte Creek in California, the Souadabscook River in Maine, and the Clearwater River in Idaho, as a result of dam removals. Natural flows and transport of sediment and nutrients can help restore downstream reaches and reconnect oceans to headwaters. Communities can gain resilience to climate change by removing river barriers and allowing rivers to function more naturally.

Dams may provide a variety of benefits, including water supply, power generation, flood control, recreation, and irrigation. While dams serve a number of human needs, society has developed ways to address many of these needs without dams. For instance, flood control can often be accomplished more effectively and at a lower cost by restoring wetlands, maintaining riparian buffers, setting back levees or moving people out of the floodplain.

Updating antiquated irrigation systems and replacing inappropriate crops can dramatically reduce the need for dams and reservoirs in the arid West. Rather than plugging rivers with multiple hydropower dams, a cheaper and less environmentally harmful solution is to use existing energy efficiency technologies.

For example, the 3MW of power lost in the removal of the Edwards Dam, on the Kennebec River in Maine, could have been replaced simply by replacing 75, light bulbs with energy efficient bulbs. In addition, many dams that have been removed no longer had any beneficial use or that use was very limited, as is illustrated by many mill dam removals.

Dam removal can be expensive in the short term, but in most cases where dams have been removed or are being considered for removal, money is actually saved over the long term. Removal eliminates the expenses associated with insurance coverage, maintenance and safety repairs, as well as direct and indirect expenses associated with fish and wildlife protection e. In addition, removal often generates income from newly available recreation opportunities — including fishing, kayaking, and rafting — which may actually result in a net economic benefit.

Ultimately, it comes down to dollars. As dams age, they often require expensive maintenance to comply with safety regulations or just to continue functioning. Sometimes, environmental issues drive up the cost; for example, the Endangered Species Act may require the owner to provide a way for fish to get past the dam. Consideration for Native American tribal rights may also influence decisions over whether to keep or kill a dam.

Dam owners—who are overwhelmingly private, but also include state, local, and federal governments—have to weigh repair costs against the benefits the dam provides. The age of waterwheel-powered looms and saws is long gone, but thousands of forlorn mill ponds still linger. Others like Kendrick Dam in Vermont supplied blocks of ice. Though the surrounding community still wanted its water, the dam could no longer provide storage. For most dams, the story is more complicated.

Two dams on the Elwha River generated hydropower, but when the owner was legally required to add fish ladders—a series of small waterfalls that salmon can use to easily scale the dam—future sales of hydroelectricity paled in comparison to the repair cost. Furthermore, the neighboring Elwha Tribe had fought for decades to restore the salmon catch—half of which legally belonged to them. The owner opted to sell the dams to the federal government in , and after nearly two decades of study and negotiation, the Department of the Interior, the Elwha Tribe, and the surrounding community had agreed on a removal plan.

In September, , construction crews began breaking up the two largest dams ever removed from U. But in reality, not all rivers host salmon and not all dams are removed with explosives. Each river, each dam, and each removal are totally different, says Laura Wildman, an engineer at a firm specializing in dam removal.

When a dam disappears suddenly, the river responds violently. Even the slower removals, which take place over months or years, can have dramatic moments.

Jennifer Bountry, a Bureau of Reclamation hydrologist who helped plan the Elwha Dam removal, explains that initially the engineers would gingerly shave off a foot of concrete off the dam and wait to see what happened.

But as the removal progressed, the river was changing so fast that she had to keep a close eye on the currents as she was recording her observations. The freed Elwha River rapidly carved out a new channel, carrying with it roughly the same volume of sediment as Mt St. Helens belched out during the infamous eruption. Freshly tie-dyed t-shirts hanging from the chain link fence sway in the breeze. Summer camp is in full swing, and Samantha Woods, director of the North and South Rivers Watershed Association, a nonprofit, walks me down a shallow slope to an ox-bow stream curling through a wide plain covered in cattails.

The heavy, humid air is thick with buzzing cicadas and singing birds. Less than a year ago, this plain was a blank, wet canvas. Where the cattails stand now was submerged beneath several feet of water impounded by a foot-tall earthen dam that had stood for at least years. In , the state determined that the dam could catastrophically collapse in a flood and required the owner—the YMCA—to fix or remove it. The dam hung in limbo for nearly a decade until storm damage reignited fears of collapse.

By then, the public had started to embrace the idea that removing the dam could be a good thing for the river. Taking it out would cost half that amount. So in October of , crews tore down the earthen blockade, drained the pond, and planted native plant seeds in the newly exposed earth.

Less than a year later, the transformation to wetlands is well underway. Woods is optimistic that if one more downstream dam comes out, herring would swim up this creek for the first time in centuries. But no one knows for sure if the herring will come back.

Millions of years of evolution have seen to that. Man cannot improve on it, only destroy it. Hello Hope you doing well. A question; In dam removal project what kind of dams take into account? I mean does it include check dam which already constructed aim to trapping sediment and reducing flood peak or anything else? My family now can kayak down it. I love having the dam gone. Would like to see it on the removal list. Must continue to restore to natural state and function the rivers and streams up stream of dam removal sites.

Reading about dam removal is so satisfying.. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Jessie Thomas-Blate. Together, we can free rivers. Show your support for the national dam removal movement by signing up for opportunities to take action for rivers, clean water and the lives that depend on them.

I agree to the privacy policy. A dam is a structure built across a river or stream to hold back water. People have used different materials to build dams over the centuries.

Ancient dam builders used natural materials such as rocks or clay. Modern-day dam builders often use concrete. Manmade dams create artificial lakes called reservoir s.

Reservoirs can be used to store water for farming, industry, and household use. They also can be used for fishing, boating, and other leisure activities. People have used dams for many centuries to help prevent flooding.

The ancient Mesopotamia ns may have been some of the first humans to build dams. The oldest known dam is the Jawa Dam, located in present-day Jordan. It was built in the fourth century B. Dams provided farmers with a steady source of water to irrigate crops.

This allowed ancient Mesopotamians to feed a growing population. The Roman s were master-dam builders too. They used dams to divert water for drinking, bathing, and irrigation. One of the oldest dams still in use is the Cornalvo Dam in Spain.

The ancient Romans built it in the first or second century C. The force of flowing water creates mechanical power. People have harnessed this power for centuries with the use of dams. Small dams powered paddle wheels in pre-industrial Europe and America.

These were used to help saw logs or grind corn and other grains.