Bye Bye Elwha...

Large dams cause extinction of fish and other aquatic species. The river's flow is altered by a dam, and this changes the ecosystems downstream where the river no longer flows, or is greatly reduced. Because of the impact of dams, birds must find new habitat, forests and wetland loss, farmlands depleted, and coastal deltas erode. A dam holds sediments back preventing them from getting to ecosystems downstream, and replenishing them naturally. When the normal sediment load of a river is unnaturally depleted, it erodes the river bed and banks downstream, causing bridges and other structures along the banks to be destablized. The riverbed becomes deeper, and this causes lower groundwater tables along the river, which can deprive local vegetation and affect wells that are in the floodplain. This also may mean crops will require more irrigation where before it wasn't necessary. The riverbed habitat is reduced for invertebrates and affects fish that spawn in them.

There is a hydroelectric dam that is being talked about in the news lately is the Elwha Dam. This hydroelectric dam west of Port Angeles Washington, is mostly contained within Washington’s Olympic National Park. Concrete structures of the dam have reduced the wild salmon spawning population from 400,000 to about 3,000. Under the Endangered Species Act, three salmon species native to this river, chinook, steelhead and bull trout, are listed as threatened. Tribal litigation, and environmental groups have been pushing for dams to be dismantled. They will dismantle the Elwha dam and another further upstream, the Glines Canyon Dam in order to restore the habitat needed for these types of native salmon to get upstream to spawn. In the USA, 241 dams have been dimantled in about the last 5 years. Many used to power things like textile mills or paper mills back during the turn of the 20th century. The Elwha is the largest demolition of a dam in American history. Once these waterways are returned to their natural state, hundreds of thousands of salmon in the river will provide nutrients to trees growing along the banks, and provide food for orcas in Puget Sound. Not to mention that people will someday again be able to fish for salmon. The project manager for the removal of the Elwha is figuring it will be 25 to 30 years for the river to return to a natural state. This restores the ecosystem from mountain to sea.

They are saying that dam removal provides the most restoration for the money spent to make it happen. Dam's provide electricity, but the environmental costs are very often far too high to make it worthwhile. Perhaps there are more ecologically sound ways to tap the potential of hydro-power, but it seems the consensus is that huge dams have not worked out.

http://www.internationalrivers.org/node/1545

http://bangordailynews.com/2011/09/17/environment/dam-removal-in-wash-part-of-growing-movement/?ref=latest