Dear EarthTalk: Exactly How is it that dams actually hurt streams?—Missy Davenport, Boulder, Colo.
Dams are symbolic of individual ingenuity and engineering prowess—controlling the circulation of a wild hurrying lake is no tiny feat. In this point in time of environmental understanding, a lot more people are questioning whether producing just a little hydroelectric energy is worth destroying riparian ecosystems from their particular headwaters when you look at the hills with their mouths at the ocean and past.
According to the non-profit American Rivers, over 1, 000 dams over the U.S. being eliminated up to now. Together with biggest dam removal project ever in now really underway in Olympic nationwide Park in Washington State in which two century-old dams along the Elwha River are coming away. But why go to all of the difficulty and cost of getting rid of dams, particularly if they add necessary renewable, pollution-free electrical energy to the power grids?
Your decision frequently precipitates to a cost/benefit analysis taking into account exactly how much power certain dam makes and exactly how much damage its existence is doing to its host river’s environment. Removing the dams on Elwha River ended up being a no-brainer, given that they produced hardly any functional electrical energy and obstructed fish passage on a single regarding the region’s premiere salmon streams. Various other cases aren’t so clear cut.
According to the Hydropower Reform Coalition (HRC), a consortium of 150 groups concerned about the impact of dams, degraded water quality is one of the chief concerns. Organic products from within and beyond your lake that could ordinarily wash downstream get accumulated behind dams and begin to take a great deal of oxygen as they decompose. Oftentimes this triggers algae blooms which, in turn, create oxygen-starved “dead areas” incompetent at supporting river life of any kind. Also, water temperatures in dam reservoirs may differ greatly involving the surface and depths, further complicating survival for marine life evolved to deal with natural temperature cycling. When dam operators discharge oxygen-deprived water with abnormal temperatures in to the lake below, they harm downstream surroundings also.
Dammed streams additionally lack the normal transportation of sediment imperative to maintaining healthy natural riparian stations. Rocks, lumber, sand as well as other natural products build-up in the mouth of the reservoir in place of propogating through the river’s meandering channel. “Downstream of a dam, the river is starved of their architectural materials and cannot supply habitat, ” reports HRC.