To drown a river beneath its own impounded water, by damming, is to kill what it was and to settle for something else. When the damming happens without good reason . . . then it’s a tragedy of diminishment for the whole planet, a loss of one more wild thing, leaving Earth just a little flatter and tamer and simpler and uglier than before. — (David Quammen, “Grabbing the Loop” in The Gift of Rivers: True Stories of Life on the Water)
The U.S. Army Corps of Engineers estimate approximately 75,000 dams greater than 6 feet tall are in the United States. The National Research Council estimate a total of dams in the United States to be over 2.5 million. Of all these dams in the United States, 2,450 of them are hydropower dams. All or most of the remaining dams are of no longer use for the public or the private company which constructed the dam in the first place.
Dams can change the chemical, physical, and biological process of rivers. Dams can hinder the flow of nutrients and sediments which are essential for the food webs downstream. Nearshore ecosystems and estuaries depend on the sediments and woody debris transported downstream to support the aquatic food web in these areas. Nutrients support the growth of producers which support the growth of the consumers.
Reservoirs which are created behind some dams alter the flow of water which in turn alters the behavior of the native fish. Salmon fry swimming downstream are exposed to warmer temperatures, disease and predation when they are swimming across reservoirs created by dams.
There are three primary reasons to raze a dam. Razing dams which are no longer serving a function can help re-establish the surrounding ecosystems, protect the citizens living downstream in case of a breach, and for economic reason because tax payers are usually the ones who are paying to keep these dams from causing in harm to the public.
Removal of dams can help increase genetic diversity of aquatic organisms as well as increase species distribution which both can help increase the chances of survival for some of our endangered and threatened species. Fish which migrate up and downstream as part of their life cycle will be able to reestablish their populations and the ecosystems which depend on these fish can also recover. The removal of the dams on the Elwha River in Washington has allowed salmon to once again travel upstream to spawn. Salmon are a keystone species for the ecosystems they travel through. Nutrients from salmon carcasses are passed on to scavengers such as eagles and bears and to the algae which feeds the zooplankton that is fed upon by salmon smolts as they travel downstream to the ocean. Besides salmon, sturgeon, paddle fish, American shad, and American eels migrate up and downstream.
Some dams were constructed to help with flood control or provide irrigation water for agriculture. Flood control can be accomplished by restoring wetlands, maintaining riparian buffers, and of course moving people out of the floodplains. Agriculture irrigation techniques can be update to more efficient irrigation equipment in addition to planting appropriate crops for the region. Water-thirsty crops should not be planted in arid regions. There are some genetically engineered crops which can tolerate drought conditions and they do well in arid climates.
As of today, thousands of unnecessary dams have been removed from our rivers in the United States. It is a group effort to identify the dams for removal, getting approval, investigating the environmental impact, organizing all the stakeholders, and so on. But this determination pays in the end for the environment and the people.
Wonderful how completely everything in wild nature fits into us, as if truly part and parent of us. The sun shines not on us but in us. The rivers flow not past, but through us, thrilling, tingling, vibrating every fiber and cell of the substance of our bodies, making them glide and sing. The trees wave and the flowers bloom in our bodies as well as our souls, and every bird song, wind song, and; tremendous storm song of the rocks in the heart of the mountains is our song, our very own, and sings our love. — (John Muir, Mountain Thoughts)
Note: photo by Steve Ringman of Seattle Times