River Currents: Defunct dams still damage rivers

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We have been reading and hearing a lot about dams lately. There is the recent story about rehabilitation of the Bennington, VT dams, the proposed purchase of the 14 hydroelectric sites by Green Mountain Power, the ongoing fuss about whether Vermont should buy the hydroelectric dams in the main Connecticut and Deerfield Rivers. There are the recent removals of two dams from the Wells River and one from the Third Branch of the White River.

There are more than 1,000 active and remnant dams in the four state Connecticut River Watershed. Dam building has gone on since the arrival of Europeans in the 1600s but with most built since 1850. Few tributary rivers or streams in our watershed regardless of size have escaped dam building. Now that our use of waterpower has moved away from direct waterpower to electric generation only a handful of these 1,000 dams, serve any economic, safety, or social function.

When people read or hear articles about removing dams, they react with statements like, "What about all that silt behind the dam; won't it smell and look ugly if the dam is removed?" or "Doesn't that dam help stop flood waters?" or "Can't we rebuild it and produce electricity?" These are mostly myths and do not balance the scales between the value to society and the harm to a river caused by dams, especially derelict dams.

Dams that have no societal value still block the migration of fish upstream as the fish try to reach spawning habitat. People mistakenly think only of anadromous fish like the American Shad or Shortnose Sturgeon when they think of migrating fish but all species of trout and several species of bass migrate from larger rivers like the Connecticut River up smaller tributaries to search out the right habitat for successful spawning. Dams on these tributaries block their migration and diminish the ability of nature to stock our streams free with our resident fish.

One of the biggest negative impact all dams have on water quality is heating up the in the open wide slow moving reservoir behind the dam. As the temperature of water rises, the levels of dissolved oxygen decline. It is a simple matter of the physical properties of water and oxygen. Not only can low levels of dissolved oxygen stress or kill all of the aquatic species in the reservoir but also the water that flows through the dam can affect the river itself for miles downstream.

What about the myths mentioned earlier like rehabilitating a dam for power generation. Old dams are expensive to rehab and usually require a complete rebuilding, the cost of which is way more expense than the power produced would ever pay for.

Over the last decade, dam removals have taken place all over America and real life experience shows that those mud flats once you remove the dam turn into natural riparian zones with plants and wildlife in as little as one growing season.

Dams other than flood control dams do not stop floodwaters. If water flows over the crest of a dam during normal flow conditions, there is no flood storage capacity. Communities have found that removing old dams has actually eased flooding conditions, especially during ice out events because the river flows more naturally. The trapped silt behind a dam uses up water storage space leaving virtually no flood storage capacity. That silt covers and destroys the open cobble habitat on the bottom of the river that all aquatic species need to survive, meaning no flood storage, and destroyed habitat.

Remnant dams not only do not stop floodwaters, they can do damage especially if the sediment behind the dam is a slurry of water and sediment. Even old dams hold significant amounts of this mix of water and slurry behind them and as dams deteriorate the odds increase that they will collapse under the stress of high water. If the owner does not invest the money to maintain a dam, Mother Nature will eventually take it out releasing the fury of that slurry mix.

New Hampshire and Vermont were concerned about dam safety as the remnants of hurricanes came through our area dropping over a foot of rain in some areas. According to a quick survey of information provided by the Dam Safety offices in the past 10 years, in Vermont 11 dams have failed in the Connecticut River Watershed, four have failed in NH.

So if you think about derelict dams, consider the damage any dam does to the riverine ecosystem. Unless the dam has an important economic or social function, removal of the dam is the best bet to reduce dam owner liability, increase public safety, and help the river. If we do remove a dam, we end up with a healthier river and you will not need to worry about the dam giving way the next time we have high water in our rivers.

David L. Deen is the River Steward for the Connecticut River Watershed Council. CRWC is celebrating over 60 years as a protector of the Connecticut River. The opinions expressed by columnists do not necessarily reflect the views of the Brattleboro Reformer.


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