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Aug. 23 was National Hydropower Day sponsored by the industry so you may hear or have heard something about hydroelectric dams. While listening to any "First Renewable" spiel there are a few other considerations about dams to keep in mind.

Few tributary rivers or streams regardless of size have escaped dam building. There are more than 1,000 active and remnant dams in the four state Connecticut River Watershed alone. Dam building has gone on since the arrival of Europeans here in the 1600s but with most built since 1850. Now that we have 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 about removing dams, they react with things 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?" Except in unique circumstances these are myths and do not balance the scales between the value to society and the harm to a river caused by dams.

What about the myth of 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 repay.

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 or slow down floodwaters. If water flows over the crest of a dam during normal flow conditions, that dam has 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.

Trapped silt behind a dam uses up water storage space leaving virtually no flood storage capacity AND that silt covers and thereby destroys the open cobble habitat on the bottom of the river that all aquatic life need to survive, meaning not only is there no flood storage but a significant loss of aquatic habitat.

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Although dams do not actually fulfill the myths, they still block the migration of fish upstream to reach spawning habitat. People mistakenly think only of anadromous fish like the Atlantic Salmon, 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 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 water 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.

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 are 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 12 years, in Vermont 11 dams have failed in the Connecticut River Watershed, four have failed in N.H.

So if you think about the myth of hydropower brought on by the Hydro Day celebration think too about the damage ALL dams do to a 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.

David L. Deen is a board member of the Connecticut River Valley chapter of Trout Unlimited and an honorary trustee of the Connecticut River Conservancy. The opinions expressed by columnists do not necessarily reflect the views of the Brattleboro Reformer.