SAXTONS RIVER — We have been reading and hearing a lot about dams lately.
All in the news recently: the rehabilitation of the Bennington 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, the recent removals of two dams from the Wells River and one from the Third Branch of the White River.
More than 1,000 active and remnant dams remain in the four-state Connecticut River Watershed. Dam building has gone on since the arrival of Europeans in the 1600s, but most have been 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 serves any economic, safety, or social function.
When people read or hear articles about removing dams, they react with questions 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 questions are mostly premised on myths and do not balance the scales between the value to society and the harm to a river caused by dams - especially derelict dams.
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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.
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One of the biggest negative impacts any dam has on water quality comes as the water heats up in the open, wide, slow-moving reservoir.
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 the aquatic species in the reservoir, but the water that flows through the dam can also 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 expensive than the power produced would ever pay for.
Over the last decade, dam removals have taken place all over the United States, and real-life experience shows that once you remove the dam, those mud flats turn into natural riparian zones with plants and wildlife in as little as one growing season.
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Unless a dam is specifically built for flood control, it will 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.
Remnant dams not only do not stop floodwaters, they also can do damage, especially if the sediment behind the dam mixes with water and turns into a slurry. 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.
Officials in 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 New Hampshire.
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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 the waters rise.