What Happens to a Lake When Its Dam is Removed

[Glenn MacGrady]

It depends.

"When engineers pull the plug on a dam, the lake behind it does not just quietly fade away. A reservoir is an artificial, still-water (lentic) system, and removing the barrier that holds it back triggers a rapid shift back into a flowing (lotic) river. Of course the water drains, often in hours rather than weeks, and then the real transformation begins as decades of trapped sediment, submerged tree stumps, and buried riverbed start to reappear. In the United States, more than 2,300 dams have come down since 1912, according to American Rivers . . . . Below, the process is broken down step by step, illustrated with four of the country's largest and most closely studied dam removals."

What Happens To A Lake When Its Dam Is Removed

What Happens To A Lake When Its Dam Is Removed: the reservoir drains in hours, the old river reappears, and sediment, fish, and plants slowly return.

www.worldatlas.com

 

[WoodsNWaters]

Then there are the legal issues. Who owns the land that was under the former reservoir?

A hydro-electric dam in Ellsworth, Maine, has lost it's generating license. One of several reasons is that the dam kills too many fish. The owners may be required to remove the dam. The shore has some public land, but much more private land. Who owned the land under the reservoir and who inherits that land? A recent article in a local newspaper said the resolution can be "very complex".

 

[ppine]

thanks for posting this. Very relevant for all river runners.
I have made runs on the Klamath River in California 3 times, the second largest river in California. Last trip the put in was right below Iron Gate Dam in 2023.
The effects of multiple dam removals has been dramatic in the last 2 years.
The anadromous fishery has responded quickly. Salmon have already traveled up stream past all of the dams and made their way across the enormous Klamath Lake. Fish are already spawning in the Williamson and Sprague Rivers well up into Oregon.

There were plenty of naysayers that said that this would never work. The large winter discharges in a river this big, have moved tremendous amounts of sediment downstream and out into the Pacific past the river mouth. The river already has more or less normal clarity. Big success story. More to follow. The Elwha River in Washington got the ball rolling some years ago.

 

[Glenn MacGrady]

What I don't understand, because I've never researched the subject, is what happened to the original purposes for which the 2,300 removed dams were originally built.

They weren't built as hobbies. I assume they were built for important (or seemingly important) purposes such as hydropower generation, flood control, capture of drinking water, capture of water for farming and other irrigation, improvement of navigation, and perhaps even recreation.

Did those purposes all disappear for all 2,300 removed dams, or were those purposes superseded by other means or technologies, or were those purposes never necessary in the first place.

 

[Punkinhead]

Id love to see time lapse videos of the areas recovering.

 

[Boatman53]

Some streams were dammed up for log driving in the spring.
Jim

 

[tketcham]

Did those purposes all disappear for all 2,300 removed dams, or were those purposes superseded by other means or technologies, or were those purposes never necessary in the first place.

Yes.

Many of those 2300 dams were smaller dams that had become liabilities for the current owners. Dams have a lifespan and when they get old they become very expensive to maintain and/or they no longer serve their purpose. A dam built for flood control for example, may no longer hold enough water to mitigate storm events and now is a flash flood risk if it breaches. Same is true of dams built for other purposes.

 

[Nick Pending]

Some of the dams (many of?) were put in just as economic stimulus for the area (sort of like the CCC kept some people employed during the depression), but there were many other reasons listed for a project just to help get the thing pushed through so the project would happen.

In the 1970s and '80s my parents lived on a small reservoir in Missouri, the Pomme de Terre Reservoir, the dam of which was on the Pomme de Terre River near the small town of Hermitage, north of Springfield, MO. Dam construction for "the Pomme", as it's locally called, was started in 1957 and finished in 1961, though normal pool for the reservoir wasn't reached until 1963. My father, a ranger at one of the Corps. of Engineer parks there as a summer job between school sessions teaching the rest of the year, told me that among the reasons listed for the Pomme de Terre Dam were power generation capabilities and flood control. Space and fittings were there for electrical turbines, but they were never installed because testing after the dam was operational indicated a design flaw that caused large water releases or even generating full power to inundate some of those same areas the dam was supposed to protect from flooding. One of the farms that would have been affected included the fields of the family of a girl my youngest brother married a little later on.

Then the Harry Truman Reservoir was constructed on the Osage River north of the Pomme de Terre with the dam near the town of Warsaw MO.

Construction was authorized for the Truman Dam in 1954, but not started until 1964 and not completed until 1979 because it took years to procure land, move people, towns, cemeteries, bridges, highways, etc., out of the flood zone. It actually forced the closure of one admittedly lightly used railroad line. Though one of the given reasons for the Truman Dam was flood control, it was constructed just a few miles upstream of high pool on the bigger Lake of the Ozarks downstream (dam completed in 1931, also on the Osage River), and when Truman Lake was filled it flooded the Pomme de Terre River to within just a few miles of the the dam on that river. Hmmmm... evidently a whole river system has to be flooded in order to prevent flooding?

Did you also notice I mentioned that the Truman Dam and reservoir system was authorized in 1954, which was three years before the Pomme de Terre Dam was started? Yup, flood control was a reason for the Pomme Dam even with plans already in motion for flooding most of what's there? Pork barrel politicking at it's finest! At least the Truman Dam does generate electricity as does the dam for the Lake of the Ozarks downstream. I don't know if any cows have been swept away by air conditioners in Kansas City or St. Louis. Maybe sharper pencils were available to those engineers.

As an aside, there's an old probable meteor crater that is indicated by the drainages in the upper end of the Truman Reservoir system. It's just a much smaller version of Recped's Manic 5 Costco chicken gorging trip described in another thread, though the water doesn't go full circle. You can check it out here:

Weaubleau structure - Wikipedia

en.wikipedia.org

It would be a heck of a portage to complete the circle. Carry a map and compass and a brace of pistols to protect yourself from moonshiners and other angry landowner sorts. Please don't tell 'em I sent yuh.
< Huge Grin >

 

[Gamma1214]

Some streams were dammed up for log driving in the spring.

At least locally, those were splash dams that were broken periodically to wash the logs downstream in the resulting flood. I doubt that the amount of ecological damage that practice inflicted would be tolerated today.

Did those purposes all disappear for all 2,300 removed dams, or were those purposes superseded by other means or technologies, or were those purposes never necessary in the first place.

There have been some dams removed around here because they provided water for the cooling towers of some coal-fired power plants. Now that many of those generating stations have been shut down, the dams are no longer needed.

I also know of one hydroelectric plant where the generating equipment got pretty outdated and the dam was starting to require costly maintenance a bit too frequently. That generating station shut down and the dam was removed because the government was providing cash for solar and wind generation but not for renovations of aged hydro plants.

The power company simply followed the free money into the trendy parts of the industry (and probably got paid to remove the hydro dam as well).