Dams are some of the world’s most impressive feats of engineering.
In the US, there are over 90,000 of them that generate electricity, control flooding and
supply water to surrounding communities.
Like the four dams here along the Klamath River stretching across the Oregon-California border.
But there’s a big dam problem.
These structures aren’t so great for the river’s fish or water quality.
After more than a decade of debate over money, ecology and salmon, officials called for a
drastic move: the demolition of all four dams.
It'll be largest river restoration and removal project that's ever been undertaken.
Now if you thought that building a dam was tough, wait until you hear how to take one
down.
The Klamath River is known for its stunning scenery and wildlife. It flows more than 400km
through parts of Oregon and California and drains a basin covering 31,000 square km.
At one stage, the river was home to the third largest salmon population on the West Coast,
providing a vital resource to local indigenous groups.
But that all changed when these hydroelectric dams were built in the
early 1900s.
From around 1895 to 1915, breakthroughs in hydroelectric design led to the construction
of many new dams and power plants – like the ones in Klamath.
Today the dams produce enough energy to power 70,000 homes at their peak, although they usually
aren’t operating at full capacity because of low water levels and other issues.
And like any major infrastructure project, there’s always a tradeoff.
While the structures have stopped potential flooding, provided tax revenue and created great spaces for having fun
- they’ve also blocked the fish from reaching spawning habitats upstream.
Because of this, the salmon population has dwindled to less than 10 percent of its original
volume. And that's not the only impact of the dam.
During the warmer months, the waters are frequently plagued with toxic blue-green algae
blooms, which occur when nutrient rich water gets trapped in the shallow reservoirs.
Environmentalists and local tribal groups have long fought to find a solution, while
some homeowners worry removing the dam will cost them tax money and lost property values.
In the end, PacifiCorp, the energy supplier itself, said removal would be cheaper than
the alternative of building fish ladders, and that the electricity the dam generated
could easily be replaced.
And in 2022, the Federal Energy Regulatory Commission officially authorised the $450M
removal of four major dams.
Copco Dams 1&2, JC Boyle Dam and Iron Gate Dam.
No dam project of this size have ever been torn down before – and it’ll require meticulous
planning and construction work to get it right.
And of course it will be costly.
With operating expenses factored in, it would cost an estimated $20 million per YEAR to
maintain the dams and address the water-quality impact in their current condition.
So removing them saves money long term.
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Now, let’s get back to the Klamath River.
There are two methods to remove a dam: instantaneous or staged.
Instantaneous removal happens quickly.
Think hours or days. We know, not exactly instantaneous.
Here a reservoir drawdown takes place, which is a process that involves releasing the water
and built up sediment stored behind the dams downstream.
Now, most dams have an emergency drainage system in case the water level needs to be
lowered quickly.
That usually takes the form of either a low level conduit, which is just a channel that
can be opened for water to flow through or a stoplog, which is essentially a stack of
logs or beams that can be raised to let water through.
Once the water is released downstream, the dam itself is demolished with explosives and
the rubble is removed from the site.
Staged removal happens over a longer period of time - usually months or years.
This method is reserved for taller dams with larger amounts of built up sediment that would
pose environmental risks if released too quickly.
In a staged demolition, rivers are pumped or diverted away from the construction site through tunnels
or channels, allowing for more control during the reservoir drawdown and sediment release.
Once the rivers are diverted and the basin is dry, the dam is demolished using tools
like excavators or explosives depending on the material.
This longer staged method is the basis for the Klamath dam removals, with slight variations
depending on size and materials in each dam.
Ultimately this project will return the river to free-flowing condition.
Starting in 2023, Copco No. 2, the smallest of the four is going to be the first to be demolished.
"We will actually get underway with the drilling of a brand new ten foot diameter tunnel through
the base of the dam from the downstream and toward the upstream face of the dam. We'll stop about 10 to 12 feet short of the upstream face of the dam in the fall of this year.
"There are a series of box culverts underneath the concrete spillway that have stop logs,
thin concrete stop logs at the upstream end of the dam.
And when we're ready to initiate the drawdown at boyle will simply blast out those stop logs."
Unlike the others, Copco No. 2 has no real reservoir, so drawdown of it won't be necessary.
But that is going to have to take place at the other dam.s
In early 2024, crews will open up low level outlets for the rest of the dams to slowly
initiate drawdown of water and sediment at a rate of 1.5 metres per day.
The three remaining drawdowns will take place at the same time to take advantage of the
water power to help mobilise and push the water through.
The river will then be diverted through new or existing diversion tunnels from the original
construction of the dams.
This causes the channel to dry up, allowing for a safe demolition of the dams.
Now dam removal itself is only part of the equation.
Following drawdown, a 2,200 acre footprint is going to remind behind the dams and that's going to be
in need of restoration through native vegetation and enhancement of habitat
before the return of the salmon.
The scale of this dam removal is unprecedented, and it hasn’t come without controversy.
There’s no doubt the complexities of the demolition and restoration require a huge
But while it may be the largest effort in US history, it doesn’t mark the first dam
removal.
In fact, the project is actually part of a larger removal trend happening across the
country.
In 2022 alone, 20 states tore down 65 dams in an effort to reconnect streams and rivers.
Now to be clear - we aren't saying every dam needs to be torn down- there are many that still provide
their intended purpose.
But as the decades go by, environmental standards change and unexpected impacts can emerge,. And then it's right to
reevaluate the benefits of these structures.
What’s happening on the Klamath River shows the power of both construction, and
deconstruction and how
Infrastructure can impact millions
of people lives.
While it’ll take years to see the effects of this dam removal, but this project shows how a powerful reminder
of how construction is constantly evolving to our ever changing world.
This video was brought to you by Masterworks, more on that at the link in the description.
There’s also the chance to dive deeper on this and the other topics on our channel over
on The World’s Best Construction Podcast – available now wherever you get your podcasts.
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