Following the eruption of Mount St.
Helens on May 18th, 1980, federal state and local agencies partnered
together to protect the communities impacted by the eruption.
The partnership continues to this day in an effort to enable the safe management
of Spirit Lake infrastructure and the Toutle River watershed with the ultimate
goal of protecting downstream communities, resources and economic development.
In 1980, the North face of Mount St.
Helens collapsed in a gigantic landslide in this placed an
enormous amount of sediment in the upper North Fork Toutle River basin.
And in fact, up near Spirit Lake, the deposit from that
landslide is almost 600 feet thick.
So there's a, a gigantic pile of sediment that sits in that upper Valley.
And over the past 40 years, you know, the river network that's established.
Has eroded parts of that landscape.
And so even though the amount of sediment that's being delivered downstream
today is vastly less than what was originally delivered in the early 1980s.
It's still substantially above what we would consider typical
background level before the eruption.
And that's simply because we have an enormous pile of sediment
up there that mother nature wants to keep moving downstream.
And so the fear
right now is that if Spirit Lake breaches, the current blockage that
resulted from the 1980 landslide, we could have a very similar event,
like what happened 3000 years ago.
So, so we've actually got a geologic analog that tells us very clearly
what the
hazard is
if Spirit Lake
happened to breach.
Right behind me in that valley, there will be about 50 to 70 feet of water
and debris rushing through and all the water, all the trees, all the rock would
be floating down catastrophically right through the valley behind me again,
and a wipe out the towns of Toutle.
Impact, uh, Castle Rock, um, break I-5 and the rail road, um,
spill all this debris into the Cowlitz River and begin down into
the Columbia River and blocking the shipping channel of Columbia.
So what is really vitally important for us
local emergency managers and to folks living here in Clowltz County is a fact
that, uh, uh, the mountain is still alive.
And, uh, thank goodness that, uh, The Army Corps of Engineers
has plans in place to dredge
the Cowlitz River because more sediment
er sediment in the bottom of a river makes floods way more dangerous.
Uh, so the cooperation between the Forest Service and the Army Corps of Engineers
is vital for the protection of this valley and the residents that live in here.
Now, the public should be aware that after the 1980 eruption the natural
outflow of Spirit Lake was blocked
by the large landslide and it caused this debris blockage
of the outlet for um Spirit Lake.
So in response to that, the U S Army Corps in partnership with
the Forest Service built a what we call the Spirit Lake tunnel.
It's a 1.6 mile 11 foot in diameter tunnel to outlet, Spirit Lake.
Ultimately the decision was made to go with the tunnel in hard rock,
because it was the most stable outlet for Spirit Lake in the long term.
Given that we didn't know how active Mount St Helens would be into the future
And we didn't know about the seismicity up in the area and the tunnel would survive
future volcanic eruptions and seismicity, better than any of the other options
and protect the people downstream
the best.
So that's why the tunnel was built.
And since it was built, it's inspected annually and repaired as needed and
performs a really vital function that the public should be aware that
because of that tunnel, it keeps Spirit Lake at a safe level, prevents any
overtopping or potential debris blockage
uh, breaching and potential mud flows downstream.
So it's a critical piece in the whole system for maintaining
that level of protection.
This tunnel helps with the proper drainage of Spirit Lake and
the Forest Service manages it.
We do annual inspections and we often have
to do repairs every year
we usually have an emergency repair of the tunnel or part of the inlet structure.
Several of these repairs are due to the tunnel is built in a dynamic
Landscape. Because there's no access roads out to the tunnel or
the inlet structures in the past
we've had to access
the area to maintain it for regular routine maintenance
and emergency repairs through helicopter, which it's a high cost
every time we use it
and we always have to look at our employee safety.
So the Forest Service plays a critical role in managing the Toutle River system.
We are only the very top 6% of the entire drainage system, but we are
the top of the drainage system
so 85 00:05:04,094 --> 00:05:09,685 what we do at Spirit Lake and managing the inlet tunnel directly
impacts the rest of the downstream community in the whole river system.
So it's critical that we work together with our partners and
communities to minimize the risks, the costs, and create a resiliency.
The work that's done in response to the Mount St.
Helens eruption really is a collaboration between many federal
agencies, state agencies, and the local community. What you see here
behind me, the sediment retention structure and the sediment plane, is not
the Corps of Engineers, uh, project.
It's really, it's a combination of the state
and other federal agencies coming together in response to this eruption,
the purpose of the project is to provide flood flood risk management
for the four communities on the lower Cowlitz River. Kelso, Longview,
Lexington, and Castle Rock. There's levees associated with all those communities.
The SRS works in conjunction with those levies by holding back
sediment here so that it doesn't deposit in the lower Cowlitz River.
But the SRS is really here to block sediment from going past to protect
those communities downstream.
And the two communities downstream should expect that the SRS is still
going to do its job in trapping sediment.
And they're going to, it's going to provide some degree of protection from
sediment depositing in their backyard.
And so it's really a collaboration regionally to manage the sediment load
coming off of the debris avalanche.
But every federal agency has a role.
Every federal agency, every state agency has a mission that
they are really focused on.
But beyond that, even the local community, which has a key role
in this, it's in their backyard
it's, it's what we protect against,
it's it,
they have a key role in deciding and understanding what
the plan is moving forward.
And in addition to that, you have local agencies like the like levee districts who
are on the ground, managing the levies.
Who have a key role in communicating with us and saying, hey, we see a problem.
or maybe they, they they're involved in the planning process to help
make those decisions moving forward.
So really it's in the Corps makes decisions, not in a vacuum,
the Corps makes decisions by reaching out to each one of these agencies
and organizations to make sure that everybody's voice is heard.
And any decision that we make has each voice as part of that decision.
To learn more about long term
management efforts and future planning at Spirit Lake, please
visit us at the link below.