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OI Salmon Conversations: Mike Langeslay, US Army Corp. of Engineers
The US Army Corp of Engineers Portland district manages and operates the federal dams. That includes making the needed physical changes at the dams that benefit the salmon. The Portland District was very open about what they do, allowing Aaron Kunz to tour several dams including the Bonneville Dam near Portland, Oregon.
Aaron interviewed the Corp. staff biologist Mike Langeslay on top of the Dalles Dam.
Aaron Kunz: Describe some of the things that have been done to this particular dam, the Dalles with fish in mind.
Early on we identified the Ice and Trash sluiceway which is along the power house as a route that fish used readily and would pass a lot of fish safely and we've operated that for years now to pass juvenile fish coming downstream. Later, we also moved to spilling for juvenile fish and those 2 routes remain our primary fish passage routes - non-turbine fish passage routes at the dam.
The one thing to understand about this dam is its unique features and why that is. It is an 'L' shaped dam unlike other dams on the Columbia/Snake River that span straight across the river and it is situated on the edge of a submerged deep canyon. The original river channel runs along the powerhouse, curves around behind me here past the end of the wall and then through the bridge gap right there. You can see kind of the tip of an island out there right to the right of one of those bridge piers. There's a submerged deep canyon along there and that's where most of the flow goes.
The spillway being an 'L' shaped project and the power house on the upstream end, a lot of fish seem to pass that power house and go through the spillway when we're spilling. What we learned early on in the spill program is that a large proportion of fish per unit flow passed the spillway. It is about a 2 to 1 ratio at 40 percent spill. And what that means is when we're spilling 40 percent of the total river which is the operation we currently do here for juvenile migration, 80 percent of the fish will go through the spillway.
At the power house about half and half split between turbines and the ice and trash sluiceway so another 10 percent would go through turbines, 10 percent through the sluiceway.
On the Oregon side of the Columbia here at the Dalles, there are predator fish just waiting for juvenile salmon to swim this way. I understand you made some modifications in recent years to the dam to account for that. A wall on the Washington side of the dam.
There are really 2 problems - one of them that you just mentioned with predator fish. The spillway is oriented in a way that aims flow from spill over to these islands directly downstream by the bridge and there is another group of islands further downstream that is just great habitat for northern pike minnow and small mouth bass and so a lot of the fish that pass the spillway would end up there and be consumed by predators.
What the wall really does here for predators - you can see this little curve at the tip of the wall and just kind of keeping spill on that side of the wall, it directs fish into that deep water canyon which is on the Washington shore out of the way of predators. We did a number of predator studies from the late 90's and early 2000's that showed that northern pike minnow and small mouth bass don't like to be in areas that are too deep or have water velocities that are over about a meter per second.
The other issue with the spillway was that it is very shallow - under 10 feet deep and all that energy from spill - you think of 40 percent of a 200,000 CFS per second river - that's a ton of energy in shallow water so there was an injury problem and the wall helps direct fish more quickly out of the spillway to address the injury issue.
Kunz: How does the spill work so it benefits the salmon?
That said, at the Dalles dam and especially with this spillway operation we have now - it is only 8 days - these gates are opened farther than at most dams. They are open about 10 feet to 14 feet. There is so much flow going through those 8 bays that there's a good velocity, kind of traction current. We don't see fish once they get to the spillway milling around and delaying passage.
I'll compare that to a dam like John Day dam where the same kind of gates but they're deeper. Fish arrive at that project and a lot of times they won't pass until later that night. The steelhead will go there and mill around and not pass until evening and so there is a delay effect. So one of the benefits of spill here is that it reduces migration delay in the forebay where fish could be vulnerable to predation.
Another thing I should mention about spill is it is kind of a balancing act between water quality, adult fish passage and juvenile passage. This one is pretty unique and we generate total dissolve gas and we have clean water act requirements to keep that total dissolve gas under a certain level. It is 120 percent during the fish passage season in the area here.
The Dalles dam because it is shallow it is a good dam to spill at because it will only generate so much gas. It dissipates - the shallowness mitigates for the TDG effect of spill where at other dams you are really capped at a certain level of spill or you will exceed gas levels. Supersaturated gasses in the river affect other aquatic organisms as well as salmon and can cause mortality or injury so that is one part of the balancing act.
Kunz: Dams play an integral part in water temperature. What is the Army Corp of Engineers doing to mitigate that?
But these other dams, these main stem dams, they are mostly run of the river, they just pass what comes into through them, they are shallower head. These reservoirs don't stratify. They pretty much mix from temperature top to bottom and so I would say they really have no control or effect over temperature beyond just in general slowing the river down a little bit dam by dam and increasing a surface area to some extent which increases your thermal budget or river warming.
Kunz: The fish ladder issue. There has been concern that they wear out adult salmon on their return. What have you done to deal with that?
They wanted us to look into studies that investigated what that energetic cost was and how did that affect reproductive success. And so the Corp. embarked on a 7-year study at the University of Idaho where we tracked them up to the Salmon River basin and looked at pre-spawn mortality. And in the end we really could not connect dam passage to pre-spawn mortality or reproductive success.
The driving factors were really temperatures in that water shed in terms of what would result in pre-spawn mortality, which fish lived to spawn and which ones died before they spawned. It was a temperature related effect but there was no apparent effect of dam passage or even delay at the dams.
Kunz: So is the science is still out on this?
While the dams cause a delay when they get to the reservoir, there are slower flows, it's easier for them to swim upstream and so there is less energetic cost to the stretch of river between dams. And you think about the example here at the Dalles dam where Celilo Falls was probably a pretty significant passage obstacle in energetic cost for adult salmon to swim over.
It is inundated now. Fish have a pretty easy time getting past those kinds of rapids. So even though the systems change and there are obstacles with dams put in the way there are other obstacles like falls and rapids that have been removed.