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#1028879 - 04/22/20 08:21 AM Redd scour
Salman Offline
Spawner

Registered: 03/07/12
Posts: 702
Can anyone tell me what redd scour from logging looks like or a picture and if theres anything that can be done about it?
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#1028900 - 04/22/20 10:09 AM Re: Redd scour [Re: Salman]
Salmo g. Offline
River Nutrients

Registered: 03/08/99
Posts: 12870
Salman,

I don't think I have any photos specifically of redd scour. I could take a photo of a gravel bar that is high and dry, but is where the river channel formerly was prior to the last high water event. Any salmon spawning redds in that former stream channel were scoured and then refilled to create the gravel bar that is there presently.

Another example of redd scour would be in lower Diobsud Creek, tributary to the Skagit River right near where the Hwy 20 bridge passes over it. The stream channel looks almost exactly the same before and after a high water event. However, I knew that all the pink salmon redds that had been constructed there were scoured away and long gone. We had installed scour chains, buried 24 to 30" deep in the creek bed. I think we recovered one or two, but the rest were completely gone, meaning that the high water had scoured the stream bed 2 1/2 to 3 feet deep and then refilled the channel with fresh gravel from upstream, carrying it down during the high energy high flow event.

I list the above as examples of what redd scour might look like. There are others ways redd scour might present itself as well.

Logging doesn't directly cause redd scour, at least in the terms of how I usually think of it. What logging does is change the runoff patterns of rain and snow, with rain events generally running off into stream more quickly due to the bare ground and lack of forest canopy. So what happens is that streams that have upstream logging will rise faster and higher (peak flow) than streams without logging. Higher flows mean higher energy, and higher energy causes scour, and deeper scour that destroy redds by mobilizing both the gravel and eggs. And that kills the eggs. And we haven't even gotten to the part where logging results in rain and snow runoff causing increased erosion, dumping huge quantities of fine silt and sediment into the water column, so even if redds are not scoured, they are smothered, reducing the critical oxygen exchange necessary for the eggs to live and develop to hatching and emergence.

What can be done about it? A lot of things, but they aren't real popular with the timber industry because it reduces profitability. The beneficial measures include buffer zones, wider buffer zones, no entry buffer zones, limited entry and harvest buffer zones, smaller logging units, longer rotations between harvests, proper abandonment of old or unused logging spur roads, fewer roads to begin with, aerial yarding of logs, paving logging road mainlines, and other actions that I can't think of right now. Then again, not logging at all is the best alternative for stream health, but then we would not have the wood fiber that is critical to our way of life. Many of the mitigating measures I listed have been adopted, going back as far as the Timber, Fish, & Wildlife Agreement legislation of 1989 and the Fish & Forests plan of, oh about 2005 I think. I don't remember exactly when that was completed. The upshot is that WA has the most restrictive forest management and timber harvest rules in the U.S. And stream health has improved in some cases, maybe a lot of cases. But it is usually a slow process, measured more in decades than years. Hope this info helps answer your question.

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#1028904 - 04/22/20 10:14 AM Re: Redd scour [Re: Salman]
Rivrguy Offline
River Nutrients

Registered: 03/03/09
Posts: 3460
Loc: Somewhere on the planet,I hope

From logging is hard to quantify as you would need data over years to verify the flow increase in high water events. A good example is 2010 flood on the Satsop and it left a four inch line of eggs right through the Schafer Park parking lot as the water receded. Redd scour is product of high water events that timber harvest effects are about impossible to quantify. Now siltation from roads and most certainly contributing to low summer flows are real. When replanted trees root systems and branch shading do not do much until 15 years old and fully functional 20 years old. With 40 year rotations that is half the life cycle in a tree farm. The larger RMZ setbacks have helped rearing areas and reduced erosion but do nothing for low summer flows.
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#1028915 - 04/22/20 11:08 AM Re: Redd scour [Re: Salman]
Salman Offline
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Registered: 03/07/12
Posts: 702
Logging increases high water flows & decreases summer flows?
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#1028917 - 04/22/20 11:27 AM Re: Redd scour [Re: Salman]
Carcassman Online   content
River Nutrients

Registered: 11/21/07
Posts: 5832
Loc: Olema,California,Planet Earth
Redd scour is when the velocity of the flow gets high enough to move the rocks that cover the redd. The higher the flow the higher the velocity, in general. But there are lots of "but"s.

If the stream can spread out into a floodplain, wide channel then the velocity decreases. Confine the channel and velocity increases.

When fish spawn, they turn over the gravel. Rocks settle by weight which means the rocks get heavier as you go deeper into the streambed. Mass spawning turns over the whole bed. This has been shown to then require a higher flow to mobilize the gravel. The result? A particular flow might scour out redds at low spawner density and totally undisturbed them at a high spawning density.

Anything that increases peak flows, whether logging, clearing for development, installation of impervious surface (roof) will increase the probability and frequency of scour.

You probably won't see an actual scoured redd as the stream will naturally smooth the spawning beds. Finding a lot of dead eggs, like Rvrguy said, is a sure sigh though.

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#1028926 - 04/22/20 12:13 PM Re: Redd scour [Re: Carcassman]
Rivrguy Offline
River Nutrients

Registered: 03/03/09
Posts: 3460
Loc: Somewhere on the planet,I hope
Absolutely low summer flows which dictate Coho and Steelhead rearing success. High water in the sense that greater runoff but if you have a full blown flood, not so much. Yes as to early run off rains before the ground soaks up as it runs off rapidly but that is not a contributing factor of any great magnitude. Think of it this way. Ground with trees stays soft and moist to some degree through summer and into the fall. Ground exposed bakes out and is is somewhat hard so rains do not soak in all that well until it absorbs water and softens. So timber harvest does increase early run off vs unharvested lands but after a point when the ground soaks not as much. Timber harvest does contribute to mass wasting as it simply puts the natural erosion process on steriods. Now urbanization contributes to mass run off 24 7 and never stops and carries substantial chemicals and organics with it. It is what it is.


Edited by Rivrguy (04/22/20 12:17 PM)
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#1028937 - 04/22/20 02:39 PM Re: Redd scour [Re: Salman]
Smalma Offline
River Nutrients

Registered: 11/25/01
Posts: 2788
Loc: Marysville
Some good information!

Other factors that influence the degree of damage being done during high water events/redd scour.

One is the length of time higher water events - the longer the flows are evaluated the more damage done.

Another is the size of substrate that the eggs are buried under. A large female Chinook eggs that under head size rocks are less prone to flood damage than eggs under fist size rocks.

As water sheds unravel it is not uncommon to find increase materials moving in the stream channel; both increases in small sediments and over volume of material moving. This tends to increase egg and even fry survivals over the situation of smaller bed load movements.

Another aspect that rarely talked about is the frequency of the larger events. Historically a fish population would typically have decades to recovery from a major event. With increased frequency of those large events on many basins what historically might be considered a 50 flood maybe now be occurring once a decade rather than a couple times a century.

Finally historically fish like Chinook had a high productivity; that is to say if for some reason like a large flood where the population was reduced to a low level that brood year might produce a 10 to 15 time fold abundance increase in a single generation. In some of our more compromised freshwater portion of our basins that productivity may have been reduced by as much 5 fold. The rebound of a stressed population can take much longer than historically.

Across the Puget Sound region through the smolt trapping on a number of rivers the relationship between flows during egg incubation and the numbers of resulting migrants has been established. The range of response between that survival and egg to migrant survival varies significantly between those basins. A measure of the health of the basins?

Finally the Stillaguamish has become the poster child illustrating the impacts from flood on Chinook survivals. Looking at the increase frequency and magnitude of peak flows in the basin underlines why Stillaguamish Chinook have become such a limiting stock for PS fisheries.

Curt

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#1028943 - 04/22/20 03:26 PM Re: Redd scour [Re: Salman]
Salman Offline
Spawner

Registered: 03/07/12
Posts: 702
So is seeing 12-18” of mud on top of big softball to watermellon size rocks scour? I couldn’t exactly see all of the spawning bed but from what I saw the mud covered an area way bigger then before.
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#1028947 - 04/22/20 04:42 PM Re: Redd scour [Re: Salman]
Carcassman Online   content
River Nutrients

Registered: 11/21/07
Posts: 5832
Loc: Olema,California,Planet Earth
Mud isn't scour. It is excess sediment carried by the stream and dropped when velocities decrease enough. The excess fines (coarse sand on down to clay) smothers the eggs regardless of whether or not the flood scoured redds.

Also, lower flows in the fall force fish to spawn in the thalweg, the line of highest velocity. All the fish forced to spawn there put their redds right where the most scour will occur of there is a freshet.

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#1028949 - 04/22/20 04:51 PM Re: Redd scour [Re: Salman]
Salmo g. Offline
River Nutrients

Registered: 03/08/99
Posts: 12870
Originally Posted By: Salman
Logging increases high water flows & decreases summer flows?


In a word, yes. But as other posts illustrate, it's a bit more complex than that.

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#1028950 - 04/22/20 04:53 PM Re: Redd scour [Re: Salman]
Salmo g. Offline
River Nutrients

Registered: 03/08/99
Posts: 12870
Originally Posted By: Salman
So is seeing 12-18” of mud on top of big softball to watermellon size rocks scour? I couldn’t exactly see all of the spawning bed but from what I saw the mud covered an area way bigger then before.


As CM posted, mud is not scour. Mud is composed of silt and fine sediment. Fine sediment that settles out on a salmonid redd smothers the eggs by limiting the flow of oxygen rich water through the incubating eggs that is necessary for their survival.

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#1028955 - 04/22/20 05:31 PM Re: Redd scour [Re: Salmo g.]
Rivrguy Offline
River Nutrients

Registered: 03/03/09
Posts: 3460
Loc: Somewhere on the planet,I hope
SG & CM I am trying think of an example to let folks the force of velocity plus volume. In 2010 in the Satsop flood I stood on the banks of the outlet at the hatchery. The river sounded like jet engine with the volume that was going by trees and all, it was ugly. I could hear boulders bouncing off the sandstone bottom and banks. It was like I threw a handful of large rocks in the cloths dryer. If you remember CM I had over 200 cubic yards of gravel blocking the hatchery outlet including a 24 diameter full length tree with root wad and all.

The gravel movement off the cliffs upstream was huge as these are glaciar till lands and the cliffs are gravel over a hundred feet high. So erosion can be very bad but also it can be good for the fish. It is the erosion that continuously resupplies the rivers and streams with gravel and with it comes the topsoil. I am sorta jumpy about setting CM off with how salmon clean up a stream but it is a fact. So flood driven erosion is normal and the nature of the flooding is the same. The difference is really people as when it affected 100 rural folks no big deal now it is 1000 bigger deal. As size the biggest flood in the Satsop I know of was in the 1930's and water got into Elton's barn. The fish survived as somehow the river and fish work things out. Add humans.......not so much.



Edited by Rivrguy (04/22/20 07:18 PM)
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#1028961 - 04/22/20 06:22 PM Re: Redd scour [Re: Salman]
Salmo g. Offline
River Nutrients

Registered: 03/08/99
Posts: 12870
Rivrguy,

In the stream channel, as the water gets deeper due to increased flow, the velocity gets faster. Faster water has higher energy, and the higher the energy the heavier the substrate that can be moved. This is a major reason why sections of rivers that are lower downstream, and more likely to be riprapped and channelized, have less effective spawning areas. The river cannot spread out as flows come up, so velocity increases and scours out redds. Where rivers can spread out over wide flood plains, spawning success is higher. Some eggs are lost to sedimentation there, but the whole redd doesn't get blown away.

Hydrology is fascinating. I wish I had studied it more.

Sg

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#1028978 - 04/22/20 07:43 PM Re: Redd scour [Re: Salmo g.]
Rivrguy Offline
River Nutrients

Registered: 03/03/09
Posts: 3460
Loc: Somewhere on the planet,I hope
As I am and old guy I can remember when Quigg Bros. dredged the Chehalis at what is now Friends Landing and barged it down stream. That is why the old docks existed to tie up the barges. Year after year they dredged and gravel migration from upstream filled it right back. When forced to stop they simply moved into an off chanell egress and dredged forward and the waste filled in behind which in the end left the lake at the landing.

Because it is only seen at low tide and not always exposed most do not realize the huge amount of gravel that moves downstream each year. It is way way more than most folks realize and I think your right SG it is fascinating.


Edited by Rivrguy (04/22/20 09:28 PM)
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#1028979 - 04/22/20 07:59 PM Re: Redd scour [Re: Salman]
Carcassman Online   content
River Nutrients

Registered: 11/21/07
Posts: 5832
Loc: Olema,California,Planet Earth
I worked on a couple of creeks where we had fish traps/racks that were permanently installed. We walked the streams weekly, the whole anadromous zone. The racks stopped bedload movement. Every year we had to dredge about 100 cubic yards of gravel from above the rack. But the word thing is that the configuration of the creek stayed the same. Riffles were in the same place, pools were in the same place. How the gravel moved through system but left the bed intact always amazed me.

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#1029010 - 04/23/20 10:07 AM Re: Redd scour [Re: Carcassman]
Salmo g. Offline
River Nutrients

Registered: 03/08/99
Posts: 12870
Originally Posted By: Carcassman
I worked on a couple of creeks where we had fish traps/racks that were permanently installed. We walked the streams weekly, the whole anadromous zone. The racks stopped bedload movement. Every year we had to dredge about 100 cubic yards of gravel from above the rack. But the word thing is that the configuration of the creek stayed the same. Riffles were in the same place, pools were in the same place. How the gravel moved through system but left the bed intact always amazed me.


Qualifier: "I'm not a hydrologist," but I think the operative word or term is "hydraulic control." I took the "Instream Flow Incremental Method" courses from CSU in 1980-82. I remember that term hydraulic control referring to either the larger substrate at pool tailouts or the underlying geography-geology below the streambed that controls the water surface elevation. The result is the pools and riffles in some reaches or some streams stay in the same place even though bedload is continuously moving downstream with higher flow events. Conversely, it also explains why riffles and pools are always moving around in less stable stream valleys like the Quinault, Queets, and Hoh. It's all part of the when, where, and why redd scour occurs.

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#1029026 - 04/23/20 03:41 PM Re: Redd scour [Re: Salman]
slabhunter Offline
River Nutrients

Registered: 01/17/04
Posts: 3660
Loc: Sheltona Beach
Years ago, I shared an image or two of the road near my home being nearly washed away after a clear cut above the development.

This was like three phones ago. I did not save it, perhaps in the archives?
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