Wilderness Stream Designation

[Fish Sticks]

Small thermal refuges can be created where water flows from the stream channel into the floodplain substrates, where it cools, then flows back into stream channel.

Geek out, if you wish: https://en.wikipedia.org/wiki/Hyporheic_zone

Yea mike mentioned the hyporrheic zone but only in tribs we have tons of other mainstream hyporrheic inputs as troutbert points out here. Wet lands, alluvial fans, in stream large wood with gradient change behind it ect.

 

[sixfootfenwick]

"but I’m not convinced that these are commonly important at the population level in PA streams".

I am too, for the vast majority of trout streams either don't need them because they are generally cold enough already or they a so few or small as to not make much difference.

I'm equally not convinced they don't matter for all streams in PA, especially brown trout streams.

Simple logic tells me only the fish that survive the summer breed in the fall and the amount of eggs pending on how many survive by this method could be significant for the next year's population in that system. Being aware of migration of brown trout in systems also adds to this.

I think lack of evidence in 42 years doesn't prove it as unimportant, I think in the case described, it was deemed unimportant enough to look for them at all .
Which makes sense because it was a population survey,not an upwelling search.

 

[sixfootfenwick]

Beyond that, I will say the posturing of years and quantity of surveys really does nothing to sway me either.
You say thousands of surveys, but I know many of those also over lapped themselves, but for the sake of arguement....

Even if you did 10000 surveys in 42 years on all different sections, that is 3,000,000 meters or 1864 miles. I believe that is very very generous a number, you know it's less than half that or more.

At that amount you surveyed 8.6 percent (rounded up) of Pennsylvanias trout water, looking for fish and not upwellings.


With all due respect that isn't convincing to me at all to buy into that position.

 

[Mike]

Beyond that, I will say the posturing of years and quantity of surveys really does nothing to sway me either.
You say thousands of surveys, but I know many of those also over lapped themselves, but for the sake of arguement....

Even if you did 10000 surveys in 42 years on all different sections, that is 3,000,000 meters or 1864 miles. I believe that is very very generous a number, you know it's less than half that or more.

At that amount you surveyed 8.6 percent (rounded up) of Pennsylvanias trout water, looking for fish and not upwellings.


With all due respect that isn't convincing to me at all to buy into that position.

I said up to 1000 survey sites; I was not thinking of repeat sites. As I mentioned, the unusual behavior of fish in thermal refugia would make it easy to locate occupied refugia that are not hidden by overhead cover during a stream fish population survey, not just when electrofishing, but during the process of measuring site lengths, measuring site widths every 30 m, collecting macroinvertebrates, land rating habitat features as well. If you are much of a biologist or ecologist, when doing fish population surveys or setting up for same, you are doing a lot more than just electrofishing fish. The idea that one needs to specifically look for occupied refugia, however, in order to find them does not suggest that they are very common. If they aren’t common, they are not likely to be contributing much at the population level.

 

[sam]

In case the OP is still paying attention here through the sidebar conversations, this list shows all the WTS and includes the biomass of the streams.

https://www.fishandboat.com/Fishing/All-About-Fish/Catch-PA-Fish/Trout/Documents/PAwildernessTroutStreams.pdf

Thank you. I have my question answered. Now I'm just enjoying reading all of the other comments.

 

[sixfootfenwick]

I said up to 1000 survey sites; I was not thinking of repeat sites. As I mentioned, the unusual behavior of fish in thermal refugia would make it easy to locate occupied refugia that are not hidden by overhead cover during a stream fish population survey, not just when electrofishing, but during the process of measuring site lengths, measuring site widths every 30 m, collecting macroinvertebrates, land rating habitat features as well. If you are much of a biologist or ecologist, when doing fish population surveys or setting up for same, you are doing a lot more than just electrofishing fish. The idea that one needs to specifically look for occupied refugia, however, in order to find them does not suggest that they are very common. If they aren’t common, they are not likely to be contributing much at the population level.

I don't disagree with most of that until you get to the very last two sentences.

I'm sure, again, they are more common than what is being let on in your wording but less common than every where or in every watershed. In some watersheds they may be common and in others non existent or rare.

If we consider common geographic geology changes that lend to them being prevalent then I bet if we purposely sampled those areas, it would be more common to find them. I'm sure this was outside of any scope in the sampling sites you were going to survey.


The point being, if you can answer, do you think the PFBC is aware of all upwelling refugia in the state? If so, have they studied them to determine, if any, the importance of the refugia to a particular watersheds population dynamic?


Also, does upwelling refugia need to be "common" as in many, to contribute to the population level in what you deem as a significant way?

According to the PFBC Large female brown trout produce 4,000 to 12,000 eggs.
Trout eggs can hatch at a 4 percent to 80 percent rate depending on water quality and conditions.

90 percent of trout fry die in the first year.

So if 5 large female brown trout find 1 refugia in a given watershed, not a "common" occurance for this watershed, using an average of 8000 eggs per female (could be more or less but I picked the middle), that is 40000 eggs. With let's say 50 percent hatching. That's 20000 fry hatched with 90 percent dying.

We are left with a 2000 trout contribution.


That seems significant to me.

🤷

Every year there are guys who hunt down Large Migratory Brown Trout on this site. In a few areas I have found them, one includes a refugia. It isn't uncommon to see them stacked like chord wood in this warm water stream at the refugia. Some are very large and come the cooler air, they are gone, presumably to breed in another area of another creek.

No one, including you or me, can begin to contemplate their contribution to population dynamics in watersheds.

You say it's unlikely, I say it's possible.

At 1000 survey sites, at 30m that is 30000 meters or 18.6 miles. That is .0012 percent of Pennsylvania's wild trout mileage and .00023 percent of all the flowing water.

 

[silverfox]

I don't disagree with most of that until you get to the very last two sentences.

I'm sure, again, they are more common than what is being let on in your wording but less common than every where or in every watershed. In some watersheds they may be common and in others non existent or rare.

If we consider common geographic geology changes that lend to them being prevalent then I bet if we purposely sampled those areas, it would be more common to find them. I'm sure this was outside of any scope in the sampling sites you were going to survey.


The point being, if you can answer, do you think the PFBC is aware of all upwelling refugia in the state? If so, have they studied them to determine, if any, the importance of the refugia to a particular watersheds population dynamic?


Also, does upwelling refugia need to be "common" as in many, to contribute to the population level in what you deem as a significant way?

According to the PFBC Large female brown trout produce 4,000 to 12,000 eggs.
Trout eggs can hatch at a 4 percent to 80 percent rate depending on water quality and conditions.

90 percent of trout fry die in the first year.

So if 5 large female brown trout find 1 refugia in a given watershed, not a "common" occurance for this watershed, using an average of 8000 eggs per female (could be more or less but I picked the middle), that is 40000 eggs. With let's say 50 percent hatching. That's 20000 fry hatched with 90 percent dying.

We are left with a 2000 trout contribution.


That seems significant to me.

🤷

Every year there are guys who hunt down Large Migratory Brown Trout on this site. In a few areas I have found them, one includes a refugia. It isn't uncommon to see them stacked like chord wood in this warm water stream at the refugia. Some are very large and come the cooler air, they are gone, presumably to breed in another area of another creek.

No one, including you or me, can begin to contemplate their contribution to population dynamics in watersheds.

You say it's unlikely, I say it's possible.

At 1000 survey sites, at 30m that is 30000 meters or 18.6 miles. That is .0012 percent of Pennsylvania's wild trout mileage and .00023 percent of all the flowing water.

While surveying an AMD impaired waterway, we've had extreme difficulty locating instream upwellings. We can see there are changes in chemistry between point A and point B, so we know there's some input, but there are no visible inputs from the riparian areas. So there is likely some instream input that isn't visible.

I just discovered two years ago on the brook trout stream I fished as a kid and have probably fished from top to bottom well into the hundreds of times that a significant portion of the stream goes subterranean and reemerges quite a way away.

I only figured that out because of the extreme drought at the time. I drove over the stream, and it was bone dry. Just out of morbid curiosity, I decided to hike the dry streambed to see how many pools of water I could find to have some sense of hope that the brook trout population would survive. What I found was the stream simply disappeared. Above it, the stream was low, but still flowing pretty good. Maybe 1/4 its "normal" flow. So in wet years, you wouldn't even notice that 1/4 the volume of the stream is going underground. I never messed with it when it was low or dry and I've seen it go dry before. At least I assumed it was dry.

I took photos of it because it was wild. I'm standing in the dry creekbed looking upstream and you can see the stream just disappears at the silt pile. You can see up under the fallen trees that there's water flowing in the stream.

Another view. What's left of the flow disappears right at the end of that log in a nondescript hole in the mud/silt.

Here's just upstream of where it goes underground. Just to show there's a decent volume of water here. In the first photo, the fallen tree at the very top of where the stream is is just to the left of this photo.

Then I started hiking downstream to see where it came back above ground and found it. It went a good 1/2 a mile downstream before coming back up in the streambed again. It was freezing cold. This is a mountain freestone stream, not some valley stream in limestone geology. It's mostly quartzite, but it has some calcareous shale with interbedded limestone, dolomite, and sandstone in a narrow band crossing the stream perpendicularly.

The point is, I'm intimately familiar with this stream in particular and it took me 30 years to discover it has this feature. It was dumb luck that I discovered it does this. This is a thermal feature. Not a limestone upwelling from some far away spring source, but a thermal feature nonetheless. Again, in a random freestoner. This really made me think about this kind of thing possibly being far more common than we realize. I'd love to thermally profile streams from top to bottom to see if this kind of thing is more common than we know.

 

[Fish Sticks]

Yea even passing through a wetland on both sides which is super common can have small thermal inputs. My front yard has 4 tiny trickles coming out of the hillside spaced apart by about 20 feet each going into a stream that is runoff dependent higher up. The trickles are filled with cress and chilly relative to what it goes into. If its in my front yard I don’t think areas of thermal refuge are this elusive white whale.

Out of the 3 local streams i fish that run through towns and get warm in summer they all have either focal portions Ive seen fish congregate on season after season at reach scale or sections of a couple hundred yards with colder stream temps i can find places to ethically fish with my thermometer when other sections are not. I think thermal heterogeneity is fairly common

 

[Mike]

I don't disagree with most of that until you get to the very last two sentences.

I'm sure, again, they are more common than what is being let on in your wording but less common than every where or in every watershed. In some watersheds they may be common and in others non existent or rare.

If we consider common geographic geology changes that lend to them being prevalent then I bet if we purposely sampled those areas, it would be more common to find them. I'm sure this was outside of any scope in the sampling sites you were going to survey.


The point being, if you can answer, do you think the PFBC is aware of all upwelling refugia in the state? If so, have they studied them to determine, if any, the importance of the refugia to a particular watersheds population dynamic?


Also, does upwelling refugia need to be "common" as in many, to contribute to the population level in what you deem as a significant way?

According to the PFBC Large female brown trout produce 4,000 to 12,000 eggs.
Trout eggs can hatch at a 4 percent to 80 percent rate depending on water quality and conditions.

90 percent of trout fry die in the first year.

So if 5 large female brown trout find 1 refugia in a given watershed, not a "common" occurance for this watershed, using an average of 8000 eggs per female (could be more or less but I picked the middle), that is 40000 eggs. With let's say 50 percent hatching. That's 20000 fry hatched with 90 percent dying.

We are left with a 2000 trout contribution.


That seems significant to me.

🤷

Every year there are guys who hunt down Large Migratory Brown Trout on this site. In a few areas I have found them, one includes a refugia. It isn't uncommon to see them stacked like chord wood in this warm water stream at the refugia. Some are very large and come the cooler air, they are gone, presumably to breed in another area of another creek.

No one, including you or me, can begin to contemplate their contribution to population dynamics in watersheds.

You say it's unlikely, I say it's possible.

At 1000 survey sites, at 30m that is 30000 meters or 18.6 miles. That is .0012 percent of Pennsylvania's wild trout mileage and .00023 percent of all the flowing water.

Sampling sites on wild trout streams would typically average at least 300 m in length if within the first 300 m thirty wild trout were captured via electrofishing. Many are between 300 and 400m long and some have gone 500 m and beyond. Other sites with lesser wild trout could typically range from 100 m to 300 m.

To my knowledge no upwelling refugia have been studied in Pa, but the PFBC is probably aware of some…either biologists or WCO’s. It was a WCO who found one occupied in the W Br Perkiomen and I found an unoccupied upwelling with my thermometer and hand, more like a spring in center channel in Willow Ck. No studies to my knowledge by PFBC or academia in Pa.

I think it was a paper provided here that suggested that the abundance of upwellings was a measure of their importance, but I may have read that elsewhere. It makes sense though at the population level. As for trout in those refugia, I have reason to believe that they have often been under temperature stress prior to seeking out and entering refugia given their mixed physical conditions. Additionally, I have been witness to an estimated 200 trout leaving a refuge for the night despite ongoing stressful temps in the surrounding waters and I assume that they returned in the morning. Having seen trout in poor condition in refugia, my educated impression would be that many of these fish despite being in refugia are under considerable physiological and behavioral stress, not feeding well, and are putting most or all of their energy into maintenance/metabolism/survival and not into somatic cell growth and not gamete production. Furthermore, under thermally stressful conditions gametes may be produced but not viable. Nevertheless, in the name of scientific inquiry I would be glad to learn whether or not upwelling thermal refugia are common in Pa streams, particularly freestoners, and whether or not they are critical to wild trout at the population level where such upwellings may exist.

As for the value of large trout with respect to reproduction, eggs from younger trout are more viable (generally of better quality). This is one of two reasons why hatcheries spawn 2-3 yr olds in quantity rather than fewer large adults to get the same number of eggs. In a stream the relatively large number of younger trout that can spawn successfully can in total produce more eggs of better quality than those produced by a few large adults in the refugia, assuming that the refugia trout eggs are viable. Additionally, and not saying you are one, many anglers get hung up on this concept of the large trout being needed to contribute their proven growth/survival genes to the population. This completely ignores the fact that these fish have already contributed multiple times when they were younger. Finally, my understanding is that the eggs in large fish captured and harvested by anglers (with professional fisheries knowledge) from refugia in Pa are reported to often be in bad shape. This would be logical if they are in the process of being reabsorbed to likely provide energy for survival.

 

[sixfootfenwick]

Sampling sites on wild trout streams would typically average at least 300 m in length if within the first 300 m thirty wild trout were captured via electrofishing. Many are between 300 and 400m long and some have gone 500 m and beyond. Other sites with lesser wild trout could typically range from 100 m to 300 m.

To my knowledge no upwelling refugia have been studied in Pa, but the PFBC is probably aware of some…either biologists or WCO’s. It was a WCO who found one occupied in the W Br Perkiomen and I found an unoccupied upwelling with my thermometer and hand, more like a spring in center channel in Willow Ck. No studies to my knowledge by PFBC or academia in Pa.

I think it was a paper provided here that suggested that the abundance of upwellings was a measure of their importance, but I may have read that elsewhere. It makes sense though at the population level. As for trout in those refugia, I have reason to believe that they have often been under temperature stress prior to seeking out and entering refugia given their mixed physical conditions. Additionally, I have been witness to an estimated 200 trout leaving a refuge for the night despite ongoing stressful temps in the surrounding waters and I assume that they returned in the morning. Having seen trout in poor condition in refugia, my educated impression would be that many of these fish despite being in refugia are under considerable physiological and behavioral stress, not feeding well, and are putting most or all of their energy into maintenance/metabolism/survival and not into somatic cell growth and not gamete production. Furthermore, under thermally stressful conditions gametes may be produced but not viable.

As for the value of large trout with respect to reproduction, eggs from younger trout are more viable (generally of better quality). This is one of two reasons why hatcheries spawn 2-3 yr olds in quantity rather than fewer large adults to get the same number of eggs. In a stream the relatively large number of younger trout that can spawn successfully can in total produce more eggs of better quality than those produced by a few large adults in the refugia, assuming that the refugia trout eggs are viable. Additionally, and not saying you are one, many anglers get hung up on this concept of the large trout being needed to contribute their proven growth/survival genes to the population. This completely ignores the fact that these fish have already contributed multiple times when they were younger. Finally, my understanding is that the eggs in large fish captured and harvested by anglers (with professional fisheries knowledge) from refugia in Pa are reported to often be in bad shape. This would be logical if they are in the process of being reabsorbed to likely provide energy for survival.

Thank you for the clarification.
In good faith, 1000 sites @ 500m would be 500000 m or 310.69 miles.

That is .02 percent of Pennsylvania's wild trout waters and .004 percent of all flowing water in the state.

That seems like a very small sample size to make a blanket determinations and say "unlikely".

I bet the eggs are in bad shape from trout caught in refugia during the summer. I wonder what those eggs look like in the fall and winter when they breed. Some of these fish have months before they lay eggs. Truth be told I have yet to see a trout in poor condition in the refugia I've observed. Then again my sample size is small.

At any rate, it hasn't been studied. I'm not surprised by this, I had more than an inkling.
It has been studied outside PA though.
I don't think those imaginary lines change much.

 

[jifigz]

While surveying an AMD impaired waterway, we've had extreme difficulty locating instream upwellings. We can see there are changes in chemistry between point A and point B, so we know there's some input, but there are no visible inputs from the riparian areas. So there is likely some instream input that isn't visible.

I just discovered two years ago on the brook trout stream I fished as a kid and have probably fished from top to bottom well into the hundreds of times that a significant portion of the stream goes subterranean and reemerges quite a way away.

I only figured that out because of the extreme drought at the time. I drove over the stream, and it was bone dry. Just out of morbid curiosity, I decided to hike the dry streambed to see how many pools of water I could find to have some sense of hope that the brook trout population would survive. What I found was the stream simply disappeared. Above it, the stream was low, but still flowing pretty good. Maybe 1/4 its "normal" flow. So in wet years, you wouldn't even notice that 1/4 the volume of the stream is going underground. I never messed with it when it was low or dry and I've seen it go dry before. At least I assumed it was dry.

I took photos of it because it was wild. I'm standing in the dry creekbed looking upstream and you can see the stream just disappears at the silt pile. You can see up under the fallen trees that there's water flowing in the stream.
View attachment 1641229391

Another view. What's left of the flow disappears right at the end of that log in a nondescript hole in the mud/silt.
View attachment 1641229393

Here's just upstream of where it goes underground. Just to show there's a decent volume of water here. In the first photo, the fallen tree at the very top of where the stream is is just to the left of this photo.
View attachment 1641229392

Then I started hiking downstream to see where it came back above ground and found it. It went a good 1/2 a mile downstream before coming back up in the streambed again. It was freezing cold. This is a mountain freestone stream, not some valley stream in limestone geology. It's mostly quartzite, but it has some calcareous shale with interbedded limestone, dolomite, and sandstone in a narrow band crossing the stream perpendicularly.

The point is, I'm intimately familiar with this stream in particular and it took me 30 years to discover it has this feature. It was dumb luck that I discovered it does this. This is a thermal feature. Not a limestone upwelling from some far away spring source, but a thermal feature nonetheless. Again, in a random freestoner. This really made me think about this kind of thing possibly being far more common than we realize. I'd love to thermally profile streams from top to bottom to see if this kind of thing is more common than we know.

I actually know a mountain freestone stream very, very well that disappears too and reemerges. It doesn't go half a mile underground but when dry with a lack of rain it vanishes. The flows that reemerge are good, strong, and cold. This stream has a healthy population of brookies with some browns tossed in both above and below the disappearing section. If you go during good flows, however, you can't tell the stream will disappear there when flows are lower. It happens on a pretty high gradient drop off, too.

I know where several in stream ground seeps are in limestone streams I know well, too. No idea how important they are or aren't to the populations but I've never noticed trout congregated around them.

I was blown away when I discovered that mtn freestone stream disappearing, though. Super cool.

 

[sixfootfenwick]

I actually know a mountain freestone stream very, very well that disappears too and reemerges. It doesn't go half a mile underground but when dry with a lack of rain it vanishes. The flows that reemerge are good, strong, and cold. This stream has a healthy population of brookies with some browns tossed in both above and below the disappearing section. If you go during good flows, however, you can't tell the stream will disappear there when flows are lower. It happens on a pretty high gradient drop off, too.

I know where several in stream ground seeps are in limestone streams I know well, too. No idea how important they are or aren't to the populations but I've never noticed trout congregated around them.

I was blown away when I discovered that mtn freestone stream disappearing, though. Super cool.

I wonder, when flows return and fish spread out, if they do, if any significant amount of them get trapped and perish when it dewaters again.

 

[Swattie87]

I actually know a mountain freestone stream very, very well that disappears too and reemerges. It doesn't go half a mile underground but when dry with a lack of rain it vanishes. The flows that reemerge are good, strong, and cold. This stream has a healthy population of brookies with some browns tossed in both above and below the disappearing section. If you go during good flows, however, you can't tell the stream will disappear there when flows are lower. It happens on a pretty high gradient drop off, too.

That stream sounds like a lovely cup of Tea.

 

[jifigz]

I wonder, when flows return and fish spread out, if they do, if any significant amount of them get trapped and perish when it dewaters again.

I doubt it, but it's possible. I have a feeling all (or at least the vast majority) fish would make it to either the upper or lower sections where water remains year round.

I actually haven't been there in a couple years. I should go check it out this summer when It's dry.

 

[Mike]

I actually know a mountain freestone stream very, very well that disappears too and reemerges. It doesn't go half a mile underground but when dry with a lack of rain it vanishes. The flows that reemerge are good, strong, and cold. This stream has a healthy population of brookies with some browns tossed in both above and below the disappearing section. If you go during good flows, however, you can't tell the stream will disappear there when flows are lower. It happens on a pretty high gradient drop off, too.

I know where several in stream ground seeps are in limestone streams I know well, too. No idea how important they are or aren't to the populations but I've never noticed trout congregated around them.

I was blown away when I discovered that mtn freestone stream disappearing, though. Super cool.

I know of a mountain ST freestoner that does so as well under low flow conditions in Berks Co as it comes off the tail of the Blue Mountain. I am not certain if it starts to cross limestone at that point or not. Long Run, Clinton Co does so too, as does Ltl Fishing Ck, Centre Co as I recall but with uncertainty, and so does the stream flowing out of the gap at Pleasant Gap, but in these three cases they are crossing into limestone territory.

 

[troutbert]

I know of a mountain ST freestoner that does so as well under low flow conditions in Berks Co as it comes off the tail of the Blue Mountain. I am not certain if it starts to cross limestone at that point or not. Long Run, Clinton Co does so too, as does Ltl Fishing Ck, Centre Co as I recall but with uncertainty, and so does the stream flowing out of the gap at Pleasant Gap, but in these three cases they are crossing into limestone territory.

Long Run, Little Fishing Creek, and Gap Run all sink into the limestone, so the water is going down into bedrock aquifers. This a very common thing in karst country.

The situation with the freestoners "disappearing" in some sections during low flow periods is very different.

As you walk along small freestoners it's very common to see sections where the streambed has a lot of exposed bedrock. During low flows you can see all the flow on top of the bedrock.

In other sections there is a layer of cobble and gravel substrate on top of the bedrock. In this case some of the water is running through the cobble and gravel. In low flow conditions the flow looks reduced here, compared to the bedrock sections.

And if the stream flow is low enough and/or the cobble/gravel layer is thick enough, ALL the water will be flowing through the cobble and gravel, and not be visible on the surface.

Then further down, the stream is running over bedrock again, or the cobble and gravel layer is thinner, so again there is more water visible on the surface.

In the high energy sections, the fast flows scour away the substrate, often right down to bedrock. In the lower energy sections, more cobble and gravel is deposited.

During low flows, it's common for small freestone streams to be dry near their mouths, where they approach the receiving stream. Some people try to "fix" this, but it's a natural occurrence. As the small stream enters the floodplain of the larger stream, it's gradient drops a lot. So the sediment the stream carries drops out there. The sediment here can be thick. During low flows the water is just flowing through that sediment, under the surface.

 

[jifigz]

I'm not familiar with any streams that have the described attributes near their mouths. I'm also certain the stream I know does not have gravel, pebbles, etc causing it to look underground or to vanish, it is underground of that I am certain. I in no way am discounting what y'all are saying, just stating my observations.

I just think it's a neat feature that somehow probably benefits the fish and it's a fun stream to fish.

 

[Fish Sticks]

Long Run, Little Fishing Creek, and Gap Run all sink into the limestone, so the water is going down into bedrock aquifers. This a very common thing in karst country.

The situation with the freestoners "disappearing" in some sections during low flow periods is very different.

As you walk along small freestoners it's very common to see sections where the streambed has a lot of exposed bedrock. During low flows you can see all the flow on top of the bedrock.

In other sections there is a layer of cobble and gravel substrate on top of the bedrock. In this case some of the water is running through the cobble and gravel. In low flow conditions the flow looks reduced here, compared to the bedrock sections.

And if the stream flow is low enough and/or the cobble/gravel layer is thick enough, ALL the water will be flowing through the cobble and gravel, and not be visible on the surface.

Then further down, the stream is running over bedrock again, or the cobble and gravel layer is thinner, so again there is more water visible on the surface.

In the high energy sections, the fast flows scour away the substrate, often right down to bedrock. In the lower energy sections, more cobble and gravel is deposited.

During low flows, it's common for small freestone streams to be dry near their mouths, where they approach the receiving stream. Some people try to "fix" this, but it's a natural occurrence. As the small stream enters the floodplain of the larger stream, it's gradient drops a lot. So the sediment the stream carries drops out there. The sediment here can be thick. During low flows the water is just flowing through that sediment, under the surface.

This energetic relationship to cobble is something I have noticed as well and I’ll add large woody debris helps this cobble deposition tremendously by forming turns, multiple well FP connected braids, and dissipating energy by making more surges go in flood plains. I have also noticed in many streams downwelling occurrs when scour in front of the the LWD occurs leaving a deep pocket of clean cobbles and inback of the LWD aquatic plants associated with ground water tend to grown in some cases. I have seen brook trout construct their redds behind these LWD jams and since their eggs are often dependent on a degree of upwelling i suspect this is why.

 

[troutbert]

This energetic relationship to cobble is something I have noticed as well and I’ll add large woody debris helps this cobble deposition tremendously by forming turns, multiple well FP connected braids, and dissipating energy by making more surges go in flood plains. I have also noticed in many streams downwelling occurrs when scour in front of the the LWD occurs leaving a deep pocket of clean cobbles and inback of the LWD aquatic plants associated with ground water tend to grown in some cases. I have seen brook trout construct their redds behind these LWD jams and since their eggs are often dependent on a degree of upwelling i suspect this is why.

Pre-disturbance there was probably far less stream sections cut down to bedrock. Loss of large woody debris, consolidation of multiple channels into single-channels, channel straightening, and separation of streams from their floodplains by flood berms, logging railroad grades, forest road grades, and digging of substrate out of streambeds has caused channel incision (downcutting).

Complex habitat such as large woody debris, meanders rather than straightened channels, access of floodwaters to floodplains, and beaver dams all lead in the opposite direction, i.e. they create grade control, more deposition of cobble and gravel in the stream channels rather than allowing channel incision.

So, in summer drought conditions, more water is flowing under the surface, helping keep it cool.

With complex habitat there are places where the current in high flows is deflected downward, carving a pool down into the thick substrate. One example is where water flows over a tree trunk. At this point the flow is directed straight downward. Another example is at meander bends, where the flow spirals with the water cutting downward at the outside of the bend. This is why pools are commonly found at bends.

The stream overall has good grade control, with thick cobble and gravel substrate over the bedrock. But at particular spots, the water carves vertically downward, carving out a depression in the substrate. The substrate acts as the sides of a bowl, which contains the water of the pool. The thicker the substrate, the deeper the pool that can be created. And the more complex habitat you have, with bends rather than a straightened channel, and lots of large woody debris, the more pool formation you will have.

In low water conditions, if you have good pool formation, there will be water in the pools and that is where the trout will survive the drought. In between the pools, in the riffle sections, where the substrate is thick, most of the water is flowing under the substate, helping keep it cool.

 

[Fish Sticks]

Pre-disturbance there was probably far less stream sections cut down to bedrock. Loss of large woody debris, consolidation of multiple channels into single-channels, channel straightening, and separation of streams from their floodplains by flood berms, logging railroad grades, forest road grades, and digging of substrate out of streambeds has caused channel incision (downcutting).

Complex habitat such as large woody debris, meanders rather than straightened channels, access of floodwaters to floodplains, and beaver dams all lead in the opposite direction, i.e. they create grade control, more deposition of cobble and gravel in the stream channels rather than allowing channel incision.

So, in summer drought conditions, more water is flowing under the surface, helping keep it cool.

With complex habitat there are places where the current in high flows is deflected downward, carving a pool down into the thick substrate. One example is where water flows over a tree trunk. At this point the flow is directed straight downward. Another example is at meander bends, where the flow spirals with the water cutting downward at the outside of the bend. This is why pools are commonly found at bends.

The stream overall has good grade control, with thick cobble and gravel substrate over the bedrock. But at particular spots, the water carves vertically downward, carving out a depression in the substrate. The substrate acts as the sides of a bowl, which contains the water of the pool. The thicker the substrate, the deeper the pool that can be created. And the more complex habitat you have, with bends rather than a straightened channel, and lots of large woody debris, the more pool formation you will have.

In low water conditions, if you have good pool formation, there will be water in the pools and that is where the trout will survive the drought. In between the pools, in the riffle sections, where the substrate is thick, most of the water is flowing under the substate, helping keep it cool.

Well said