Deep holes in streams and most rivers vs temperature

[Mike]

A common misconception expressed here and elsewhere is that deep holes present refuge for trout during warm water conditions in streams and rivers. This is not the case. The water circulates enough such that it does not stratify as it does in lakes and even some farm ponds. Thus, water temp is the same or nearly the same top to bottom. For instance, in the Delaware R in Phila where the water is 40 ft deep, the summer temp difference from surface to bottom is 0.1-0.2 degrees C. In streams you will not find a difference unless there is a spring in the hole or perhaps a density current created by an incoming trib adjacent to the hole. You may find some temp differences from surface to bottom on river impoundments, depending on flow, and perhaps a near 100 ft hole like the one on the Delaware at Narrowsburg, NY may stratify, but that would be an unusual case.

 

[foxtrapper1972]

So no 32" hogs summering behind Safe Harbor Dam...Darn it!

 

[JG63]

Fish the riffles - where the oxygen and food is present. Fish take refuge in holes to shy away from herons and fisher people.

 

[brookieaddict]

I think most folks understand in warming spring weather they go shallow to not only enjoy the warm water but to forage . Predators are the main reason for going deep, except when the lemmings jump off of Chickes rock then everyones shallow even the lemmings.

 

[troutbert]

Some deep pools have groundwater flowing into them, so have cold water in the depths.

Some deep pools do not have this, so are warm the whole way down.

It depends on the geology.

 

[wildtrout2]

Interesting info Mike, thanks. I would have thought otherwise.

 

[foxfire]

My days skinny-dipping as a kid in deeper pools tend to disagree with you

 

[MKern]

Deeper holes also give refuge for weather events, mainly flooding.

 

[pcray1231]

My days skinny-dipping as a kid in deeper pools tend to disagree with you

Same (cept not skinny dipping). But still, at times I have felt temperature differentials in streams from surface to bottom. I can't say I took detailed notes of exactly where and it may be a result of underwater springs.

What Mike says does make sense and I know some of the famous guys go wading about marginal streams in the summer "feeling" for springs like that. While a stream may not be vertically stratified overall, a spring seep can remain vertically AND horizontally stratified for hundreds of yards downstream. So when you feel it, it doesn't mean you are standing on said spring, but it's upstream of you somewhere, and you can track it down.

For example, in Penns Creek, there is a measurable temperature difference from the influence of Pine/Elk, from one side of the stream to the other. And that holds downstream the whole way to under the walking bridge below Coburn. Nearly a mile of water. Take a thermometer in mid summer. See for yourself!

So it's not so much looking for a deep hole where fish will hold over. But moreso looking for temperature differentials stratified ANYWHERE in said stream, usually resulting from some upstream cold water influence such as a cold trib or underwater spring seep. And that could be a long ways upstream.

The best time to see horizontal stratification, though, is high and muddy conditions. If the main stem is chocolate milk, a clear tributary or large spring will have clearer water, and you can SEE the stratification, rather than relying on your feelers or thermometer....

 

[MKern]

Maybe the felt temperature differences while swimming has more to exposure to sun light and not water temp. You just feel warmer in the warmth of the sun, but the suns rays don't penetrate as far further down.

 

[Chaz]

foxfire wrote:
My days skinny-dipping as a kid in deeper pools tend to disagree with you

What? You quit when you grew up?

 

[Cold]

Maybe the felt temperature differences while swimming has more to exposure to sun light and not water temp. You just feel warmer in the warmth of the sun, but the suns rays don't penetrate as far further down.

Wouldn't that imply that, regardless of reason, the deeper water was indeed colder than the surface?

Nearly any river I've ever gone swimming in has been noticeably cooler about 4-6 feet down, regardless of the time of year, ambient air temp, geology, or other stream features.

While the OP may make a valid point about currents "stirring up" different water temps, my own experience suggests that, regardless of currents, the water at the bottom of deep holes in streams is absolutely colder than at the top...for whatever reason.

If pressed, I'd have to say it's a combination of less light/solar radiation penetrating the upper water, as well as the slower current, meaning that water not only cools down from the lack of light, but it also hangs around longer...so the fast moving water up above is also warmer, meaning that it'll tend to roll over the colder water below.

Anyone who's drifted a nymph through a deep hole can verify that the current at the bottom is often/usually slower than that at the surface.

 

[MKern]

Not really. If I stand outside in the sun I feel warmer, but if the sun goes behind the clouds I feel colder. However, the air temp hasn't changed I'm absorbing the heat/sun's energy faster and easier than the air around me.

 

[Cold]

To be totally fair, the opposite is true: you're absorbing the sin's energy far more slowly than the air around you. The opposite is also true too, when the sun goes away the air loses that energy more quickly than you do, so you feel cold. The air temp has changed, and in fact is the very reason you feel cold: relative to the air, you're much warmer.

This is, of course, speaking only of the air/skin direct heat transfer, though, which really isn't the issue. The main reason the sun warms you up is radiant energy, which has nothing to do with the air temperature. It's the radiant energy which is absorbed by the upper surface of the water and which largely dissipates before reaching the bottom of the pool.

 

[Alnitak]

I believe about 18 months ago I posted a thread here regarding the deep trenches/holes in the lower Susquehanna River gorge when the topic of large trout using the river came up. The data I found online showed that just as Mike pointed out, the bottom of several of the 100+ foot deep holes was not much different in temperature than the surface. Too much mixing from current flow for good temperature stratification to develop.

 

[Fly-Swatter]

+1

One could argue the perceived or "felt" temperature of water at the surface v. deeper is deceiving and the measured temperature of surface v. deeper does not support the feeling.

THe specific heat of water and the effect of solar radiation on our skin seem to support this.

 

[Cold]

Radiant heat vs conducted heat.

Kinda like how on a winter morning, there will be frost in the shadows but not out in the sun, even though the overall air temps may be the same.

There's not a study out there that will convince me that the bottom of a deep pool isn't colder (in warm weather) than the surface. It just isn't so. In very cold weather, the opposite will be true, as the ground will help to insulate the deeper water from the colder temps caused by the air at the surface.

 

[afishinado]

Cold wrote:
Radiant heat vs conducted heat.

Kinda like how on a winter morning, there will be frost in the shadows but not out in the sun, even though the overall air temps may be the same.

There's not a study out there that will convince me that the bottom of a deep pool isn't colder (in warm weather) than the surface. It just isn't so. In very cold weather, the opposite will be true, as the ground will help to insulate the deeper water from the colder temps caused by the air at the surface.

Mike wrote:
..in the Delaware R in Phila where the water is 40 ft deep, the summer temp difference from surface to bottom is 0.1-0.2 degrees C.

You don't need a study....just a thermometer! And ^ that's in 40' of water1

Flowing water constantly mixes and doesn't allow stratification. Until Mike posted this, I thought this was common knowledge and universally accepted like gravity or the Earth moving around the sun.

 

[Cold]

Again, radiant heat vs. conductive heat.

The fish (or human, or anything else) holding at the bottom of the pool isn't getting as much of the former as one at the surface, and it's a significant enough that in spite of the latter being the same at both depths, there is a difference.

By the rationale of measuring only water temp as the be-all end-all, there's no point in finding shade on a hot summer day. The air temp is all the same, so it's just as hot in the shade as it is out in the sun.

 

[markp]

Cold,

While you are right the object that is being hit by the sun's radiation will be warmer than an object fully submerged that really is not the important part of this argument. I think the argument here is suitability to carry over a fish from year to year, of which Dissolved Oxygen is the major limiting factor, not the physical temperature of the fish. Dissolved Oxygen content is determined by the amount of water disturbance and the water's ability to hold that Oxygen in solution, which is largely determined by temperature. So while that portion of my body in shallow water is physically warmer than the portion in deeper water due to radiation the water itself is still the same temperature and therefore the DO carrying capacity is still the same at my head and at my toes.

As an example of this a fish that is sitting out on a sunny day in a tailout will feel significantly warmer physically than a trout at the bottom of a pool. But, because the water is the same temperature the trout will both have the same ability to breath (both low disturbance areas). If the trout in the tailout is feeling too warm physically it can literally swim under a cutbank in 12" of water and feel the same temperature as that fish in 40' of water. Rememeber a trout does not typically die because of heat exhaustion so physical temperature is rarely the issue but from oxygen deprivation caused by the diminished ability of warmer water to hold oxygen. The continued mixing of flowing water means that water at the bottom of that pool will have the same O2 carrying capacity as the water at the top, meaning a fish in either position will have the same ability to live.

Hope this helps and was not just another person talking in a circle.

Mark