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Boundaries of the question:

  • The question is about rivers where water flows in cold area of the earth. Whether it's because of the winter or it's simply cold all year long. Usually, the top layer of the river freeze and water underneath continue to flow freely.
  • The question is about the temperature of the liquid water only. So, the temperature of the solid water is irrelevant to the question.
  • This question is only about fresh water rivers only. So salty rivers are not part of the question.

The question itself:

What is the temperature of the flowing water in icy river?
More precisely, does the temperature of the water drop below 0 °C?
If it does, is this common? If it doesn't, does it get close to it at all?

Attempted research to find the answer :

I had in mind that the current allowed the water to stay liquid, but that might be wrong because there is no proof to it. However, this answer says:

For flowing water to freeze, the temperature would have to be exceptionally cold.

Which seems to agree that current can lower the freezing point.

I found a great document about the temperature of the water within lake, but didn't find any reliable answer for rivers.


EDIT
I have come to believe that temperatures don't typically fall below 0 °C, based upon aggregating the following information...

Using this, we can probably conclude that water won't cool down enough during it's journey down the river. Thus, the water would need to be already colder at the start of the journey. We know that the start is a lake with calm water. So, it's unlikely to happen because the lake would freeze completely and stop flowing out into the river.

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    $\begingroup$ They're related questions (and indeed, the addon, asking whether it is common, may tie closely to the given question's answers). But there's an entirely different focus (whether the water can reach subzero liquid vs whether it can freeze 100% solid)... and it only appears that the final couple sentences in the #1 answer address possible movement effects at all (and vaguely, without explanation, numbers, observations, etc). So I'm 100% behind keeping this one open. $\endgroup$ – JeopardyTempest Mar 8 '17 at 4:47
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    $\begingroup$ @Michael Jeodardy understood the question well. It's about the temperature of the flowing liquid water. Perhaps the title of the question is misleading to some? Would "What is the coldest water temperature of liquid water in rivers?" be better for the title? $\endgroup$ – AXMIM Mar 8 '17 at 20:48
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This is a complex question.

I will assume the following to be able to frame an answer properly:

  1. Let's take a general cold area as a baseline, such as the High Arctic or 70°+ N latitude;
  2. The reference for this example can be Pond Inlet, on Baffin Island, an example where long-term records are available (72° N). The following data assumptions will be based on the normals provided by this station. But what is discussed is likely to be valid for a large area of the High Arctic - like 70°+ N latitude;
  3. In this area, the normal (1981-2010) mean annual air temperature is -14.6° C is fairly representative
  4. Also, in this area, the normal yearly degree days to reach thawing (TDD - the sum of daily average temperatures above 0° C) is 473 degrees.
  5. The bulk of the TDD sum (473 degrees) occurs during June, July and August; only 2 degrees in May, 31 in September and 1 in October, so thawing is most likely minimal outside these three months. As a consequence there are two fairly distinct seasons: the thaw season (summer, duration 3 months) and the freezing season (winter, duration 9 months).
  6. Pro-glacial rivers are not considered (river taking their source from glaciers, different story)
  7. Lakes are not considered (different story)

This all means that the cold region's rivers are not thermally static through time. Even in the High Arctic, an icy river can be frozen along both its vertical and horizontal profile during a good part of the long winter, and thaw completely during the short summer. But other considerations exists.

Let's examine what can happen when the snow thaw is sometime in June. The discharge signature for a river in the High Arctic is nival, with a discharge peak occurring during early summer due to the massive input of snowmelt water, and additional weaker responses from the small rain amounts. This looks like this:

Source: Woo (2012) Permafrost Hydrology Source: Woo (2012) Permafrost Hydrology, fig 10.14; from river McMaster, 74° N.

So what basically is happening here?

  1. Peak is during June.
  2. Afterward, once the snow had melted completely, the discharge lowered drastically.
  3. By late August, there is almost no more water in the river, and it may be completely recessed.
  4. Then winter arrives.

During the next several months, snow will accumulate in the landscape. In a landscape there are snow sources and snow sinks (Pomeroy et al. 1997); sources may be higher lands, outcrops, plateaus, or exposed areas, and sinks lower areas, such as depression or channels. Our typical nival river will be a sink in this context.

Because of this, it is not only patches of ice that will be found in the river channel, but tightly packed snow that builds up at the base when it is a thick layer (or is looser when the snowpack is thin). In any case snow will be most likely metamorphized in structure as a result of surface thaw and the water snowmelt infiltration -> snow percolation -> re-ice events during the winter.

What is happening in June, in more detail?
Let's analyse this further with a more detailed (though raw and unprocessed) graph from a small stream in a gully near Pond Inlet, with resolution available up to the nearest day:

Pressure and temperature in the bed of a stream gully, summer 2010 Source: Stream temperature and water pressure in a stream located in a gully on Bylot Island, 85 km from Pond Inlet; raw, partial data from my PhD work. Temperature in blue, scale on the right, and pressure in black, scale on the left. Dates on the x-axis.

By looking at the pressure line (in black), it can be interpreted that there was no water until June 16th when the pressure increased drastically. Temperature (in blue) stayed at -2 °C until the 17th. Water was infiltrating into the snow at this time, contributing to the slowly rising pressure, but the water did not reach the sensor until the 17th when the temperature starts rising. During the 18th, temperature rises to -0.5 °C, then hovers in these negative temperature for almost 24 hours. This supercooled water temperature is due to a mix of factors, such as increased pressure from the water on snow, the release of latent heat due to the metamorphized snow thawing, and the near zero temperature of the water, in balance with the snow.

When a critical mass of water accumulates near the logger emplacement in the stream channel, the bulk of the snow melt and water then shifts to positive temperatures, still near zero, with diurnal/nocturnal shifts (blue line becoming wave-like).

Note: This small stream is minimally impacted by the geothermal flux (heat flowing up from the ground below).

Summary, in relation to the questions:

  1. Temperature will be mostly above zero; but may be under and near zero for short periods when the water is mixing with snow and ice in a channel;
  2. Yes - as shown in the second figure, water was at -0.5 °C for about 24 hours;
  3. I think it is common, as thawing temperatures do reach very high latitudes such as Ward Hunt Island (83° N), and thus this process likely concerns a large area, including probably the entire Canadian Archipelago (lowlands at least). But this transition process does not last long at any location. Additionally, it is worth noting that High Arctic rivers are difficult to access, monitor, and study, so it is difficult to generalize this with confidence; other factors or contexts could exist where conclusions may differ.
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    $\begingroup$ Great answer Entienne. I certainly learned a lot, appreciate you taking the time to write it up. I hope you don't mind, because it was so useful I touched up the language to try to make it as approachable as possible to the general public. I tried carefully to not change any meanings, but if you have any trouble with my changes, feel free to shift back! $\endgroup$ – JeopardyTempest Jul 12 '17 at 6:05
  • $\begingroup$ Did have one question: when you say "the release of latent heat due to the metamorphized snow thawing", are you meaning to indicate the absorption of heat by the thawing metamorphized snow (thus cooling the water)? $\endgroup$ – JeopardyTempest Jul 12 '17 at 6:09
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    $\begingroup$ @JeopardyTempest Thank you - in fact I really appreciate the editing, this was a long one. Regarding your question - yes this was almost is what I meant - it does not cool the water, but can contribute to keep it somewhat stable just under the 0 degree C threshold. Let's underline that there is a mix of factors in interaction at this time, so this is not the sole source of this one day thermal stability. $\endgroup$ – Etienne Godin Jul 12 '17 at 13:23

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