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> Do glaciers matter?
Andy Reynolds
post Jul 2 2005, 03:17 AM
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Do the Mackenzie River's glacial tributaries contribute much to the sediment load? Are there any glacial tributaries in the Lena River watershed? It looks like you are having a really interesting time!

Andy
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Max_Holmes
post Jul 4 2005, 12:47 AM
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Hi Andy,

Those are really good questions.

At the moment I'm sitting in a hotel in Yellowknife, which is on the shores Great Slave Lake. Great Slave Lake is in the middle of the Mackenzie River watershed. When the Mackenzie flows out of Great Slave Lake, its sediment load is very low because all the sediments settle out in the lake. So almost all of sediment that the Mackenzie River transports to the Arctic Ocean is picked up between here and Tsiigehtchic where we were earlier this week.

Where exactly does all the sediment come from? Frankly, I'm not sure. My assumption is that the tributaries coming in from the mountainous region to the west are responsible for most of the sediment load. In contrast, the tributaries to the east (which has much less topography) probably have a low sediment load. But these are just hypotheses (guesses!) on my part - I'd like to have the data to answer more definetively.

Though glacial streams do have very high sediment loads, I'm not sure how the abundance of glaciers differs between the Lena and Mackenzie watersheds. Again, my guess is that the difference is sediment flux is due more to the rock and soil types in the watershed, but I'd really like to learn more about this.

We could probably make good progress toward answering these questions by spending a bit of time in a library (or more likely on the internet). I'll see what I can come up with and I'd encourage you to do the same. You've asked some really fundamental questions that I'd like to be able to answer - please let me know if you figure it out!

Max

PS: I've attached a paper we published a few years ago about sediment flux from arctic rivers to the ocean. But it just addresses downstream fluxes, not where within the watershed sediment is being generated.


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Attached File  Holmes_et_al._Sediment_Flux_2002.pdf ( 333.32k ) Number of downloads: 19
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Max_Holmes
post Jul 4 2005, 01:13 AM
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Hi Andy,

Below is an abstract from a paper that was published in 1998 about sediment flux to the Mackenzie River Delta. It indicates that the majority of the sediment is coming from the west bank tributaries, particularly the Liard. The Liard drains a large part of the Canadian Rocky Mountains. The other west back tribs are also coming from the Canadian Rockies. We still need to figure out whether glaciers in the Canadian Rockies are a prime reason for the high sediment flux or if other characteristics of the watersheds are the explanation. Of course the other part of the question is why sediment flux in the big Eurasian arctic rivers is so incredibly low...

Have fun,

Max

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Magnitude and sources of sediment input to the Mackenzie Delta, Northwest Territories, 1974-94
Arctic, Jun 1998 by Carson, MA, Jasper, JN, Conly, F Malcolm

Save a personal copy of this article and quickly find it again with Furl.net. It's free! Save it.
Abstract. Hydrometric and sediment data collected by Environment Canada in the Mackenzie Basin during the period 197494 have been analyzed to produce detailed estimates of sediment inputs to the Mackenzie Delta, based largely on sediment rating equations. The mean annual sediment supply to the delta is determined as 128 million tonnes (Mt), of which about 4 Mt is sandy bed material moved in by the Mackenzie River itself. Virtually all of this sediment (more than 99%) is supplied to the delta during the May-October period, the peak months being May (27%), June (36%), and July (19%). About 17% of the fine-sediment load is supplied by the Peel River; the rest is delivered by the Mackenzie. The largest single contributor to the Mackenzie River wash load (103 Mt) is the Liard River (41 Mt). The preliminary estimate of the contribution of the other west-bank tributaries, in combination, is about 36 Mr, though this figure is probably too low. The precision of these estimates using the sediment rating approach (compared to time-integration during months with reasonable sampling frequency) is about 10% for the mean monthly sediment loads and about 5% for the mean annual sediment load during the 1974-94 period. The absolute accuracy of sediment load estimates is more difficult to assess because published flow data for delta inflow stations are acknowledged to be much less reliable for the spring breakup period than for other times of the year.
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Max_Holmes
post Jul 9 2005, 09:46 PM
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Hi again,

Here is an interesting photo of two rivers, one glacial and the other not. Obviously glaciers can have a huge impact on sediment concentration in rivers! We still need to figure out if that is the explanation for the high sediment flux in the Mackenzie and Yukon rivers in comparison to the Lena River (and other big Russian rivers).

Max


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