The chemistry, mineralogy, and rates of transport of sediments in the ...
The chemistry, mineralogy, and rates of transport of sediments in the ...
The chemistry, mineralogy, and rates of transport of sediments in the ...
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19<br />
<strong>and</strong> velocity (Fig . 1) . For <strong>the</strong>se reasons, Group 3 rivers, <strong>and</strong> <strong>the</strong><br />
Mackenzie at Norman Wells, were excluded from most <strong>of</strong> <strong>the</strong> regression<br />
analyses . This group <strong>of</strong> rivers tends to be ra<strong>the</strong>r productive biologically,<br />
<strong>and</strong> is frequently a migration route for fish (Brunskill et at ., 1973 ;<br />
Hatfield, 1972) .<br />
Comparison <strong>of</strong> Sediment Transport <strong>in</strong> <strong>the</strong> Mackenzie Valley with O<strong>the</strong>r<br />
Subarctic, Arctic, <strong>and</strong> Temperate Regions .<br />
Table 16 <strong>in</strong>dicates that <strong>the</strong> large Subarctic <strong>and</strong> Arctic rivers-(Group<br />
1 <strong>in</strong> Table 1) <strong>of</strong> <strong>the</strong> Mackenzie <strong>and</strong> Porcup<strong>in</strong>e watershed <strong>transport</strong> relatively<br />
large amounts <strong>of</strong> suspended sediment per unit watershed area, compared to<br />
o<strong>the</strong>r major North American rivers . This occurs despite 6-7 months <strong>of</strong> . ice<br />
cover <strong>and</strong> frozen watersheds dur<strong>in</strong>g <strong>the</strong> relatively long w<strong>in</strong>ters <strong>of</strong> <strong>the</strong><br />
Mackenzie Valley, compared to year-around open-water flow <strong>in</strong> some <strong>of</strong> <strong>the</strong><br />
Temperate Zone rivers-listed <strong>in</strong> Table 16 . This may be <strong>the</strong> result <strong>of</strong> less<br />
l<strong>and</strong> stabilization by vegetation <strong>in</strong> <strong>the</strong> headwaters <strong>of</strong> <strong>the</strong>se large rivers<br />
<strong>in</strong> <strong>the</strong> Mackenzie Valley, . <strong>the</strong> presence <strong>of</strong> degrad<strong>in</strong>g permafrost tables, <strong>and</strong><br />
relatively great relief <strong>in</strong>most <strong>of</strong> <strong>the</strong>se watersheds .<br />
Corbel (1964) estimated, based largely on precipitation <strong>and</strong> evapotranspiration,<br />
an average erosion rate <strong>of</strong> 52 mt kn -2yr-1 for <strong>the</strong> entire<br />
Mackenzie watershed, which is remarkably-close to our largely measured<br />
estimate <strong>of</strong> 68 mt km- 2yr-1 (Table 16) . Our Eq . 5, or improvements on<br />
it from more detailed <strong>and</strong> longer records <strong>of</strong> data, could be used with<br />
similar equations developed by Jansen <strong>and</strong> Pa<strong>in</strong>ter (1974) to estimate<br />
erosion <strong>rates</strong> for unsampled watersheds <strong>in</strong> <strong>the</strong> Mackenzie Valley lowl<strong>and</strong>s .<br />
A separate evaluation <strong>of</strong> small mounta<strong>in</strong> streams will have to be made,<br />
because Eq .-2-5 do not apply to <strong>the</strong>se types <strong>of</strong> watersheds . It seems<br />
likely that our Eq . 2-5 will not be <strong>of</strong> use for predict<strong>in</strong>g sediment or<br />
particulate nutrient <strong>transport</strong> <strong>rates</strong> <strong>in</strong> most o<strong>the</strong>r areas - <strong>of</strong> <strong>the</strong> North<br />
American Arctic <strong>and</strong> Subarctic . . <strong>The</strong> Mackenzie Valley appears to be<br />
somewhat exceptional'' <strong>in</strong> <strong>the</strong> relative abundance <strong>of</strong> trees <strong>and</strong> higher<br />
vegetation,- a relatively moderate climate, <strong>and</strong> an abundance <strong>of</strong> easily<br />
eroded lacustr<strong>in</strong>e <strong>and</strong> glaci<strong>of</strong>luviatile <strong>sediments</strong> <strong>in</strong> <strong>the</strong> Mackenzie Valley<br />
lowl<strong>and</strong>s . Most watersheds <strong>of</strong> <strong>the</strong> eastern North American Subarctic <strong>and</strong><br />
Arctic have a much more severe climate, less vegetation, <strong>of</strong>ten less<br />
erodible (or soluble) surface soils, <strong>and</strong> less' relief .<br />
Table 16 also <strong>in</strong>dicates that <strong>the</strong> smaller (Group 2) watersheds have<br />
moderate or low <strong>rates</strong> <strong>of</strong> <strong>transport</strong> <strong>of</strong> <strong>sediments</strong>, compared to o<strong>the</strong>r Arctic,<br />
Subarctic <strong>and</strong> Temperate zone watersheds . This proportional relationship<br />
between a) watershed area or annual discharge, <strong>and</strong> b) annual <strong>transport</strong><br />
rate found for Mackenzie watersheds is <strong>the</strong> <strong>in</strong>verse <strong>of</strong> <strong>the</strong> same relationships<br />
found <strong>in</strong> temperate North American watersheds (see Ritter, 1967) .<br />
Accord<strong>in</strong>g to Ritter, smaller watersheds (Ad .c80 km 2 ) . <strong>in</strong> temperate regions<br />
<strong>of</strong> North America have greater-sediment <strong>transport</strong> <strong>rates</strong> than larger rivers .<br />
,We emphasize that <strong>the</strong> smaller watersheds <strong>in</strong> Group 2 <strong>of</strong> Table 1 are all <strong>in</strong><br />
<strong>the</strong> Mackenzie lowl<strong>and</strong>s, <strong>and</strong> do not <strong>in</strong>clude any <strong>of</strong> <strong>the</strong> numerous mounta<strong>in</strong> streams<br />
<strong>in</strong> <strong>the</strong> Nahanni, Mackenzie, Richardson, <strong>and</strong> British Mounta<strong>in</strong>s to <strong>the</strong> west .