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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7<br />
<strong>The</strong> total mass <strong>of</strong> <strong>sediments</strong> removed yearly from <strong>the</strong> watershed <strong>of</strong><br />
each river, is given <strong>in</strong> Table 3 . <strong>The</strong> rivers <strong>of</strong> Group 1, with large watershed<br />
areas <strong>and</strong> annual discharges, carried vast amounts <strong>of</strong> <strong>sediments</strong> compared to<br />
<strong>the</strong> smaller rivers <strong>and</strong> streams <strong>of</strong> Group 2 . In order to compare natural erosion<br />
.<strong>rates</strong> <strong>of</strong> sediment from large <strong>and</strong> small watersheds, <strong>the</strong> annual mass <strong>of</strong> sediment<br />
<strong>transport</strong>ed was divided by <strong>the</strong> watershed area <strong>of</strong> <strong>the</strong> river . This<br />
resulted <strong>in</strong> an estimate <strong>of</strong> <strong>the</strong> average annual mass <strong>of</strong> sediment carried<br />
away from a square kilometer <strong>of</strong> <strong>the</strong> l<strong>and</strong> dra<strong>in</strong>age area <strong>of</strong> a river . This<br />
treatment <strong>of</strong> <strong>the</strong> data (Table 3) <strong>in</strong>dicates that <strong>the</strong> watersheds <strong>of</strong> small<br />
streams yielded much less sediment to <strong>the</strong> stream-per unit watershed area<br />
than did <strong>the</strong> large watersheds <strong>in</strong> Group 1 .<br />
<strong>The</strong> annual mass <strong>of</strong> sediment <strong>transport</strong>ed per unit watershed area was<br />
positively related to annual discharge (Fig . 2) . Rivers with annual discharges<br />
greater-than about 5 km3yr-1 <strong>transport</strong>ed 36 to 126-metric tons <strong>of</strong><br />
suspended sediment per km2 <strong>of</strong> watershed area, while rivers <strong>and</strong> streams with<br />
discharges from 0 .01 to 2 km3yr-1 <strong>transport</strong>ed 0 .2'to 12 metric tons <strong>of</strong><br />
<strong>sediments</strong> km-2yr-l . Some idea <strong>of</strong> <strong>the</strong> seasonal variation <strong>in</strong> <strong>the</strong>se parameters<br />
can be obta<strong>in</strong>ed from Fig . 2, where,-,3 years <strong>of</strong> discharge <strong>and</strong> sediment <strong>transport</strong><br />
are given for <strong>the</strong> Willowlake River, Liard River at Ft . Liard, <strong>and</strong> South<br />
Nahanni River above Virg<strong>in</strong>ia Falls : . .<br />
Bedload<br />
We tried to estimate <strong>the</strong> annual movement <strong>of</strong> cobbles <strong>and</strong> small boulders<br />
<strong>in</strong> <strong>the</strong> bed- <strong>of</strong> Jean Marie River (50'km SE <strong>of</strong> Ft . Simpson) . Jean Marie<br />
River has a watershed area (2,960 km-2) a little larger than Mart<strong>in</strong> River,<br />
<strong>and</strong> is probably similar to Mart<strong>in</strong> River <strong>in</strong> its annual discharge pattern,<br />
although it carries very low concentrations <strong>of</strong> suspended <strong>sediments</strong> (see<br />
Campbell •et aZ ., 1975) . We recovered over 90% <strong>of</strong> <strong>the</strong> pa<strong>in</strong>ted stones that<br />
were placed <strong>in</strong> . <strong>the</strong> stream bed, <strong>and</strong> found that <strong>the</strong> maximum distance moved<br />
<strong>in</strong> a year was less than 2 meters . Small stones (0 .10 kg) moved <strong>the</strong> most,<br />
while larger boulders (10-27 kg) moved very little (maximum <strong>of</strong> 0 .2 m for<br />
10 kg stones) or not at all .<br />
Oxygen Dem<strong>and</strong> <strong>of</strong> Sediments <strong>in</strong> Water<br />
Sediments from <strong>the</strong> banks <strong>of</strong>, <strong>the</strong> Harris River do consume measurable<br />
.amounts <strong>of</strong> 02 from water at 20-220C <strong>in</strong> <strong>the</strong> dark (Table 4) . <strong>The</strong>se data<br />
<strong>in</strong>dicate that 02 consumption per unit time was not related to <strong>the</strong> mass <strong>of</strong><br />
sediment added, nor to <strong>the</strong> fraction <strong>of</strong> organic matter <strong>in</strong> <strong>the</strong> added <strong>sediments</strong><br />
. However, Table 4 does <strong>in</strong>dicate that <strong>sediments</strong> added to oxygenated<br />
water may cause a reduction <strong>in</strong> 02' concentrations over a period <strong>of</strong> 10-30<br />
days .<br />
Similar experiments were .done <strong>in</strong> situ on Harris River on 1 August<br />
1974 . In this small, clear water stream, sealed, clear glass bottles<br />
(with vary<strong>in</strong>g amounts <strong>of</strong> suspended <strong>sediments</strong> added) were suspended <strong>in</strong> <strong>the</strong>