Material Fluxes on the Surface of the Earth (1994) / Chapter Skim
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Geomorphic/Tectonic Control of Sediment Discharge to the Ocean: The Importance of Small Mountainous Rivers
Geomorphic/Tectonic Control of Sediment Discharge to the Ocean: The Importance of Small Mountainous Rivers
Pages 74-85
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From page 74... ...
A notable exception is the influence of human activity, climate, and geology on the rivers draining southern Asia and Oceania. Sediment fluxes from small mountainous rivers, many of which discharge directly onto active margins (e.g., western South and North America a most high-standing oceanic islands)
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From page 75... ...
reported that sediment yield increases by about seven-fold for every order of magnitude decrease in drainage basin area, but this correlation considered only rivers with sediment loads >15 million tons (mt) /yr, thereby excluding rivers with smaller sediment loads.
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From page 76... ...
Still, as seen in the following analysis, our elevation-based classification seems valid. Geomorphologists and hydrologists often use the terms "yield," "sediment yield," or "specific yield" to compare sediment loads between disparate river basins by normalizing sediment load relative to size of the river basin (t/km2/yr)
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From page 77... ...
, no upland, lowland or coastal plain river has a sediment load >20 mt, even though more than 25 upland and lowland rivers have drainage basin areas >100,000 km2. In contrast, nearly 60 mountainous rivers have loads 220 mt (Table 1, Milliman and Syvitski, 1992~.
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From page 78... ...
MILLIMAN AND JAMES P.M. SYVITSKI DISCHARGE OF SEDIMENT BY WORLD RIVERS Most nvers draining eastern North Amenca are upland, lowland, or coastal plain nvers, with correspondingly low sediment loads.
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From page 79... ...
G = COASTAL PLAIN (<100m) Europe FIGURE 5.4 Relation of sediment yield and runoff for the seven topographic categories of river basins listed in Table 1 (Milkman and Syvitski, 1992)
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From page 80... ...
Although poorly documented in western literature, the rivers draining the Caucasus Mountains and the Anatolian and Taurus mountains in Turkey have high sediment yields, which is to be expected from rivers draining the same collision orogen as the Alps. Before dam construction in the 1950s, the three largest Turkish rivers emptying into the Black Sea discharged an estimated 50 mt of sediment annually (Hay, 19871.
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From page 81... ...
are nonmountainous, and many small rivers in western Africa are lowland rivers, with correspondingly low sediment loads/yields. The major sediment discharge comes from rivers draining the rift mountains in eastern Africa (Nile, Zambesi, Limpopo, Rifiji)
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From page 82... ...
In contrast, average net precipitation and runoff generally affect sediment discharge to a lesser extent. For example, the Orange, Sous, and Isser rivers, which drain arid basins, have similar or slightly lower sediment yields than mountainous rivers with moderate rainfall, whereas rivers draining areas with very heavy precipitation (e.g., Solo, Purari, Cooper)
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From page 83... ...
, the annual sediment discharge 2000-2500 yr ago may have been considerably <10 bt. Extensive human influence in Oceania and southern Asia suggests that sediment loads in this area are disproportionately elevated.
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From page 84... ...
was 140 mt, compared to normal annual load for the Columbia of 10 mt (Hubbell et al., 1983~; for the few years after the eruption, the Columbia River discharged an estimated 35 mt/yr (Meade and Parker, 19851. Smaller mountainous rivers are therefore more likely to discharge larger percentages of their sediment loads directly to the sea than do larger rivers.
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From page 85... ...
. Sediment yield and spurious correlation—Toward a better portrayal of the annual suspended-sediment load of rivers, Geomorphology 1, 309-316.
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