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Earth and Space Sciences · 术语表

什么是 Sediment load？

又称： bed load · suspended load · dissolved load

Definition 23.2 High School Earth and Space Sciences · 第 23 章 — The Destruction of Mountains

The sediment load of a river is the material it carries, in three forms: the bed load, large grains rolled, pushed or bounced along the bottom; the suspended load, small grains held up in the moving water; and the dissolved load, ions in solution, such as calcium and chloride, left by chemical weathering.

A braided river in a glacial mountain valley: shallow channels split and rejoin between bars of gravel that the water moves only in floods. AI-generated illustration.

示例

Example 23.4 (The Mississippi)

Before 1900, the Missouri–Mississippi river system carried about 400 million tonnes of sediment a year to the sea, from a basin of about $2\,980\,000\,\mathrm{km}^{2}$ . With the dissolved load, $400/0.85 \approx 471$ million tonnes, that is $4.71 \times 10^{11}/2830 \approx 1.66 \times 10^{8}\,\mathrm{m}^{3}$ of rock a year. Spread over $2.98 \times 10^{12}\,\mathrm{m}^{2}$ , it is a layer

\frac{1.66 \times 10^{8}}{2.98 \times 10^{12}} \approx 5.6 \times 10^{-5}\,\mathrm{m} \text{ a year, about } 56\,\mathrm{m}/\mathrm{Myr}.

Between 1987 and 2006 the river carried only 145 million tonnes a year, which gives about $20\,\mathrm{m}/\mathrm{Myr}$ : dams built on the Missouri in the 1950s trap about 100 to 150 million tonnes a year, and other works hold back more.

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