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Earth and Space Sciences · 术语表

什么是 Base level and knickpoint？

又称： base level · knickpoint

Definition 18.13 University Earth and Space Sciences — Year 3 · 第 18 章 — Quantitative Geomorphology

The base level of a river is the elevation of its outlet, below which it cannot cut: the sea, a lake, or the trunk river it joins. A knickpoint is a place where the gradient of a river’s long profile increases abruptly, from a steepened reach to a waterfall.

Left, the upland river after a fall of 25\, m of its base level (n = 1): the knickpoint, a waterfall of constant height, reaches 1.7, 3.3 and 4.6\, km above the outlet after 300, 600 and 900\, kyr; below it the river has the old shape, 25\, m lower. Right, chi plot (A_0 = 1\, km2, = 0.5) of the trunk and three tributaries at 900\, kyr: below = 900\, m every channel lies on the steady-state line through the outlet (dashed), above it on the old line, 25\, m higher. The waterfalls of the trunk and of tributary 3 sit at the same (red triangle); tributaries 1 and 2 join the trunk above it and have not yet been reached. — Left, the upland river after a fall of $25\,\mathrm{m}$ of its base level ( $n = 1$ ): the knickpoint, a waterfall of constant height, reaches 1.7, 3.3 and $4.6\,\mathrm{km}$ above the outlet after 300, 600 and $900\,\mathrm{kyr}$ ; below it the river has the old shape, $25\,\mathrm{m}$ lower. Right, chi plot ( $A_0 = 1\,\mathrm{km}^{2}$ , $\theta = 0.5$ ) of the trunk and three tributaries at $900\,\mathrm{kyr}$ : below $\chi = 900\,\mathrm{m}$ every channel lies on the steady-state line through the outlet (dashed), above it on the old line, $25\,\mathrm{m}$ higher. The waterfalls of the trunk and of tributary 3 sit at the same $\chi$ (red triangle); tributaries 1 and 2 join the trunk above it and have not yet been reached.

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