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W. M. Davis (1899) applied the term in a more specialized way to the talweg and valley of a river; where the erosional or degradational sector ends, the sedimentational or aggradation stage begins.
Mackin (1948), however, points out that the usual state of a stream is that of “grade” (as first proposed by Davis), and thus “degrading” or “aggrading” are both special cases where the equilibrium is shifting. “Regarding” refers to a simultaneous alteration in both senses in different sectors (Johnson, 1932). Short-term changes (scour and fill) should not be included in these terms, which refer to the general regime.
An “aggraded valley floor” (according to Cotton, 1952, p. 193) is a broad alluvial flat that is thicker than the depth of the stream channel.
- Cotton, C. A., 1952, Geomorphology, sixth ed., New York, John Wiley & Sons, 505pp.Google Scholar
- Davis, W. M., 1899, The geographical cycle, Geograph. J., 14, 481–504 (also Geographical Essays, New York, Dover, reprint, 1954).Google Scholar
- Mackin, J. H., 1948, Concept of the graded river, Bull. Geol. Soc. Am., 59, 463–512.Google Scholar
- Moody, A. E., 1907, Aggradation and degradation of valleys, Ohio Nat., 8, 191–197.Google Scholar
- Salisbury, R. D., 1893, Annual Report (for 1892), Surface geology, New Jersey Geol. Surv., 37–166.Google Scholar