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Eric -
First, my disclaimer: Because of the diverse nature of landscapes, the
variation in longitudinal stream/river profiles is almost limitless.
For this reason it is important to keep in mind that stream width,
depth, velocity, slope, and channel roughness interact differently
across such systems.
That being said, some broad patterns have been observed. As you stated,
slopes are generally steeper in the headwaters then become more gradual
downstream. Width, depth, and discharge may increase as well, but width
tends to increase more so than depth (in general). However, Leopold
(1962, American Scientist 511-537) found that velocity may vary little
from upstream areas. Of course velocity does increase with gradient,
but Leopold's observation of low variation in longitudinal velocities
can be partially explained by the fact that as one moves downstream
depth increases and channel roughness decreases (fewer boulders, more
sand). This results in decreased resistance in downstream areas,
offsetting the effects of a more gradual slope. This
velocity-slope-resistance relationship is summarized in the Manning
equation. Your student's stream ecology professor may indeed be
correct.
For more information see J.D. Allan's book Stream ecology: Structure and
function of running waters (1995) or Gordon et al.'s Stream hydrology:
An introduction for ecologist's (1992). Contact me directly if you need
more references. Good luck.
Jarrad Kosa
e-mail: [log in to unmask]
KY Dept. of Fish and Wildlife Resources
#1 Game Farm Rd.
Frankfort, KY 40601
phone: (502) 564-5448, ext. 363
fax: (502) 564-4519
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