Surface Films Affecting Velocity Profiles of Slowly Moving Water in Open Channels

Kemper, W.D. and Humpherys, A.S. and Bondurant, J.A. (1984) Surface Films Affecting Velocity Profiles of Slowly Moving Water in Open Channels. Irrigation Science. 5:235-250.

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Abstract

Rates of movement of surface films and underlying water were
measured using observable solid and liquid tracers. Water flow rate, surface
width, water depth, and channel length were varied in flumes in which the
water was allowed to flow over a broad weir crest at the tail end. In some runs
the surface was blocked 5 cm in front of the weir. When this was done, velocity
of the surface film immediately upstream from the block decreased to a small
fraction of its previous value and this area of slow surface velocity built
upstream with time, extending to as far as several meters under steady state
conditions. In this reach, the film at the air-water interface of the water causes
drag on the moving water similar to that at a solid-water interface.
Water surface in channels one cm wide and 100 cm long stopped moving
when the shear force caused by water flowing beneath it dropped to less than
0.0013 dynes/cm². This indicates structure in the surface which does not deform
or shear at rates proportional to the force applied. Average water flow velocities
from 0.3 to 1 cm per second provided shear stresses in excess of 0.002 dynes/cm²
and moved these surface films. However, the velocity distribution across the
surface of the channel was not parabolic, and indicated that most of the shear in
the film was taking place near the edges of the channel. Extrapolation of these
observations to water film dimensions present in unsaturated soils indicates that
air-water interfaces in unsaturated soils are usually static.

Item Type:	Article
NWISRL Publication Number:	0535
Subjects:	Mass Import - unclassified
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:52
Last Modified:	13 Jan 2017 23:08
Item ID:	425
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/425