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Read Full Article (file size: 421956 bytes) Cited by
JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 111,
F04009,
doi:10.1029/2006JF000467,
2006
Form drag in rivers due to small-scale natural topographic features: 1. Regular sequences
Jason W. Kean
U.S. Geological Survey, Boulder, Colorado, USA
J. Dungan Smith
U.S. Geological Survey, Boulder, Colorado, USA
Abstract
Small-scale topographic features are commonly found on the boundaries of natural rivers, streams, and floodplains. A simple
method for determining the form drag on these features is presented, and the results of this model are compared to laboratory
measurements. The roughness elements are modeled as Gaussian-shaped features defined in terms of three parameters: a protrusion
height, H; a streamwise length scale, σ; and a spacing between crests, λ. This shape is shown to be a good approximation to a wide variety of natural topographic bank features. The form drag on
an individual roughness element embedded in a series of identical elements is determined using the drag coefficient of the
individual element and a reference velocity that includes the effects of roughness elements further upstream. In addition
to calculating the drag on each element, the model determines the spatially averaged total stress, skin friction stress, and
roughness height of the boundary. The effects of bank roughness on patterns of velocity and boundary shear stress are determined
by combining the form drag model with a channel flow model. The combined model shows that drag on small-scale topographic
features substantially alters the near-bank flow field. These methods can be used to improve predictions of flow resistance
in rivers and to form the basis for fully predictive (no empirically adjusted parameters) channel flow models. They also provide
a foundation for calculating the near-bank boundary shear stress fields necessary for determining rates of sediment transport
and lateral erosion.
Received 11
January
2006;
accepted 11
August
2006;
published 6
December
2006.
Keywords: drag;
flow resistance;
roughness.
Index Terms: 1825 Hydrology: Geomorphology: fluvial (1625); 1858 Hydrology: Rocks: chemical properties; 1860 Hydrology: Streamflow; 1861 Hydrology: Sedimentation (4863); 1847 Hydrology: Modeling.
Read Full Article (file size: 421956 bytes) Cited by
Citation: Kean, J. W., and J. D. Smith
(2006),
Form drag in rivers due to small-scale natural topographic features: 1. Regular sequences,
J. Geophys. Res.,
111,
F04009,
doi:10.1029/2006JF000467.
This paper is not subject to U.S. copyright. Published in 2006 by the
American Geophysical Union.
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