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The effect of bed mobility on resistance to overland flow
Author(s) -
Hu Shixiong,
Abrahams Athol D.
Publication year - 2005
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.1223
Subject(s) - flume , flow (mathematics) , bed load , flow resistance , hydrology (agriculture) , sediment , geology , momentum (technical analysis) , flow velocity , mechanics , geotechnical engineering , sediment transport , environmental science , physics , geomorphology , finance , economics
When sediment grains are transported as bed load in overland flow, there is a net transfer of momentum from the flow to the grains. When these grains collide with other grains, whether on the bed or in the flow, streamwise flow velocity decreases and resistance to flow increases. Resistance to flow generated in this manner is termed bed‐load transport resistance. Resistance to flow f over a plane bed may be partitioned into grain resistance f g and bed‐load transport resistance f bt . We use the symbols f btf and f btm to denote f bt for flows over fixed beds and over mobile beds, respectively, and we compute the effect of bed mobility on flow resistance f mob by subtracting f btf from f btm . The data for this study come from 54 flume experiments with fixed beds and 38 with mobile beds. On average f mob is approximately equal to half of f btm , which is about one‐quarter of f . Hence, f mob is about one‐tenth of f . Predictive equations are developed for f btf , f btm and f mob using dimensional analysis to identify the relevant independent variables and regression analysis to evaluate the coefficients associated with these variables. Values of f mob are always positive which implies that mobile beds offer greater resistance to flow than do fixed beds. Evidently bed‐load grains colliding with mobile beds lose more momentum to the bed than do grains colliding with fixed beds. In other words, grain collisions with mobile beds are less elastic than those with fixed beds. Copyright © 2005 John Wiley & Sons, Ltd.