FIELD EVALUATION OF EMPIRICAL EQUATIONS IN STRAIGHT ALLUVIAL CHANNELS |
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| Authors: | Mark R Welford |
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| Institution: | Department of Geology and Geography , Georgia Southern University , Landrum Box 8149 Statesboro, Georgia 30460-8149 |
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| Abstract: | Six experimentally derived formulae that predict the conditions for alternate bar formation and equilibrium bar dimensions are assessed using field data. The study site is an artificially straightened section of the Embarras River located approximately 16 km south of Champaign, Illinois. Data were collected on channel form, gradient, alternate bar dimensions, bar sediment size, and flow conditions over a two-year study period. Experimental flume studies suggest that alternate bars form in wide, straight, shallow streams, have wavelengths between 4 and 15 channel widths, and have heights that are roughly equal to the average depth of flow. Bar formation under unsteady flow conditions can be predicted accurately by the experimentally derived steady-flow formulae, but these formulae fail to predict bar dimensions sucessfully. These results suggest that the process of bar formation in artificially straightened, sand-bedded natural streams may occur outside the range of flow conditions predicted by existing empirical models. Further work should focus on attempting to isolate physical mechanisms responsible for alternate bar formation in straight natural streams with heterogeneous bed material and flashy flow regimes Key words: alluvial channels, artificial channels, geomorphology, rivers, sedimentology]. |
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