Flow and Bed Topography in the Mississippi River
1991
Thorne, Colin R. | Hubbard, Lisa J.
A data base for bend geometry, flow pattern and bed topography of selected bends on the Lower Mississippi River was compiled. Preliminary analysis was undertaken to establish the applicability of analytical and empirical models to predict scour depth and outer bank velocity at bends. The results indicate that the 1982 model (by J.S. Bridge) of bend flow may be used to predict scour depth associated with formative flows in the channel, usually with an accuracy of about + or - 10 to 20%. Scour predictions for flows other than those around the formative discharge are prone to greater uncertainty and tend to underestimate the observed scour depth. Application of the model is not recommended for such flows. Velocity may also be predicted for formative flows provided that the ratio of bend radius to width is greater than about 4. The WES design line for outer bank velocity prediction is very conservative in that it always over predicts the observed outer bank velocity. It did not do quite as well as the Bridge model, overall. In many cases observed near bank velocities were similar to or less than the mean velocity at the crossing upstream. This runs contrary to established theory and observation and casts some doubt on the validity of the data. The validity of the field data deserves further investigation.
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