Fundamentals of Engineering Design
Figure 5.36 Slope as Function of Discharge (USACE, 1994)
The charts are more compatible with single-channel sand or gravel systems with relatively low
bed material transport. A multichannel system will tend to have greater overall widths and
slopes but smaller depths. However, individual branches may fit the curves reasonably in
relation to their partial bank-full discharges.
If bed material transport is high, the slopes indicated in Figure 5.36 may be too low and the
depths in Figure 5.35 may be too high. This is especially true for channels with sand beds and
of ephemeral channels where much of the flow occurs as flash floods with very high sediment
transport. In perennial-flow gravel rivers with single channels, slopes are unlikely to be more
than three times greater than those indicated by Figure 5.36. Width is fairly insensitive to bed
material transport unless the stream is multichanneled or braided. If bed material transport
is high, it is preferable to use a sediment budget analysis. This is when field observations and
checks of velocity, shear stress, or hydraulic geometry indicate a substantial degree of actual
or potential bed instability and sediment transport.