Fundamentals of Fluvial Geomorphology and Channel Processes
Figure 3.15 Hickahala Creek Watershed, Slope-drainage Area Relationship
stability numbers: Ng is a measure of bank stability and Nh is a measure of sediment continuity. For a
channel to be stable, sediment continuity and bank stability are essential.
Ng is defined as the ratio between the existing bank height and angle (h) and the critical bank
height at the same bank angle (hc). Bank stability is attained when Ng is less than unity (Ng < 1).
Therefore, Ng provides a rational basis for evaluating the requirements for bank stabilization and for
evaluating the consequences of further bed degradation.
The hydraulic stability number, Nh, is defined as the ratio between the desired sediment supply
and the actual sediment transport capacity. Sediment continuity yields Nh = 1.0. It is important to note
that the definition of Nh includes sediment transport and supply, which is in contrast to most channel design
procedures. Hydraulic stability in the channel is attained when Nh = 1. If Nh is < 1 the channel will
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