Individual and step sequence stability lie at the nexus of a number of research topics in steep channels, including issues related to channel boundary roughness. While all steps in a step-pool sequence contribute to channel roughness, only stable steps can contribute in a predictable manner. If the number and spacing of steps frequently vary due to step instability, reliable estimates of total flow resistance and sediment transport rates through the channel during high flows will be difficult to develop. Information on step stability also has the potential to inform about the probability of step formation and destruction processes. For example, if the step destruction process under a known set of flow and sediment transport rates becomes predictable, the probability of step destruction for a given flow may become predictable. Because sediment transport rates have been shown to increase in the years immediately following a step destabilizing flow (Lenzi et al., 2004; Turowski et al., 2009), this type of predictability would prove useful. Pool development and scour depth are also related to step stability because a pool can form only while a step is stable. However, excessive scouring can also lead to step failure. The current research into pool formation and pool hydrodynamics is well summarized by Comiti and Mao (Chapter 26, this volume).
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