Substrate Influences on Step-Pool Sequences in the Christopher Creek Drainage, Arizona

Step-pool sequences formed in alluvial and bedrock channel segments of the Christopher Creek drainage in central Arizona suggest that bedform geometries may reflect subtle differences in relative substrate resistance and in the ratio of driving forces to resisting forces. Three alluvial channel segments and two bedrock channel segments along a 72-km2 drainage and a 4-km2 drainage facilitated comparison across different substrates and hydraulic environments. As substrate resistance increased or the ratio of hydraulic driving forces and boundary resisting forces decreased, channel gradient increased, the ratio of step height to length normalized by gradient decreased, and pool dimensions normalized by gradient decreased. These changes in bedform geometry suggest that as the ratio of driving to resisting forces increases, proportionally more flow energy is dissipated within the flow as turbulence and shearing (as in the alluvial reaches) rather than being applied to erosion of the channel boundaries (as in the bedrock reaches).