Abstract Numerous mechanisms have been proposed for the formation of step‐pools in steep streams. Which of these mechanisms is responsible for constructing step‐pools may depend on flow conditions, with existing theory best developed for near‐critical flow conditions. Under subcritical flow conditions, however, channel roughness has been observed to exert control on step formation. To improve representation of step‐pool development under sub‐critical flow conditions, we develop a quantitative model exploring step‐pool construction in response to roughness variation. We incorporate variable roughness into a quasi‐2D Saint‐Venant Exner model in which steps emerge around roughness patches, consistent with the roughness‐based mechanism observed in previous experimental work. We compare model results to a field site that developed step‐pools in areas of high roughness in an initially plane‐bedded reach. Model results provide a mechanistic link between roughness variation and step spacing. For disturbed rivers similar to our field site, the location of rough patches may help inform expectations for early step‐pool evolution following river disturbance.
Erikson et al. (Sun,) studied this question.