Channel-forming flow: representations and variability

Determining the channel-forming flow is a critical stage in the channel restoration design process. While there are several 'representations' of this flow (the bankfull, recurrence interval and effective discharges), previous research has revealed that they are not necessarily equivalent and further investigation based on a dataset of U.S. meandering sand-bed streams supports further their differentiation under certain conditions. This uncertainty presents a challenge to the channel designer early in the design process. This paper explores the variability between the channel-forming flow representations and provides an explanation based on flow variability to account for some of the differentiation. The paper closes with a discussion of a 'sediment impact assessment' as a closure loop to the design process, in order to better account for the full range of sediment-transporting flows and ensure long term dynamic stability.