An approach for measuring confinement and assessing the influence of valley setting on river forms and processes

Valley setting and confinement (or lack thereof) are primary controls on river character and behaviour. Although there are various proxies for valley confinement, direct measures that quantify the nature and extent of confinement are generally lacking and/or inconsistently described. As such they do not lend themselves to consistent analysis over large spatial scales. Here we clearly define forms of confinement to aid in quantification of degrees of confinement. Types of margin that can induce confinement are differentiated as a valley margin, valley bottom margin, and/or anthropogenic margin. Such margins sometimes overlap and share the same location, and in other situations are separated, giving immediate clues as to the valley setting. We apply this framework to examples from Australia, United States and New Zealand, showing how this framework can be applied across the spectrum of river diversity. This method can help to inform interpretations of reach-scale river behaviour, highlighting the role of antecedent controls on contemporary forms and processes. Clear definitions of confinement are shown to support catchment-scale analysis of river patterns along longitudinal profiles, and appraisals of the geomorphic effectiveness of floods and sediment flux in catchments (e.g. process zone distribution, lateral sediment inputs and (dis)connectivity).