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

Abstract

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).

Short-term geomorphological evolution of proglacial systems

“…Where lateral moraines are developed they provide space between their crests and an adjacent hillslope, intercepting rockfalls and debris flows (Heckmann et al, 2016b). The width and gradient of a (proglacial) valley, and the existence or lack of lateral confinement by moraines or stretches of bedrock has profound impacts on sediment transfer and geomorphological activity (Laute and Beylich, 2014;Temme and Lange, 2014;Beylich and Laute, 2015;Fryirs et al, 2016) and the accommodation space for intermediate storage landforms (e.g. Cavalli et al, in review).…”

A geomorphic assessment to inform strategic stream restoration planning in the Middle Fork John Day Watershed, Oregon, USA

“…Reach breaks are identified through changes in valley setting and associated channel confinement (Fryirs, Wheaton, & Brierley, 2016b), river planform, the assemblage of geomorphic units (i.e. floodplain and channel landforms; cf.…”

“…Valley confinement is a key driver of reach breaks throughout a watershed (e.g. Fryirs, Wheaton, & Brierley, 2016a;Montgomery & Buffington, 1997) (see Plate 3). The degree of confinement controls the ability of a channel to adjust laterally and, to some extent, vertically on the valley bottom.…”

“…The degree of confinement controls the ability of a channel to adjust laterally and, to some extent, vertically on the valley bottom. Measures of confinement are used to differentiate valley settings (Brierley & Fryirs, 2005;Fryirs et al, 2016a).…”

Mapping valley bottom confinement at the network scale

“…Geomorphologists have developed a good understanding of primary controls upon channel geometry and planform in fully alluvial settings in which the channel creates its own morphology, based upon relations between slope, discharge, bed material size and bank strength (e.g. These end-members, and the continuum of rivers that lie between them, are influenced by confinement, which characterizes the extent to which a channel freely adjusts across the valley bottom (Fryirs and Brierley, 2010;Fryirs et al, 2016). Such situations contrast starkly with fully imposed (forced) morphologies of bedrock rivers (e.g.…”