Cross-section, bedform and bar unit asymmetry in river channel networks: an investigation into morphologic complexity and diversity at multiple spatial scales

摘要

Complexity and diversity are typically assessed by determining the variety of geomorphic structures within a river (e.g., benches, bars, islands, riffles, etc.) or its external variability. An alternative approach is to examine the variety of forms within a specific geomorphic structure (e.g., the variety of riffle morphologies along a river) or its internal variability. Although both of these approaches have merit, in systems containing only a small number of unique geomorphic structures, considering external variability alone may underestimate morphologic diversity and complexity. One way to assess internal variability is through the use of asymmetry. Asymmetry is a measure of how unbalanced a feature is (in terms of either its form or process) and in geomorphic terms, implies a tendency towards irregularity and complexity. This investigation determined the internal variability and thus geomorphic complexity and diversity as a function of increasing channel dimension (progressing from lower order through to higher order streams) in an upland river network. This was achieved by assessing the internal variability of pool-riffle sequences (bar units) and their constituent components (e.g. pools and riffles) using a set of asymmetry indices. The results of this Study show that asymmetry does not vary with scale and that the morphologic diversity of bed forms and bar units is also scale independent.