Refining Geomorphic Heterogeneity as a Framework for Assessing River Corridor Processes and Characteristics

Abstract

Heterogeneity, or messiness, is a broadly desirable characteristic of river corridors and an indicator of many of the geomorphic processes that sustain fluvial ecosystems. However, quantifying geomorphic heterogeneity is complicated by a lack of consistent metrics, methods of dividing up the river corridor into the patches that form the basis for those metrics, and guidance on interpreting metrics. Drawing from both geomorphic and landscape ecology concepts, we offer ideas and guidance intended to help investigators, from researchers to restoration practitioners, more effectively and reliably use heterogeneity to describe river corridor processes and characteristics. We define geomorphic heterogeneity as having both a spatial and temporal dimension. Spatially, heterogeneity can be described by diversity, or the evenness and richness of geomorphic units, and spatial configuration, or the arrangement of geomorphic units relative to one another. Temporally, heterogeneity can be described by turnover rate, or the rate of change of geomorphic units. Interpretation of heterogeneity metrics depends integrally on the definition of the geomorphic unit schema on which metrics are based. Contextual information, such as measurements of process space, disturbance frequency, and geomorphic trajectory, can also be key to using effective measurements of heterogeneity. Geomorphic applications of heterogeneity require carefully defined geomorphic unit schemas that reflect processes and characteristics of interest, robust metrics of heterogeneity whose meaning is appropriate to the question at hand, and interpretation of those metrics based on the context of expected geomorphic processes and the frequency of disturbance.

Rehabilitating Valley Floors to a Stage 0 Condition: A Synthesis of Opening Outcomes

“…Wood mapping in imagery was supplemented by qualitative assessment of 1-h interval timelapse imagery collected during high flows at two locations in the project area. At Deer Creek in the central Oregon Cascades, wood movement was monitored in detail by mapping all visible pieces in orthomosaics generated from aerial imagery (Scott et al, 2022). Orthomosaics were created by collecting images from drone flights at low altitude over the site, then processing images using structure-from-motion photogrammetry with a ground resolution on the order of 1 cm.…”