Drivers of Geomorphic Heterogeneity in Unconfined Non‐Perennial River Corridors

Abstract

AbstractRiver corridors along non‐perennial stream networks provide diverse physical and ecological functions that are thought to be related to the spatial and temporal variability of geomorphic units, also known as geomorphic heterogeneity. While studies on the characteristics and drivers of geomorphic heterogeneity have been developed in perennial streams, similar studies in ephemeral streams are lacking. Given the ubiquity of non‐perennial streams globally, we aim to answer questions regarding the magnitude and drivers of geomorphic heterogeneity in ephemeral river corridors as well as how geomorphic unit assemblages reflect processes related to flood disturbance. Geomorphic units were mapped in 30 unconfined river corridors within six non‐perennial watersheds in Utah and Arizona, USA. Landscape heterogeneity metrics—Shannon's Diversity Index, Shannon's Evenness Index, and patch density—were used to quantify geomorphic heterogeneity within each reach. Additionally, variables that potentially constrain or drive heterogeneity were quantified, including floodplain shape, grain size, large wood abundance, and proxies for flood disturbance. While heterogeneity positively correlated with metrics for morphology and disturbance, statistical models suggest that morphologic context, particularly river corridor width, was a more important predictor for estimating geomorphic heterogeneity. Still, geomorphic units reflected aggradation processes indicative of a range of flood energies, suggesting a strong tie between heterogeneity and disturbance. Results suggest that geomorphic heterogeneity may be resilient to changes in flood disturbance frequency or magnitude, but future studies investigating long‐term temporal heterogeneity are needed.