Drivers of geomorphic heterogeneity in unconfined non-perennial river corridors

Authors: SCAMARDO, J. - Colorado State University; Nichols, Mary; RITTENOUR, T. - Utah State University; WOHL, E. - Colorado State University

Submitted to: Journal of Geophysical Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: River corridors along streams that do not have water year-round are known to provide diverse physical and ecological functions that are thought to be related to geomorphic heterogeneity. Geomorphic heterogeneity refers to the variability of geomorphic patches within the river corridor in space and time. While studies on the magnitude and drivers of geomorphic heterogeneity are emerging in perennial streams that have water in them throughout the year, similar studies in non-perennial (normally dry) streams are lacking. Because non-perennial streams are found throughout the globe, we aim to answer questions regarding the magnitude and drivers of geomorphic heterogeneity in non-perennial river corridors and to understand how flood disturbance affects channel and floodplain shape. Geomorphic units were mapped in 30 river corridors within six non-perennial watersheds in Utah and Arizona, USA. Landscape heterogeneity metrics were used to quantify geomorphic heterogeneity within each reach. Additionally, variables that may 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 channel shape and disturbance, statistical models suggest that floodplain width was a more important predictor for estimating geomorphic heterogeneity. Sediment accumulation occurred across a range of flood energies, suggesting a strong tie between heterogeneity and flood disturbance.

Technical Abstract: River corridors along non-perennial stream networks are known to provide diverse physical and ecological functions that are thought to be related to geomorphic heterogeneity. Geomorphic heterogeneity refers to the spatial and temporal variability of geomorphic units, which are geomorphic patches within the river corridor formed by a given set of processes. While studies on the magnitude and drivers of geomorphic heterogeneity are emerging 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 non-perennial river corridors as well as how geomorphic units and heterogeneity 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 may 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 floodplain 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.