Development of a geomorphic monitoring strategy for stage 0 restoration in the South Fork McKenzie River, Oregon, USA

Abstract

The South Fork McKenzie River (SFMR) in western Oregon, USA hosts one of the largest Stage 0 stream restoration projects implemented to date. Stage 0 refers to a multichannel planform with strong hydrologic connectivity to the adjacent floodplain and surface–subsurface connectivity. Stage 0 restoration was implemented on a 900‐m‐long reach of the SFMR by re‐grading the channel and floodplain using 65,000 m3 of sediment to raise the channel bed. Thousands of large logs were added and the ends of some logs were buried in the sediment to provide foundations for future log jams. Our primary objective is to present a monitoring protocol based on randomly located sampling plots. We also analyze results from 2 years of data collection since project implementation. Within each plot, we measured canopy cover, wood volume, flow depth and velocity, organic cover (area covered by coarse and fine organic material), and substrate grain size. We used intracluster correlation coefficients and variance of measured variables to assess heterogeneity at three spatial scales: within plots, between adjacent plots, and across the entire site. Here, we evaluate changes in the first 2 years after restoration (i.e., not pre‐ vs. post‐restoration). We hypothesized that heterogeneity within a plot would decrease as the plot adjusted to local‐scale hydraulics and sediment and particulate material transport. We hypothesized that heterogeneity would increase between adjacent plots and across the entire site. We found that spatial heterogeneity of geomorphic variables decreased within plots. Heterogeneity of organic cover, sediment size, and flow depth increased between adjacent plots, although other variables did not change. Site‐scale heterogeneity decreased for all variables except organic cover and substrate. We interpret the observed geomorphic responses to reflect decreased longitudinal connectivity and increased lateral and vertical connectivity at the restoration site.

(Dis)connectivity in hydro‐geomorphic systems – emerging concepts and their applications

“…Three studies combined aspects of longitudinal and lateral connectivity, either in the channel-floodplain (Hinshaw et al, 2022) or the catchment perspective (González-Romero et al, 2021;Turley et al, 2021). We deemed only one article to explicitly solely focus on lateral connectivity (Martini et al, 2022).…”

“…Poeppl et al, In press). In this SI, five contributions have dealt with connectivity in mountain environments, with a specific focus on fluvial processes by Hinshaw et al (2022; South Fork McKenzie River basin, Cascade Mountains, Oregon, USA), Kemper et al (2022; Yampa River basin, Rocky Mountains, Colorado, USA), and Khan et al (2021; Richmond River catchment, Great Dividing Range, Australia), on hillslope processes by Martini et al (2022; Rio Cordon catchment, Italian Alps), or on both environments as shown by Turley et al (2021; Tahoma Creek catchment, Cascade Mountains, Washington, USA). Two papers investigated connectivity relationships in river and catchment systems (Bizzi et al, 2021: Vjosa River, Albania; González‐Romero et al, 2021: Segura River catchment, Spain), while two contributions had a specific focus on delta, estuary and wetland environments (Hiatt et al, 2022; Singh et al, 2022; Sonke et al, 2022).…”

“…Most studies focus on sediment connectivity (Bizzi et al, 2021; González‐Romero et al, 2021; Martini et al, 2022), including Kemper et al (2022) who concentrate on catchment‐scale connectivity using vegetation establishment as a proxy for when sediment was eroded or deposited in particular locations in the catchment. Only one study focuses on other types of matter than sediment and water: Hinshaw et al (2022) examine changes in connectivity of water, sediment and organic matter through time after a restoration method that aims to increase lateral connectivity.…”

“…There is a clear focus on longitudinal connectivity of sediment (Bizzi et al, 2021; Kemper et al, 2022; Khan et al, 2021; Turley et al, 2021), followed by that of water fluxes in estuarine channels and wetlands (Hiatt et al, 2022; Sinha et al, 2022). Three studies combined aspects of longitudinal and lateral connectivity, either in the channel‐floodplain (Hinshaw et al, 2022) or the catchment perspective (González‐Romero et al, 2021; Turley et al, 2021). We deemed only one article to explicitly solely focus on lateral connectivity (Martini et al, 2022).…”

“…Hinshaw et al (2022) addressed the problem of how to examine SC and FC after a new restoration strategy of Stage-0 restoration and to accurately determine how the newly restored SC translates to FC.…”