The Transience of Channel‐Spanning Logjams in Mountain Streams

Abstract

Large wood (>10 cm diameter and 1 m long) creates numerous geomorphic and ecologic effects in stream corridors (active channel and floodplain). By creating obstructions and increasing hydraulic roughness, large wood affects the distribution of hydraulic force (Manners et al., 2007;Shields & Smith, 1992) and therefore hyporheic exchange flows and solute dynamics (Doughty et al., 2020;Sawyer et al., 2011), as well as the transport of sediment and particulate organic matter (Hinshaw et al., 2020;Wohl & Scott, 2017). The presence of large wood can influence the type and dimensions of channel bedforms (MacFarlane & Wohl, 2003); the presence and grain-size distribution of alluvium (Faustini & Jones, 2003;Massong & Montgomery, 2000;Ryan et al., 2014); and the characteristics of reach-scale gradient, cross-sectional geometry, and planform geometry (Collins et al., 2012;O'Connor et al., 2003). The flow obstructions and erosionally resistant points associated with wood accumulations can increase channel-floodplain hydrologic and sediment connectivity, as well as altering channel migration rate and floodplain turnover time (

Interactions of Logjams, Channel Dynamics, and Geomorphic Heterogeneity Within a River Corridor

“…Although the correlation between logjams and total sinuosity illustrated in Figure 5 does not unequivocally indicate cause and effect, the distribution of data suggests total sinuosity is more conservative through time and does not change substantially even if wood presence and distribution nearly double. In previous work, we have observed scenarios in which a logjam present for only one runoff season deflected flow onto the floodplain and created secondary channels that persisted for years, even if the logjam broke up during the original or subsequent peak flows (Wohl & Iskin, 2022). We also observed this scenario in 2022 during high flows at the Swan River where the floodplain was inundated, as described previously.…”

“…• Bar and secondary channel formation (Collins et al, 2012;Montgomery & Abbe, 2006;Polvi & Wohl, 2013) • Meander geometry and rate/direction of meander migration (Abbe & Montgomery, 1996;Daniels & Rhoads, 2004;Gurnell et al, 2002;Hickin, 1984;Piégay, 1993) • Topographic and substrate heterogeneity within the channel (e.g., scour exposing coarse sediment at the upstream flow divergence around the wood; fine sediment deposition in zones of slower flow created by the wood) (Gurnell et al, 2005) • Instream aggradation (Brooks et al, 2003) • Channel avulsion and formation/abandonment of secondary channels (Collins et al, 2012;Jeffries et al, 2003;Wohl, 2011;Wohl & Iskin, 2022) • Floodplain roughness (Wohl, 2013(Wohl, , 2020 • Channel-floodplain connectivity (Keys et al, 2018;Sear et al, 2010;Wohl, 2013) • Lateral and vertical accretion of floodplains (Sear et al, 2010;Wohl, 2013) Logjams can also respond to river corridor geomorphic heterogeneity. Spatially heterogeneous river corridors are more likely to recruit and retain wood relative to transport-dominated homogeneous river corridors (Collins et al, 2012;Wyżga & Zawiejska, 2005).…”

Beyond the Case Study: Characterizing Natural Floodplain Heterogeneity in the United States

“…This data set only includes wood volume per area from a limited number of transects and does not include the spatial distribution or concentration (e.g., jams) of the wood on the floodplain. Wood loads can be dynamic in space and time (Iroumé et al., 2015; Ruiz‐Villanueva et al., 2016; Tonon et al., 2017; Wohl et al., 2019; Wohl, 2013) and the distribution of wood in a channel or floodplain can change substantially over 1–2 years (Wohl and Iskin, 2022). This highlights the need for more detailed study of large wood on floodplains to determine its effect on fluvial processes as related to floodplain heterogeneity.…”

Geomorphic context in process‐based river restoration

“…As noted earlier, both restoring processes and restoring the context in which processes can occur constitute process‐based restoration, and both approaches benefit from understanding the historical and contemporary geomorphic contexts. The contemporary reintroduction of large wood and engineered logjams to channels with the intent of enhancing fish habitat (Nagayama & Nakamura, 2010; Pess et al, 2012) or creating hydraulic roughness that slows downstream passage of flood waves (Short et al, 2019), for example, can be most effectively undertaken with some knowledge of where large wood is likely to be deposited, form logjams, and remain relatively stable based on wood‐trapping capacity in the river corridor (Gregory et al, 2022; Scott & Wohl, 2018; Wohl & Iskin, 2022; Wyżga & Zawiejska, 2010)—in other words, based on knowledge of wood regimes and wood process domains (Wohl, Kramer, et al, 2019). Analogously, contemporary reintroduction of beaver ( Castor spp.)…”