All Logjams Are Not Created Equal

Livers, Bridget; Wohl, Ellen

doi:10.1029/2021jf006076

Cited by 15 publications

(14 citation statements)

References 71 publications

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“…Correspondingly, inchannel edge density also increased (although part of this increase is likely due to avulsion, discussed below; Figure 4C). This indicates the importance of wood rearrangement and jam formation in enabling rearrangement of the channel bed, similar to other systems in which wood has been observed to constrict, plunge, and backwater flow to create pools (Livers & Wohl, 2021;Martens & Devine, 2022;Pess et al, 2022). substantial floodplain inundation and reworking.…”

Section: Phase 2 Restorationsupporting

confidence: 71%

“…In forested, multi-channel riverscapes, wood is a key element that can sustain a Stage 0 valley bottom: it creates spatial and temporal heterogeneity (Fausch & Northcote, 1992;Wohl et al, 2022), maintains lateral connectivity (Keys et al, 2018), mediates flows of water and sediment (Ader et al, 2020;Davidson & Eaton, 2013;Wohl & Scott, 2017), and drives channel migration and floodplain reworking (Collins et al, 2012). The presence of wood (especially channel-spanning wood; Livers & Wohl, 2021) strongly correlates with the geomorphic processes that restoration to Stage 0 seeks to sustain. However, the mechanisms by which wood sustains these processes are only vaguely understood.…”

Section: Introductionmentioning

confidence: 99%

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Widespread Wood Placement and Regrading Drive Lateral Connectivity and Reworking of the Channel and Floodplain in a Valley Bottom Reset to Stage 0

Scott¹

2023

Preprint

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Valley bottom process reset, or the excavation of high surfaces and fill of incised channels combined with large wood addition, is a new method for creating multi-channel river-wetland corridors (also referred to as Stage 0 valley bottoms). Valley bottom process reset seeks to increase lateral flow and sediment connectivity to retain flow and sediment and kickstart geomorphic processes that may sustain aquatic and riparian habitat. This anthropogenic intervention provides an opportunity to examine relationships among wood-induced hydraulic roughness, valley bottom topography, and geomorphic processes such as overbank flow and sediment transport, avulsion, sediment retention, and pool scour. Here, I present a 6-year case study of a two-phase valley bottom process reset along Deer Creek, OR indicates that kickstarting processes that reshape the floodplain requires a substantial increase in roughness and hydrologic connectivity. A first phase of construction enhanced hydrologic but not sediment connectivity, largely failing to kickstart avulsion and floodplain reworking even during a likely 2- to 5-year recurrence interval flood. A second, more intensive phase of construction substantially reduced the threshold flow necessary for overbank flow and incision of floodplain reworking, as evidenced by the occurrence of these processes after only a < 2-year recurrence interval flood. During this flood, a spatially distributed wood lattice rearranged into discrete jams that scoured pools, retained sediment, and drove geomorphically effective overbank flows. While valley bottom regrading likely contributed to these geomorphic effects, the spatial correlation between newly incised floodplain channels and areas of wood aggregation indicates a substantial role of wood-induced hydraulic roughness and channel blockage. Wood drove floodplain reworking via two mechanisms: in-channel wood jams backwatered and constructed flow into the floodplain, and small wood jams formed in the floodplain forest further constricted flow through nascent channels to facilitate channel incision.

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Section: Phase 2 Restorationsupporting

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Widespread Wood Placement and Regrading Drive Lateral Connectivity and Reworking of the Channel and Floodplain in a Valley Bottom Reset to Stage 0

Scott¹

2023

Preprint

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“…This might be due to the limited supply of fine sediments from the surrounding catchment (Berg, Carlson, & Azuma, 1998). It was also likely that finer sediments were flushed away by underflows as the NFM woody dams were not in contact with the stream bed (Livers & Wohl, 2021).…”

Section: Sediment Storagementioning

confidence: 99%

Geomorphic effects of natural flood management woody dams in upland streams

Leeuwen

Klaar

et al. 2022

River Research & Apps

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One popular Natural Flood Management (NFM) technique involves the construction of channel-spanning woody dams in low-order streams that maintain a clearance height above base flows. While extensive research has examined the geomorphic effects of natural wood accumulations, little has been documented of NFM woody dams, which are structurally distinct from natural accumulations and may produce different patterns of erosion and deposition. This consideration is crucial because changes in physical habitat characteristics have implications for flood management objectives as well as ecosystem structure and functioning. This study adopted a Before-After Control-Impact (BACI) design to assess the geomorphic effects of NFM woody dams in the upper River Cover catchment, United Kingdom. One baseline survey prior to and three monitoring surveys up to 2 years following dam construction were conducted. Structure-from-Motion (SfM) photogrammetry was employed to capture topographic change, supplemented by bathymetric surveys.Results highlight that where the dams remained secure in place, they promoted instream habitat diversity by creating underflow pools. Sediment storage was observed only where the dams had clearance heights <0.3 m from the stream bed.Additionally, the dams commonly led to bank erosion, likely enhanced by inherent bank instability in the study catchment as observed along the control reaches. However, volumes of sediments eroded and deposited were not statistically different between the control and woody dam reaches. Longer monitoring is required to determine whether these effects on channel morphology and habitat diversity will persist, amplify, or diminish over time, and to better understand the longevity of NFM woody dams.

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“…Other projects have a hybrid design in which a limited amount of fixed wood is designed to trap and accumulate mobile wood pieces to create larger wood accumulations with time (Abbe & Brooks, 2011). Reintroduced large wood is also more likely to be single logs or structurally simple engineered logjams, although structurally complex pieces and jams are likely to create greater habitat diversity (Harvey et al., 2018) and backwater storage (Livers & Wohl, 2021; Welling et al., 2021). The reach‐scale geomorphic context and the natural wood regime (Wohl et al., 2019) are important considerations when restoring using either fixed or mobile introduced wood.…”

Section: Introductionmentioning

confidence: 99%

“…Here, we use 11 years of annual surveys of a population that totaled ∼300 logjams each year to evaluate logjam persistence. We focus on logjams that span the bankfull active channel because these logjams can have particularly strong influences on physical and ecological variables (Andreoli et al., 2007; Livers & Wohl, 2016, 2021; Welling et al., 2021), although the specific effects depend on factors such as logjam porosity, height relative to peak flow depth, and erodibility of the adjacent banks (e.g., Dixon, 2016). We examine three basic questions: how long individual logjams are present in the study area (jam persistence) and the cumulative residence time of logjams that disappear and then re‐form at the same site (site persistence); what factors influence logjam and site persistence; and how the geomorphic effects of logjams relate to logjam persistence.…”

Section: Introductionmentioning

confidence: 99%

The Transience of Channel‐Spanning Logjams in Mountain Streams

Wohl

Iskin

2022

Water Resources Research

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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 (

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All Logjams Are Not Created Equal

Cited by 15 publications

References 71 publications

Widespread Wood Placement and Regrading Drive Lateral Connectivity and Reworking of the Channel and Floodplain in a Valley Bottom Reset to Stage 0

Widespread Wood Placement and Regrading Drive Lateral Connectivity and Reworking of the Channel and Floodplain in a Valley Bottom Reset to Stage 0

Geomorphic effects of natural flood management woody dams in upland streams

The Transience of Channel‐Spanning Logjams in Mountain Streams

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