When do plants modify fluvial processes? Plant‐hydraulic interactions under variable flow and sediment supply rates

Manners, R.; Wilcox, Andrew C.; Li, Kui; Lightbody, A.; Stella, John C.; Sklar, L. S.

doi:10.1002/2014jf003265

Cited by 68 publications

(85 citation statements)

References 64 publications

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“…The hand winch was attached at a height of 0.5 m to a fence post placed 2 m downstream of the plant. Thus, the traction force was oriented at approximately 14° from the horizontal plane direction, consistent with measurements of the pronation of juvenile vegetation during high flows (Manners et al, ). Before running each pull‐out test, we watered the sediment around the plant to simulate the wet conditions during a flood.…”

Section: Methodssupporting

confidence: 85%

A Physical Model for the Uprooting of Flexible Vegetation on River Bars

2019

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Sediment deposition and bank accretion are promoted by the establishment and growth of pioneer plant species, a direct consequence of plant survival during flood events. Similarly, the uprooting of riparian vegetation on river bars during floods can subsequently alter hydraulics, sediment dynamics, and bar evolution. In this work, we focus on the removal of flexible seedlings due to both hydraulic forces and bed erosion, specifically examining failure mechanisms associated with root pull‐out. We provide a conceptual model and a new physical equation for predicting the flow and bed erosion conditions that promote the uprooting of plants. The model was validated by means of flume experiments employing two species of vegetation (i.e., common oats and a willow native to Europe). Furthermore, the Ombrone Pistoiese River (Tuscany, IT) was used as a case study to validate the physical model with respect to observed vegetation removal during a flood event. The results illustrate the capability of our model to predict conditions for vegetation removal and suggest that sediment transport is a necessary ingredient even for very young seedlings.

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Section: Methodssupporting

confidence: 85%

A Physical Model for the Uprooting of Flexible Vegetation on River Bars

2019

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“…This aligns with recent studies showing that sediment supply mediates the eco-geomorphological response to floods (Diehl, Merritt, Wilcox, & Scott, 2017;Manners et al, 2015). This aligns with recent studies showing that sediment supply mediates the eco-geomorphological response to floods (Diehl, Merritt, Wilcox, & Scott, 2017;Manners et al, 2015).…”

Section: A Large Flood In An Unregulated Braided River Caused Channsupporting

confidence: 91%

Short‐term geomorphological and riparian vegetation responses to a 40‐year flood on a braided, dryland river

Shafroth

Lee

Leverich³

et al. 2019

Ecohydrology

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In December 2010, a 40-year flood occurred in the lower Virgin River (SE Nevada, southwestern United States), a braided river segment with riparian vegetation largely dominated by invasive shrubs in the genus Tamarix. We assessed geomorphological and vegetation responses to this large magnitude disturbance event by comparing pre-and post-flood remote sensing and field survey data in four river reaches. Analyses of orthophotos and light detection and ranging-derived topography showed that both the active channel area and channel width increased between 80% and 258%, representing an increase from 13% to 30% of the total river corridor area. Erosion predominated in the outer bends of the enlarged channel and deposition in the pre-flood channel, causing local avulsions of the low-flow channel. Field-based topographic data recorded before and after the flood in 385 plots also showed that deposition occurred in parts of the floodplain that were not eroded. Two thirds of woody vegetation cover (mainly dominated by Tamarix, with some native shrub Pluchea sericea) was lost in areas that eroded (~20% of the river corridor). In the remaining~80% of stable river corridor (aggrading or no change in elevation) Tamarix remained dominant. Following erosion, but also where sediment deposition predominated under the Tamarix canopy, the most common colonizing vegetation in the understory was comprised of annual plants, especially Salsola tragus. Our study supported previous studies describing large floods in braided rivers; we documented the first phase of a cycle of channel widening and increase in vegetation heterogeneity that is commonly followed by narrowing and vegetation homogenization.

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“…This research expands on the work of Manners et al. () and Diehl, Wilcox, et al. (), who analysed within the same experiment the interactions of plants and sediment transport conditions on flow hydraulics, sediment transport, and bed morphology.…”

Section: Introductionsupporting

confidence: 55%

“…Deficit runs had zero sediment feed. Sediment flux data were not collected during deficit phase of runs 1 and 2. c Range of values measured between discharge of 0.17–0.36 m 3 /s (Manners et al., ). d Average and one standard deviation of values measured during deficit phase.…”

Section: Methodsmentioning

confidence: 99%

“…Plants can act as river engineers (Gurnell, ), and their traits, including size, density, stem flexibility, and root architecture, influence ecogeomorphic processes (Diehl, Merritt, Wilcox, & Scott, ). Flume experiments have studied interactions between herbaceous plants and hydrogeomorphic processes (Braudrick, Dietrich, Leverich, & Sklar, ; Crouzy & Perona, ; Edmaier et al., ; Nepf, ; Perona et al., ), yet studies that quantify the effects of plant architecture on their risk of loss during floods are rare, especially for woody plants, the dominant species in riparian zones (but see Burylo, Rey, Bochet, & Dutoit, ; Griffin, Perignon, Friedman, & Tucker, ; Manners et al., ).…”

Section: Introductionmentioning

confidence: 99%

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Can environmental flows moderate riparian invasions? The influence of seedling morphology and density on scour losses in experimental floods

Stella

Diehl

et al. 2018

Freshwater Biology

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Environmental flow releases are an effective tool to meet multiple management objectives, including maintaining river conveyance, restoring naturally functioning riparian plant communities, and controlling invasive species. In this context, predicting plant mortality during floods remains a key area of uncertainty for both river managers and ecologists, particularly with respect to how flood hydraulics and sediment dynamics interact with the plants’ own traits to influence their vulnerability to scour and burial. To understand these processes better, we conducted flume experiments to quantify different plant species’ vulnerability to flooding across a range of plant sizes, patch densities, and sediment condition (equilibrium transport versus sediment deficit), using sand‐bed rivers in the U.S. southwest as our reference system. We ran 10 experimental floods in a 0.6 m wide flume using live seedlings of cottonwood and tamarisk, which have contrasting morphologies. Sediment supply, plant morphology, and patch composition all had significant impacts on plant vulnerability during floods. Floods under sediment deficit conditions, which typically occur downstream of dams, resulted in bed degradation and a 35% greater risk of plant loss compared to equilibrium sediment conditions. Plants in sparse patches dislodged five times more frequently than in dense patches. Tamarisk plants and patches had greater frontal area, larger basal diameter, longer roots, and lower crown position compared to cottonwood across all seedling heights. These traits were associated with a 75% reduction in tamarisk seedlings’ vulnerability to scour compared to cottonwood. Synthesis and applications. Tamarisk's greater survivability helps to explain its vigorous establishment and persistence on regulated rivers where flood magnitudes have been reduced. Furthermore, its documented influence on hydraulics, sediment deposition, and scour patterns in flumes is amplified at larger scales in strongly altered river channels where it has broadly invaded. Efforts to remove riparian vegetation using flow releases to maintain open floodways and/or control the spread of non‐native species will need to consider the target plants’ size, density, and species‐specific traits, in addition to the balance of sediment transport capacity and supply in the river system.

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When do plants modify fluvial processes? Plant‐hydraulic interactions under variable flow and sediment supply rates

Cited by 68 publications

References 64 publications

A Physical Model for the Uprooting of Flexible Vegetation on River Bars

A Physical Model for the Uprooting of Flexible Vegetation on River Bars

Short‐term geomorphological and riparian vegetation responses to a 40‐year flood on a braided, dryland river

Can environmental flows moderate riparian invasions? The influence of seedling morphology and density on scour losses in experimental floods

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