Short-term post-wildfire dry-ravel processes in a chaparral fluvial system

Florsheim, Joan L.; Chin, Anne; O'Hirok, L.; Storesund, Rune

doi:10.1016/j.geomorph.2015.03.035

Cited by 24 publications

(21 citation statements)

References 17 publications

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“…The initial dry‐ravel sediment pulse released after the 2013 Springs Fire formed dry‐ravel deposits along channel margins measured in the contiguous lower and upper portion of the study reach and upstream through the burned zone shortly after the fire stored 0.21 m 3 /m of sediment (~107.5 m 3 over a 504 m channel length). Of the total volume within this longer reach, ~70.9 m 3 remained after the 2014 storm, suggesting that 34% was mobilized and transported (comparable to that measured for the lower portion of the reach alone, reported in Florsheim et al , ). This sediment eroded from dry ravel deposits accounted for 34% of the volume of the deposit that filled the lower portion of the reach during the 2014 storm.…”

Section: Resultssupporting

confidence: 80%

“…The total volume V T of sediment stored in the n dry‐ravel deposits for the reach is: V T = Σ V c i + Σ V r i where i = 1, …, n . In the present study, dry‐ravel volumes reported in Florsheim et al () for the lower portion of the study reach are extended upstream through the burned area.…”

Section: Methodssupporting

confidence: 48%

“…The Big Sycamore Creek study area lacks floodplains such as are present lower in the fluvial system, and is therefore characterized by a high degree of connectivity between steep hillslopes and the channel. The present research builds on prior work that investigated step-pool dynamics (Chin, 1999(Chin, , 2002 and extends prior analysis in the lower portion of the study reach regarding hillslope dry-ravel dynamics following the 2013 Springs Fire (Florsheim et al, 2016). In channels with steps and pools, such as Big Sycamore Creek, coarse bed material tends to be mobile only during high magnitude flows (Chin, 1998) with a low sediment supply between wildfires that is limited by soil production rates (Lamb et al, 2011).…”

Section: Study Areamentioning

confidence: 76%

“…Volumes of dry ravel deposits representing sediment supply from hillslope erosion during and immediately following the fire were measured following the approach used in Florsheim et al () to evaluate short‐term changes in hillslope dry‐ravel processes. Field measurement of dry ravel deposits included height ( h ) from the base of the deposit in the channel margin to the top on the hillslope, and length ( l ) along the longitudinal profile of the channel using a stadia rod and tape measure, respectively; depth ( d ) of each deposit was measured perpendicular to height using a steel rebar probe.…”

Section: Methodsmentioning

confidence: 99%

“…In steep semi-arid chaparral basins, dry ravel is a dominant hillslope process by which weathered sediment is transported downslope by gravity (Anderson, et al, 1959;Krammes, 1965;Rice, 1982;Florsheim et al, 1991;DiBiase and Lamb, 2013;Wohlgemuth, 2015). Therefore, in steep chaparral environments, wildfire initiates a dry ravel sediment pulse to hillslope-channel margins in tributaries and in main channels (Florsheim et al, 1991(Florsheim et al, , 2016Gabet, 2003;Lamb et al, 2011Lamb et al, , 2013. In steep step-pool stream channels, sediment contributed by dry ravel that consists of gravel and smaller sediment contrasts with the coarser cobble and boulder pre-fire channel bed material (Florsheim et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

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Effect of storms during drought on post‐wildfire recovery of channel sediment dynamics and habitat in the southern California chaparral, USA

Florsheim

Chin

Kinoshita

et al. 2017

Earth Surf Processes Landf

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Current global warming projections suggest a possible increase in wildfire and drought, augmenting the need to understand how drought following wildfire affects the recovery of stream channels in relation to sediment dynamics. We investigated post-wildfire geomorphic responses caused by storms during a prolonged drought following the 2013 Springs Fire in southern California (USA), using multi-temporal Terrestrial Laser Scanning and detailed field measurements. After the fire, a dry-season dry-ravel sediment pulse contributed sand and small gravel to hillslope-channel margins in Big Sycamore Creek and its tributaries. A small storm in WY 2014 generated sufficient flow to mobilize a portion of the sediment derived from the dryravel pulse and deposited the fine sediment in the channel, totaling ~0.60 m 3 /m of volume per unit length of channel. The sediment deposit buried step-pool habitat structure and reduced roughness by over 90%. These changes altered sediment transport characteristics of the bed material present before and after the storm; the ratio of available to critical shear stress ( o / c ) increased by five times. Storms during WY 2015 contributed additional fine sediment from tributaries and lower hillslopes and hyperconcentrated flow transported and deposited additional sediment in the channel. Together these sources delivered sediment on the order of six times that in 2014, further increasing  o / c . These storms during multi-year drought following wildfire transformed channel dynamics. The increased sediment transport capacity persisted during the drought period characterized by the longer residence time of relatively fine-grained post-fire channel sedimentation. This contrasts with wetter years, when post-fire sediment is transported from the fluvial system during the same season as the post-fire sediment pulse. Results of this short-term study highlight the complex and substantial effects of multi-year drought on geomorphic responses following wildfire. These responses influence pool habitat that is critical to longer-term post-wildfire riparian ecosystem recovery.

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Section: Resultssupporting

confidence: 80%

Section: Methodssupporting

confidence: 48%

Section: Study Areamentioning

confidence: 76%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effect of storms during drought on post‐wildfire recovery of channel sediment dynamics and habitat in the southern California chaparral, USA

Florsheim

Chin

Kinoshita

et al. 2017

Earth Surf Processes Landf

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Controls Over Sediment Flux Along Soil‐Mantled Hillslopes: Insights From Granular Dynamics Simulations

BenDror

Goren

2018

JGR Earth Surface

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Sediment flux from soil‐mantled hillslopes controls the volume of sediments delivered to rivers, the rate of rock exhumation, and the topographic evolution of hillslopes. Recent studies have inferred a nonlinear relation between hillslope gradient and sediment flux, but the functional forms proposed to date generally lack mechanistic explanations. Furthermore, although environmental disturbances have been invoked as facilitating sediment mobilization on soil‐mantled hillslopes that reside below the angle of repose (the threshold for slope‐driven motion), the way in which disturbances control the flux has received little investigation. Here we develop and employ a discrete element granular dynamics numerical model to study the relations between flux, slope, and disturbance characteristics at the grain scale. The numerical grains are subjected to gravitational body forces, contact forces, and random external perturbation forces, which are used to represent natural disturbances and which are characterized by perturbation magnitude and wavelength. Simulation results reveal an abrupt transition between two regimes. Low and intermediate slopes show granular creep, whereby grain velocity rapidly decays with depth. High slopes, albeit still below the angle of repose, show deep, granular slides, where all available material participates in the sliding motion. These two regimes can be described by two different theories for flow down an inclined plane. The simulations reveal that the external perturbations effectively reduce the angle of repose and that the nonlinearity in the slope‐flux relation emerges from each regime separately and from the transition between them in particular. Simulations further demonstrate a positive correlation of sediment flux with perturbation magnitude and wavelength.

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First Consideration About Post 2017 Wildfire Erosion Response and Debris Flow in Susa Valley (NW Italy)

Vacha

Mandrone

Garbarino

et al. 2020

Understanding and Reducing Landslide Disaster Risk

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Short-term post-wildfire dry-ravel processes in a chaparral fluvial system

Cited by 24 publications

References 17 publications

Effect of storms during drought on post‐wildfire recovery of channel sediment dynamics and habitat in the southern California chaparral, USA

Effect of storms during drought on post‐wildfire recovery of channel sediment dynamics and habitat in the southern California chaparral, USA

Controls Over Sediment Flux Along Soil‐Mantled Hillslopes: Insights From Granular Dynamics Simulations

First Consideration About Post 2017 Wildfire Erosion Response and Debris Flow in Susa Valley (NW Italy)

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