Slope, grain size, and roughness controls on dry sediment transport and storage on steep hillslopes

DiBiase, Roman A.; Lamb, Michael P.; Ganti, Vamsi; Booth, Adam M.

doi:10.1002/2016jf003970

Cited by 58 publications

(102 citation statements)

References 77 publications

(179 reference statements)

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“…The K s and h f values within the model domain were assigned on a cell‐by‐cell basis by randomly selecting values from a distribution fit to these 89 measured values by empirical cumulative distribution function. We further assumed, based on field observations of exposed bedrock in steeper portions of the study area, that locations with a slope over 45° were not soil‐mantled (DiBiase et al, ).…”

Section: Methodsmentioning

confidence: 99%

Evolution of Debris‐Flow Initiation Mechanisms and Sediment Sources During a Sequence of Postwildfire Rainstorms

et al. 2019

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Wildfire alters vegetation cover and soil hydrologic properties, substantially increasing the likelihood of debris flows in steep watersheds. Our understanding of initiation mechanisms of postwildfire debris flows is limited, in part, by a lack of direct observations and measurements. In particular, there is a need to understand temporal variations in debris‐flow likelihood following wildfire and how those variations relate to wildfire‐induced hydrologic and geomorphic changes. In this study, we use a combination of in situ measurements, hydrologic monitoring equipment, and numerical modeling to assess the impact of wildfire‐induced hydrologic and geomorphic changes on debris‐flow initiation during seven postwildfire rainstorms. We predict the impact of hillslope erosion on debris‐flow initiation by combining terrestrial laser scanning surveys of a hillslope burned during the 2016 Fish Fire with numerical modeling of sediment transport throughout a 0.12‐km2 basin in southern California. We use measurements of sediment thickness within the channel to constrain numerical experiments and to assess the role of channel sediment supply on debris‐flow initiation. Results demonstrate that debris flows initiated during rainstorms where hillslopes contributed minimally to the event sediment yield and suggest that large inputs of sediment from rill and gully networks are not essential for runoff‐generated debris flows. Simulations suggest that both the gradual entrainment of sediment and the mass failure of channel bed sediment can increase sediment concentration to levels associated with debris flows. Finally, postwildfire debris‐flow initiation appears closely linked to the same rainfall intensity‐duration threshold despite temporal changes in the sediment source, initiation processes, and hydraulic roughness.

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Section: Methodsmentioning

confidence: 99%

Evolution of Debris‐Flow Initiation Mechanisms and Sediment Sources During a Sequence of Postwildfire Rainstorms

et al. 2019

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“…The mixture is deposited when flow energy decreases in the downslope area. Third, the microcollapse of soil on unstable slopes and subsequent mass movement can bury litter at the bottom of rills (DiBiase, Lamb, Ganti, & Booth, ). Fourth, the uprooting in many forest ecosystems overturns the topsoil and litter layer, therefore causing soil–litter mixture.…”

Section: Introductionmentioning

confidence: 99%

Hydraulics of overland flow influenced by litter incorporation under extreme rainfall

Wang

Zhang

Wang

et al. 2018

Hydrological Processes

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Water erosion on hillslopes is a worldwide environmental problem, which is a rainfall‐induced process, especially extreme rainfall. The great intensity of extreme rainfall strongly enhances the power of overland flow to detach soil and transport sediment. Plant litter is one of the most important constituents of ecosystems that often covers the soil surface and can be incorporated into topsoil. However, little attention has been paid to its effect on flow hydraulics owing to the veiled nature. This study aimed to examine the effects of incorporated litter on the hydraulic properties under extreme rainfall condition. To reach this goal, six litter rates of 0, 0.05, 0.10, 0.20, 0.35, and 0.50 kg m−2 and four litter types collected from deciduous trees, coniferous trees, shrubs, and herbs were incorporated into topsoil. Then, simulated rainfall experiments were performed on five slope gradients (5°, 10°, 15°, 20°, and 25°) with an extreme rainfall intensity of 80 mm h−1. The results showed that Froude number and flow velocity of the overland flow decreased, whereas flow resistance increased exponentially with litter incorporation rate. Litter type had an influence on flow hydraulics, which can mainly be attributed to the variations in surface coverage of the exposed litter and the litter morphology. Flow velocity and Darcy–Weisbach coefficient increased markedly with slope gradient. However, the variation of slope gradient did not modify the relationships between flow hydraulics and incorporated litter rate. The random roughness, resulting from heterogeneous erosion due to the uneven protection of surface exposed litter, increased linearly with litter incorporated rate. As rainfall proceeded, flow hydraulics varied with incorporated litter rate and slope gradient complicatedly due to the increases in flow rate and coverage of the exposed litter and the modification of soil surface roughness.

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“…The denominator represents the maximum rate of regolith removal by disturbance: It is the rate one would obtain if each disturbance triggers a ravel event that transports the disturbed material to the base of the slope. In other words,

E_{v}^{'} = 1

can be thought of as representing “perfect” nonlocal transport (e.g., DiBiase et al, ; Doane et al, ; Tucker & Bradley, ). Cases with

E_{v}^{'} < 1

arise either when some displaced regolith remains on the slope (indicating local, diffusive‐like transport) or when the regolith cover is incomplete.…”

Section: Resultsmentioning

confidence: 99%

Modeling the Shape and Evolution of Normal‐Fault Facets

et al. 2020

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Facets formed along the footwalls of active normal‐fault blocks display a variety of longitudinal profile forms, with variations in gradient, shape, degree of soil cover, and presence or absence of a slope break at the fault trace. We show that a two‐dimensional, process‐oriented cellular automaton model of facet profile evolution can account for the observed morphologic diversity. The model uses two dimensionless parameters to represent fault slip, progressive rock weathering, and downslope colluvial‐soil transport driven by gravity and stochastic disturbance events. The parameters represent rock weathering and soil disturbance rates, respectively, scaled by fault slip rate; both can be derived from field‐estimated rate coefficients. In the model's transport‐limited regime, slope gradient depends on the ratio of disturbance to slip rate, with a maximum that represents the angle of repose for colluvium. In this regime, facet evolution is consistent with nonlinear diffusion models of soil‐mantled hillslope evolution. Under the weathering‐limited regime, bedrock becomes partly exposed but microtopography helps trap some colluvium even when facet gradient exceeds the threshold angle. Whereas the model predicts a continuous gradient from footwall to colluvial wedge under transport‐limited behavior, fully weathering‐limited facets tend to develop a slope break between footwall and basal colluvium as a result of reduced transport efficiency on the rocky footwall slope. To the extent that the model provides a reasonable analogy for natural facets, its behavior suggests that facet profile morphology can provide useful constraints on relative potential rates of rock weathering, soil disturbance, and fault slip.

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Slope, grain size, and roughness controls on dry sediment transport and storage on steep hillslopes

Cited by 58 publications

References 77 publications

Evolution of Debris‐Flow Initiation Mechanisms and Sediment Sources During a Sequence of Postwildfire Rainstorms

Evolution of Debris‐Flow Initiation Mechanisms and Sediment Sources During a Sequence of Postwildfire Rainstorms

Hydraulics of overland flow influenced by litter incorporation under extreme rainfall

Modeling the Shape and Evolution of Normal‐Fault Facets

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