Channel responses to varying sediment input: A flume experiment modeled after Redwood Creek, California

Madej, Mary Ann; Sutherland, Diane G.; Lisle, Thomas E.; Pryor, Bonnie

doi:10.1016/j.geomorph.2008.07.017

Cited by 96 publications

(94 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is consistent with the view that the immediate controls of this fl ux (unlike the washload fl ux, which is supply-limited) are fl ow strength and bed surface grain size distribution (Wilcock, 2001). The sediment supply from upstream is relevant only indirectly via its effect on surface size distribution: reduced supply induces surface coarsening which reduces transport rates, and increased supply does the opposite, as demonstrated experimentally or numerically by Dietrich et al (1989), Hoey and Ferguson (1997), and Madej et al (2009) among others. A consequence of our assumption of supply at capacity is that there is no change in bed elevation or composition at the head of the reach, but the gradient is free to alter.…”

Section: Morphodynamic Modelmentioning

confidence: 99%

Numerical modelling of climate change impacts on Saint‐Lawrence River tributaries

Verhaar

Biron

Ferguson

et al. 2010

Earth Surf Processes Landf

View full text Add to dashboard Cite

The impacts of climate-induced changes in discharge and base level in three tributaries of the Saint-Lawrence River, Québec, Canada, are modelled for the period 2010-2099 using a one-dimensional morphodynamic model. Changes in channel stability and bed-material delivery to the Saint-Lawrence River over this period are simulated for all combinations of seven tributary hydrological regimes (present-day and those predicted using three global climate models and two greenhouse gas emission scenarios) and three scenarios of how the base level provided by the Saint-Lawrence River will alter (no change, gradual fall, step fall). Even with no change in base level the projected discharge scenarios lead to an increase in average bed material delivery for most combinations of river and global climate model, although the magnitude of simulated change depends on the choice of global climate model and the trend over time seems related to whether the river is currently aggrading, degrading or in equilibrium. The choice of greenhouse gas emission scenario makes much less difference than the choice of global climate model. As expected, a fall in base level leads to degradation in the rivers currently aggrading or in equilibrium, and amplifi es the effects of climate change on sediment delivery to the Saint-Lawrence River. These differences highlight the importance of investigating several rivers using several climate models in order to determine trends in climate change impacts.

show abstract

Section: Morphodynamic Modelmentioning

confidence: 99%

Numerical modelling of climate change impacts on Saint‐Lawrence River tributaries

Verhaar

Biron

Ferguson

et al. 2010

Earth Surf Processes Landf

View full text Add to dashboard Cite

show abstract

“…Rivers with very high sediment supply are often braided (2), and aggradation occurs when the sediment supply to a channel is in excess of the channel's capacity to transport that sediment (14). Additionally, the bed surface can armor through size selective transport in low supply conditions (1, 3), or the bed surface grain size can fine in response to high sediment supply (15). Despite the prevalence of these observations, we lack a coherent understanding of how these responses are expressed in τ p bf , which is a function of both grain size and channel geometry.…”

Section: Significancementioning

confidence: 99%

“…Thus, both continent-wide trends and paired sites suggest that rivers in high erosion rate landscapes, where sediment supplies are high, have adjusted to maintain high bankfull Shields stresses rather than maintaining threshold conditions at bankfull flow. 15). Although it is difficult to observe armoring of channels during high-flow conditions, the armor ratio of the channel measured at low flow appears to provide an index of the sediment supply and transport conditions during the formative flows (26)(27)(28).…”

Section: Significancementioning

confidence: 99%

Sediment supply controls equilibrium channel geometry in gravel rivers

Pfeiffer

Finnegan

Willenbring

2017

Proc. Natl. Acad. Sci. U.S.A.

128

112

View full text Add to dashboard Cite

In many gravel-bedded rivers, floods that fill the channel banks create just enough shear stress to move the median-sized gravel particles on the bed surface (D 50 ). Because this observation is common and is supported by theory, the coincidence of bankfull flow and the incipient motion of D 50 has become a commonly used assumption. However, not all natural gravel channels actually conform to this simple relationship; some channels maintain bankfull stresses far in excess of the critical stress required to initiate sediment transport. We use a database of >300 gravel-bedded rivers and >600 10Be-derived erosion rates from across North America to explore the hypothesis that sediment supply drives the magnitude of bankfull shear stress relative to the critical stress required to mobilize the median bed surface grain size (τ bf * =τ c * ). We find that τ bf * =τ c * is significantly higher in West Coast river reaches (2.35, n = 96) than in river reaches elsewhere on the continent (1.03, n = 245). This pattern parallels patterns in erosion rates (and hence sediment supplies). Supporting our hypothesis, we find a significant correlation between upstream erosion rate and local τ bf * =τ c * at sites where this comparison is possible. Our analysis reveals a decrease in bed surface armoring with increasing τ bf * =τ c * , suggesting channels accommodate changes in sediment supply through adjustments in bed surface grain size, as also shown through numerical modeling. Our findings demonstrate that sediment supply is encoded in the bankfull hydraulic geometry of gravel bedded channels through its control on bed surface grain size.river channel geometry | sediment supply | sediment transport W hat determines the shape of alluvial rivers? These selfformed channels emerge through the interaction of flowing water and transported sediment. Explaining widely observed trends in river channel hydraulic geometry remains an ongoing challenge in the field of geomorphology. Gravel-bedded alluvial rivers (whose bed and banks comprise sediment transported by the river) approach equilibrium geometry through feedbacks between deposition, erosion, and bed surface armoring as well as through channel slope change (1-3). These responses in channel geometry and surface grain size accommodate perturbations in the water and sediment supply regimes. Thus, sediment supply is among the key controls on the morphology of all river channels, and understanding linkages between sediment supply and channel morphology is a central question in much of fluvial geomorphology, civil engineering, and river restoration.Decades of observations in gravel-bedded alluvial channels support the pervasiveness of threshold channels (4-6) in which the channel dimensions adjust such that the threshold for motion of the median bed surface grain size (D 50 ) occurs at, or just below, bankfull flow. These observations are reinforced by theoretical work (7) showing that, at bankfull flow, a straight channel with noncohesive banks will maintain a stable channel width with a ...

show abstract

“…The widening and sedimentation associated with these events often result in channel expansion and simplification [e.g., Meyer, 2001]. The transport capacity of the enlarged channel would thus be reduced under more typical flow conditions, and a series of hydraulic and morphologic adjustments would ensue so as to achieve a new balance between sediment supply and transport capacity [e.g., Madej, 2001;Madej et al, 2009]. An analogous sequence of changes might be expected to occur as a river that has been simplified during restoration gradually develops more complex, natural topography featuring bar forms of higher amplitude.…”

Section: Introductionmentioning

confidence: 99%

Effect of point bar development on the local force balance governing flow in a simple, meandering gravel bed river

2011

View full text Add to dashboard Cite

[1] The patterns of depth, velocity, and shear stress that direct a river's morphologic evolution are governed by a balance of forces. Analyzing these forces, associated with pressure gradients, boundary friction, channel curvature, and along-and across-stream changes in fluid momentum driven by bed topography, can yield insight regarding the establishment and maintenance of stable channel forms. This study examined how components of the local force balance changed as a meandering channel evolved from a simple, flat-bedded initial condition to a more complex bar-pool morphology. A numerical flow model, constrained by measurements of velocity and water surface elevation, characterized the flow field for four time periods bracketing two floods. For each time increment, runs were performed for discharges up to bankfull, and individual force balance components were computed from model output. Formation and growth of point bars enhanced topographic steering effects, which were of similar magnitude to the pressure gradient and centrifugal forces. Convective accelerations induced by the bar reduced the cross-stream pressure gradient, intensified flow toward the outer bank, and routed sediment around the upstream end of the bar. Adjustments in the flow field thus served to balance streamwise transport along the inner bank onto the bar and cross-stream transport into the pool. Even in the early stages of bar development, topographically driven spatial gradients in velocity played a significant role in the force balance at flows up to bankfull, altering the orientation of the shear stress and sediment transport to drive bar growth.Citation: Legleiter, C. J., L. R. Harrison, and T. Dunne (2011), Effect of point bar development on the local force balance governing flow in a simple, meandering gravel bed river,

show abstract

Channel responses to varying sediment input: A flume experiment modeled after Redwood Creek, California

Cited by 96 publications

References 39 publications

Numerical modelling of climate change impacts on Saint‐Lawrence River tributaries

Numerical modelling of climate change impacts on Saint‐Lawrence River tributaries

Sediment supply controls equilibrium channel geometry in gravel rivers

Effect of point bar development on the local force balance governing flow in a simple, meandering gravel bed river

Contact Info

Product

Resources

About