Floodplain morphology, sedimentology, and development processes of a partially alluvial channel

Thayer, James B.; Ashmore, Peter

doi:10.1016/j.geomorph.2016.06.040

Cited by 22 publications

(24 citation statements)

References 53 publications

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“…Our results support the notion that valley morphology, a meso‐scale physical constraint, plays a key role in modulating biophysical interactions across scales, ultimately impacting how inundation patterns are manifested in the river‐floodplain valley and the development of valley landforms (Nanson and Croke , Miller , Jain et al. , Fryirs and Brierley , Thayer and Ashmore , Cienciala and Pasternack ).…”

Section: Discussionsupporting

confidence: 83%

“…As functions of streamflow regimes, inundation regimes result from complex, multi-scalar interactions among biophysical attributes (Woltemade 1994, Woltemade and Potter 1994, Baker and Wiley 2009, Fryirs and Brierley 2013 and anthropogenic impacts on hydrology via direct regulation (e.g., Karim et al 2015, Stone et al 2017), land use (e.g., Foufoula-Georgiou et al 2015), and engineered structures in the floodplain (e.g., Munoz et al 2018). Our results support the notion that valley morphology, a meso-scale physical constraint, plays a key role in modulating biophysical interactions across scales, ultimately impacting how inundation patterns are manifested in the river-floodplain valley and the development of valley landforms (Nanson and Croke 1992, Miller 1995, Jain et al 2008, Fryirs and Brierley 2010, Thayer and Ashmore 2016, Cienciala and Pasternack 2017.…”

Section: Discussionsupporting

confidence: 72%

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River‐valley morphology, basin size, and flow‐event magnitude interact to produce wide variation in flooding dynamics

2019

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Inundation dynamics are a key driver of ecosystem form and function in river-valley bottoms.Inundation itself is an outcome of multi-scalar interactions and can vary strongly within and among river reaches. As a result, establishing to what degree and how inundation dynamics vary spatially both within and among river reaches can be challenging. The objective of this study was to understand how river-valley morphology, basin size, and flow-event magnitude interact to affect inundation dynamics in river-valley bottoms. We used 2D hydraulic models to simulate inundation in four river reaches from Maryland's Piedmont physiographic province, and qualitatively and quantitatively summarized within-and amongreach patterns of inundation extent, duration, depth, shear stress, and wetting frequencies. On average, reaches from confined valley settings experienced less extensive flooding, shorter durations and shallower depths, stronger gradients of maximum shear stress, and relatively infrequent wetting compared to reaches from unconfined settings. These patterns were generally consistent across flow-event magnitudes. Patterns of within-reach flooding across event magnitudes revealed complex interactions between hydrology and surface topography. We concluded that valley morphology had a greater impact on flooding patterns than basin size: Inundation patterns were more consistent across reaches of similar morphology than similar basin size, but absolute values of inundation characteristics varied between large and small basins. Our results showed that the manifestation of out-of-bank flows in valley floors can vary widely depending on geomorphic context, even within a single physiographic province, which suggests that hydrologic and hydraulic conditions experienced on the valley floor may not be well represented by existing hydrologic metrics derived from discharge data alone. We thus support the notion that 2D hydraulic models can be useful hydrometric tools for cross-scale investigations of floodplain ecosystems.

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Section: Discussionsupporting

confidence: 83%

Section: Discussionsupporting

confidence: 72%

River‐valley morphology, basin size, and flow‐event magnitude interact to produce wide variation in flooding dynamics

2019

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“…In depositional landscapes formed by continental ice sheets, such as those in the depositional zone of the Laurentide Ice Sheet of North America, modern river valleys are commonly eroded into glacial sediments rather than into the underlying bedrock (Ashmore and Church, 2001;Ebisa Fola and Rennie, 2010;Gran et al, 2013;Desloges, 2014, 2015;Thayer and Ashmore, 2016). These glacial sediments are exposed in river channels.…”

Section: Introductionmentioning

confidence: 99%

“…Some of these glacially-derived boundary materials are easily eroded and yield non-cohesive sediments that form local alluvial deposits. Consequently, river banks may include both glacial and alluvial layers, and channel beds may be fully exposed (cohesive) glacial sediments or have a (transient) cover of alluvial deposits varying in extent, thickness and grain size that include rounded clasts of eroded cohesive glacial sediments (Ashmore and Church, 2001;Gran et al, 2013;Thayer and Ashmore, 2016). The combination of nonalluvial (but highly erodible) boundaries and morphological adjustability led Ashmore and Church (2001) to refer to rivers of this type in glacial sediments as 'semi-alluvial' (see also Khan and Kostaschuk, 2011;Meshkova et al, 2012;Phillips and Desloges, 2014;Thayer and Ashmore, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, river banks may include both glacial and alluvial layers, and channel beds may be fully exposed (cohesive) glacial sediments or have a (transient) cover of alluvial deposits varying in extent, thickness and grain size that include rounded clasts of eroded cohesive glacial sediments (Ashmore and Church, 2001;Gran et al, 2013;Thayer and Ashmore, 2016). The combination of nonalluvial (but highly erodible) boundaries and morphological adjustability led Ashmore and Church (2001) to refer to rivers of this type in glacial sediments as 'semi-alluvial' (see also Khan and Kostaschuk, 2011;Meshkova et al, 2012;Phillips and Desloges, 2014;Thayer and Ashmore, 2016). Although this term has also been used with resistant bedrock boundaries and partial alluvial cover (Turowski et al, 2008), the two types of channel (bedrock and cohesive glacial sediments) are distinct with respect to geomorphic history, boundary material mechanics, erosion processes and rate of adjustability to changing flow regime.…”

Section: Introductionmentioning

confidence: 99%

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Flume tests on fluvial erosion mechanisms in till‐bed channels

Pike

Gaskin

Ashmore

2017

Earth Surf Processes Landf

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Semi-alluvial stream channels eroded into till and other glacial sediments are common in areas of extensive glacial deposition such as the Great Lakes region and northern interior plains of North America. The mechanics of erosion and erosional weakness of till results in the dominance of fluvial scour and mass erosion due to spontaneous fracture at planes of weakness under shearing flow. There have been few controlled tests looking at erosional mechanisms and resistance of till in river channels. We subjected small blocks of till to unidirectional flows in a laboratory flume to measure the threshold shear stress for erosion and observed the erosion mechanics. Critical shear stress for erosion varied from 7 to 8 Pa for samples with initial saturated moisture content in which a combination of fluvial scour and mass cracking/block erosion dominated. When dried, micro-fissures occurred in the sample and erosional resistance of the till was extremely low at <1 Pa with erosion appearing to be by fluvial scour. When mobile gravel was added to the test conditions, the gravel reduced the erosion threshold slightly because of the enhanced scour around and below the gravel particles and the tendency for the gravel to aid in crack enlargement. Thus a partial or thin gravel cover over the till may provide no protection from erosion. The erosion processes and effects reflect the complex and contingent mechanics and properties of till, and suggest that the erosion characteristics of till bed semi-alluvial channels differ from abrasion or plucking dominated processes in more resistant bedrock.

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2020

Rivers in the Landscape

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Floodplain morphology, sedimentology, and development processes of a partially alluvial channel

Cited by 22 publications

References 53 publications

River‐valley morphology, basin size, and flow‐event magnitude interact to produce wide variation in flooding dynamics

River‐valley morphology, basin size, and flow‐event magnitude interact to produce wide variation in flooding dynamics

Flume tests on fluvial erosion mechanisms in till‐bed channels

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