Linking geomorphic change due to floods to spatial hydraulic habitat dynamics

Tamminga, Aaron; Eaton, Brett C.

doi:10.1002/eco.2018

Cited by 20 publications

(24 citation statements)

References 104 publications

(156 reference statements)

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“…At best, morphological classifications are fuzzy due to the natural variability encountered in the field (e.g. channel reach morphologies (Helm, 2019;Tamminga and Eaton, 2018)), and at worst, they are rather arbitrary (see Section 3.1.1). There have been recent advances in qualitative, process-based classifications of channel features (Hassan et al, 2007;Montgomery and Buffington, 1997;Venditti et al, 2017).…”

Section: Proposed Definitions Of Bed Statementioning

confidence: 99%

Toward bed state morphodynamics in gravel-bed rivers

Adams

2020

Progress in Physical Geography: Earth and Environment

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In fluvial geomorphology, one of the most pervasive paradigms is that the size of the grains present in a river exercises an important effect on its character. In gravel-bed rivers, there is considerable scatter in the relations between so-called “representative grain sizes” and basic channel processes and morphologies. Under a grain size paradigm, our ability to rationalize the characteristics of a given channel and predict how it will respond to a change in conditions is limited. In this paper, I deconstruct this paradigm by exploring its historical origins in geomorphology and fluid dynamics, and identify three of its underlying premises: (1) the association between grain diameter and fluid drag derived from Nikuradse’s experiments with sand-coated surfaces; (2) the use of grain size by early process geomorphologists to describe general trends across large samples of sand-bed rivers; and (3) a classificatory approach to discerning bed structures originally developed for bed configurations found in sand-bed rivers. The conflation of sand- and gravel-bed rivers limits our ability to understand gravel-bed morphodynamics. Longstanding critique of the grain size paradigm has generated alternative ideas but, due to technological and conceptual limitations, they have remained unrealized. One such unrealized idea is the morphology-based definition of bed state – an important degree of freedom within fluvial systems, particularly in reaches where adjustments to planform are not easily achieved. By embracing recent advancements in fluid dynamics and remote sensing, I present an alternative or complementary concept of bed state based on the notion that fluvial systems act to maximize flow resistance. The proposed quantitative index represents the relative contribution of morphologic adjustments occurring at different spatial scales (discriminated using a wavelet transform) to a stable channel configuration. By explicitly acknowledging the complexity of bed adjustments we can move toward a more complete understanding of channel stability in gravel-bed rivers.

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Section: Proposed Definitions Of Bed Statementioning

confidence: 99%

Toward bed state morphodynamics in gravel-bed rivers

Adams

2020

Progress in Physical Geography: Earth and Environment

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“…Our results indicate that these morphologic changes will be confined within a physical template defined by nearly stationary pools and riffles created during the threshold‐crossing phase, suggesting that the threshold‐crossing events are the formative flows. There is also evidence for this happening in the field: Tamminga and Eaton (2018) documented similar behaviour in the Elbow River, which experienced a threshold‐crossing event in 2013 that completely re‐structured the stream channel (Tamminga et al . 2015).…”

Section: Discussionmentioning

confidence: 90%

Channel stability in steep gravel–cobble streams is controlled by the coarse tail of the bed material distribution

Eaton

MacKenzie

Booker

2020

Earth Surf Processes Landf

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Researchers have associated channel-forming flows with reach-average shear stresses close to the entrainment threshold for the surface D 50. We conducted experiments using a model of a generic steep, gravel-cobble stream to test this association. Our results suggest that channel-forming flows fully mobilize the D 50 , and produce shear stresses close to the entrainment threshold for the largest grains in the bed. The channel dimensions were set by flows capable of mobilizing between 85% and 90% of the bed surface, which produced a brief period of lateral instability lasting about 1h, followed by a prolonged period of relative stability during which modest adjustments occurred, but during which the reach-average hydraulics remained about the same. The adjustments during the unstable phase of the experiments are characterized by rapid bank erosion, extensive deposits on the channel bed and a restructuring of the major morphologic elements of the stream. The adjustments during the stable phase of the experiments involved barform migration and bed surface coarsening but did not appreciably modify the physical template established by the end of the unstable phase. The behaviour we observed is not consistent with the concept of a dynamic equilibrium associated with a formative flow that is just capable of entraining the bed surface D 50. Instead, it suggests that rapid adjustments occur once a stability threshold is exceeded, which creates a template that constrains channel activity until another event drives the system across the stability threshold, and re-sets the template. While we believe that it is probably too simplistic to associate a channel-forming discharge with the entrainment threshold for a single grain size, our results suggest that the D 95 is a more logical choice than the D 50

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“…Because of stream morphodynamics, flow hydraulics and aquatic habitat are closely linked and sensitive to changes in the governing conditions [41,42], any alteration of the natural variability of the flow conditions results in a variation of both the local hydro-morphology and the fluvial habitat. Both high and low flow conditions affect the aquatic habitat, with a different magnitude depending on the geomorphic structure of the riverbed (i.e., gravel or sand) and its channel forms (i.e., braided, single-thread, meandering, etc.…”

Section: Discussionmentioning

confidence: 99%

Numerical Modelling as a Support Tool for River Habitat Studies

Nones¹

2019

Preprint

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Numerical modelling is becoming a major tool for supporting environmental studies at different scales, thanks to the capability of up-to-date codes in reproducing the natural behaviour in a quite reliable manner. In evaluating the habitat diversity of anthropized rivers, however, many issues are rising because of the intrinsic complexity of the processes involved. Using a reach of the Po River in Italy as a case study, the present works aims to provide an estimate of the changes of the Eco-Environmental Diversity as a response to different constant flow discharges. The goals are achieved by means of two solvers of the iRIC suite, applied in sequence to firstly simulate the fluvial hydrodynamics and subsequently provide an estimate of the habitat conditions. Despite the simplifications intrinsically present in the models and the ones introduced for practical purposes, the results pointed out that the reduction of the flow discharge recently observed can threat the overall biological status of the river. Because of the modelling uncertainties, on the other side, these preliminary outcomes show the need for more research, both in terms of data acquisition and numerical schematization, for adequately evaluate the effects of transient hydrology on the river ecosystems. Moreover, additional field surveys are necessary to calibrate and validate the used model for having sufficiently reliable estimates.

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Linking geomorphic change due to floods to spatial hydraulic habitat dynamics

Cited by 20 publications

References 104 publications

Toward bed state morphodynamics in gravel-bed rivers

Toward bed state morphodynamics in gravel-bed rivers

Channel stability in steep gravel–cobble streams is controlled by the coarse tail of the bed material distribution

Numerical Modelling as a Support Tool for River Habitat Studies

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