Erodibility of cohesive sediment: The importance of sediment properties

Grabowski, Robert; Droppo, Ian G.; Wharton, Geraldene

doi:10.1016/j.earscirev.2011.01.008

Cited by 456 publications

(345 citation statements)

References 155 publications

Supporting

Mentioning

335

Contrasting

Unclassified

Order By: Relevance

“…The interface is located where the bed has just eroded through, so that hðX; tÞ = 0 and X = ðC=h 0 Þ 2 t 2 . Uniform acceleration thus results from the proportionality of erosion rate and shear stress, a law that is consistent with bulk measurements of other cohesive materials (15). Our direct determination of this This article is a PNAS Direct Submission.…”

supporting

confidence: 55%

Sculpting of an erodible body by flowing water

Ristroph

Moore

Childress

et al. 2012

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

112

View full text Add to dashboard Cite

Erosion by flowing fluids carves striking landforms on Earth and also provides important clues to the past and present environments of other worlds. In these processes, solid boundaries both influence and are shaped by the surrounding fluid, but the emergence of morphology as a result of this interaction is not well understood. We study the coevolution of shape and flow in the context of erodible bodies molded from clay and immersed in a fast, unidirectional water flow. Although commonly viewed as a smoothing process, we find that erosion sculpts pointed and cornerlike features that persist as the solid shrinks. We explain these observations using flow visualization and a fluid mechanical model in which the surface shear stress dictates the rate of material removal. Experiments and simulations show that this interaction ultimately leads to selfsimilarly receding boundaries and a unique front surface characterized by nearly uniform shear stress. This tendency toward conformity of stress offers a principle for understanding erosion in more complex geometries and flows, such as those present in nature.R eflecting on his scientific discoveries, Isaac Newton compared himself to a boy on the seashore who marvels at having found a yet smoother stone (1). For pebbles and mountains alike, our curiosity about natural sculptures stems perhaps from the realization that these shapes reflect countless incremental events acting over eons. Morphology is often the only clue available as we attempt to reconstruct the physical history of the Earth as well as of our neighboring worlds (2-6). Recreating geologically inspired situations in the laboratory offers an opportunity to connect the development of structures to the underlying processes at work (7). This approach has been used to study phenomena across many scales, for example, the rounding of rocks by abrasion (8), the formation of rivers (9) and drainage channels (10), and the drift of continental plates driven by mantle convection (11).Rather than mimic a particular geological scenario, we conduct experiments that isolate a central aspect common to all erosive processes: the interdependent evolution of shape and flow (3). As described in Methods, we study the erosion of soft clay bodies by fast-flowing water, allowing us to witness what is an intractably slow process in nature. We consider unidirectional flow and canonical initial geometries-a thin flat bed of clay, a cylinder, and a sphere-with an eye toward informing mathematical models that intimately link the coevolving flow and shape (12, 13). Our experiments typically involve centimeter-scale bodies immersed in flows of 40-70 cm/s, yielding high Reynolds numbers of order 10 4 . Importantly, the solid boundaries recede at rates (approximately centimeters per hour) that are many orders slower than the flow speed, preserving the large separation of time-scales characteristic of natural erosion.Considering first the case of a 3D body, we form a clay sphere of diameter 4.9 cm and support it within a water tunnel with a cro...

show abstract

supporting

confidence: 55%

Sculpting of an erodible body by flowing water

Ristroph

Moore

Childress

et al. 2012

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

112

View full text Add to dashboard Cite

show abstract

“…One example is the bulk density, which is a measure of the different proportion of sediments, water and gases in the sediment sample. Hence, the bulk density indicates the degree of consolidation for cohesive sediments [35]. Consequently, there is usually a positive correlation of bulk densities with sediment stability: in other words, high bulk densities result in high erosion thresholds and low erosion rates.…”

Section: Discussionmentioning

confidence: 99%

Combining Field and Laboratory Measurements to Determine the Erosion Risk of Cohesive Sediments Best

Noack

Gerbersdorf

Hillebrand

et al. 2015

Water

View full text Add to dashboard Cite

Abstract:In contrast to non-cohesive sediments, the incipient motion of cohesive sediments is characterized by much more complex interactions between several sedimentary, biological, and chemical parameters. Thus, site-specific investigations are required to obtain information about the erosion stability of cohesive materials. This becomes even more relevant for contaminated sediments, stored in riverine sediments as a "burden of the past", because of their remobilization potential during flood events. This article represents a twofold measuring strategy for the detection of erosion thresholds: an in situ device for determination of critical shear stresses in the field, and a laboratory approach where sediment cores are withdrawn and subsequently analyzed over depth. The combined measuring strategy was applied in the River Elbe and at selected sites of the catchment of the River Saale. The results show a great variety of erosion thresholds over depth, demonstrating the need to conduct vertical analyses, especially when addressing buried layers with contaminations. The latter is only possible in the laboratory but the in situ device revealed clear benefits in capturing the loose flocculent layer on top of the sediment that might be easily lost during sediment retrieval and transport. Consequently, it is ideal to combine both approaches for a comprehensive insight into sediment stability. OPEN ACCESSWater 2015, 7 5062

show abstract

“…This has further implications, for instance, the transport and storage of nutrients, xenobiotic compounds, pollutants such as heavy metals and even pathogens such as Escherichia coli that are often associated with fine sediments (Droppo et al 2009;Pachepsky and Shelton 2011;. Understanding the factors that mediate sediment transport becomes increasingly important with future climate scenarios such as sea level rise, increased storm events and the erosion of coastal sediments (Grabowski et al 2011).…”

Section: Is Sediment Biostabilisation Important?mentioning

confidence: 99%

“…However, whether it is about mimicking cohesion (Lick et al 2004) or adding a combination of cohesion and adhesion coefficients (Righetti and Lucarelli 2007), there is still a significant lack of suitable data and appropriate measuring devices to strengthen the empirical dataset and validate the models (Grabowski et al 2011). …”

Section: The Ecosystem Approachmentioning

confidence: 99%

Form, function and physics: the ecology of biogenic stabilisation

et al. 2018

View full text Add to dashboard Cite

Purpose The objective of this work is to better understand the role that biological mediation plays in the behaviour of fine sediments. This research is supported by developments in ecological theory recognising organisms as Becosystem engineers^and associated discussion of Bniche construction^, suggesting an evolutionary role for habitat modification by biological action. In addition, there is acknowledgement from engineering disciplines that something is missing from fine sediment transport predictions. Materials and methods Advances in technology continue to improve our ability to examine the small-scale 2D processes with large-scale effects in natural environments. Advanced molecular tools can be combined with state-of-the-art field and laboratory techniques to allow the discrimination of microbial biodiversity and the examination of their metabolic contribution to ecosystem function. This in turn can be related to highly resolved measurements and visualisation of flow dynamics. Results and discussion Recent laboratory and field work have led to a paradigm shift whereby hydraulic research has to embrace biology and biogeochemistry to unravel the highly complex issues around on fine sediment dynamics. Examples are provided illustrating traditional and more recent approaches including using multiple stressors in fully factorial designs in both the laboratory and the field to highlight the complexity of the interaction between biology and sediment dynamics in time and space. The next phase is likely to rely on advances in molecular analysis, metagenomics and metabolomics, to assess the functional role of microbial assemblages in sediment behaviour, including the nature and rate of polymer production by bacteria, the mechanism of their influence on sediment behaviour. Conclusions To fully understand how aquatic habitats will adjust to environmental change and to support the provision of various ecosystem services, we require a holistic approach. We must consider all aspects that control the distribution of sediment and the erosion-transport-deposition-consolidation cycle including biological and chemical processes, not just the physical. In particular, the role of microbial assemblages is now recognised as a significant factor deserving greater attention across disciplines.

show abstract

Erodibility of cohesive sediment: The importance of sediment properties

Cited by 456 publications

References 155 publications

Sculpting of an erodible body by flowing water

Sculpting of an erodible body by flowing water

Combining Field and Laboratory Measurements to Determine the Erosion Risk of Cohesive Sediments Best

Form, function and physics: the ecology of biogenic stabilisation

Contact Info

Product

Resources

About