On the stabilizing influence of silt on sand beds

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dc.contributor.authorBartzke, Gerhard
dc.contributor.authorBryan, Karin R.
dc.contributor.authorPilditch, Conrad A.
dc.contributor.authorHuhn, Katrin
dc.date.accessioned2014-01-21T21:12:08Z
dc.date.available2014-01-21T21:12:08Z
dc.date.copyright2013-07-29
dc.date.issued2013
dc.description.abstractIn marine environments, sediments from different sources are stirred and dispersed, generating beds that are composed of mixed and layered sediments of differing grain sizes. Traditional engineering formulations used to predict erosion thresholds are however, generally for unimodal sediment distributions, and so may be inadequate for commonly occurring coastal sediments. We tested the transport behavior of deposited and mixed sediment beds consisting of a simplified two-grain fraction (silt (D50  =  55 µm) and sand (D50 =  300 µm)) in a laboratory-based annular flume with the objective of investigating the parameters controlling the stability of a sediment bed. To mimic recent deposition of particles following large storm events and the longer-term result of the incorporation of fines in coarse sediment, we designed two suites of experiments: (1) “the layering experiment”: in which a sandy bed was covered by a thin layer of silt of varying thickness (0.2–3 mm; 0.5–3.7 wt %, dry weight in a layer 10 cm deep); and (2) “the mixing experiment” where the bed was composed of sand homogeneously mixed with small amounts of silt (0.07–0.7 wt %, dry weight). To initiate erosion and to detect a possible stabilizing effect in both settings, we increased the flow speeds in increments up to 0.30 m/s. Results showed that the sediment bed (or the underlying sand bed in the case of the layering experiment) stabilized with increasing silt composition. The increasing sediment stability was defined by a shift of the initial threshold conditions towards higher flow speeds, combined with, in the case of the mixed bed, decreasing erosion rates. Our results show that even extremely low concentrations of silt play a stabilizing role (1.4% silt (wt %) on a layered sediment bed of 10 cm thickness). In the case of a mixed sediment bed, 0.18% silt (wt %, in a sample of 10 cm depth) stabilized the bed. Both cases show that the depositional history of the sediment fractions can change the erosion characteristics of the seabed. These observations are summarized in a conceptual model that suggests that, in addition to the effect on surface roughness, silt stabilizes the sand bed by pore-space plugging and reducing the inflow in the bed, and hence increases the bed stability. Measurements of hydraulic conductivity on similar bed assemblages qualitatively supported this conclusion by showing that silt could decrease the permeability by up to 22% in the case of a layered bed and by up to 70% in the case of a mixed bed.en_NZ
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dc.identifier.citationBartzke, Gerhard, Bryan, K. R., Pilditch, C. A. & Huhn, K. (2013). On the stabilizing influence of silt on sand beds. Journal of Sedimentary Research, 83(8), 691-703.en_NZ
dc.identifier.doi10.2110/jsr.2013.57en_NZ
dc.identifier.urihttps://hdl.handle.net/10289/8419
dc.language.isoenen_NZ
dc.publisherSociety for Sedimentary Geologyen_NZ
dc.relation.isPartOfJournal of Sedimentary Researchen_NZ
dc.relation.ispartofJournal of Sedimentary Research
dc.relation.urihttp://jsedres.geoscienceworld.org/content/83/8/691.abstracten_NZ
dc.rightsThis is an author’s accepted version of an article published in the journal: Journal of Sedimentary Research. © 2013 SEPM.en_NZ
dc.subjectsediment mixturesen_NZ
dc.subjectstabilizationen_NZ
dc.subjectannular flumeen_NZ
dc.subjectpore-space pluggingen_NZ
dc.subjectinflow blockingen_NZ
dc.titleOn the stabilizing influence of silt on sand bedsen_NZ
dc.typeJournal Articleen_NZ
pubs.begin-page691en_NZ
pubs.elements-id38741
pubs.end-page703en_NZ
pubs.issue8en_NZ
pubs.volume83en_NZ
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