112 research outputs found
Within-Event Spatially Distributed Bedload: Linking Fluvial Sediment Transport to Morphological Change
Maps of apparent bedload velocity are presented along with maps of associated channel change. Apparent bedload velocity is the bias in acoustic Doppler current profiler (aDcp) bottom track (Doppler sonar) due to near-bed particle motion (Rennie et al. 2002). The apparent bedload velocity is correlated to bedload transport (Rennie and Villard 2004), and thus serves as an indicator of local bedload transport. Spatially distributed aDcp surveys in a river reach can be used to generate maps of channel bathymetry, water velocity, bed shear stress, and apparent bedload velocity (Rennie and Church 2010). It is possible to relate the observed spatial patterns of bedload and forcing flow. In this paper, the technique is used to measure bedload flux pathways during two sequential aDcp spatial surveys conducted in a Rees River, New Zealand braid bar diffluence-confluence before and after a major flood event that inundated the entire braid plain. The aDcp surveys were complemented with terrestrial laser scans (TLS) of the bar topography. Linking aDcp bathymetry and TLS topography allowed for generation of complete digitial elevation models (DEMs) of the reach, from which morphological change between surveys were determined. Most intriguingly, the primary bedload pathway observed during the first survey resulted in sufficient deposition during the major flood event to fill and choke off an anabranch. This is perhaps the first direct field measurement of spatially distributed bedload and corresponding morphological change
Geomorphology of the Rees Valley, Otago, New Zealand
We present a 1:33,333 geomorphological map of the Rees Valley, Otago, New Zealand. The Rees River drains an area of ~405 km2 and feeds into the head of Lake Wakatipu. This area has been affected by a range of geomorphological processes including tectonic activity, glacial erosion and deposition, mass movement, fluvial action, and base (lake) level change. Mapping was achieved by a combination of interpretation from SPOT 5 HRG satellite imagery and ground-truthing. The map presents the current distribution of landforms and sediments associated with the wide variety of contemporary and past geomorphological processes. It represents the most detailed and finest resolution geomorphological map of this region to date, and hence a number of features have been mapped and described for the first time. The map will assist on-going studies in the Rees catchment that seek to understand fluvial sediment transport and associated flood hazards, the dynamics of former glaciers, base level change associated with a drop in the level of Lake Wakatipu, and mass movement hazards. Š 2013 Simon J. Cook
Modelling braided river morphodynamics using a particle travel length framework
Numerical models that predict channel evolution are an
essential tool for investigating processes that occur over timescales which render field
observation intractable. The current generation of morphodynamic models, however, either
oversimplify the relevant physical processes or, in the case of more physically
complete codes based on computational fluid dynamics (CFD), have computational
overheads that severely restrict the spaceâtime scope of their application. Here we
present a new, open-source, hybrid approach that seeks to reconcile these modelling
philosophies. This framework combines steady-state, two-dimensional CFD hydraulics with a
rule-based sediment transport algorithm to predict particle mobility and transport paths
which are used to route sediment and evolve the bed topography. Data from two contrasting
natural braided rivers (Rees, New Zealand, and Feshie, United Kingdom) were used for
model verification, incorporating reach-scale quantitative morphological change budgets
and volumetric assessment of different braiding mechanisms. The model was able to
simulate 8 of the 10 empirically observed braiding mechanisms from the parameterized bed
erosion, sediment transport, and deposition. Representation of bank erosion and bar edge trimming
necessitated the inclusion of a lateral channel migration algorithm. Comparisons between
simulations based on steady effective discharge versus event hydrographs discretized into
a series of model runs were found to only marginally increase the predicted volumetric
change, with greater deposition offsetting erosion. A decadal-scale simulation indicates
that accurate prediction of event-scale scour depth and subsequent deposition present a
methodological challenge because the predicted pattern of deposition may never âcatch
upâ to erosion if a simple path-length distribution is employed, thus resulting in
channel over-scouring. It may thus be necessary to augment path-length distributions to
preferentially deposit material in certain geomorphic units. We anticipate that the model
presented here will be used as a modular framework to explore the effect of different
process representations, and as a learning tool designed to reveal the relative
importance of geomorphic transport processes in rivers at multiple timescales.</p
Assessment of a numerical model to reproduce event-scale erosion and deposition distributions in a braided river
Becky Goodsell and Eric Scott are thanked for field assistance. Antony Smith assisted with figure
production. The field campaign wa funded by NERC Grant NE/G005427/1 and NERC Geophysical Equipment Facility Loan 892. Richard Williams was funded by NERC Grant NE/G005427/1during fieldwork and by a British Hydrological Society Travel Grant whilst visiting NIW
Burrowing Invasive Species: An Unquantified Erosion Risk at the Aquatic-Terrestrial Interface
Comparison of the Disease Activity Score Using Erythrocyte Sedimentation Rate and C-reactive Protein in African Americans with Rheumatoid Arthritis
The Disease Activity Score based on 28 joints (DAS28) has been increasingly used in clinical practice and research studies of rheumatoid arthritis (RA). Studies have reported discordance between DAS28 based on erythrocyte sedimentation rate (ESR) versus C-reactive protein (CRP) in RA patients. However such comparison is lacking in African-Americans with RA
An African Ancestry-Specific Allele of CTLA4 Confers Protection against Rheumatoid Arthritis in African Americans
Cytotoxic T-lymphocyte associated protein 4 (CTLA4) is a negative regulator of T-cell proliferation. Polymorphisms in CTLA4 have been inconsistently associated with susceptibility to rheumatoid arthritis (RA) in populations of European ancestry but have not been examined in African Americans. The prevalence of RA in most populations of European and Asian ancestry is âź1.0%; RA is purportedly less common in black Africans, with little known about its prevalence in African Americans. We sought to determine if CTLA4 polymorphisms are associated with RA in African Americans. We performed a 2-stage analysis of 12 haplotype tagging single nucleotide polymorphisms (SNPs) across CTLA4 in a total of 505 African American RA patients and 712 African American controls using Illumina and TaqMan platforms. The minor allele (G) of the rs231778 SNP was 0.054 in RA patients, compared to 0.209 in controls (4.462Ă10â26, Fisher's exact). The presence of the G allele was associated with a substantially reduced odds ratio (OR) of having RA (AG+GG genotypes vs. AA genotype, OR 0.19, 95% CI: 0.13â0.26, pâ=â2.4Ă10â28, Fisher's exact), suggesting a protective effect. This SNP is polymorphic in the African population (minor allele frequency [MAF] 0.09 in the Yoruba population), but is very rare in other groups (MAFâ=â0.002 in 530 Caucasians genotyped for this study). Markers associated with RA in populations of European ancestry (rs3087243 [+60C/T] and rs231775 [+49A/G]) were not replicated in African Americans. We found no confounding of association for rs231778 after stratifying for the HLA-DRB1 shared epitope, presence of anti-cyclic citrullinated peptide antibody, or degree of admixture from the European population. An African ancestry-specific genetic variant of CTLA4 appears to be associated with protection from RA in African Americans. This finding may explain, in part, the relatively low prevalence of RA in black African populations
The Effect of Community-Level Socio-Economic Conditions on Threatening Racial Encounters
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