117 research outputs found
University to Receive Diversity and Inclusion Award
Copia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 200
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 space–time 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 “catch up” 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
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 space–time 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 “catch
up” 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
Episodic photic zone euxinia in the northeastern Panthalassic Ocean during the end-Triassic extinction
Severe changes in ocean redox, nutrient cycling, and marine productivity accompanied most Phanerozoic mass extinctions. However, evidence for marine photic zone euxinia (PZE) as a globally important extinction mechanism for the end-Triassic extinction (ETE) is currently lacking. Fossil molecular (biomarker) and nitrogen isotopic records from a sedimentary sequence in western Canada provide the first conclusive evidence of PZE and disrupted biogeochemistry in neritic waters of the Panthalassic Ocean during the end Triassic. Increasing water-column stratification and deoxygenation across the ETE led to PZE in the Early Jurassic, paralleled by a perturbed nitrogen cycle and ecological turnovers among noncalcifying groups, including eukaryotic algae and prokaryotic plankton. If such conditions developed widely in the Panthalassic Ocean, PZE might have been a potent mechanism for the ETE.National Science Foundation (U.S.) (Grant EAR-1147402)Exobiology Program (U.S.) (Grants NNX09AM88G and NNA08CN84A)American Association of Petroleum Geologists (Grant-In-Aid)Mary-Hill and Bevan M. French Fund for Impact Geolog
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