403 research outputs found
Modeling of Fluvial Geomorphic Processes in River Channels Impacted by Agriculture
Mini-Symposium: Modeling Methodology for Agricultural Researc
An improved meander migration formulation based on streambank erosion processes
River morphodynamics and sediment transportRiver morphology and morphodynamic
Linguistics
Contains reports on seven research projects.National Science Foundation (Grant G-16526)National Institutes of Health (Grant MH-04737-02)United States Air Force, Electronic Systems Division (Contract AF19(628)-2487
Using Computer Models to Design Gully Erosion Control Structures for Humid Northern Ethiopia
Mini-Symposium: Modeling Methodology for Agricultural Researc
Three-dimensional flow structure and bed morphology in large elongate meander loops with different outer bank roughness characteristics
© 2016. American Geophysical Union. All Rights Reserved. Few studies have examined the three-dimensional flow structure and bed morphology within elongate loops of large meandering channels. The present study focuses on the spatial patterns of three-dimensional flow structure and bed morphology within two elongate meander loops and examines how differences in outer bank roughness influence near-bank flow characteristics. Three-dimensional velocities were measured during two different eventsâa near-bankfull flow and an overbank event. Detailed data on channel bathymetry and bed form geometry were obtained during a near-bankfull event. Flow structure within the loops is characterized by strong topographic steering by the point bar, by the development of helical motion associated with flow curvature, and by acceleration of flow where bedrock is exposed along the outer bank. Near-bank velocities during the overbank event are less than those for the near-bankfull flow, highlighting the strong influence of the point bar on redistribution of mass and momentum of the flow at subbankfull stages. Multiple outer bank pools are evident within the elongate meander loop with low outer bank roughness, but are not present in the loop with high outer bank roughness, which may reflect the influence of abundant large woody debris on near-bank velocity characteristics. The positions of pools within both loops can be linked to spatial variations in planform curvature. The findings indicate that flow structure and bed morphology in these large elongate loops is similar to that in small elongate loops, but differs somewhat from flow structure and bed morphology reported for experimental elongate loops
Successful conservation of global waterbird populations depends on effective governance
Understanding global patterns of biodiversity change is crucial for conservation research, policies and practices. However, for most ecosystems, the lack of systematically collected data at a global level limits our understanding of biodiversity changes and their local-scale drivers. Here we address this challenge by focusing on wetlands, which are among the most biodiverse and productive of any environments and which provide essential ecosystem services, but are also amongst the most seriously threatened ecosystems. Using birds as an indicator taxon of wetland biodiversity, we model time-series abundance data for 461 waterbird species at 25,769 survey sites across the globe. We show that the strongest predictor of changes in waterbird abundance, and of conservation efforts having beneficial effects, is the effective governance of a country. In areas in which governance is on average less effective, such as western and central Asia, sub-Saharan Africa and South America, waterbird declines are particularly pronounced; a higher protected area coverage of wetland environments facilitates waterbird increases, but only in countries with more effective governance. Our findings highlight that sociopolitical instability can lead to biodiversity loss and undermine the benefit of existing conservation efforts, such as the expansion of protected area coverage. Furthermore, data deficiencies in areas with less effective governance could lead to underestimations of the extent of the current biodiversity crisis.</p
Some considerations concerning the challenge of incorporating social variables into epidemiological models of infectious disease transmission
Incorporation of âsocialâ variables into epidemiological models remains a challenge. Too much detail and models cease to be useful; too little and the very notion of infection âa highly social process in human populationsâmay be considered with little reference to the social. The French sociologist Emile Durkheim proposed that the scientific study of society required identification and study of âsocial currents.â Such âcurrentsâ are what we might today describe as âemergent properties,â specifiable variables appertaining to individuals and groups, which represent the perspectives of social actors as they experience the environment in which they live their lives. Here we review the ways in which one particular emergent property, hope, relevant to a range of epidemiological situations, might be used in epidemiological modelling of infectious diseases in human populations. We also indicate how such an approach might be extended to include a range of other potential emergent properties to repre
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