Dynamics and Mechanics of Bed-Load Tracer Particles

Understanding the mechanics of bed load at the flood scale is necessary to link hydrology to landscape evolution. Here we report on observations of the transport of coarse sediment tracer particles in a cobble-bedded alluvial river and a step-pool bedrock tributary, at the individual flood and multi-annual timescales. Tracer particle data for each survey are composed of measured displacement lengths for individual particles, and the number of tagged particles mobilized. For single floods we find that measured tracer particle displacement lengths are exponentially distributed; the number of mobile particles increases linearly with peak flood Shields stress, indicating partial bed load transport for all observed floods; and modal displacement distances scale linearly with excess shear velocity. These findings provide quantitative field support for a recently proposed modeling framework based on momentum conservation at the grain scale. Tracer displacement is weakly negatively correlated with particle size at the individual flood scale; however cumulative travel distance begins to show a stronger inverse relation to grain size when measured over many transport events. The observed spatial sorting of tracers approaches that of the river bed, and is consistent with size-selective deposition models and laboratory experiments. Tracer displacement data for the bedrock and alluvial channels collapse onto a single curve – despite more than an order of magnitude difference in channel slope – when variations of critical Shields stress and flow resistance between the two are accounted for. Results show how bed load dynamics may be predicted from a record of river stage, providing a direct link between climate and sediment transport

Impulse Framework for Unsteady Flows Reveals Superdiffusive Bed Load Transport

Sediment transport is an intrinsically stochastic process, and measurement of bed load in the environment is further complicated by the unsteady nature of river flooding. Here we present a methodology for analyzing sediment tracer data with unsteady forcing. We define a dimensionless impulse by integrating the cumulative excess shear velocity for the duration of measurement, normalized by grain size. We analyze the dispersion of a plume of cobble tracers in a very flashy stream over two years. The mean and variance of transport distance collapse onto well-defined linear and power-law relations, respectively, when plotted against cumulative dimensionless impulse. Data suggest that the asymptotic limit of bed load tracer dispersion is superdiffusive, in line with a broad class of geophysical flows exhibiting strong directional asymmetry (advection), thin-tailed step lengths and heavy-tailed waiting times. The impulse framework justifies the use of quasi-steady flow approximations for long-term river evolution modeling

Animal archeology: Domestic pigeons and the nature-culture dialectic

©2 20 00 05 5--2 20 00 07 7 Q Qu ua al li it ta at ti iv ve e S So oc ci io ol lo og gy y R Re ev vi ie ew w V Vo ol lu um me e I II II I I Is ss su ue e 1 1 w ww ww w. .q qu ua al li it ta at ti iv ve es so oc ci io ol lo og gy yr re ev vi ie ew w. Abstract This paper historically traces the purposive domestication of pigeons in order to examine the dialectical relationship between nature and culture. It is demonstrated that each instance of the domestication of the pigeon for a new function (i.e., food, messenger) also entailed the construction of a role of the bird in human society, replete with symbolic representations and moral valuations. Yet it is also argued that, though animals are repositories for social meaning, and culture is literally inscribed into the physical structure of domesticated animals, such meanings are patterned and constrained according to the biological features of the animal itself. The ubiquitous and unwanted "street pigeon" now found around the globe is the descendent of escaped domestic pigeons, occupying the unique and ambiguous category of "feral"-neither truly wild nor domestic. Ironically, the very traits that were once so desirous and that were naturally selected for are now what make the feral pigeon so hard to get rid of and so loathsome. Keywords Pigeon; Human-animal Relations; Domestication; Nature; History; Wildlife Pigeons are one of the most common, and problematic, birds in the world today. Throughout history, however, they have perhaps taken on more symbolic and functional roles than any other bird. Modified over millennia through genetic manipulation to serve as messengers and a food source, and used to represent images of love, peace, the holy spirit, and even heroism, the "street" pigeons that populate our cities today confront us as our own cultural detritus. They are no longer useful for most of society and are more likely than not to be deemed "out of place&quot

Animal archeology: Domestic pigeons and the nature-culture dialectic

This paper historically traces the purposive domestication of pigeons in order to examine the dialectical relationship between nature and culture. It is demonstrated that each instance of the domestication of the pigeon for a new function (i.e., food, messenger) also entailed the construction of a role of the bird in human society, replete with symbolic representations and moral valuations. Yet it is also argued that, though animals are repositories for social meaning, and culture is literally inscribed into the physical structure of domesticated animals, such meanings are patterned and constrained according to the biological features of the animal itself. The ubiquitous and unwanted “street pigeon” now found around the globe is the descendent of escaped domestic pigeons, occupying the unique and ambiguous category of “feral”- neither truly wild nor domestic. Ironically, the very traits that were once so desirous and that were naturally selected for are now what make the feral pigeon so hard to get rid of and so loathsome. 

Mameyes River RFID Tracer Cobbles

<p>Positions of RFID equiped coarse sediment tracer particles before and after floods at the single flood to annual timescales in the Mameyes River, PR. Please see accompanying metadata file "RFID Tracer Documentation". Tracer particle locations are available in both a cartesian coordinate system, as well as a streamwise normal coordinate system.</p> <p> </p

Critical Filter Hydrograph and Field Site Data

These files represent hydrographs and associated field data. Please see the readme file for more information. Each .zip file contains an illustrated readme/methods file

Bisley3 RFID Sediment Tracer Data

<p>Positions of RFID equiped coarse sediment tracer particles before and after floods at the single flood to annual timescales in the Mameyes River tributary within catchment 3 of the Bisley Experimental Forest, PR. Please see accompanying metadata file "RFID Tracer Documentation". Tracer particle locations are available in both a cartesian coordinate system, as well as a streamwise normal coordinate system.</p