Jonathan Nelson (Former Employee)
Science and Products
Filter Total Items: 36
Geomorphic data collected within and adjacent to Nebraska Public Power District's Cottonwood Ranch Property, Platte River, Nebraska, Water Year 2001
River-channel topographic surveys were conducted and bed-material samples were collected along transects across the Platte River during water year 2001 (October 1, 2000 to September 30, 2001). A total of 57 transect lines or cross sections were established within three study reaches located along the middle channel of the Platte River in a 2,650-acre parcel of land owned by the Nebraska Public Pow
Authors
Paul Kinzel, Randolph Parker, Johnathan Nelson, R. Burman, Aashley Heckman
Direct numerical simulation of bedload transport using a local, dynamic boundary condition
Temporally and spatially averaged models of bedload transport are inadequate to describe the highly variable nature of particle motion at low transport stages. The primary sources of this variability are the resisting forces to downstream motion resulting from the geometrical relation (pocket friction angle) of a bed grain to the grains that it rests upon, variability of the near-bed turbulent vel
Authors
M.W. Schmeeckle, J. M. Nelson
Colorado River sediment transport: 2. Systematic bed‐elevation and grain‐size effects of sand supply limitation
The Colorado River in Marble and Grand Canyons displays evidence of annual supply limitation with respect to sand both prior to [Topping et al, this issue] and after the closure of Glen Canyon Dam in 1963. Systematic changes in bed elevation and systematic coupled changes in suspended‐sand concentration and grain size result from this supply limitation. During floods, sand supply limitation either
Authors
David J. Topping, David M. Rubin, Jonathan M. Nelson, Paul J. Kinzel, Ingrid C. Corson
Variability of bed mobility in natural, gravel‐bed channels and adjustments to sediment load at local and reach scales
Local variations in boundary shear stress acting on bed‐surface particles control patterns of bed load transport and channel evolution during varying stream discharges. At the reach scale a channel adjusts to imposed water and sediment supply through mutual interactions among channel form, local grain size, and local flow dynamics that govern bed mobility. In order to explore these adjustments, we
Authors
Thomas E. Lisle, Jonathan M. Nelson, John Pitlick, Mary Ann Madej, Brent L. Barkett
Spatially averaged flow over a wavy boundary revisited
Vertical profiles of streamwise velocity measured over bed forms are commonly used to deduce boundary shear stress for the purpose of estimating sediment transport. These profiles may be derived locally or from some sort of spatial average. Arguments for using the latter procedure are based on the assumption that spatial averaging of the momentum equation effectively removes local accelerations fr
Authors
S.R. McLean, S.R. Wolfe, J. M. Nelson
Predicting boundary shear stress and sediment transport over bed forms
To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccu
Authors
S.R. McLean, S.R. Wolfe, J. M. Nelson
Relation of inversely graded deposits to suspended-sediment grain-size evolution during the 1996 flood experiment in Grand Canyon
Before Glen Canyon Dam was completed upstream from Grand Canyon, floods scoured sand from the channel bed and deposited sand on bars within recirculating eddies. After completion of Glen Canyon Dam in 1963, peak discharge of the mean annual floods dropped front about 2600 to 900 m3/s, and 85% of the sediment supply was eliminated. Under the postdam flow regime, sand bars in eddies have degraded. I
Authors
D. M. Rubin, J. M. Nelson, D.J. Topping
Interactions between pool geometry and hydraulics
An experimental and computational research approach was used to determine interactions between pool geometry and hydraulics. A 20-m-long, 1.8-m-wide flume was used to investigate the effect of four different geometric aspects of pool shape on flow velocity. Plywood sections were used to systematically alter constriction width, pool depth, pool length, and pool exit-slope gradient, each at two sepa
Authors
Douglas M. Thompson, Jonathan M. Nelson, Ellen E. Wohl
Predictive techniques for river channel evolution and maintenance
Predicting changes in alluvial channel morphology associated with anthropogenic and natural changes in flow and/or sediment supply is a critical part of the management of riverine systems. Over the past few years, advances in the understanding of the physics of sediment transport in conjunction with rapidly increasing capabilities in computational fluid dynamics have yielded now approaches to prob
Authors
J. M. Nelson
Role of near-bed turbulence in bedload transport
Bedload transport by a turbulent fluid moving over an erodible sediment bed results from complex interactions between flow field of the overlying fluid and the grains making up the bed. To develop a better view of these interactions, a method that combines high-speed photography with laser-Doppler velocimetry was devised. The methodology permits correlation of bedload transport with local turbulen
Authors
Jonathan M. Nelson, Ronald L. Shreve, Stephen R. McLean
Mean flow and turbulence fields over two-dimensional bed forms
Detailed laser-Doppler velocity and Reynolds stress measurements over fixed two-dimensional bed forms are used to investigate the coupling between the mean flow and turbulence and to examine effects that play a role in producing the bed form instability and finite amplitude stability. The coupling between the mean flow and the turbulence is explored in both a spatially averaged sense, by determini
Authors
Jonathan M. Nelson, Stephen R. McLean, Stephen R. Wolfe
The initial instability and finite-amplitude stability of alternate bars in straight channels
The initial instability and fully developed stability of alternate bars in straight channels are investigated using linearized and nonlinear analyses. The fundamental instability leading to these features is identified through a linear stability analysis of the equations governing the flow and sediment transport fields. This instability is explained in terms of topographically induced steering of
Authors
Jonathan M. Nelson
Science and Products
Filter Total Items: 36
Geomorphic data collected within and adjacent to Nebraska Public Power District's Cottonwood Ranch Property, Platte River, Nebraska, Water Year 2001
River-channel topographic surveys were conducted and bed-material samples were collected along transects across the Platte River during water year 2001 (October 1, 2000 to September 30, 2001). A total of 57 transect lines or cross sections were established within three study reaches located along the middle channel of the Platte River in a 2,650-acre parcel of land owned by the Nebraska Public Pow
Authors
Paul Kinzel, Randolph Parker, Johnathan Nelson, R. Burman, Aashley Heckman
Direct numerical simulation of bedload transport using a local, dynamic boundary condition
Temporally and spatially averaged models of bedload transport are inadequate to describe the highly variable nature of particle motion at low transport stages. The primary sources of this variability are the resisting forces to downstream motion resulting from the geometrical relation (pocket friction angle) of a bed grain to the grains that it rests upon, variability of the near-bed turbulent vel
Authors
M.W. Schmeeckle, J. M. Nelson
Colorado River sediment transport: 2. Systematic bed‐elevation and grain‐size effects of sand supply limitation
The Colorado River in Marble and Grand Canyons displays evidence of annual supply limitation with respect to sand both prior to [Topping et al, this issue] and after the closure of Glen Canyon Dam in 1963. Systematic changes in bed elevation and systematic coupled changes in suspended‐sand concentration and grain size result from this supply limitation. During floods, sand supply limitation either
Authors
David J. Topping, David M. Rubin, Jonathan M. Nelson, Paul J. Kinzel, Ingrid C. Corson
Variability of bed mobility in natural, gravel‐bed channels and adjustments to sediment load at local and reach scales
Local variations in boundary shear stress acting on bed‐surface particles control patterns of bed load transport and channel evolution during varying stream discharges. At the reach scale a channel adjusts to imposed water and sediment supply through mutual interactions among channel form, local grain size, and local flow dynamics that govern bed mobility. In order to explore these adjustments, we
Authors
Thomas E. Lisle, Jonathan M. Nelson, John Pitlick, Mary Ann Madej, Brent L. Barkett
Spatially averaged flow over a wavy boundary revisited
Vertical profiles of streamwise velocity measured over bed forms are commonly used to deduce boundary shear stress for the purpose of estimating sediment transport. These profiles may be derived locally or from some sort of spatial average. Arguments for using the latter procedure are based on the assumption that spatial averaging of the momentum equation effectively removes local accelerations fr
Authors
S.R. McLean, S.R. Wolfe, J. M. Nelson
Predicting boundary shear stress and sediment transport over bed forms
To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccu
Authors
S.R. McLean, S.R. Wolfe, J. M. Nelson
Relation of inversely graded deposits to suspended-sediment grain-size evolution during the 1996 flood experiment in Grand Canyon
Before Glen Canyon Dam was completed upstream from Grand Canyon, floods scoured sand from the channel bed and deposited sand on bars within recirculating eddies. After completion of Glen Canyon Dam in 1963, peak discharge of the mean annual floods dropped front about 2600 to 900 m3/s, and 85% of the sediment supply was eliminated. Under the postdam flow regime, sand bars in eddies have degraded. I
Authors
D. M. Rubin, J. M. Nelson, D.J. Topping
Interactions between pool geometry and hydraulics
An experimental and computational research approach was used to determine interactions between pool geometry and hydraulics. A 20-m-long, 1.8-m-wide flume was used to investigate the effect of four different geometric aspects of pool shape on flow velocity. Plywood sections were used to systematically alter constriction width, pool depth, pool length, and pool exit-slope gradient, each at two sepa
Authors
Douglas M. Thompson, Jonathan M. Nelson, Ellen E. Wohl
Predictive techniques for river channel evolution and maintenance
Predicting changes in alluvial channel morphology associated with anthropogenic and natural changes in flow and/or sediment supply is a critical part of the management of riverine systems. Over the past few years, advances in the understanding of the physics of sediment transport in conjunction with rapidly increasing capabilities in computational fluid dynamics have yielded now approaches to prob
Authors
J. M. Nelson
Role of near-bed turbulence in bedload transport
Bedload transport by a turbulent fluid moving over an erodible sediment bed results from complex interactions between flow field of the overlying fluid and the grains making up the bed. To develop a better view of these interactions, a method that combines high-speed photography with laser-Doppler velocimetry was devised. The methodology permits correlation of bedload transport with local turbulen
Authors
Jonathan M. Nelson, Ronald L. Shreve, Stephen R. McLean
Mean flow and turbulence fields over two-dimensional bed forms
Detailed laser-Doppler velocity and Reynolds stress measurements over fixed two-dimensional bed forms are used to investigate the coupling between the mean flow and turbulence and to examine effects that play a role in producing the bed form instability and finite amplitude stability. The coupling between the mean flow and the turbulence is explored in both a spatially averaged sense, by determini
Authors
Jonathan M. Nelson, Stephen R. McLean, Stephen R. Wolfe
The initial instability and finite-amplitude stability of alternate bars in straight channels
The initial instability and fully developed stability of alternate bars in straight channels are investigated using linearized and nonlinear analyses. The fundamental instability leading to these features is identified through a linear stability analysis of the equations governing the flow and sediment transport fields. This instability is explained in terms of topographically induced steering of
Authors
Jonathan M. Nelson