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Portland State University

Civil and Environmental Engineering Faculty Publications and Presentations

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Articles 361 - 373 of 373

Full-Text Articles in Engineering

Tidal Asymmetry In An Estuarine Pycnocline 2. Transport, David A. Jay, Cynthia N. Cudaback Feb 2001

Tidal Asymmetry In An Estuarine Pycnocline 2. Transport, David A. Jay, Cynthia N. Cudaback

Civil and Environmental Engineering Faculty Publications and Presentations

Flood currents in shallow estuaries are driven by an along-channel barotropic and baroclinic pressure gradient that increases monotonically toward the bottom, while friction retards near-bottom currents. Therefore, in many estuaries there is a middepth maximum in flood currents. We explore this phenomenon using a simple three-layer model in which each layer has vertically uniform currents and constant density. In this model the middle layer is of intermediate density and grows by shear-induced entrainment from the other two layers. This very simple model produces a middepth maximum in flood currents and simulates observed currents in the Columbia River entrance channel within …

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Tidal Asymmetry In An Estuarine Pycnocline: Depth And Thickness, Cynthia N. Cudaback, David A. Jay Nov 2000

Tidal Asymmetry In An Estuarine Pycnocline: Depth And Thickness, Cynthia N. Cudaback, David A. Jay

Civil and Environmental Engineering Faculty Publications and Presentations

Tidal variations in estuarine stratification are revealed by the depth and thickness of the density interface. The depth of the interface may be predicted using an inviscid two-layer model that combines baroclinic estuarine circulation with barotropic tidal currents [Helfrich, 1995]. Here we present results from a two-layer model modified to include the effects of bottom friction and interfacial mixing. Modeled layer thickness and speed compare favorably with prior analytic studies [Farmer and Armi, 1986; Pratt, 1986]. We use a bulk Richardson number criterion to estimate the thickness of the pycnocline from two-layer model results; the predicted pycnocline depth and thickness …

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Improvements In Modeling Dissolved Oxygen In Activated Sludge Systems, Jacek Makinia, Scott A. Wells Jan 1999

Improvements In Modeling Dissolved Oxygen In Activated Sludge Systems, Jacek Makinia, Scott A. Wells

Civil and Environmental Engineering Faculty Publications and Presentations

The aim of this research was to show the impact of the flow conditions and variations in the aeration intensity on changes in the predicted dissolved oxygen (DO) concentrations in a full-scale activated sludge reactor. The Activated Sludge Model No. 1 was used to describe the biochemical processes. The studies were performed at the Rock Creek wastewater treatment plant in Hillsboro, OR (USA). The simulation results were compared with data originating from two 24-hour experiments. The model that best reflected the spatial and diurnal distributions of the DO concentrations was the one-dimensional advection-dispersion equation with a variable overall oxygen mass …

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The Columbia River Plume Study: Subtidal Variability In The Velocity And Salinity Fields, B. M. Hickey, Leonard J. Pietrafesa, David A. Jay, William C. Boicourt May 1998

The Columbia River Plume Study: Subtidal Variability In The Velocity And Salinity Fields, B. M. Hickey, Leonard J. Pietrafesa, David A. Jay, William C. Boicourt

Civil and Environmental Engineering Faculty Publications and Presentations

A comprehensive study of the strongly wind driven midlatitude buoyant plume from the Columbia River, located on the U.S. west coast, demonstrates that the plume has two basic structures during the fall/winter season, namely, a thin (~5~15 m), strongly stratified plume tending west to northwestward during periods of southward or light northward wind stress and a thicker (~10~40 m), weakly stratified plume tending northward and hugging the coast during periods of stronger northward stress. The plume and its velocity field respond nearly instantaneously to changes in wind speed or direction, and the wind fluctuations have timescales of 2-10 days. Frictional …

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Interaction Of Fluctuating River Flow With A Barotropic Tide: A Demonstration Of Wavelet Tidal Analysis Methods, David A. Jay, Edward P. Flinchem Mar 1997

Interaction Of Fluctuating River Flow With A Barotropic Tide: A Demonstration Of Wavelet Tidal Analysis Methods, David A. Jay, Edward P. Flinchem

Civil and Environmental Engineering Faculty Publications and Presentations

Wavelet transforms provide a valuable new tool for analysis of tidal processes that deviate markedly from an assumption of exact periodicity inherent in traditional harmonic analysis. A wavelet basis adapted to nonstationary tidal problems is constructed and employed to analyze the modulation of the external tide in a river by variations in streamflow. Interaction of a surface tide with river flow is the best available demonstration of the continuous wavelet transform (CWT) methods developed. It is the simplest and perhaps the only nonstationary tidal process for which both sufficient data and dynamical understanding exist to allow detailed comparisons between CWT …

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Data Assimilation In Models With Convective Adjustment, Robert N. Miller, Edward D. Zaron, Andrew F. Bennett Nov 1994

Data Assimilation In Models With Convective Adjustment, Robert N. Miller, Edward D. Zaron, Andrew F. Bennett

Civil and Environmental Engineering Faculty Publications and Presentations

Practical hydrostatic ocean models are often restricted to statically stable configurations by the use of a convective adjustment. A common way to do this is to assign an infinite boat conductivity to the water at a given level if the water column should become statically unstable. This is implemented in the form of a switch. When a statically unstable configuration is detected, it is immediately replaced with a statically stable one in which heat is conserved. In this approach, the model is no longer governed by a smooth set of equations, and usual techniques of variational data assimilation must be …

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Particle Trapping In Estuarine Tidal Flows, David A. Jay, Jeffery D. Musiak Oct 1994

Particle Trapping In Estuarine Tidal Flows, David A. Jay, Jeffery D. Musiak

Civil and Environmental Engineering Faculty Publications and Presentations

Particle trapping in estuarine turbidity maxima (ETM) is caused primarily by convergent mean and/or tidal fluxes of sediment. The result is an approximately bell-shaped along-channel distribution of vertically integrated, tidal cycle mean suspended sediment concentration. Observations from the Columbia River estuary suggest that (1) strong two-layer or internal along-channel residual and overtide flows are generated by time-varying stratification and (2) correlations between the near-bed velocity and the suspended sediment fields at these frequencies are important in landward transport of sediment. A new spatially and temporally integrated form of the sediment conservation equation has been derived to analyze this trapping process. …

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Green's Law Revisited: Tidal Long-Wave Propagation In Channels With Strong Topography, David A. Jay Nov 1991

Green's Law Revisited: Tidal Long-Wave Propagation In Channels With Strong Topography, David A. Jay

Civil and Environmental Engineering Faculty Publications and Presentations

Green's Law states that tidal long-wave elevation ζ and tidal transport Q vary with width b and depth h according to ζ ≌ b−1/2h−1/4 and Q ≌ b+1/2h+/4. This solution is of limited utility because it is restricted to inviscid, infinitesimal waves in channels with no mean flow and weak topography (those with topographic scale L ≫ wavelength λ). An analytical perturbation model including finite-amplitude effects, river flow, and tidal flats has been used to show that (1) wave behavior to lowest order is a function of only two nondimensional parameters representing, respectively, …

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A Mathematical Model For Outgassing And Contamination, W. Fang, M. Shillor, E. Stahel, E. Epstein, C. Ly, J. Mcniel, Edward D. Zaron Jan 1991

A Mathematical Model For Outgassing And Contamination, W. Fang, M. Shillor, E. Stahel, E. Epstein, C. Ly, J. Mcniel, Edward D. Zaron

Civil and Environmental Engineering Faculty Publications and Presentations

A model for the mathematical description of the processes of outgassing and contamination in a vacuum system is proposed. The underlying assumptions are diffusion in the source, convection and diffusion in the cavity, mass transfer across the source-cavity interface, and a generalization of the Langmuir isotherm for the sorption kinetics on the target. Three approximations are considered where the asymptotic behavior of the model for large time is shown as well as the dependence and sensitivity of the model on some of the parameters. Some numerical examples of the full model are then presented together with a proof of the …

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Residual Circulation In Shallow Estuaries 1. Highly Stratified, Narrow Estuaries, David A. Jay, J. Dungan Smith Jan 1990

Residual Circulation In Shallow Estuaries 1. Highly Stratified, Narrow Estuaries, David A. Jay, J. Dungan Smith

Civil and Environmental Engineering Faculty Publications and Presentations

Long-wave theory and simple turbulence closures have been used to show that three distinct types of circulation (highly stratified, weakly stratified, and partially mixed) arise in narrow, shallow estuaries from the finite amplitude of the tide and the interaction of stratification with vertical mixing. Each type has a different dominant process causing the vertical exchange of salt and fresh water on the flood, and each gives rise to a characteristic residual circulation. The tidal circulation in highly stratified shallow estuaries, described herein, is the result of a finite amplitude internal motion driven by the barotropic tide; shear instabilities at the …

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Residual Circulation In Shallow Estuaries 2. Weakly Stratified And Partially Mixed, Narrow Estuaries, David A. Jay, J. Dungan Smith Jan 1990

Residual Circulation In Shallow Estuaries 2. Weakly Stratified And Partially Mixed, Narrow Estuaries, David A. Jay, J. Dungan Smith

Civil and Environmental Engineering Faculty Publications and Presentations

Long-wave theory is used herein to analyze circulation in weakly stratified and partially mixed estuaries. Unlike the highly stratified systems considered in part 1, the flows considered here have only a minimal tidal-frequency internal wave component. These estuaries may therefore be modeled as the sum of weakly interacting barotropic and baroclinic modes. The dominant factors driving the residual flow are finite amplitude barotropic effects in weakly stratified estuaries and a combination of barotropic effects and steady horizontal density gradient forcing in partially mixed estuaries. The dominant vertical exchange mechanism in the weakly stratified case is bottom boundary-induced turbulence, and that …

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The Dynamics Of The Columbia River Estuarine Ecosystem: Volume I And Volume Ii, Creddp, Charles A. Simenstad, David A. Jay, C. David Mcintire, Willa Nehlsen, Christopher R. Sherwood, Lawrence F. Small Jun 1984

The Dynamics Of The Columbia River Estuarine Ecosystem: Volume I And Volume Ii, Creddp, Charles A. Simenstad, David A. Jay, C. David Mcintire, Willa Nehlsen, Christopher R. Sherwood, Lawrence F. Small

Civil and Environmental Engineering Faculty Publications and Presentations

Integrates results from the CREDDP studies into a comprehensive synthesis. Includes physical setting and processes; relationships between physical and biological processes and among functional groups of organisms; species, biomass and productivity per habitat type per region. Approximately 360 pages per volume.

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Circulatory Processes In The Columbia River Estuary, David A. Jay May 1984

Circulatory Processes In The Columbia River Estuary, David A. Jay

Civil and Environmental Engineering Faculty Publications and Presentations

Covers tidal circulation, density distribution, vertical mixing, salt transport, and low-frequency flow processes, with contributions to estuarine circulation theory.

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