About

Arthur Nowell was a student of philosophy and engineering before focusing his research on turbulence and boundary layer fluid mechanics. He has served as dean and department chair for the School of Oceanography at the University of Washington for 23 years, making him one of the longest-serving deans at UW. As a scientist and educator, his goal is to train students of science not only to be good researchers but also to be comfortable with the complexity and moral ambiguity of science. His research also includes maritime piracy, where he helps develop forecasts in real-time, complex environments to guide military and social responses to modern pirates, thereby helping to keep the oceans free for all users.

Research topics

• Geology
• Oceanography
• Environmental science
• Mechanics
• Geotechnical engineering

Selected publications

• The Effects of Sediment Transport and Deposition on Infauna: Results Obtained in a Specially Designed Flume

  Lecture notes on coastal and estuarine studies · 2013-03-16 · 1 citations

  book-chapter1st authorCorresponding
  PublisherDOI

• Turbulence in open channels : an experimental study of turbulence structure over boundaries of differing hydrodynamic roughness

  cIRcle (University of British Columbia) · 2010-01-01

  articleOpen access1st authorCorresponding

  River channels modify their boundaries by entrainment and transfer of sediment. The flow represents a turbulent boundary layer which must be examined to understand the relation between channel morphology and its modifying flow. Discrete roughness elements with variable spacings were used, in flume experiments to simplify the study of the relation between flow resistance and boundary morphology. The patterns were intended to model gravel bed channels. The results are compared with wind tunnel and atmospheric boundary layer studies In order to examine the influence of the free surface and the applicability of the extensive results in air to open channel flow. Streamwise and vertical velocities were measured throughout the depth of flow at constant Reynolds number over a rough boundary. The roughness density was modelled by plastic blocks and the hot film measurements were subsequently digitally analysed. Density is defined as the ratio of the surface area of blocks, in plan view, to the total area of the bad. Results on six densities between 1/8 and 1/80, based on plan areas, are presented in detail. Three layers were identified in the flow: an outer shear layer, a wake layer extending to two roughness heights above the bed, and a wall layer below the top of the roughness elements. No extensive range of linear correlation of shear velocity with the logarithm of a roughness density function was found, possibly due to the surface between the roughness blocks being hydrodynamically rough. The greatest resistance to flow was presented by density 1/12: at higher densities 'skimming' flow occurred indicated by a shift in the 'bed' to the top of the roughness elements. The shape of the energy spectrum varied across the flow depth, the free surface acting as a boundary constraining the range of inertial transfer. Most of the turbulent energy was contained below 7.25 Hz while the cospectrum of u and v indicated that most of the stress lay below that frequency. No significant turbulent transfers occurred beyond 5 Hz while the coherence was below. 0.2 beyond 10 Hz. No significant inertial subrange was detected in the spectra or the cospectra. The moments of the velocity derivative indicated a strongly intermittent process and exhibited a marked change at the free surface, the kurtosis there being nearly twice that found elsewhere in the flow. The probabilistic structure of the velocity fluctuations showed that the series were non-Gaussian in form and not strictly self-similar. All the series yielded Hurst coefficients of approximately 0.8. An explanation of this result is postulated in terms of the superimposition of several intermittent processes. Measurements in the flow approaching a single block indicated that vorticity amplification occurred. When obstacle width was increased to one third of channel width the isolated block behaved as a two dimensional obstacle (i.e. like a bar). Results from measurements in four natural gravel channels indicated that the flume reproduced successfully the spectral and probabilistic structure of the flow. The results are applied in a phenomenologica1 explanation of the shape of the Shields entrainment function and in an explanation of the differences in entrainment and transport between sand and gravel. The results on the flow around an isolated block are applied to the construction of a statistical flow stability model for gravel entrainment. The hierarchy of processes {low frequency 'waves', bursts, wake shedding and dissipation), operating intermittently and acting non-linearly may be viewed as instabilities which are responsible for the generation and dissipation of turbulence. Such instabilities are discussed in relation to the hierarchy of morphological features observed in natural channels.

  PublisherDOI

• Continental shelf sedimentology: scales of investigation define future research opportunities

  Journal of Sea Research · 1999-03-01 · 25 citations

  articleSenior author
  PublisherDOI

• Boundary layer measurements and their implications for sediment transport on the eastern Norwegian Sea continental slope

  Deep Sea Research Part I Oceanographic Research Papers · 1998-04-01 · 12 citations

  article
  PublisherDOI

• Support for U.S. graduate education in the ocean sciences: Are research assistantships overutilized as a source of funding?

  Eos · 1998-02-03 · 1 citations

  articleSenior author

  The ocean sciences offer graduate students a unique and exciting educational experience, but is that experience ideally suited to the next step of a student's career, namely postgraduate employment? To begin to answer this question one must consider first whether the requirements of the career that is sought would be met better by a master's or a Ph.D. Often the master's degree is looked upon as a stepping stone along the path to a Ph.D., and then a career in research. Consequently, most of the graduate experiences in ocean sciences are exclusively focused on research. The financial support of students encourages this focus since most of the funding is provided within a specific research project in the form of a research assistantship.

  PublisherDOI

• Comparison of two models of aggregation in continental‐shelf bottom boundary layers

  Journal of Geophysical Research Atmospheres · 1995-11-15 · 52 citations

  articleSenior author

  Comparison of two models of aggregation and disaggregation of fine sediment in continental‐shelf bottom boundary layers delineates conditions under which these processes can be modeled simply. Model 1 predicts the evolution of the particle size distribution based on layer‐averaged mean sediment concentrations. Model 2 avoids the simplifying assumptions of model 1 by representing suspension dynamics with a Monte Carlo simulation of the joint probability density function of number concentration in the various particle size classes. In contrast to model 1, this technique bases aggregation rates on local concentrations and explicitly treats the effect of concentration correlations on aggregation rates. Each model produces a time series of particle size distribution in a steady, horizontally uniform, nondepositing, continental‐shelf bottom boundary layer. Comparisons are made for suspensions that are initially polydisperse and monodisperse, for shear velocities of 0.01 and 0.005 m s −1 , for fractal dimensions of 1.92 and 2.4, for initial layer‐averaged sediment concentrations of 1, 2.5, 10, and 25×10 −3 kg m −3 , and for sticking efficiencies of 0.1 and 1.0. In general, model 1 is accurate for suspensions that are initially polydisperse and do not develop strong vertical structure. Results suggest that as long as maximal settling velocity does not exceed roughly 0.6u * , vertical gradients in sediment concentration do not degrade substantially the accuracy of layer‐averaged mean models for concentrations typical of the continental shelf. When initial suspensions are monodisperse and/or vertical gradients are large, transport‐limited aggregation can slow overall aggregation rates of model 2 relative to model 1, or important interactions can occur between particle types that both show strong vertical structure, speeding overall aggregation rates in model 2. In the future the effects on the accuracy of layer‐averaged mean models of short‐ and long‐term unsteadiness, erosion, and deposition will be explored.

  PublisherDOI

• In situ measurements of particle settling velocity on the northern California continental shelf

  Continental Shelf Research · 1994-08-01 · 27 citations

  articleSenior author
  PublisherDOI

• An introduction to the Sediment TRansport Events on Shelves and Slopes (STRESS) program

  Continental Shelf Research · 1994-08-01 · 25 citations

  articleSenior author
  PublisherDOI

• Sediment transport events on shelves and slopes: STRESS

  Pergamon eBooks · 1994-01-01 · 1 citations

  bookSenior author
  Publisher

• Enhanced deposition to pits: A local food source for benthos

  Journal of Marine Research · 1993-02-01 · 113 citations

  article

  Particle deposition experiments using mimics of biogenous negative relief (“pits”) and low-excess-density particles in a small annular flume indicate a significantly enhanced deposition rate (number of particles per time) compared to smooth, flat patches of the same diameter. This study included flow visualizations as well as observations of particle residence times, particle concentrations in the pits, and particle fluxes to the pits from the main flow. Experimental conditions of particle concentration, shear velocity, and particle settling velocity mimicked the dynamic characteristics (low excess density and large size) of organic-rich floes and flow conditions in the subtidal and deep sea where biogenous pits are common features. Results suggest that pits provide benthic organisms an important capture mechanism for such floes. Flow visualizations concur qualitatively with previously reported results for twodimensional cavity flow, with unique features due to the conical shape of the pits. When the Rouse number (settling velocity/shear velocity) was much less than 1, pit deposition rate increased with increasing pit aspect ratio (AR = depth/diameter; ranging from 0.25 to 2) and always exceeded deposition to a flat patch of comparable diameter. For the single aspect ratio tested (AR = 0.5) under conditions of increasing turbulence, deposition to the pit increased under transitional flow, but then decreased to near zero when conditions reached fully rough flow. Relative enhancement of deposition to this pit decreased with increased ambient bed roughness since grave1 beds also effectively collect particles. Particle concentration inside pits decreased weakly with pit aspect ratio but greatly increased with increasing roughness Reynolds number. Particle residence time increased somewhat with pit aspect ratio but decreased significantly with increasing roughness Reynolds number. Particle flux into pits from the main flow increased with both increasing aspect ratio and increasing roughness Reynolds number. Enhancement of food supply to pit inhabitants thus depends on the flow regime.

  PublisherDOI

Frequent coauthors

• Peter A. Jumars

  26 shared

• Charles D. Hollister

  11 shared

• Robert F. L. Self

  University of Washington

  6 shared

• James E. Eckman

  University of California, San Diego

  5 shared

• Paul S. Hill

  Dalhousie University

  5 shared

• W. Brian Dade

  Dartmouth College

  4 shared

• Thomas F. Gross

  Genesis HealthCare

  4 shared

• Richard W. Sternberg

  University of Washington

  4 shared

Labs

• Arthur NowellPI