Seminars

Raleigh L Martin
 PhD Student University of Pennsylvania, Department of Earth & Environmental Science
 

Abstract: Field and lab studies indicate that bedform geometries lag changes in flow through floods, producing hysteretic relationships between bed morphology, roughness, and water discharge.  Disequilibrium between bedform geometries and flow parameters complicates our ability to interpret stratigraphy for paleoenvironmental reconstruction.  This summer, I am conducting experiments in the SAFL Tilting Bed Flume to explore this bedform hysteresis.  In these experiments, repeat sonar scans are used to continuously track the response of sand bedform morphologies to abrupt changes in water discharge.   The timescale of bedform adjustment appears to be driven by three primary factors: 1. directionality of adjustment, 2. preexisting bedform geometry, and 3. sediment flux.  Directionality of adjustment (rising versus falling water discharge) determines whether bedforms grow quickly by irreversible merger (rising flows) or shrink slowly through secondary bedform cannibalization of relict larger bedforms (falling flows).  Preexisting bedform geometry (height and length) determines the amount of bed deformation required for adjustment to new equilibrium, and sediment flux determines the rate at which this change is effected.  These three factors all favor faster adjustment of bedforms to rising flows.  I will present preliminary results on bedform adjustment hysteresis for a variety of increasing and decreasing discharge changes.

Jorge Lorenzo-Trueba
PhD Student
Saint Anthony Falls Laboratory
University of Minnesota

Abstract:

During almost four years I have been directly involved in one of the leading tasks of the National Center of Earth Dynamics (NCED): restoring a sustainable Mississippi Delta. One main subject of my thesis work has been to develop numerical and analytical modeling tools able to track the shoreline and the alluvial-bedrock transition of fluvial-deltas under base-level changes (e.g., sea-level and subsidence). Moreover, I have expanded this framework to explicitly account for biomass production and decay via plant growth, burial, and microbial processes; wetland vegetation plays an essential role in determining how coastal morphology and ecosystems respond to sea-level rise. I propose an explicit coupling between biogeochemical and physical processes, which offers a novel approach with significant potential to understand this important, but currently poorly understood, component of delta evolution.

Bio:

Jorge Lorenzo Trueba earned a Civil Engineering in 2006 from the Politechnic University started his doctoral studies at SAFL in 2007. His research aims at understanding how physical and biological processes, and the coupling between them, influence delta evolution across a wide range of time and space scales. His research methods focus on the development of mathematical and computational models supported by laboratory experiments and field observation

Luther Aadland, Ph.D.
River Ecologist
Stream Habitat Program
Minnesota Department of Natural Resources

Abstract:

Rivers and watersheds have been dramatically altered through land-use changes, channelization, dam and levee construction, and increasingly, climate change. This has resulted in hydrologic and geomorphic changes, fragmentation of habitat and energy flow patterns, and impaired water quality leading to alarming extirpation and extinction rates of aquatic species. Most river management has been directed at altering and constraining hydrologic, geomorphic, and biological processes. In many cases, this strategy has resulted in further problems. While interest in river restoration has grown, it has not kept pace with ongoing degradation. In addition, restoration efforts have not always addressed underlying problems or have failed to restore fundamental ecological process and resilience. The long-term success of restoration will hinge on the extent to which human constraints are relaxed, ecological processes restored, and migratory pathways re-established. Case examples including channel and floodplain restoration, dam removal, and fish passage will be discussed in this context.

Bio:

Luther has worked as a river ecologist for the Minnesota Department of Natural Resources for the past 24 years. During that time, his work, research, and publications have included a wide variety of topics that integrate physical and biological processes of rivers and the design of river restoration, naturelike fish passage, dam removal, erosion control, and flood damage reduction projects. Primary goals of these projects have been to work with natural river processes, restore ecological functions, and eliminate or reduce maintenance needs and costs. Luther also teaches workshops on applied fluvial geomorphology, dam removal, fish passage, river assessment, aquatic habitat, and river restoration.

Masoud Kayhanian
Research Professor
Department of Civil & Environmental Engineering
University of California at Davis

Abstract:

First flush is a phenomenon that occurs when a larger concentration or mass of pollutants are associated with initial portion of a storm event as compared to the rest of the event. This seminar will introduce proper definition for both concentration and mass first flush. The first flush concept is also used for monitoring of O&G as well as its implication for pollutant treatment and toxicity removal. A methodology will be introduced to identify the best time to obtain a single runoff sample for O&G measurement to be considered as representative of the storm event. In addition, several methods will be introduced to estimate the O&G EMC without additional sampling. Mathematical modeling and simulations are also use to show the benefit of first flush treatment compared to the conventional BMPs.

Short bio:

Dr. Kayhanian is Research Professor in the Department of Civil and Environmental Engineering at the University of California at Davis. Most of his current research activities are related to stormwater runoff characterization and treatment. He has published over 150 peer reviewed and conference proceeding papers. He is the contributing editor of Stormwater and the member of the editorial board for the Journal of Scientia Iranica and the Global Journal of Environmental Science and Technology.

Christopher J. Zappa, Ph.D.
Lamont Doherty Earth Observatory,
Columbia University

Abstract:

Atmosphere-ocean interactions play a crucial role in the regional and global budgets of biogeochemical trace gases and in the transport of volatile pollutants. A plethora of processes has been shown in individual studies to play varying roles in regulating air-sea gas fluxes, which continually work to adjust the balance of constituents in the upper ocean. Therefore, a better understanding of mechanisms controlling air-water gas exchange and ocean mixing is needed to improve model predictions of the spatial variability of air-sea fluxes.

Wind has been the predominant driver of gas exchange in the open ocean because it plays a central role in the generation of turbulence through the transfer of momentum to waves and currents. Rain also plays a significant role in the exchange of CO2 between the ocean and atmosphere, through surface layer chemical dilution and via export of carbon from the atmosphere by wet deposition.

Wei Zhang
Postdoctoral Research Associate
Saint Anthony Falls Laboratory
University of Minnesota

Abstract: Complex topography affects the distribution of turbulent fluxes of momentum and heat in thermally stratified boundary layers. Neutrally stratified boundarylayer flows over simplified topography (for example, blocks or sinusoidal hills) have been extensively studied by wind-tunnel experiments and numerical simulation such as Large-Eddy Simulation (LES). Atmospheric stability, however, is seldom considered due to the difficulty of physical simulation in wind tunnel. In addition, accurate prediction of separated flow induced by steep hills remains a challenge to LES modeling. Experimental investigation of various thermal stratification effects (neutral, stable and convective) on the boundary-layer flows over a steep 2-D hill were conducted at the Saint Anthony Falls Laboratory atmospheric boundary-layer wind tunnel. The 2-D model hill has a steepest slope of 0.73 and its shape follows h=Hcos(πx/L) for -L/2 ≤ x ≤ L/2 (H=7cm and L=14.5 cm). The hill is fully immersed in the surface layer with a ratio of the height to the boundary layer depth (H/δ) about 0.12. High-resolution Particle Image Velocimetry (PIV) provided dynamic flow information of the onset of separation, the recirculation zone and flow reattachment location. Turbulent momentum and heat fluxes as the function of height were characterized using a triple-wire at selected stream-wise locations. Emphasis is on the effects of atmospheric stability on the dynamics of flow separation induced by the hill as well as the flow recovery process. The present study can hopefully improve our understanding of thermally-stratified boundary layer flow behavior over a steep 2-D hill from well-controlled tests, and provide reliable database for development and validation of LES models.

Stefano Gonella
Assistant Professor
Department of Civil Engineering
University of Minnesota Twin Cities

Abstract

As a discipline, wave mechanics has existed for over a century as a special branch of solid mechanics. Nevertheless, new and intriguing applications of this field continue to present themselves in the arena of modern engineering problems. The key feature that makes waves attractive is their extreme sensitivity to the inherently inhomogeneous nature of solids, and ultimately their ability to detect small scale and localized features, such as microstructural changes, interphases and defects. When properly inspected and interpreted, a wavefield provides a complete and reliable signature of a solid. The talk introduces a wave propagation simulation methodology, based on Mindlin’s microelastic continuum theory, as a tool to dynamically characterize microstructured solids in a way that naturally accounts for their inherent heterogeneities. Wave motion represents a natural benchmark problem to appreciate the full benefits of microelastic theories, as in high-frequency dynamic regimes do microstructural effects unequivocally elucidate themselves. Through a finite-element implementation of the microelastic continuum, and the interpretation of the resulting computational multiscale wavefields, one can estimate the effect of microstructures upon the wave propagation modes, phase and group velocities. By accounting for microstructures without explicitly modeling them, this method allows reducing the computational time with respect to classical methods involving direct numerical simulation of the heterogeneities.

W. Cully Hession, PhD, PE
Associate Professor Center for Watershed Studies
Biological Systems Engineering
Virginia Tech

ABSTRACT

Public agencies spend significant funds on stream restoration projects to improve the quality of impaired stream reaches. Many sources of uncertainty can potentially influence the final design, such as the natural stochasticity of input variables, measurement errors from the field, and the uncertainties inherent to the parameters and conceptualizations of the equations used for the design model. For this study, a two-phase uncertainty analysis was performed on a two-stage channel stream restoration design for Stroubles Creek in Blacksburg, VA, USA. Monte Carlo Simulation was used to calculate a range of channel dimensions including channel width, channel depth, bench width and bench flow depth from stochastic variables, such as bankfull discharge and grain size distribution, and calculated parameters, such as Manning’s n and critical Shield’s number. Results of this research indicate the final stream restoration design outcomes can vary over one to four orders of magnitude with respect to the deterministic solution, reinforcing the high uncertainty and risk associated with stream restoration.

Dr. Matthew Barone
Wind and Water Power Technologies Department
Sandia National Laboratories

ABSTRACT
Wind energy is an increasingly vital component of the electricity generation system in the United States. As of late 2009, the total installed capacity of wind generated power in the U.S. was over 35,000 MW, representing over 3% of the nation’s total electricity generation capacity. By contrast, the marine hydrokinetic industry, which involves development of in-stream current turbine and wave power devices, is in its infancy in the U.S. This talk focuses on the aero- and hydrodynamics of both wind and hydrokinetic turbines, from the perspective of ongoing Department of Energy research programs at Sandia National Laboratories. The history and current status of wind turbine rotor aerodynamics is reviewed, and remaining research challenges involving complex flow phenomena and aero-acoustic rotor noise are described. In contrast to wind turbines, where the 3-bladed upwind rotor configuration dominates the market, a “preferred” hydrokinetic turbine configuration has yet to be identified. The diversity of proposed configurations opens up new research opportunities for hydrodynamic analysis and design. An overview of these research areas is given, along with a description of hydrodynamic performance model development efforts at Sandia.

Jon Svendsen
Research Associate Fisheries, Wildlife and Conservation Biology
University of Minnesota

ABSTRACT Members of the family Embiotocidae exhibit a distinct gait transition from exclusively pectoral fin oscillation to combined pectoral and caudal fin propulsion with increasing swimming speed. The pectoral-caudal gait transition occurs at a threshold speed termed U p-c. The objective of this study was to partition aerobic and anaerobic swimming costs at speeds below and above the U p-c in the striped surfperch Embiotoca lateralis using swimming respirometry and video analysis to test the hypothesis that the gait transition marks the switch from aerobic to anaerobic power output. Exercise oxygen consumption was measured at 1.4, 1.9 and 2.3 L s-1. The presence and magnitude of excess post-exercise oxygen consumption (EPOC) was evaluated after each swimming speed. Data demonstrated that 1.4 L s-1 was below the U p-c, whereas 1.9 and 2.3 L s-1 were above the U p-c. The two latter swimming speeds included caudal fin propulsion in a mostly steady and unsteady (burst assisted) mode, respectively. There was no evidence of EPOC after swimming at 1.4 and 1.9 L s-1 indicating that the pectoral-caudal gait transition was not a threshold for anaerobic metabolism. At 2.3 L s-1, E. lateralis switched to an unsteady burst and flap gait. This swimming speed resulted in EPOC suggesting that anaerobic metabolism constituted 25% of the total costs. Burst activity correlated positively with the magnitude of the EPOC. Collectively, these data indicate that steady axial propulsion does not lead to EPOC whereas transition to burst assisted swimming above U p-c is associated with anaerobic metabolism in this labriform swimmer.