Seminars

seminar room safl

Every other week during the academic year, SAFL hosts prominent figures in environmental science and fluid mechanics. They come from all over the US and the world to share their insight and inspire us to tackle important questions in the field. These seminars are free and open to the public. Join us to learn about the latest research advancements and network with contacts in the field.


SAFL seminars are held on Tuesdays from 3:00 to 4:15 p.m. unless otherwise noted. Join us in the SAFL Auditorium or via Zoom.

 
Spring 2024 Seminar Series
Tuesday, Jan 23-Katey Anthony
Tuesday, Feb 6th-No Seminar 
Tuesday, Feb 20th-Neal Iverson
Tuesday, March 12- Jennifer Stucker 
 
Tuesday, March 26th-Mike Shelley
Tuesday, April 9th-Sergio Fagherazzi
Tuesday, April 23rd-Ruben Juanes
Tuesday, May 7th-Walter Musial

Recordings
We will record seminars and post them here when given permission by the speaker. To see if a recording is available, scroll down this page to "Past Seminars."

Seminar Notifications
To sign-up for our SAFL Seminar email list, click here.


Upcoming Seminars

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Past Seminars

Restoring Ecological Health and Resilience to Damaged Rivers on a Changing Planet

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.

First Flush Phenomenon: Proper Definition and Treatment Implication

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.

Precipitation Effects on the Global Air-Sea CO2 Flux

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.

Turbulent boundary layer flow over a steep 2-D hill: atmospheric stability effects

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.

Characterization of Heterogenous Solids via Wave Methods in Computational Microelasticity

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.

Quantifying and utilizing uncertainty in stream restoration design

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.

Aero/hydrodynamics of wind and hydrokinetic turbines

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.

Partition of aerobic and anaerobic swimming costs related to gait transitions in a labriform swimmer

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.

Ontogenic shift in critical fluid flow threshold and habitat use by the caddisfly Dicosmoecus gilvipes, and implications for ecosystem processes

Mike Limm
NCED Postdoctoral Associate
St. Anthony Falls Laboratory

ABSTRACT

Disturbance by flooding can dramatically disrupt population and community structure in stream ecosystems. If strongly interacting species are affected, energy and nutrient dynamics may be altered. In a Northern California stream we quantify the impact of the limnephilid caddisfly Dicosmoecus gilvipes on periphyton structure and ecosystem processes, quantify how Dicosmoecus vulnerability to disturbance can vary with ontogeny, and investigate how their case design influences fluid flow resistance.

Dicosmoecus larvae reduced periphyton accrual, gross primary productivity, and ammonium uptake, and their impact persisted 46 days after the larvae were removed. Critical fluid flow threshold (sufficient to dislodge larvae from substrates) increased with larval size, as did larval flow velocity preference. The lateral extensions Dicosmoecus build on their case provided stability against overturning in fast flow and may improve their ability to forage efficiently in turbulent flow conditions. Our results suggest any change in flood timing, frequency, and/or magnitude due to river regulation or climate conditions may impact Dicosmoecus populations and alter ecosystem processes in Northern California streams.

Quantifying the effectiveness of soil remediation techniques in compact urban soils

Nicholas Olson
M.S. Candidate
Department of Civil Engineering,
UMN Advisors: John Gulliver and John Nieber

ABSTRACT A field experiment was conducted to determine the effectiveness of remediation techniques to alleviate soil compaction and increase infiltration. Deep tillage and compost addition are two techniques commonly used in agricultural practices to reduce the level of soil compaction. These techniques were implemented on three sites in the metropolitan area. Each site was divided into three plots: tilled, tilled with compost addition, and a control plot for comparison. To determine the effectiveness of each remediation technique, before and after measurements of saturated hydraulic conductivity (Ksat), soil bulk density, and soil strength were used to assess the level of compaction. Deep tillage was effective at reducing the soil strength. Soil strength was approximately half that of the control plot in the first six inches of soil. However, tilling did not significantly improve the bulk density of the soil. At two of the sites, tilling was ineffective at improving the infiltration capacity of the soil. Tilling may have damaged natural pathways in the soils, thus reducing the permeability. Tilling was effective at remediating the soil at one site, which may not have had as extensive a network of natural pathways as the previous two sites. The geometric mean of Ksat was 2.1 to 2.3 times that of the control plot. Compost addition was the most effective soil remediation technique. Similar reductions in soil strength were found in the tilled plot. Soil bulk densities on the compost plots were 18-37% lower than the control plots. The infiltration capacity of the soil was improved. The geometric mean of Ksat on the compost plots was 2.7 to 5.7 times that of the control plots. The results of these findings will be useful in revising stormwater Best Management Practices to include guidelines on soil compaction prevention and remediation of compacted sites.