Seminars

Presentation of the 2023 Roger E.A. Arndt Fellowship

Distinguished Speaker: Alfredo Soldati, Professor of Fluid Mechanics at the Technische Universität Wien – TU Wien (Austria)

Title: Dynamics of complex particles in turbulence

Abstract: Turbulent flows with suspended anisotropic particles of non-spherical shape are a common occurrence in many industrial (e.g. paper making, pharmaceutical processing, soot emission) and natural processes (e.g. pollen species, icy clouds, and plankton and marine snow). The dynamics of small anisotropic particles is determined by velocity gradients and in turn by the smallest turbulence scales, and although we have a fundamental understanding on the dynamics of such turbulence scales, since no closed form of the drag on non-spherical particles is available, predictive understanding of the dynamics of anisotropic particles remains elusive. This insufficient knowledge is at the basis of our lack of predictive tools to describe anthropogenic oceanic pollution of plastic microfibers, which are elongated, anisotropic and of the order of the smallest scales of turbulence. In this talk, we will briefly review the models used to describe the dynamics of small ellipsoidal particles in turbulence, and then we will add a further complexity consisting on allowing the elongated particles to be slightly curved: this slight curvature will be instrumental in determining the complete rotational dynamics of the particles in turbulence. Experiments performed in the TU Wien Turbulent Water Channel will be presented elaborating on the full dynamics of small non- axisymmetric –quasi-straight to slightly curved – fibers. We will highlight the role of fibers curvature on spinning and tumbling rates and we will propose conceptual models and scalings laws.

Figure 1: Measurement of a non-axisymmetric fibre traveling close to the wall of a turbulent channel flow, represented here by the grey surface. Front view is shown. Fibre is colored according to the instantaneous tumbling rate ΩtΩt normalized by the mean value computed over the entire track |ΩtΩt| (From M. Alipour, M. De Paoli, and A. Soldati (2022) “Influence of Reynolds number on the dynamics of long non-axisymmetric fibers in channel flow turbulence”, J. Fluid Mech. 934, A18-27.)

About: Alfredo Soldati is a Professor of Fluid Mechanics at the Technische Universität Wien – TU Wien (Austria). The focus of the research of his group is on multiphase flows, and specifically on the fundamentals of turbulent dispersed flows of particles, bubbles, and droplets.

After his PhD in chemical Engineering at the University of Pisa (Italy), and a visiting appointment at UCSB (CA), Dr. Soldati became assistant, associate and full professor at the University of Udine. He has been guest Professor at EPFL (Switzerland), at INP Toulouse (France) and at Scuola Superiore Sant’Anna Pisa (Italy). He is fellow of the American Physical Society (APS) and of the European Mechanics Society (EUROMECH), the recipient of the 2007 Knapp award and of the 2015 Lewis F. Moody Award from the American Society of Mechanical Engineers (ASME), the recipient of the International Prize and Gold Medal Panetti–Ferrari, from Accademia delle Scienze di Torino, Italia, and is awarded the 2020 ASME Freeman Scholarship and Lecture. Dr. Soldati is currently part time professor at University of Udine, and he is the Rector of the International Center for Mechanical Sciences, CISM. Dr. Soldati is Co-Editor in Chief of International Journal of Multiphase Flow.
 

Award Recipient: Amy Tinklenberg, Aerospace Engineering and Mechanics at the University of Minnesota.

Abstract: Predicting the fall speed of frozen hydrometeors in the atmosphere is complicated by their unique geometries as well as by the air turbulence. Snowflakes and ice crystals often exhibit rimed branches resembling perforated shapes, which make them permeable to the air flow. This alters their wake dynamics in ways that have not been characterized in turbulence. As analogue to plate crystals, here we consider thin disks of 3 mm in diameter and compare geometries with and without perforations. These are dropped at controlled volume fractions into a large chamber generating a large region of approximately zero-mean-flow homogeneous air turbulence. Two turbulence levels are considered and contrasted with quiescent air conditions. The disks are imaged at 4300 Hz and their linear and rotational motion is reconstructed. Comparison of the solid and perforated disk behaviors in quiescent air shows that the perforated disks fall at a slower velocity than the solid disks. The perforated disks also fall more stably compared to the solid, which may either fall flat or tumble. In turbulence, both disk types experience a reduction in their average settling velocity, as compared to quiescent air, but the perforated disks are more mildly influenced by this effect.

About the recipient: Amy is a Ph.D. Candidate in Aerospace Engineering and Mechanics at the University of Minnesota. She works with advisor Filippo Coletti (ETH Zürich) and co-advisor Michele Guala (UMN). She experimentally investigates the settling dynamics of solid and perforated disks in both quiescent and turbulent air, aimed at better understanding and predicting frozen hydrometeor settling in the atmosphere. Originally from Minnesota, she received her Bachelor's in Mechanical Engineering from the University of St. Thomas (2019), followed by her Master’s in Aerospace Engineering and Mechanics from the University of Minnesota (2022). 

Daniel Griffin, Associate Professor of Geography at the  University of Minnesota 

Abstract: Tree rings record unique information about environmental water variability on timescales from days to centuries. Toward improved methods and outcomes with tree-ring data development, my research group has integrated automated ultra-high resolution imaging systems with our open-source, cloud-native software platform for digital data curation, visualization, and interactive analysis. We have operationalized imaging of entire collections of wood specimens at better-than-microscope resolution, and are setting new open science standards for data development in the field of dendrochronology. In this SAFL Seminar, I will review our technology progress and prospects, and summarize two case studies that demonstrate the power and potential of tree-ring research on water in the environment. 
Along the Upper Mississippi River, we are using tree rings to investigate the role of streamflow variability in modulating ecosystem-scale primary productivity in floodplain forests. Through new analysis of 800 tree core samples from 13 sites between Saint Paul and Dubuque, we found an unexpected and remarkable positive covariance between tree growth and Mississippi discharge that is increasing over time (R^2 = 0.19 for 1929–1973; R^2 = 0.65 for 1974–2018). Our findings point to streamflow extremes as a dominant control on ecosystem-wide forest productivity, and raise questions about interactions amongst the biogeophysical processes that will influence forest resilience and ecosystem services in a changing climate.
    
In California, our oak tree-ring data have been critical for quantitatively rigorous reconstructions of drought frequency, duration, and magnitude, and for demonstrating that the recent drought was unusual within the context of the last 12 centuries. We have also reconstructed annual streamflow history for the past 600 years, and are preparing for new work focused on providing California water resource managers with information they seek about the long-term history of extreme high flows. Our analysis targets include heavy precipitation episodes and discharge extremes related to the "atmospheric river” events that deliver exceptional precipitation quantities and flooding on timescales of hours to days, complicating water engineering strategies and triggering catastrophic damage to societal infrastructure.

About: Daniel Griffin is an Associate Professor of Geography who joined the University of Minnesota Faculty in 2014. A dendrochronologist, Griffin specializes in the development and interpretation of tree-ring records from old-growth forests. He teaches undergraduate courses on biogeography, climatology, and the geography of Minnesota, and a graduate seminar on climate extremes and environmental change. Griffin earned his B.S. in Earth Science from the University of Arkansas in 2002 and his Ph.D. in Geography and Global Change from the University of Arizona in 2013. For his postdoctoral research on North American paleoclimate, he was awarded a NOAA Climate & Global Change Fellowship and a Woods Hole Oceanographic Institution Scholarship. Griffin's research has been supported by grants from the National Science Foundation, the United States Geological Survey, the Environmental Protection Agency, and the National Oceanic and Atmospheric Administration.

Xiaojing (Ruby) Fu, Assistant Professor of Mechanical and Civil Engineering at California Institute of Technology. 

Abstract: Icy porous materials such as snow or firn are ubiquitous in both Earth and planetary settings. Their microstructures (e.g., porosity) play an important role in dictating the reflectivity, fluid storage capacity, thermal conductivity, and mechanical properties of the larger-scale systems. Thus, understanding the complex physics that control the microstructure evolution of icy porous media is an important component in creating robust predictions of Earth’s cryosphere in response to climate warming, and in devising engineering strategies for the exploration of icy moons in our solar system. While it is well known that gravity-driven compaction leads to densification of the pore structure over depth, less is known about the role of meltwater in reshaping the structures of icy porous media across scales.

In this talk, I will describe our recent efforts in understanding how the movement of liquid water through porous ice reshapes its porosity structure via flow instability and phase transitions of water.  I will first discuss the pore-scale problem and present a phase-field model that simultaneously captures the phase transitions of water amongst its liquid, solid and vapor phases. With this model, we show that the presence of quiescent meltwater films can accelerate the microstructural coarsening of porous snow during the process of metamorphism.  Next, I will describe a Darcy-scale model that demonstrates how melt refreezing coupled with unstable infiltration reshapes the porosity structure of snow and leads to the formation of ice pipes and ice lenses commonly observed in the field. I will conclude by discussing the implications of these new physical insights for large-scale meltwater transport and hydrological processes in snow and glacial systems.

About: Xiaojing (Ruby) Fu is an Assistant Professor of Mechanical and Civil Engineering at California Institute of Technology. She received her BS in Applied Mathematics from Clarkson University, a MS in Computational Engineering, and a PhD in Civil & Environmental Engineering from MIT. She is awarded the Miller Postdoctoral Fellowship at UC Berkeley in 2018, hosted by the Earth & Planetary Science department. She joined Caltech in 2021 and leads the Mechanics of Porous Media Flow group. Her group studies the physics of multiphase fluid mechanics through porous media and how it shapes our natural and engineered environments, using theory, modeling, and laboratory experiments. 
 

Tim Garrett, professor in Atmospheric Sciences at the University of Utah and Chief Scientific Advisor at Particle Flux Analytics Inc. 

Abstract: A long-standing problem in fluid dynamics is how nonspherical inertial particles settle in a turbulent fluid. From a theoretical standpoint, the problem appears nearly intractable, at least without introducing substantial idealizations. We have approached the problem observationally by focusing on snowflakes using a combination of Lagrangian motion tracking and the first direct automated microphysical measurements of snowflake mass and density using a hotplate-based disdrometer. Examining an exceptionally broad range of turbulence and microphysical conditions, we observe that snowflakes can have settling speeds much lower or higher than the terminal fall speed in still air, and that the magnitude of the enhancement can be parameterized as a power-law function of snowflake shape and the turbulent intensity. While the distribution of the turbulence-induced settling enhancement is highly asymmetric, remarkable simplicity and symmetry is seen for turbulence-induced accelerations. Fat tails encompass ~1% of measurements forcing snowflake accelerations as high as 14 times gravity, and root-mean-square accelerations are many times higher than anticipated for fluid tracers in homogeneous isotropic turbulence. Notably a single, symmetric, rms-normalized frequency distribution describes snowflake accelerations independent of turbulent Reynolds number. Perplexingly, the same distribution even applies to Eulerian variability in snowflake terminal velocities, a quantity that is ostensibly independent of turbulence. The picture presented is that, despite the apparent complexity of the problem, the accelerations of natural, non spherical particles settling in irregular turbulence are governed by some underlying simplicity, and that there may be a hidden link between instantaneous snowflake movements measured near the ground and the microphysical processes that determine their terminal fall speed variability higher up in clouds.
          

About: Tim Garrett received his B.Sc in Physics from the University of Waterloo. He went on to complete his M.S. and his Ph.D. in Atmospheric Sciences from the University of Washington. He works on clouds and precipitation as they relate to climate. 

Kyungsoo Yoo,  Professor in the Department of Soil, Water, and Climate at the University of Minnesota and the lead of the Soil Geomorphology and Biogeochemstry Group

Abstract: Earthworms are fascinating animals. Where they are abundant, they are one of the biggest consumers of plant biomass. Simultaneously, they are ecosystem engineers that shape the structure of soils. In the formerly glaciated and peri-glacial regions of the world, including Minnesota, the ice and cold wiped out native earthworms before the Holocene. With climate warming, forests and prairies reoccupied the newly emerging lands following the retreating glaciers. Earthworms, however, being slow creatures, could not keep up. The vast ecosystems in High Latitudes have evolved without earthworms. Only recently, the status quo has been fundamentally and rapidly altered globally. Expanding imperialism, farming, gardening, logging, housing developments, recreational hiking and fishing, and other human activities helped spread exotic earthworms worldwide.

Here, I show the global-scale expansion of European earthworms and their drastic impacts on soils in Minnesota, Fennoscandia, and Alaska. I will also show how a new wave of jumping worms of Asian origin may replace European earthworms while creating entirely new soils. My primary goal is to excite engineers and earth scientists about the yet unexplored research opportunities in exploring how Earth's surface processes respond to Global W"o"rming.                  

About: Professor Yoo received his B.S. in Physics at Yonsei University in Seoul, South Korea. He went on to receive a Master's in Atomic Physics at the same university. He received his Ph.D. in Ecosystem Sciences at the University of California - Berkeley and received his Postdoctoral Fellowship at the same university studying Soil Geomorphology. He is currently a Professor in the Department. of Soil, Water, and Climate at the University of Minnesota. 

Xiang Cheng, Associate Professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota

Abstract: A flagellated bacterium exhibits fascinating swimming behaviors both as an individual cell and as a member of collectively moving swarm. I discuss two recent experimental works in my group on the swimming behaviors of Escherichia coli, a prominent example of flagellated bacteria. First, we study the motility of flagellated bacteria in colloidal suspensions of varying sizes and volume fractions. We find that bacteria in dilute colloidal suspensions display the quantitatively same motile behaviors as those in dilute polymer solutions, where a size-dependent motility enhancement up to 80% is observed accompanied by a strong suppression of bacterial wobbling. By virtue of the well-controlled size and the hard-sphere nature of colloids, this striking similarity not only resolves the long-standing controversy over bacterial motility enhancement in complex fluids, but also challenges all the existing theories using polymer dynamics in addressing the swimming of flagellated bacteria in dilute polymer solutions. We further develop a simple hydrodynamic model incorporating the colloidal nature of complex fluids, which quantitatively explains bacterial wobbling dynamics and mobility enhancement in both colloidal and polymeric fluids. Second, we study the collective motion of dense bacterial suspensions as a model of active fluids. Using a light-powered E. coli strain, we map the detailed phase diagram of bacterial flows and image the transition kinetics of bacterial suspensions towards collective motions. In particular, we examine the configuration and dynamics of individual bacteria in collective motions. Together, our study sheds light onto the puzzling motile behaviors of bacteria in complex fluids and provides insights into the collective swimming of bacterial suspensions relevant to a wide range of microbiological and biomedical processes.                  

About: Xiang Cheng received his B.S. in physics from Peking University in China in 2002. He then moved to U.S. and obtained his Ph.D. in physics from the University of Chicago in 2009. He worked as a postdoctoral associate in the Department of Physics at Cornell University from 2009 to 2013. He is currently an associate professor at the Department of Chemical Engineering and Materials Science at the University of Minnesota. Dr. Cheng has received several academic awards, including Arthur B. Metzner Early Career Award from Society of Rheology, NSF Career Award, Packard Fellowship, DARPA Young Faculty Award, 3M non-tenured faculty award and McKnight Land-Grant Professorship. His research group studies biophysics and soft materials physics in experiments, with a special focus on the emergent flow behaviors in biological and soft matter systems. Particularly, his research interests include bacterial locomotion, hydrodynamics of active fluids, rheology of colloidal suspensions and dynamics of liquid-drop impact processes.

Join us on Tuesday, May 2nd at 3pm for a celebration of the 2023 Nels Nelson Memorial Fellowship recipient Noah Gallagher, with a distinguished lecture by Prof. Peter Sullivan.

Peter Sullivan, Senior Scientist in the Mesoscale and Microscale Laboratory at the National Center for Atmospheric Research and affiliate faculty in the Civil Engineering Department at Colorado State University

Distinguished lecture: Marine boundary layers coupled to ocean surface heterogeneity: Secondary circulations in LES process studies

Abstract: Numerical simulations of the atmospheric boundary layer often adopt a horizontally homogeneous lower boundary - a simplifying assumption that is seldom if ever found in nature.  Field observations are collected above spatially varying land and ocean surfaces, and then surface heterogeneity is a source of uncertainty when comparing simulations and observations.  The ocean surface in particular features high spatial variability in sea surface temperature (SST), currents, and surface waves over a broad range of horizontal scales. The present work uses large-eddy simulation (LES) to examine the impact of heterogeneous SST on the marine atmospheric boundary layer. The imposed heterogeneity is a single-sided warm or cold front with temperature jumps varying over a horizontal distance between $[0.1 - 6]$\,km characteristic of an upper ocean mesoscale or submesoscale regime. A specially designed numerical Fourier-fringe technique is implemented in the LES to overcome the usual assumptions of horizontally homogeneous periodic flow.  The winds oriented across (or perpendicular) to the fronts develop secondary circulations with rotation varying with the sign of the front. Warm fronts feature overshoots in the temperature field, non-linear temperature and momentum fluxes, a local maximum in the vertical velocity variance and an extended spatial evolution of the boundary layer with increasing distance from the SST front.

Large eddy simulation (LES) is also used to elucidate eddy impacts on the atmospheric boundary layer (ABL) forced by winds, convection, and an eddy with varying radius; the maximum azimuthal eddy speed is 1\,m\,s$^{-1}$.  Simulations span the unstable regime $-1/L = [0, \infty]$ where $L$ is the Monin-Obukhov (M-O) stability parameter. Eddy currents induce a surface stress anomaly that induces Ekman pumping in a dipole horizontal pattern.  The dipole is understood as a consequence of surface winds aligned or opposing surface currents.  In free convection a vigorous updraft is found above the eddy center and persists over the ABL depth. With winds and convection, current stress coupling also generates a dipole in surface temperature flux even with constant sea surface temperature.  Wind, pressure, and temperature anomalies are most sensitive to an eddy under light winds. Flow over an isolated eddy develops a coherent ABL "wake" and secondary circulations downwind.  Kinetic energy exchanges by wind-work indicate an eddy-killing effect on the oceanic eddy current, but only a spatial rearrangement of the atmospheric wind-work.

About: Peter Sullivan is a Senior Scientist in the Mesoscale and Microscale Laboratory at the National Center for Atmospheric Research and an affiliate faculty in the Civil Engineering Department at Colorado State University. Peter received his Bachelor's and Ph.D Degrees in Civil Engineering from Colorado State University and a Master's Degree in Mechanical Engineering from University of British Columbia. Prior to coming to NCAR, Peter worked for six years as a Senior Specialist Engineer in Aerodynamics Research at the Boeing Company where he worked on shock/boundary-layer interaction, drag reducing riblets, and the design of the 777 transonic airplane.

Peter's research interests at NCAR are: simulations and measurements of geophysical turbulence, subgrid-scale modeling, air-sea interaction, effects of surface gravity waves on marine boundary layers, submesoscale turbulence in the upper ocean, impacts of stratification, turbulent flow over hills, and numerical methods. He uses large-eddy and direct numerical simulations to investigate turbulent processes in both the atmospheric boundary layer and the ocean mixed layer. These turbulence simulation codes run on large parallel supercomputers. Peter has participated in and planned field campaigns, Horizontal Array Turbulence Study, Ocean Horizontal Array Turbulence Study, and Canopy Horizontal Array Turbulence Study focused on the measurement of subgrid scale variables in the atmospheric surface layer.

2023 Nels Nelson Memorial Fellowship recipient Noah Gallagher, advised by Prof. John Gulliver

Presentation title: Assessing Stormwater Adaptations for Extreme Rainfall Events

Abstract: Extreme rainfall events in recent decades are more frequent and intense. The increase in precipitation has large ramifications for urban landscape design, stormwater runoff management, and flood control. This presentation will share the final results and recommendations of a research project: Climate Change Adaptation of Urban Stormwater Infrastructure, funded by the Local Road Research Board (LRRB) of MN, which evaluated several different stormwater management strategies and their effectiveness in the face of climate driven extreme rainfall events. The strategies include upsizing storm sewer pipes, adding wet ponds, retrofitting existing stormwater ponds to be “smart” ponds, adding rain gardens, and others. In order to evaluate the efficacy of a strategy, the project team used the U.S. EPA’s SWMM software to model adaptations to three Minnesota watersheds for a variety of rainfall depths and return periods. The cost of adaptations was also considered, leveraging data from the Water Research Foundation’s “Community-enabled Lifecycle Analysis of Stormwater Infrastructure Costs” (CLASIC). With these research results, stormwater managers can compare and contrast different adaptation strategies to aid their decision making when updating and adapting their stormwater management systems.

About: Noah Gallagher is a Ph.D. student in the Department of Civil, Environmental and Geo-Engineering working with the Stormwater Research Group led by Dr. John Gulliver at St. Anthony Falls Laboratory. His research focuses on modeling extreme precipitation events, particular future events that have been enlarged by climate change. This work aims to better link watershed models to observable landscape characteristics and use results of those models to recommend the most cost effective methods for adapting to these large return interval events. Prior to starting graduate work, Noah received his Bachelors of Environmental Engineering from the University of Minnesota, where he worked with SAFL's Stormwater Group and CEGE's Novak Lab on laboratory and field measurements for a variety of projects.

Keith Moored, Associate Professor in the Department of Mechanical Engineering and Mechanics at Lehigh University

Abstract: Fish schools are fascinating examples of self-organization in nature. They serve many purposes from enhanced foraging, and protection against predators to improved socialization and migration.  Beyond the implications for biology, engineers can take inspiration from the hydrodynamic benefits of schooling to apply to the design of schools of next-generation bio-robotic vehicles.  This new class of schooling unmanned underwater vehicles would enable unprecedented efficiency, maneuverability, agility and stealth; as well as unlock novel missions that require distributed tasks or swarming.  However, our understanding of the hydrodynamic interactions in schools is primitive.  Importantly, the links from the organization, synchronization, and kinematics of individuals to the performance and stability of a school has yet to established. 

In this talk I will present recent work examining the influence of school organization and synchronization on the locomotion performance and stability of simple interacting pitching hydrofoils.  Experiments and potential flow simulations will detail the flow interactions that occur between a pair of pitching hydrofoils – a minimal school – with an out-of-phase synchronization. It is discovered that the flow interactions provide cohesion between the foils and, specifically, that there is a two-dimensionally stable equilibrium arrangement that arises.  This stable side-by-side arrangement is verified numerically and, for the first time, experimentally for freely-swimming foils undergoing dynamic recoil motions.  Significant thrust and efficiency benefits are also determined for various organizations of the minimal school.  Focusing in on the side-by-side organization, the origin of the forces that balance to produce an equilibrium arrangement are discovered. New physics-based scaling laws are developed for the hydrofoils’ equilibrium arrangement, thrust generation, and power consumption, which are found to be in good agreement with inviscid simulations and viscous experiments.  Going beyond a minimal school, we examine stable arrangements for larger schools of foils by searching for repeating patterns of known stable arrangements.  Advances toward examining stable arrangements in real fish schools, and bio-robots alike will be discussed.

About: Dr. Keith Moored is an Associate Professor in the Department of Mechanical Engineering and Mechanics at Lehigh University.  He received a B.S. in Aerospace Engineering and a B.A. in Physics at the University of Virginia in 2004, and his Ph.D. in Mechanical and Aerospace Engineering also from the University of Virginia in 2010. From 2010-2013, he was a Postdoctoral Research Associate and Lecturer in Mechanical and Aerospace Engineering at Princeton University.  Dr. Moored’s research interests are in bio-inspired propulsion, unsteady aerodynamics and fluid-structure interaction.  He is currently leading an ONR MURI topic on the hydrodynamics of schooling and has previously been a PI on another MURI topic on non-traditional propulsion.  He has received an NSF CAREER award for examining the fluid dynamic interactions among schooling swimmers. 

Christopher Zahasky, Assistant Professor in the Department of Geoscience at the University of Wisconsin-Madison

Abstract: Quantification and prediction of aqueous and bacterial contaminants in groundwater requires a fundamental understanding of multiscale permeability, and mechanisms of bacteria transport and attachment in geological materials. In this seminar, I’ll first discuss the use of positron emission tomography (PET) for the measurement of in situ transport processes in geologic systems, including both tracers and colloidal bacteria. Using these datasets, combined with numerical models, we construct a convolutional neural network (CNN) for rapid 3D sub-core permeability inversion of geologic cores samples. I’ll then discuss a second study using these experimental methods to quantify sub-core transport and attachment of E.coli bacteria. Our results illustrate that bacteria attachment is not uniform but can be described by statistical distributions of attachment coefficients that are dependent on system conditions. These experimental methods, combined with deep learning and numerical workflows, provides a robust approach to better understand bacterial transport mechanisms, improve model parameterization, and accurately predict how local geologic conditions can influence the fate and transport bacteria and other contaminants in groundwater.

About: Dr. Christopher Zahasky is an assistant professor at the University of Wisconsin-Madison in the Department of Geoscience. Prior to coming to the University of Wisconsin-Madison, he was a postdoctoral scholar at Imperial College London and Stanford University. He completed his PhD and MSc degrees in Energy Resources Engineering at Stanford University. He completed his Bachelor of Science degree in Geology at the University of Minnesota. His research interests are focused on understanding the fundamental physics and mechanisms of fluid, colloid, and solute transport in geologic systems across length and time scales using experimental observations validated and generalized with analytical and numerical models.

Join us on Tuesday, April 11th at 3pm for a celebration of the 2023 Alvin Anderson Award recipient Shanti Penprase, with a distinguished lecture by Dr. Kenneth Belitz.

Kenneth Belitz, Research Hydrologist in the Water Resources Mission Area of the United States Geological Survey (USGS)

Distinguished lecture: Old problems, new approach: Applications of Ensemble-Tree Machine Learning to Hydrogeology

Abstract: Ensemble tree modeling is a machine learning method well suited for representing complex non-linear phenomena. As such, ensemble tree modeling can be applied to a wide range of questions in hydrogeology, including questions related to hydrogeologic mapping.  Some questions are problems of regression in which one seeks an estimate of a continuous variable.  For example, what is the depth to the water table across a region of interest? Other questions are problems of classification.  For example, across a region of interest and over a range of depths, is groundwater oxic or reduced?

The U.S. Geological Survey National Water Quality Assessment project (NAWQA) has used ensemble tree methods to address questions related to groundwater quality at regional and national scales. Some of our models evaluate the three-dimensional distribution of factors that can affect groundwater quality, such as pH, redox, and groundwater age. In turn, the modeled factors were used in subsequent models to map the three-dimensional distribution of contaminant concentrations. In our experience, ensemble tree models are a powerful tool for answering difficult questions. They can be used as a complement to process-based modeling and to make predictions at scales that preclude the use of process-based approaches.

About: Dr. Kenneth Belitz is a Research Hydrologist in the Water Resources Mission Area of the United States Geological Survey (USGS). He received his B.A. in Geology from Binghamton University, and Ph.D. in hydrogeology from Stanford University in 1985.  His dissertation examined the evolution of large-scale groundwater flow in the Denver Basin under the direction of Dr. John Bredehoeft. Throughout his career, Ken has simultaneously pursued two fronts: improving the fundamental hydrogeologic framework of the conterminous U.S., and employing numerical models – and, most recently, machine learning – in novel ways to better understand regional-scale groundwater quality and to project our current understanding into unsampled space.

Upon completing his Ph.D., Ken joined the USGS California Water Science Center, where he constructed a model of the western San Joaquin Valley; this model and its underlying framework became the gold standard and basis for subsequent models of this critically important aquifer system. From 1990-1997 Ken taught at Dartmouth University and Queens College of New York, before returning to the USGS in 1998 to lead an interdisciplinary team studying the water quality of the intensely urbanized Santa Ana River Basin as part of the USGS National Water Quality Assessment (NAWQA) Program. In this capacity, Ken began to develop a systematic approach to large-scale groundwater-quality assessment founded on a deep understanding of groundwater flow. From 2003-2012, Ken up-scaled this approach to obtain representative, unbiased water-quality data for the groundwater resources of the entire state of California. This work yielded new insights into the processes behind the spatial distribution of critical contaminants including perchlorate, pharmaceuticals, and hexavalent chrome. Ken then led the design and implementation of the groundwater component for the USGS NAWQA Program’s third decade. The design characterizes water quality in the most productive principal aquifers, cumulatively representing 85 percent of the Nation’s GW-derived drinking-water supplies. Ken’s work has given us an unbiased and surprising perspective on the relative risks of geogenic and anthropogenic contaminants, while evaluating constituents not previously sampled for at the national scale. Ken is a GSA Fellow and has received numerous USGS awards for his publications and service.

2023 Alvin Anderson Award recipient Shanti Penprase, advised by Prof. Andy Wickert

Presentation title: Impacts of glacially-driven base level change on river channel long profile across timescales: Whitewater River, southeastern Minnesota

Abstract: Changes in water and sediment supply from the Laurentide Ice Sheet resulted in alternating episodes of aggradation and incision for the upper Mississippi River and its tributaries. In this presentation, I present work on the impacts of changing Mississippi River bed elevation on the Whitewater River, a tributary of the Mississippi whose catchment remained unglaciated during the Last Glacial Maximum. By connecting the formation of terraces in tributaries with the evolution of the mainstem Mississippi, we build on our understanding of the regional geomorphic response to base-level fluctuation. We use a combination of topographic analysis and geochronologic methods to reconstruct changes in the channel long profile of the Whitewater River during this time. This work better constrains the timing and extent of fluvial-network response to changes in the Laurentide Ice Sheet, particularly within river systems that were not directly connected to the ice front. Further, this field-based data set on river response to base-level change and terrace genesis captures real-world complexity in a natural system and can catalyze greater understanding of river long-profile response to abrupt base-level fall.
 

About: Shanti Penprase is a PhD candidate in the Department of Earth & Environmental Sciences working with Professor Andy Wickert. Her research combines field methods, geochronology, and computational approaches to explore how river systems in Minnesota evolved from the most recent glacial–post-glacial transition to the start of Euro-American agriculture. Prior to UMN, she earned her BA in Geology from Carleton College and worked in water quality and community outreach in the Twin Cities for several years. In addition to research, Shanti is passionate about teaching, mentorship, and working collaboratively to build community knowledge and engagement.