About

Evan A. Variano is a Professor of Civil and Environmental Engineering at UC Berkeley. His research focuses on environmental fluid mechanics and the physics of fluid motion in the environment. His expertise includes phenomena on a variety of scales, from microscopic mixing to the coupled ocean-atmosphere system that transports heat and carbon dioxide around the globe. His work explores cutting-edge experimental techniques to measure fluid phenomena, with particular emphasis on turbulence and solute transport. His research addresses engineering problems related to restoring or preserving natural environments such as wetlands, rivers, and oceans, as well as designing systems where water or air flow must be controlled, including ventilation, treatment, and turbomachinery. His research techniques include imaging flows with dense vegetation or sediment suspensions, flow-structure interaction for free-floating or loosely anchored structures, and measuring fluxes of gases and aerosols at interfaces. His work also investigates the dynamics of transport and mixing in environmental flows, management approaches for wetlands that control greenhouse gas emissions, sediment in water quality, and the influence of flow on aquatic organisms.

Research topics

• Mechanics
• Physics
• Meteorology
• Optics
• Geometry
• Geology
• Remote sensing
• Mathematics
• Geography
• Environmental science
• Classical mechanics
• Materials science

Selected publications

• Firewood, four wheelers, and chest freezers: The importance of modern energy to Alaska Native subsistence in Yedatene Na’

  Energy Research & Social Science · 2025-05-03

  articleOpen accessSenior author

  A Just Transition to renewable energy requires decolonizing approaches that center disenfranchised communities and their values. For Alaska Native communities, one of these values is subsistence hunting, fishing, and gathering that is fundamentally tied to Indigenous Knowledge. We investigated the relationship between renewable energy and subsistence in Yedatene Na’ (The Native Village of Cantwell). To do so, we centered and learned from Indigenous Knowledge Experts using semi-structured interviews ( n = 10) and participant-observation methods. Alaska Native people have always been adaptive and inventive in preserving their subsistence practice. In our investigation, we found that people in Yedatene Na' have continued adapting, as shared from the living memories of modern day community experts who continue practicing subsistence with modern technologies. Adaptation has been complex and non-linear, with new and old technologies coexisting in the community, such as diesel-powered heating stoves alongside wood stoves. Many of these technologies were adopted to address colonial pressures of assimilation, such as the adoption of chest freezers to preserve access to traditional foods in response to hunting regulations. Most importantly, we found that these technologies are integral to ongoing Indigenous Knowledge in Yedatene Na’, such as gas-powered vehicles providing elders access to hunting grounds. Throughout the renewable energy transition, the toolset for subsistence will continue to change, as it always has. Policies that seek to encourage renewable energy should empower Native communities to adopt technologies that preserve their subsistence culture and stop technologies that would be harmful to their subsistence culture, thus supporting a Just Transition.

  PublisherDOI

• Development of a forced advection sampling technique (FAST) for quantification of methane emissions from orphaned wells

  Atmospheric measurement techniques · 2025-07-10 · 1 citations

  articleOpen accessCorresponding

  Abstract. Orphaned wells, meaning unplugged and non-producing wells lacking responsible owners, pose a significant and undersampled environmental challenge due to their vast number and unknown associated emissions. We propose, develop and test an alternative method for estimating emissions from orphaned wells using a forced advection sampling technique (FAST) that can overcome many of the limitations in current methods (cost, accuracy, safety). In contrast to existing ambient Gaussian plume methods, our approach uses a fan-generated flow to force advection between the emission source and a point methane (CH4) sensor. The fan flow field is characterized using a colocated sonic anemometer to measure the 3D wind profile generated by the fan. Using time-series measurements of CH4 concentration and wind, a simple estimate of the CH4 emission rate of the source can be inferred. The method was calibrated using outdoor controlled-release experiments and then tested on four orphaned wells in Lufkin, TX, and Osage County, OK. Our results suggest that the FAST method can provide a low-cost, portable, fast and safe alternative to existing methods with reasonable estimates of orphaned well emissions over a range of leak rates below 40 g h−1 and within certain geometric and atmospheric constraints.

  PublisherOA PDFDOI

• Development of a Forced Advection Sampling Technique (FAST) for Quantification of Methane Emissions from Orphaned Wells

  2024-10-09 · 1 citations

  preprintOpen accessCorresponding

  Abstract. Orphaned wells, meaning wells lacking responsible owners, pose a significant and poorly understood environmental challenge due to their vast number and unknown associated emissions. We propose, develop, and test a novel method for estimating emissions from orphaned wells using a Forced Advection Sampling Technique (FAST) that can overcome many of the limitations in current methods (cost, accuracy, safety). In contrast to existing ambient Gaussian plume methods, our approach uses a fan-generated flow to create a jet between the emission source and a point methane (CH4) sensor. The fan flow field is characterized using a collocated sonic anemometer to measure the 3D wind profile generated by the fan. Using time-series measurements of CH4 concentration and wind, a simple estimate of the CH4 emission rate of the source can be inferred. The method was calibrated using outdoor controlled release experiments and then tested on four orphaned wells in Lufkin, TX, and Osage County, OK. Our results suggest that the FAST method can provide a low-cost, portable, fast and safe alternative to existing methods with reasonable estimates of orphaned well emissions over a range of leak rates.

  PublisherOA PDFDOI

• Measurements of trajectories and spatial distributions of diatoms (Coscinodiscus spp.) at dissipation scales of turbulence

  Experiments in Fluids · 2021-07-01 · 14 citations

  article
  PublisherDOI

• Analytical solution for the Kelvin–Helmholtz instability under a submerged canopy-oscillatory flow

  Journal of Hydraulic Research · 2021-06-01 · 3 citations

  article

  Following on from a theoretical solution to the Kelvin–Helmholtz (KH) instability under submerged canopy-oscillatory flow environments a relationship between the incoming free surface wave frequency and KH frequency was developed. The KH frequencies (fKH) are higher than those from the incoming wave expressed by fKH ≈[2.83,5.02]fw. In addition, the analytical expression, along with the energy spectra analysis of the vertical turbulent flux of momentum (Su′w′) for cases when the KH dominates vertical mixing, allowed us to observe the spectral shortcut mechanism. Based on comparisons between the KH time scale and the mean horizontal transport of mass time scale, it can be concluded that the instability has no effect on the wave-induced steady current process. The instability plays an important role on vertical mixing but not on the horizontal transport of mass.

  PublisherDOI

• Spinning and tumbling of long fibers in isotropic turbulence

  Physical Review Fluids · 2021-04-20 · 26 citations

  articleOpen access

  We simultaneously measure both the spinning and the tumbling components of rotation for long inertial fibers in isotropic turbulence. The spinning rates of these fibers are higher than the tumbling rates, manifesting dynamics analogous to sub-Kolmogorov fibers in turbulent flows. Similar to how sub-Kolmogorov fibers preferentially align with the local vorticity, long fibers preferentially align with the large scale coherent vortex filaments that can be as long as the integral scale of the turbulent flow.

  PublisherOA PDFDOI

• Droplet and particle methods to investigate turbulent particle laden jets

  Aerosol Science and Technology · 2021-07-21 · 4 citations

  articleOpen access

  The SARS-CoV-2 pandemic has heightened the interest in particle-laden turbulent jets generated by breathing, talking, coughing and sneezing, and how these can contribute to disease transmission. We present quantitative measurement methods for such flows, while exploring and offering improvements for common shortcomings. We generate jets consisting of either liquid droplets or solid particles in an isothermal, quiescent and electrically isopotential experimental chamber that was constructed to control the effects of ambient forcing on jet behavior. For liquid droplets, we find promise in surface deposition analysis based on fluorescent tracer use. For particles, we explore the performance of commercially available adhesive sampling strips and develop conductive grounded carbon tape based sampling strips. We explore ways in which the smallest of thermal gradients or electrostatic charge issues can affect particle dispersion, and suggest practical methods to address these issues. The developed methods are applied to study the simultaneous deposition of (Formula presented.) 25, 50 and 200 μm solid particles from a particle laden turbulent jet with a mean velocity of 33.2 m/s. The deposition location as a function of particle size was compared to results from a simple numerical RANS model, and illustrates ways in which imprecise initial or boundary conditions can lead to a notable deviation from experimental results. The differences in deposition pattern seen in experimental and numerical results despite a carefully controlled environment and characterized particle ejection indicate the need for a more stringent numerical model validation, especially when studying fate and transport of mid-range (neither purely aerosol or ballistic) sized particles.

  PublisherOA PDFDOI

• A new particle for measuring mass transfer in turbulence

  Experiments in Fluids · 2021-01-01 · 10 citations

  articleOpen accessSenior author

  Abstract We present a method for creating a new type of model particle that allows us to measure the mass transfer rate from the particle surface to the surrounding water. We use hollow glass spheres and sugar to create neutrally buoyant particles in a variety of molded shapes. These particles are an alternative to traditional gypsum objects for measuring mass transfer, with the important characteristic of being neutrally buoyant. This is an inexpensive method that allows for custom particle shapes to be manufactured with different densities. We test the utility of these particles by measuring their dissolution rates in homogeneous, isotropic turbulence in our laboratory turbulence tank. Our measurements fit our proposed model, and give a faster dissolution rate for rod-shaped particles than for disc-shaped ones. Graphic abstract

  PublisherOA PDFDOI

• Turbulence statistics in a negatively buoyant multiphase plume

  Journal of Fluid Mechanics · 2020 · 13 citations

  Senior authorCorresponding
  • Mechanics
  • Physics
  • Meteorology

  We investigate the turbulence statistics in a multiphase plume made of heavy particles (particle Reynolds number at terminal velocity is 450). Using refractive-index-matched stereoscopic particle image velocimetry, we measure the locations of particles whose buoyancy drives the formation of a multiphase plume, together with the local velocity of the induced flow in the ambient salt–water. Measurements of the mean axial flow in the plume centreplane follow Gaussian profiles and that of the mean radial flow is consistent with integral plume theory. The turbulence characteristics resemble those measured in a bubble plume, including strong anisotropy in the normal Reynolds stresses. However, we observe structural differences between the two multiphase plumes. First, the skewness of the probability density function of the axial velocity fluctuations is not that which would be predicted by simply reversing the direction of a bubble plume. Second, in contrast to a bubble plume, the particle plume has a non-negligible fluid-shear production term in the turbulent kinetic energy (TKE) budget. Third, the radial decay of all measured terms in the TKE budget is slower than those in a bubble plume. Despite these dissimilarities, a bigger picture emerges that applies to both flows. The TKE production by particles (or bubbles) roughly balances the viscous dissipation, except near the plume centreline. The one-dimensional power spectra of the velocity fluctuations show a power law that puts both the particle and bubble plume in a category different from single-phase shear-flow turbulence.

  PublisherOA PDFDOI

• ECOSTRESS and CIMIS: A Comparison of Potential and Reference Evapotranspiration in Riverside County, California

  AGU Fall Meeting Abstracts · 2020-12-01

  article
  Publisher

Recent grants

• Collaborative Research: Trajectories and spatial distributions of diatoms at dissipation scales of turbulence

  NSF · $316k · 2013–2017

• Effects of particle shape and fluid shear on the kinematics and mass transfer of large particles in turbulent flow

  NSF · $310k · 2016–2020

Frequent coauthors

• Margaret Byron

  Pennsylvania State University

  23 shared

• Gabriele Bellani

  15 shared

• Edwin A. Cowen

  Cornell University

  15 shared

• C. Poindexter

  13 shared

• Ankur Bordoloi

  Delft University of Technology

  13 shared

• Rachel M. Allen

  Woods Hole Oceanographic Institution

  12 shared

• Nimish Pujara

  University of Wisconsin–Madison

  12 shared

• David T. Ho

  University of Hawaiʻi at Mānoa

  12 shared

Education

• Ph.D., Environmental Engineering

  University of California, Berkeley

  1994

• M.S., Environmental Engineering

  University of California, Berkeley

  1990

• B.S., Environmental Engineering

  University of California, Berkeley

  1988

Awards & honors

• UC Berkeley Presidential Chair Fellow
• Hellman Faculty Fellow
• UC Berkeley Postdoctoral Mentor award (2018)
• UC Berkeley Excellence in Lab Safety Award (2018)
• ASCE Student Chapter award (2009)