Hydrologic Discovery - Oral Presentations (Videos)

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This international symposium of May, 2012 presents a broad overview of the state-of-the-art in hydrologic discovery in honor of two legendary leaders of this process – Wilfried H. Brutsaert and Jean-Yves Parlange – upon the occasion of their retirements at Cornell University.

The oral presentation videos from this symposium are provided as Streaming Videos. Also, QuickTime files are provided that are playable on Apple Devices or on computers using a QuickTime player (free downloads for Macintosh and Windows computers). Both high definition (HD) and standard definition (SD) files are provided.

The high definition QuickTime videos may be played using a computer video player with H.264 codec, 1280x720 pixels, millions of colors, AAC audio at 44100Hz and 29.97 frames per second. The data rate is 5Mbps. File sizes are on the order of 600-900 MB. (Other formats may be added later.) Free QuickTime players for Macintosh and Window computers may be located using a Google search on QuickTime.

We have provided a companion set of standard definition videos (to reduce downloading from 15+ minutes for HD to 5+ minutes for SD versions. However, on a multitasking computer you may continue working during the downloading, but must wait until an entire file has been downloaded before playing it. In addition, the slides used in the presentation are included as PDF files for the benefit of the serious student and to provide clarity in the mathematical expressions in the SD versions.


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    K1. Reflections by Colleagues
    (Internet-First University Press, 2012-05)
    Once downloaded, these high definition QuickTime videos may be played using a computer video player with H.264 codec, 1280x720 pixels, millions of colors, AAC audio at 44100Hz and 29.97 frames per second. The data rate is 5Mbps. File sizes are on the order of 600-900 MB. (Other formats may be added later.) Free QuickTime players for Macintosh and Window computers may be located using a Google search on QuickTime. The DVD was produced by J. Robert Cooke.
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    J1. Tribute to Spouses
    (Internet-First University Press, 2012-05)
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    I2. On the Brutsaert Baseflow Recessions and Their Geomorphic Origins
    Rinaldo, Andrea; Parlange, Marc; Mutzner, Raphael; Tomasic, Nevena; Ceola, Serena; Bertuzzo, Enrico; Rodriguez-Iturbe, Ignacio (Internet-First University Press, 2012-05)
    Moving from a classic study on the base flow characteristics of six basins in the Finger Lakes region [1], a set of Brutsaert recession curves (the lower envelope of available records of |dQ/dt| as a function of Q, where Q is at-a-station gauged flow rate) has been constructed from Swiss streamflow data relatively unaffected by snowmelt. The Lecture builds on the functional dependences found in [1] (chiefly through Boussinesq’ nonlinear solution of free-surface groundwater flow, yielding a specific relation to local drainage area and total stream length) and on the expedient avoidance of proper time references, to apply and generalize recent results aimed at the geomorphic origins of recession curves [2], that is, fully integrating sizable geometric and topologic complexity. In particular, such results propose a link between river network morphology and the parametrization in [1], in particular by assimilating the basic scaling exponent a (i.e. |dQ/dt|µQa) to that characterizing the empirical relation N(x) µ G(x)a (where x is the downstream distance from the channel heads, N(x) is the number of channel reaches exactly located at distance x from their heads, and G(x) is the total drainage network length at a distance greater or equal to x down to the gauging station where Q is recorded [2]). Application of the method, originally tested on DTMs and daily discharge observations in 67 US basins, suggests a definite linkage of active drainage and source functions with the basic features of the Brutsaert envelopes. The possible morphological predictability of base flow features is central to transport processes at catchment scales, not least for its implications on our understanding of the geomorphic structure of the hydrologic response [3] and of the stationarity of the ensuing travel time distributions leading to the so-called old water paradox [4]. These issues are briefly discussed in the Lecture. Here, through a broad survey of Swiss field data, we go on suggest that the method [2] provides excellent results only in catchments where drainage density (roughly defined as the ratio of total channel network length to its drainage area [L-1], defined at a station) can be regarded as spatially constant. When uneven drainage densities are observed, chiefly in our test cases for high mountainous areas where drainage density varies significantly owing to complex cryosphere dynamics and geologic or pedologic constraints, the method’s assumptions do not hold. In the Lecture a detailed reexamination of the premises of the approaches [1,2] is proposed. A revision is then proposed, which includes geomorphic corrections based on a proper description of the drainage density seen as a random space function [5]. Such corrections properly vanish should drainage density become spatially constant. Overall, it is recognized a definite geomorphic origin for Brutsaert recessions, with notable implications. REFERENCES [1] W. Brutsaert & J.L. Nieber, Regionalized drought flow hydrograph from a mature glaciated plateau, Water Resources Research, 13(3), 637-643, 1977 [2] B. Basudev & M. Marani, Geomorphological origin of recession curves, Geophysical Research Letters, 37, L24403, 2010 [3] I. Rodriguez-Iturbe and J.B. Valdes, The geomorphologic structure of the hydrologic response, Water Resources Research, 15(6), 1409-1420, 1979 [4] G. Botter, E. Bertuzzo, A. Rinaldo, Transport in the hydrologic response: Travel time distributions, soil moisture dynamics, and the old water paradox, Water Resources Research, 46, W03514, 2010 [5] G. Tucker, F. Catani and R.L. Bras, Statistical analysis of drainage density from digital terrain data, Geomorphology, 36, 187-202, 2001
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    I1. Green’s Function and Watershed Modelling
    Yeh, Gour-Tsyh (Internet-First University Press, 2012-05)
    Watershed modelling deals with multiple processes occurring in multiple media. The processes include flow and thermal, salinity, sediment, and biogeochemical transport. The multiple media cover stream/river/canal/open channel networks, lakes/reservoirs, land surfaces, and subsurface media. Analytical and numerical models are commonly employed for simulations to understand sciences or to assess environmental consequences. Why analytical models offer the advantage of clearly and easily explaining the physics involved, the numerical models give practical applications of assessing the impact and interaction among processes and media. This presentation will discuss the issues and difficulties associated with the employment of Green functions to yield analytical models and troubles associated with the use of numeric to generate computational models. Various means of overcoming these difficulties and troubles will be outlined and addressed.
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    H2. Hot Thermodynamics for Frozen Soils
    Groenevelt, Pieter H. (Internet-First University Press, 2012-05)
    Q. What is the driving force that lifts buildings, pipelines and roads into the air when the soil underneath freezes? A. Ask Clapeyron……A unifying theory is proposed, bringing together the CRRELL School of Duwayne Anderson and the CORNELL School of Bob Miller, leading to the definition of a Heave Index for the sensitivity of soils to exhibit frost heave. While traveling through the Northern parts of Idaho and Montana with my colleagues, Wilco van Loon (left) and Ed Perfect (right), we were warned about the hazards of freezing soil
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    H1. Groenevelt Autobiography
    Groenevelt, Pieter H. (Internet-First University Press, 2012-05)
    Pieter H. Groenevelt, using time reallocated due to absence of a speaker, provided a broad view of his life experience and expressed his heartfelt gratitude for the generosity beyond belief he received after World War II.
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    G2. Snippets from Infiltration: Where Approximate Becomes Exact
    Broadbridge, Philip (Internet-First University Press, 2012-05)
    The Darcy-Buckingham macroscopic approach to soil-water modelling, leading to a nonlinear Richards’ diffusion-convection equation, has been very useful for many decades. Some sharp results of the 1970s by W. Brutsaert and J.-Y. Parlange have been an influence on many, including myself. Since the 1980s, several groups have used an integrable one-dimensional version of Richards’ equation, with realistic nonlinear transport coefficients, to predict experimentally verifiable quantities. Neat expressions have been derived for time to incipient ponding, for the dependence of sorptivity on pond depth and for the second and higher infiltration coefficients. These exact results are at odds with those of the traditional Green-Ampt model. In the limit of delta-function diffusivity, the water content profile approaches a step function, so the water content is everywhere close to either the boundary value or the initial value. As explained by Barry et al (1995), far from there being a unique “Green-Ampt limit”, practical predictions in the limit of a delta function diffusivity depend subtly on the relationship between diffusivity and conductivity at intermediate values of water content. In fact, the traditional Green-Ampt predictions, with a constant potential at the wet front, may be recovered from a linear, rather than step-function behaviour of conductivity vs water content. A number of practical predictions of the integrable model agree exactly with those of the approximate analytic method originated earlier by Parlange, involving approximations within an integrand after expressing the water conservation equation in integral form. The exactly solvable model refutes the traditional Green-Ampt model and validates the quasi-analytic integral formulation.
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    G1. Infiltration into Soils
    Assouline, Shmuel (Internet-First University Press, 2012-05)
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    F3. Regional Evaporation Using Atmospheric Boundary Layer Profiles (a.k.a Brutsaert’s Balloons)
    Kustas, William P. (Internet-First University Press, 2012-05)
    Land surface temperature (LST) from thermal remote sensing is a surface boundary condition that is strongly linked to the partitioning of the available energy between latent (evapotranspiration) and sensible heat flux. Numerous modeling approaches have been developed ranging in level of complexity from semi-empirical to numerically-based soil-vegetation-atmosphere schemes. Many of the approaches require an accurate LST because the heat fluxes are related to the surface-air temperature differences. There is also difficulty estimating appropriate exchange coefficients for heterogeneous landscapes having a mixture of soil and vegetation temperatures influencing the LST observation and associated aerodynamic temperature. For regional applications this also means requiring an accurate air temperature distribution over the area of interest. These requirements have rendered many of the modeling approaches unusable for routine applications over complex land surfaces. However a two-source energy balance (TSEB) modeling scheme using time differencing in LST observations coupled to an atmospheric boundary layer growth model has been developed to adequately address the major impediments to the application of LST in large scale evapotranspiration determination. The modeling system, Atmospheric Land EXchange Inverse (ALEXI), using geostationary LST observations and the disaggregation methodology (DisALEXI) together with data fusion techniques will be described. This modeling system is currently providing regional and continental scale evapotranspiration estimates in the U.S. and plans are to develop a global product.
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    F2. Evaporation from Lake Kasumigaura: Bulk Coefficients and Spatial Distribution of Latent Heat Flux
    Michiaki, Sugita; Zhongwang, Wei; Aiko, Miyano; Hiroya, Ikura (Internet-First University Press, 2012-05)
    Study of lake evaporation includes various aspects of Dr Brutsaert’s interests such as the exchange processes on water surface, the development of internal boundary layer, estimation of evaporation rate, among others. In the present study, issues on air-water interaction were first revisited. Secondly, horizontal distribution of latent heat fluxes over the lake surface was estimated to study its variability. For these purposes, 10 Hz water vapor, temperature, and wind velocity data have been obtained at the Koshin Observatory located near the center of Lake Kasumigaura, the second largest lake in Japan (220 km2 with mean depth of 4 m) since June of 2007. The corresponding fluxes were determined by applying the eddy correlation method to estimate the bulk coefficients. Agreement and disagreement with previous studies on the bulk transfer coefficients were identified. Also, the influence of lake current, wave, gustiness was investigated. Based on the derived functional form for the bulk coefficient, horizontal distribution of latent heat flux was estimated by first deriving a 100-m grid map of air temperature, wind speed and humidity over the lake area from interpolation of the observed data at meteorological stations in and around Lake Kasumigaura. The bulk method was then applied to each grid to derive latent heat flux every six hours over a year, by assuming the same surface temperature as that at the Koshin Observatory. This was acceptable as the satellite infrared images indicated the presence of quasi-uniform surface water temperature, presumably to reflect well-mixed water body of the shallow lake. The results indicate larger fluxes at the lake center with smaller values near lake shores, mainly to reflect wind speed differences. In comparison, humidity and air temperature is of lessor importance to cause latent heat variability. The mean evaporation over the entire lake surface was found to be 976 (±56) mm/y, while that at the Koshin observatory was 878 mm/y.
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    F1. An index of maximal land-atmosphere coupling and its use in estimating evaporative fraction across a range of Ameriflux sites
    Salvucci, Guido D.; Gentine, Pierre (Internet-First University Press, 2012-05)
    Examination of heat and moisture fluxes at a wide range of Ameriflux sites reveals what appears to be an emergent property of the relative humidity profile, possibly due to strong coupling of the land-atmosphere system. Specifically, the magnitude of the gradient of relative humidity profile near the surface (i.e. at a nominal source height Zo+d) appears to be minimized over the course of a diurnal cycle, possibly reflecting a tendency toward thermodynamic equilibration between the land surface and boundary layer. The analysis leading to this observation is conducted as follows: Temperature and specific humidity profiles are calculated to be consistent with a simple Penman-Monteith model of evaporation, i.e. they: 1) follow simple law-of-the wall scaling (log((z-d)/Zo) consistent with the observed screen height windspeed, temperature and humidity; 2) reflect excess water vapor resistance due to stomatal and/or soil moisture limitations as expressed with a canopy resistance term; and 3) yield fluxes that are in energy balance with observed net radiation and ground heat flux. With rough estimates of the roughness and displacement heights (herein based on observed vegetation height), the preceding analysis yields a relative humidity profile, at each measurement time (e.g. half hour), for any given value of canopy resistance. At each Ameriflux site (here we focus on the Vaira Ranch, California, and the Duke Forest, North Carolina, as end-members), we calculate a set of 48 half-hourly RH profiles for each of 100 values of canopy resistance. We then calculate the sum of the 48 squared gradients of RH, evaluated at the source (Zo+d), for each canopy resistance. We find that the canopy resistance that yields the smallest mean squared gradient on a given day tends to be a close estimate of the canopy resistance that best reproduces the observed evaporation and sensible heat fluxes (and thus evaporative fraction). The ability to use this apparent intrinsic property of the coupled land-atmosphere system as a means to estimate evaporative fraction is particularly dramatic at the Vaira Ranch site, which undergoes a major seasonal dry down. In the analysis, the screen height temperature and humidity are observed, while the surface temperature and humidity are estimated by varying the canopy resistance. However, we interpret that the resulting minimization of near surface RH differences is more likely a rapid response of the boundary layer temperature and humidity to more slowly varying surface conductance, as opposed to a response of the surface to the atmosphere. In other words, we interpret the "selected" canopy resistance parameter as being the value most likely to have yielded the observed air temperature and humidity. Possible feedbacks that could yield the observed RH behavior are being systematically explored in a simplified coupled diffusion and radiative transfer model, and will be discussed.
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    E4. Probing the Atmospheric Boundary Layer: a Life-long Adventure Thanks to Wilfried Brutsaert
    Parlange, Marc; Katul, Gabriel; Eichinger, William; Albertson, John; Szilagyi, Jozsef; Cahill, Tony; Porte-Agel, Fernando; Kleissl, Jan; Pahlow, Markus; Bou-Zeid, Elie; Higgins, Chad; Adam, Mariana; Kumar, Vijayant; Chamecki, Marcelo; Vercauteren, Nikki; Froidevaux, Martin; Calaf, Marc; Nadeau, Daniel; Simeonov, Valentin; Meneveau, Charles (Internet-First University Press, 2012-05)
    During the 1986 Hapex-Mobilhy field campaign, deep in the middle of Les Landes pine forest of southwest France, we released more than 500 radiosondes to measure vertical profiles of temperature, humidity and wind speed in the atmospheric boundary layer (ABL). We were not there to sample the after effects of the Chernobyl disaster (or follow the world cup in Mexico), as many of the locals thought at the time, but rather to understand the blending properties of the turbulent atmosphere over variable terrain. Since that time we have continued in search of a better understanding of how the atmosphere responds to complex terrain, development of an improved formulation of evaporation into the atmosphere for hydrologic purposes, the measurement of turbulence and the numerical simulation of the ABL. Some field campaigns and findings will be highlighted including results on Taylor’s hypothesis using the EPFL raman lidar at Seedorf, Switzerland. Though instrumentation and computing have improved and the field sites change, the many pleasures of discussing science, life and running with Dr. Brutsaert remains the same today.
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    E3. Large Eddy Simulation Study of Scalar Transport in a Wind Turbine Array Atmospheric Boundary Layer
    Meneveau, Charles (2012-05)
    The structure of the turbulent atmospheric boundary layer is affected by the presence of thermal stratification. Brutsaert’s contributions to understanding and parameterizing such effects have had great impact in the field. We describe our efforts trying to parameterize thermal effects on atmospheric boundary layers in the presence of large wind farms using Large Eddy Simulation. As a first step, we examine the structure of passive scalar transport in the wind turbine array boundary layer (WTABL). Initial results from this project (performed in collaboration with Marc Calaf and Marc B. Parlange of EPFL, and funded by the National Science Foundation) will be presented.
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    E2. Working with Wilfried Brutsaert: Some Old and New Results on Radiative Dissipation of Temperature Fluctuations and Scalar Similarity in the Surface Layer
    Dias, Nelson Luís (2012-05)
    There is a style of thinking and approaching a problem to be learned from every good teacher. In this presentation, an attempt is made at giving an objective account of two subjects that I worked on as W. Brutsaert’s graduate student (radiation and scalar similarity), but highlighting the personal influence and style that I came to know and that helped to illuminate the way. Longwave radiation interacts with temperature fluctuations, by dissipating them in a process which has similarities to molecular effects, but which has a very different spectral behavior. The pioneering work of Brutsaert on the subject served as a basis to extend the original ideas to the spectral domain and, by doing this, identifying some new governing dimensionless parameters that can help to determine the extent to which radiative effects are important in the stable surface layer. A full comparison of the spectral approach with Brutsaert’s early formulation for the radiative dissipation had not been made, however, and some simple spectral shapes are used to show how this can be done. Moving to scalar similarity, the motivations for questioning the validity of Reynolds’ analogy between any two scalars are briefly reviewed. A lot of the physical basis to assume scalar similarity rests on the validity of a simple equilibrium between gradient production and molecular dissipation of scalar variance, and on the ratio between their molecular diffusivities being of order 1. As the essence of these results is revisited, they are recast in a way that gives them more generality, away from the original emphasis on temperature-humidity similarity and towards (hopefully) applicability to such important atmospheric components as carbon dioxide and methane. As in the case of radiation, some further results are also commented: the subject continued to attract the attention of other researchers from the Brutsaert School, and such topics as chessboard variability and its prediction of the importance of the active/passive role of scalars; experimental evidence on differences between the Monin-Obukhov Similarity functions for temperature and humidity; and the similarity hypothesis application to the bandpass eddy-covariance method are briefly reviewed. Finally, some on-going research is reported on scalar similarity that allows diagnosing the validity of the aforementioned equilibrium between gradient production and molecular dissipation with dimensionless parameters, and to further the understanding of the effects of molecular diffusivities and the active/passive role of scalars by means of numerical simulations of a chaotic system.
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    E1. Mean Velocity Profile in a Sheared and Thermally Stratified Atmospheric Boundary Layer
    Katul, Gabriel G.; Konings, Alexandra; Porporato, Amilcare (Internet-First University Press, 2012-05)
    Most human activity and biological processes occur within the lower atmosphere, a thermally stratified region characterized by shear and buoyancy-driven turbulence. Thermal stratification arises because of diurnal heating and cooling resulting in finite sensible heat flux at the Earth’s surface, while turbulence is mechanically produced due to the reduced mean velocity near the ground. The coexistence of shear- and buoyancy-generated turbulence leads to many difficulties in describing the flow properties in the lower atmosphere. Even for a stationary, horizontally homogeneous, high Reynolds number flow above an infinite flat and heated (or cooled) surface, the description of elementary flow statistics such as the mean velocity profile (MVP) has resisted complete theoretical treatment. There are inklings of a possible universal behavior in the MVP across a wide range of thermal stratification conditions as demonstrated by the collapse of data from multiple field experiments using dimensional analysis, known as Monin-Obukhov similarity theory. The Monin-Obukhov similarity framework has shaped micrometeorology and surface hydrology for more than 60 years now, and it remains the corner stone of virtually every single textbook on lower-atmospheric turbulence. The stability correction functions (SCF) are used in all climate, atmospheric, air quality, hydrologic, and ecological applications, including models of land-surface processes when land-surface fluxes are to be coupled to the state of the atmosphere. Yet, despite the SCF’s wide usage, even phenomenological theories that predict their canonical shape are still lacking. A previous link between the spectrum of turbulence and the MVP is expanded here to include the effects of thermal stratification on the turbulent kinetic energy dissipation rate and eddy-size anisotropy. The resulting theory provides a novel explanation for the power-law exponents and coefficients of MVP already reported from numerous field experiments. When taken together with a similar derivation for Manning’s equation and the Reynolds number dependence of the Nikuradse friction-factor, a blueprint for a unifying theory that bridges the Kolmogorov turbulent kinetic energy spectrum to widely used empirical results describing high Reynolds number flows in hydrology is beginning to unfold.
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    D2. On a Derivable Formula for Long-Wave Radiation from Clear Skies: A Theoretical and Practical Contribution
    Jacobs, Jennifer (Internet-First University Press, 2012-05)
    This talk will focus on the theoretical and practical contribution of Wilfried Brutsaert’s 1975 article On a Derivable Formula for Long-Wave Radiation from Clear Skies. This seminal intellectual advancement will be considered in light of its central importance to past, present and future atmospheric, hydrologic and remote sensing communities. This retrospective recognition also serves to provide insights on recognizing and fostering distinctive scholarship in the present day.
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    D1. Parameterization for Atmospheric Radiation: Some New Perspectives
    Liou, Kuo-Nan (Internet-First University Press, 2012-05)
    We first introduce Wilfried Brutsaert’s contributions to atmospheric radiation in terms of his original work on deriving a simplified broadband emissivity for calculating downwelling long-wave radiation at the ground. This is followed by a discussion of sorting atmospheric absorption lines based on the concept of the correlated k-distribution approach, which can effectively be coupled with the multiple scattering processes of cloud and aerosol particles for spectral radiative flux calculations. Subsequently, a number of unsolved and challenging problems in radiative transfer are discussed, leading to the presentation of three-dimensional radiative transfer over inhomogeneous mountains/snow in conjunction with surface energy budget and within the context of absorbing aerosols and mountain/snow albedo feedback in a regional climate system.
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    C3. On Wettability and Unstable Flow in Porous Media
    Wallach, Rony (Internet-First University Press, 2012-05)
    The effect of contact angle (CA) between water and porous media on flow regime in water repellent and sub-critically repellent soils will be illustrated and discussed. Water flow pattern that was monitored in a thin transparent flow chamber that ensures a 2D flow for water repellent soils (initial contact angle θ > 900) and sub-critical repellent porous media (permanent contact angle 300 < θ < 750) was remarkably affected by the CA. Plumes that were initiated by a point source at the soil surface (local perturbation) had different shape, size and longitudinal and transversal water content distributions for different contact angles and water application rates. The contact angle and water application rate control in particular the development of sharp water content decrease along the peripheral wetting front and non-monotonous water content variation along vertical cross section directions that are associated with unstable flow. For the low water application rate, thin and long plumes with saturation overshot behind the wetting front were observed for higher contact angles and wide plumes with lower average water content flow for the lower contact angles. On the contrary, negligible differences among the plumes were observed in all media for the high water application rates. Differences among the plumes became apparent only during the following drainage stage. The plumes in the media of high contact angle barely changed during the drainage period while the water content gradient along vertical cross sections turned positive at the lower part and negative along the upper part of the plumes in the media of lower contact angle. The discussion will include simulations made by a model developed for a bundle of capillaries of constant and variable cross section area and different contact angles.
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    C2. Preferential Flow and Extensions to Richards Equation
    DiCarlo, David A (Internet-First University Press, 2012-05)
    Multi-phase flow instabilities have always been a great interest in fluid flow in porous media, as they can create fingers and drastically change the travel times of solutes to ground water and/or change the sweep efficiency. Yves Parlange has been at the forefront of this research for the past 40 years, beginning with his classic papers on front stability with Hill. In the last decade, it has become apparent that gravity driven instabilities profiles cannot be described by traditional unsaturated continuum flow models (e.g. the Richards Equation). In this talk, I will detail this connection, and in turn, show how measurements of flow instabilities are key to developing the correct physical extensions of multi-phase flow.
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    C1. Macro-scale Evidence of Pore-scale Processes: The Promise and Peril seen in 40 years of Studying Fingered Flow
    Selker, John (Internet-First University Press, 2012-05)
    Fingered flow in coarse textured media has long been studied as an exemplar system for exhibiting the interplay between gravity and capillarity at easily observable scales. Early work by Parlange and Hill explained the system using linear stability analysis of solutions to the Richard’s equation, and were able to explain the relationship between finger width and media texture. These results were largely confirmed by the doctoral work of Glass, under the supervision of Parlange and Steenhuis. However thereafter several tests of the fundamental behavioral dependencies have been seen as being inconsistent with the theory, and have remained actively examined. Recent strategies to explain fingered flow behavior have seemingly given up on mechanistic physics and invoked new sources of hydrodynamic potential based on curvature of the wetting front. Others attribute the results to an expression of time-dependency in the soil characteristic curve. This talk presents highlights of this history illustrating the outstanding issues in this field, as well as pointing out the remarkable insights and conundrums that this easily-seen behavior has evoked over the 40 years since being reported in the literature.