John R. Nimmo, Ph. D.
John R. Nimmo is a Research Physicist Emeritus for the USGS Water Resources Mission Area.
John R. Nimmo, Research Physicist Emeritus, is working toward establishment of a sound twenty-first century framework of water flow processes in soil and rock. His specialty is the unsaturated zone, between land surface and the water table. He collaborates with other USGS scientists to advance hydrologic science through observation and experiment, mathematical modeling, and development of theory.
Research overview
Problems of water availability and water quality require measurement, prediction, and understanding of the unsaturated-zone dynamics of water and substances it carries—applications include aquifer recharge estimation, ecosystem preservation and restoration, contaminant transport, and hydrologic impacts of land-use and climate change. Through collaboration with the geographically-based Water Science Centers, other units of the Water Mission Area, and the larger scientific community, great progress is possible through in-depth investigations, theory and method development, and field experiments.
Current and recent emphases include:
(1) Preferential flow through unsaturated soil and rock.
(2) Aquifer recharge estimation, including episodic as well as continuous components.
(3) Expert-guided automated techniques of hydrograph analysis for exchanges of water between aquifers and the land surface, the unsaturated zone, and streams and lakes.
(4) Effects of climate change, especially storm characteristics and precipitation, on water resources.
(5) Vulnerability of aquifers to contamination through unsaturated-zone transmission.
(6) Advancement of measurement techniques for unsaturated hydraulic properties, especially simple, low-technology methods for rapid characterization of areally-diverse field sites.
Career Overview
I earned a Ph.D. in physics in 1983 at the University of Wisconsin, with a specialty in porous media physics and minor in soil science. I then began full-time work in the USGS. My early career focused mainly on lab experiments and measurement techniques related to soil hydraulic properties, with the main application being aquifer-recharge estimation. Since the 1990s I have broadened my research efforts: (1) topically, to permit a more complete treatment of the inherently multidisciplinary concerns of earth science, (2) methodologically, to select from a large toolbox of lab, field, theoretical, and modeling techniques to best approach a given problem, and (3) geographically, to broaden the applicability of my work to a wide range of climate, geology, soils, hydrology, vegetation, and land use. Besides research, I contribute much effort to teaching, consultation, review of research papers and programs, and leadership of scientific groups within and outside the USGS.
Science and Products
Laboratory and field hydrologic characterization of the shallow subsurface at an Idaho National Engineering and Environmental Laboratory waste-disposal site
Hydrologic and meteorological data for an unsaturated-zone study area near the Radioactive Waste Management Complex, Idaho National Engineering and Environmental Laboratory, Idaho, 1990-96
Modeling structural influences on soil water retention
Modeling of soil water retention from saturation to oven dryness
The feasibility of recharge rate determinations using the steady-state centrifuge method
Improved apparatus for measuring hydraulic conductivity at low water content
Semiempirical model of soil water hysteresis
Centrifugal techniques for measuring saturated hydraulic conductivity
Comment on the treatment of residual water content in “A consistent set of parametric models for the two-phase flow of immiscible fluids in the subsurface” by L. Luckner et al.
Hydraulic conductivity of a sandy soil at low water content after compaction by various methods
Unsaturated flow in a centrifugal field: Measurement of hydraulic conductivity and testing of Darcy's Law
The temperature dependence of isothermal moisture vs. potential characteristics of soils.
Science and Products
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Filter Total Items: 84
Laboratory and field hydrologic characterization of the shallow subsurface at an Idaho National Engineering and Environmental Laboratory waste-disposal site
No abstract available.AuthorsJ. R. Nimmo, S. M. Shakofsky, J. F. Kaminsky, G. S. LordsHydrologic and meteorological data for an unsaturated-zone study area near the Radioactive Waste Management Complex, Idaho National Engineering and Environmental Laboratory, Idaho, 1990-96
No abstract available.AuthorsK. S. Perkins, J. R. Nimmo, J. R. PittmanModeling structural influences on soil water retention
A new model quantities the effect of soil structure, considered as the arrangement of particles in the soil, on soil water retention. The model partitions the pore space into texture-related and structure-related components, the textural component being what can be deduced to exist if the arrangement of the particles were random, and the structural component being the remainder. An existing model,AuthorsJ. R. NimmoModeling of soil water retention from saturation to oven dryness
Most analytical formulas used to model moisture retention in unsaturated porous media have been developed for the wet range and are unsuitable for applications in which low water contents are important. We have developed two models that fit the entire range from saturation to oven dryness in a practical and physically realistic way with smooth, continuous functions that have few parameters. Both mAuthorsCinzia Rossi, John R. NimmoThe feasibility of recharge rate determinations using the steady-state centrifuge method
The establishment of steady unsaturated flow in a centrifuge permits accurate measurement of small values of hydraulic conductivity (K). This method can provide a recharge determination if it is applied to an unsaturated core sample from a depth at which gravity alone drives the flow. A K value determined at the in situ water content indicates the long-term average recharge rate at a point. TestsAuthorsJ. R. Nimmo, David A. Stonestrom, K.C. AkstinImproved apparatus for measuring hydraulic conductivity at low water content
A modification of the steady-state centrifuge method (SSCM) for unsaturated hydraulic conductivity (K) measurement improves the range and adjustability of this method. The modified apparatus allows mechanical adjustments to vary the measured K by a factor of 360. In addition, the use of different flow-regulating ceramic materials can give a total K range covering about six orders of magnitude. TheAuthorsJ. R. Nimmo, K.C. Akstin, K.A. MelloSemiempirical model of soil water hysteresis
In order to represent hysteretic soil water retention curves accurately using as few measurements as possible, a new semiempirical model has been developed. It has two postulates related to physical characteristics of the medium, and two parameters, each with a definite physical interpretation, whose values are determined empirically for a given porous medium. One parameter represents the fractionAuthorsJ. R. NimmoCentrifugal techniques for measuring saturated hydraulic conductivity
Centrifugal force is an alternative to large pressure gradients for the measurement of low values of saturated hydraulic conductivity (Ksat). With a head of water above a porous medium in a centrifuge bucket, both constant-head and falling-head measurements are practical at forces up to at least 1800 times normal gravity. Darcy's law applied to the known centrifugal potential leads to simple formuAuthorsJohn R. Nimmo, Karen A. MelloComment on the treatment of residual water content in “A consistent set of parametric models for the two-phase flow of immiscible fluids in the subsurface” by L. Luckner et al.
Luckner et al. [1989] (hereinafter LVN) present a clear summary and generalization of popular formulations used for convenient representation of porous media fluid flow characteristics, including water content (θ) related to suction (h) and hydraulic conductivity (K) related to θ or h. One essential but problematic element in the LVN models is the concept of residual water content (θr; in LVN, θw,AuthorsJohn R. NimmoHydraulic conductivity of a sandy soil at low water content after compaction by various methods
To investigate the degree to which compaction of a sandy soil influences its unsaturated hydraulic conductivity K, samples of Oakley sand (now in the Delhi series; mixed, thermic, Typic Xeropsamments) were packed to various densities and K was measured by the steady-state centrifuge method. The air-dry, machine packing was followed by centrifugal compression with the soil wet to about one-third saAuthorsJohn R. Nimmo, Katherine C. AkstinUnsaturated flow in a centrifugal field: Measurement of hydraulic conductivity and testing of Darcy's Law
A method has been developed to establish steady state flow of water in an unsaturated soil sample spinning in a centrifuge. Theoretical analysis predicts moisture conditions in the sample that depend strongly on soil type and certain operating parameters. For Oakley sand, measurements of flux, water content, and matric potential during and after centrifugation verify that steady state flow can beAuthorsJohn R. Nimmo, J. Rubin, D.P. HammermeisterThe temperature dependence of isothermal moisture vs. potential characteristics of soils.
A method has been developed for rapid, transient measurement of hysteretic soil-moisture characteristics as a function of temperature. -from AuthorsAuthorsJ. R. Nimmo, E.E. Miller