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
Preferential flow occurs in unsaturated conditions
Effects of native forest restoration on soil hydraulic properties, Auwahi, Maui, Hawaiian Islands
Linking soil moisture balance and source-responsive models to estimate diffuse and preferential components of groundwater recharge
Assessing controls on perched saturated zones beneath the Idaho Nuclear Technology and Engineering Center, Idaho
Field tracer investigation of unsaturated zone flow paths and mechanisms in agricultural soils of northwestern Mississippi, USA
Hydraulic Property and Soil Textural Classification Measurements for Rainier Mesa, Nevada Test Site, Nevada
Measurement of field-saturated hydraulic conductivity on fractured rock outcrops near Altamura (Southern Italy) with an adjustable large ring infiltrometer
Response to Germann's "Comment on 'theory for source-responsive and free-surface film modeling of unsaturated flow'"
Theory for source-responsive and free-surface film modeling of unsaturated flow
Vadose water
Estimation of Unsaturated Zone Traveltimes for Rainier Mesa and Shoshone Mountain, Nevada Test Site, Nevada, Using a Source-Responsive Preferential-Flow Model
Rapid measurement of field-saturated hydraulic conductivity for areal characterization
Science and Products
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Preferential flow occurs in unsaturated conditions
Because it commonly generates high-speed, high-volume flow with minimal exposure to solid earth materials, preferential flow in the unsaturated zone is a dominant influence in many problems of infiltration, recharge, contaminant transport, and ecohydrology. By definition, preferential flow occurs in a portion of a medium – that is, a preferred part, whether a pathway, pore, or macroscopic subvolumAuthorsJohn R. NimmoEffects of native forest restoration on soil hydraulic properties, Auwahi, Maui, Hawaiian Islands
Over historic time Hawai'i's dryland forests have been largely replaced by grasslands for grazing livestock. On-going efforts have been undertaken to restore dryland forests to bring back native species and reduce erosion. The reestablishment of native ecosystems on land severely degraded by long-term alternative use requires reversal of the impacts of erosion, organic-matter loss, and soil structAuthorsKimberlie S. Perkins, John R. Nimmo, Arthur C. MedeirosLinking soil moisture balance and source-responsive models to estimate diffuse and preferential components of groundwater recharge
Results are presented of a detailed study into the vadose zone and shallow water table hydrodynamics of a field site in Shropshire, UK. A conceptual model is developed and tested using a range of numerical models, including a modified soil moisture balance model (SMBM) for estimating groundwater recharge in the presence of both diffuse and preferential flow components. Tensiometry reveals that theAuthorsM.O. Cuthbert, R. Mackay, J. R. NimmoAssessing controls on perched saturated zones beneath the Idaho Nuclear Technology and Engineering Center, Idaho
Waste byproducts associated with operations at the Idaho Nuclear Technology and Engineering Center (INTEC) have the potential to contaminate the eastern Snake River Plain (ESRP) aquifer. Recharge to the ESRP aquifer is controlled largely by the alternating stratigraphy of fractured volcanic rocks and sedimentary interbeds within the overlying vadose zone and by the availability of water at the surAuthorsBenjamin B. Mirus, Kim S. Perkins, John R. NimmoField tracer investigation of unsaturated zone flow paths and mechanisms in agricultural soils of northwestern Mississippi, USA
In many farmed areas, intensive application of agricultural chemicals and withdrawal of groundwater for irrigation have led to water quality and supply issues. Unsaturated-zone processes, including preferential flow, play a major role in these effects but are not well understood. In the Bogue Phalia basin, an intensely agricultural area in the Delta region of northwestern Mississippi, the fine-texAuthorsK. S. Perkins, J. R. Nimmo, C.E. Rose, R.H. CoupeHydraulic Property and Soil Textural Classification Measurements for Rainier Mesa, Nevada Test Site, Nevada
This report presents particle size analysis, field-saturated hydraulic conductivity measurements, and qualitative descriptions of surficial materials at selected locations at Rainier Mesa, Nevada. Measurements and sample collection were conducted in the Rainier Mesa area, including unconsolidated sediments on top of the mesa, an ephemeral wash channel near the mesa edge, and dry U12n tunnel pond sAuthorsBrian A. Ebel, John R. NimmoMeasurement of field-saturated hydraulic conductivity on fractured rock outcrops near Altamura (Southern Italy) with an adjustable large ring infiltrometer
Up to now, field studies set up to measure field-saturated hydraulic conductivity to evaluate contamination risks, have employed small cylinders that may not be representative of the scale of measurements in heterogeneous media. In this study, a large adjustable ring infiltrometer was designed to be installed on-site directly on rock to measure its field-saturated hydraulic conductivity. The propoAuthorsMaria C. Caputo, L. de Carlo, C. Masciopinto, J. R. NimmoResponse to Germann's "Comment on 'theory for source-responsive and free-surface film modeling of unsaturated flow'"
Germann's (2010) comment helpfully presents supporting evidence that I have missed, notes items that need clarification or correction, and stimulates discussion of what is needed for improved theory of unsaturated flow. Several points from this comment relate not only to specific features of the content of my paper (Nimmo, 2010), but also to the broader question of what methodology is appropriateAuthorsJ. R. NimmoTheory for source-responsive and free-surface film modeling of unsaturated flow
A new model explicitly incorporates the possibility of rapid response, across significant distance, to substantial water input. It is useful for unsaturated flow processes that are not inherently diffusive, or that do not progress through a series of equilibrium states. The term source-responsive is used to mean that flow responds sensitively to changing conditions at the source of water input (e.AuthorsJ. R. NimmoVadose water
Vadose water is subsurface water between the land surface and the saturated zone below the water table. The vadose (or unsaturated) zone includes soil water, which is immediately available to the biosphere. It acts as a controlling agent in the transmission of water and other substances between various components of the earth system: aquifers, land surface, bodies of water, atmosphere, and so on.AuthorsJohn R. NimmoEstimation of Unsaturated Zone Traveltimes for Rainier Mesa and Shoshone Mountain, Nevada Test Site, Nevada, Using a Source-Responsive Preferential-Flow Model
Traveltimes for contaminant transport by water from a point in the unsaturated zone to the saturated zone are a concern at Rainier Mesa and Shoshone Mountain in the Nevada Test Site, Nevada. Where nuclear tests were conducted in the unsaturated zone, contaminants must traverse hundreds of meters of variably saturated rock before they enter the saturated zone in the carbonate rock, where the regionAuthorsBrian A. Ebel, John R. NimmoRapid measurement of field-saturated hydraulic conductivity for areal characterization
To provide an improved methodology for characterizing the field‐saturated hydraulic conductivity (Kfs) over broad areas with extreme spatial variability and ordinary limitations of time and resources, we developed and tested a simplified apparatus and procedure, correcting mathematically for the major deficiencies of the simplified implementation. The methodology includes use of a portable, fallinAuthorsJ. R. Nimmo, K. M. Schmidt, K. S. Perkins, J. D. Stock