Paul A Ferre
- Professor, Hydrology / Atmospheric Sciences
- Distinguished Professor, Hydrology / Atmospheric Sciences
- Professor, Environmental Science
Ty Ferre attended South Lakes High School in Reston, VA. He attended the Colorado School of Mines, earning a degree in Geophysical Engineering in 1988. He completed a PhD in Earth Sciences at the University of Waterloo in Ontario, Canada, in 1998. After a short post doctoral position at the University of Victoria, British Columbia, Canada, he began at the University of Arizona in 1999. He is married with two children, ages 13 and 15.
- Ph.D. Earth Sciences
- University of Waterloo, Waterloo, Ontario, Canada
- Design and analysis of time domain reflectometry probes for measuring water content and electrical conductivity under steady and transient flow conditions
- B.S. Geophysical Engineering
- Colorado School of Mines, Golden, Colorado, United States
- University of Arizona, Tucson, Arizona (1999 - Ongoing)
- University of Victoria (1998 - 1999)
- University of Waterloo (1997 - 1998)
- Darcy Lecturer
- National Groundwater Association, Fall 2016
- Research Fellow
- Verschulen Centre, Cape Breton University, Fall 2013
Dr. Ferre is interested in promoting 'learning by doing'. He teaches a broad range of classes, from fundamentals, to numerical modeling, to field methods, to decision making. His courses are largely Socratic in approach, helping students to learn through questioning. Recently, he has adopted the idea of the flipped classroom, actively developing video-based learning modules to complement in class discussions.
Dr. Ferre works in the areas of hydrogeophysics and vadose zone hydrology. In addition to these technical aspects of subsurface hydrology, he is interested in how data and models can be merged more effectively. How can data inform multiple competing models that can, in turn, guide decision making? Similarly, how can ensembles of models guide effective data collection?
DissertationHWRS 920 (Fall 2020)
Earth: Our Watery HomeHWRS 170A1 (Fall 2020)
Risk Asmnt for Enviroment SysHWRS 443A (Fall 2020)
Risk Asmnt for Environment SysHWRS 543A (Fall 2020)
ThesisHWRS 910 (Fall 2020)
DissertationHWRS 920 (Spring 2020)
Field Hydrology MethodsHWRS 413A (Spring 2020)
Field Hydrology MethodsHWRS 513A (Spring 2020)
Master's ReportHWRS 909 (Spring 2020)
ThesisHWRS 910 (Spring 2020)
DissertationHWRS 920 (Fall 2019)
Fund Of Subsurface HydrHWRS 518 (Fall 2019)
Master's ReportHWRS 909 (Fall 2019)
ThesisHWRS 910 (Fall 2019)
Field Hydrology SynthesisHWRS 413B (Summer I 2019)
Field Hydrology SynthesisHWRS 513B (Summer I 2019)
ThesisHWRS 910 (Summer I 2019)
Appl Groundwater ModelHWRS 482 (Spring 2019)
Appl Groundwater ModelHWRS 582 (Spring 2019)
DissertationHWRS 920 (Spring 2019)
Field Hydrology MethodsHWRS 413A (Spring 2019)
Field Hydrology MethodsHWRS 513A (Spring 2019)
Independent StudyHWRS 599 (Spring 2019)
Master's ReportHWRS 909 (Spring 2019)
ThesisHWRS 910 (Spring 2019)
DissertationHWRS 920 (Fall 2018)
Independent StudyHWRS 599 (Fall 2018)
Risk Asmnt for Enviroment SysHWRS 443A (Fall 2018)
Risk Asmnt for Environment SysHWRS 543A (Fall 2018)
Vadose Zone HydrologyHWRS 405 (Fall 2018)
Vadose Zone HydrologyHWRS 505 (Fall 2018)
ThesisHWRS 910 (Summer I 2018)
Appl Groundwater ModelHWRS 482 (Spring 2018)
Appl Groundwater ModelHWRS 582 (Spring 2018)
DissertationHWRS 920 (Spring 2018)
Field HydrologyHWRS 413A (Spring 2018)
Field HydrologyHWRS 513A (Spring 2018)
Independent StudyHWRS 599 (Spring 2018)
Independent StudyHWRS 699 (Spring 2018)
Master's ReportHWRS 909 (Spring 2018)
ThesisHWRS 910 (Spring 2018)
DissertationHWRS 920 (Fall 2017)
Earth: Our Watery HomeHWRS 170A1 (Fall 2017)
Fund Of Subsurface HydrHWRS 518 (Fall 2017)
Independent StudyHWRS 599 (Fall 2017)
ThesisHWRS 910 (Fall 2017)
Vadose Zone HydrologyHWRS 405 (Fall 2017)
Vadose Zone HydrologyHWRS 505 (Fall 2017)
ThesisHWRS 910 (Summer I 2017)
DissertationHWRS 920 (Spring 2017)
Field HydrologyHWRS 413A (Spring 2017)
Field HydrologyHWRS 513A (Spring 2017)
Independent StudyHWRS 599 (Spring 2017)
Independent StudyHWRS 699 (Spring 2017)
ThesisHWRS 910 (Spring 2017)
DissertationHWRS 920 (Fall 2016)
Independent StudyHWRS 599 (Fall 2016)
ThesisHWRS 910 (Fall 2016)
ThesisENVS 910 (Summer I 2016)
DissertationHWRS 920 (Spring 2016)
Field HydrologyHWRS 413A (Spring 2016)
Field HydrologyHWRS 513A (Spring 2016)
ThesisENVS 910 (Spring 2016)
ThesisHWRS 910 (Spring 2016)
- Troch, P. A., Zeng, X., Van Haren, J. L., Tuller, M., Sibayan, M., Schaap, M. G., Saleska, S. R., Ruiz, J., Rasmussen, C., Pohlmann, M. A., Pelletier, J. D., Monson, R. K., Maier, R. M., Kim, M., Huxman, T. E., Ferre, P. A., Durcik, M., DeLong, S. B., Cueva, A., , Chorover, J. D., et al. (2017). Controlled Experiments of Hillslope Coevolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological Changes. In Hydrology of Artificial and Controlled Experiments. Rijeka, Croatia: IN TECH d.o.o.
- Tuller, M., Sibayan, M., Schaap, M. G., Saleska, S. R., Ruiz, J., Rasmussen, C., Pohlmann, M. A., Pelletier, J. D., Monson, R. K., Maier, R. M., Kim, M., Huxman, T. E., Ferre, P. A., Durcik, M., DeLong, S. B., Cueva, A., Chorover, J. D., Bugaj, A., Breshears, D. D., , Adams, J. R., et al. (2018). Controlled Experiments of Hillslope Coevolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological Changes. In Hydrology of Artificial and Controlled Experiments(pp 25-74). Rijeka, Croatia: IntechOpen Limited.
- Dwivedi, R., Eastoe, C., Knowles, J. F., Wright, W. E., Hamann, L., Minor, R., Mitra, B., Meixner, T., McIntosh, J., Ferre, P., Castro, C., Niu, G., Barron-Gafford, G. A., Abramson, N., Papuga, S. A., Stanley, M., Hu, J., & Chorover, J. (2020). Vegetation source water identification using isotopic and hydrometric observations from a subhumid mountain catchment. ECOHYDROLOGY, 13(1).
- Clutter, M., Clutter, M., Ferre, P. A., Ferre, P. A., Zhang, F., Zhang, F., Gupta, H. V., & Gupta, H. V. (2019). Robust predictive design of field measurements for evapotranspiration barriers using universal multiple linear regression. Water Resources Research. doi:10.1029/2019WR026194More infoClutter M, PA Ferre, F Zhang and HV Gupta (2019), Robust predictive design of field measurements for evapotranspiration barriers using universal multiple linear regression, Water Resources Research, https://doi.org/10.1029/2019WR026194.
- Dwivedi, R., Meixner, T., McIntosh, J. C., Ferre, P., Eastoe, C. J., Niu, G., Minor, R. L., Barron-Gafford, G. A., & Chorover, J. (2019). Hydrologic functioning of the deep critical zone and contributions to streamflow in a high-elevation catchment: Testing of multiple conceptual models. HYDROLOGICAL PROCESSES, 33(4), 476-494.
- White, A., Moravec, B., McIntosh, J., Olshansky, Y., Paras, B., Sanchez, R. A., Ferre, T., Meixner, T., & Chorover, J. (2019). Distinct stores and the routing of water in the deep critical zone of a snow-dominated volcanic catchment. HYDROLOGY AND EARTH SYSTEM SCIENCES, 23(11), 4661-4683.
- Bode, F., Ferre, T. y., Zigelli, N., Emmert, M., & Nowak, W. (2018). Reconnecting Stochastic Methods With Hydrogeological Applications: A Utilitarian Uncertainty Analysis and Risk Assessment Approach for the Design of Optimal Monitoring Networks. WATER RESOURCES RESEARCH, 54(3), 2270-2287.
- Chen, W., Jin, M., Ferre, T., Liu, Y., Xian, Y., Shan, T., & Ping, X. (2018). Spatial distribution of soil moisture, soil salinity, and root density beneath a cotton field under mulched drip irrigation with brackish and fresh water (vol 215, pg 207, 2018). FIELD CROPS RESEARCH, 226, 83-83.
- Chen, W., Wang, Z., Jin, M., Ferre, T., Wang, J., Huang, J., & Wang, X. (2018). Effect of Sodium Chloride and Manganese in Irrigation Water on Cotton Growth. AGRONOMY JOURNAL, 110(3), 900-909.
- Clutter, M., & Ferre, T. (2018). Examining the Potentials and Limitations of Using Temperature Tracing to Infer Water Flux through Unsaturated Soils. VADOSE ZONE JOURNAL, 17(1).
- Corona, C. R., Gurdak, J. J., Dickinson, J. E., Ferre, T., & Maurer, E. P. (2018). Climate variability and vadose zone controls on damping of transient recharge. JOURNAL OF HYDROLOGY, 561, 1094-1104.
- Cousquer, Y., Pryet, A., Atteia, O., Ferre, T., Delbart, C., Valois, R., & Dupuy, A. (2018). Developing a particle tracking surrogate model to improve inversion of ground water Surface water models. JOURNAL OF HYDROLOGY, 558, 356-365.
- Dickinson, J. E., & Ferre, T. (2018). Filtering of Periodic Infiltration in a Layered Vadose Zone: 2. Applications and a Freeware Screening Tool. VADOSE ZONE JOURNAL, 17(1).
- Sickman, J. O., Williams, M. W., Ferre, P. A., Molotch, N., Meixner, T., & Driscoll, J. (2018). Event-response ellipses: a method to quantify and compare the role of dynamic storage at the catchment scale in snowmelt-dominated systems. Water, 10(12), 1824. doi:10.3390/w10121824
- Velasco, E. M., Gurdak, J. J., Dickinson, J. E., Ferre, P. A., & Corona, C. R. (2016). Interannual to multidecadal climate forcings on groundwater resources of the U.S. West Coast. Journal of Hydrology: Regional Studies. doi:10.1016/j.ejrh.2015.11.018
- Vilhelmsen, T. N., & Ferre, T. (2018). Extending Data Worth Analyses to Select Multiple Observations Targeting Multiple Forecasts. GROUNDWATER, 56(3), 399-412.
- Behroozmand, A. A., Knight, R., Mueller-Petke, M., Auken, E., Barfod, A., Ferre, T., Vilhelmsen, T. N., Johnson, C. D., & Christiansen, A. V. (2017). Successful Sampling Strategy Advances Laboratory Studies of NMR Logging in Unconsolidated Aquifers. GEOPHYSICAL RESEARCH LETTERS, 44(21), 11021-11029.
- Chen, W., Jin, M., Xian, Y., & Ferre, T. (2017). Combined Effect of Sodium Chloride and Boron in Irrigation Water on Cotton Growth. AGRONOMY JOURNAL, 109(4), 1388-1396.
- Christensen, N. K., Ferre, T., Fiandaca, G., & Christensen, S. (2017). Voxel inversion of airborne electromagnetic data for improved groundwater model construction and prediction accuracy. HYDROLOGY AND EARTH SYSTEM SCIENCES, 21(2), 1321-1337.
- Corona, C. R., Gurdak, J., Dickinson, J. E., Ferre, P. A., & Maurer, E. P. (2017). Climate Variability and Vadose Zone Controls on Damping of Transient Recharge. Journal of Hydrology. doi:10.1016/j.jhydrol.2017.08.028
- Ferre, P. A. (2016). Improving the impact of soil science by reconsidering the interactions of data, models, and decisions — An ongoing discussion during the 2016 Darcy lecture tour. Journal of Japanese Soil Science, 51-59.
- Ferre, P. A. (2017). Extending data worth analyses to select multiple observations targeting multiple forecasts. Groundwater. doi:10.111/gwat.12595
- Ferre, P. A. (2017). Modelers: Is Objectivity Overrated?. GROUNDWATER, 55(5), 603-603.
- Ferre, P. A. (2017). Revisiting the Relationship Between Data, Models, and Decision-Making. GROUNDWATER, 55(5), 604-614.
- Joodavi, A., Zare, M., Ziaei, A. N., & Ferre, T. (2017). Groundwater management under uncertainty using a stochastic multi-cell model. JOURNAL OF HYDROLOGY, 551, 265-277.
- Kikuchi, C. P., & Ferre, T. (2017). Analysis of subsurface temperature data to quantify groundwater recharge rates in a closed Altiplano basin, northern Chile. HYDROGEOLOGY JOURNAL, 25(1), 103-121.
- Chellasamy, M., Ferre, T., & Greve, M. H. (2016). Evaluating an ensemble classification approach for crop diversity verification in Danish greening subsidy control. INTERNATIONAL JOURNAL OF APPLIED EARTH OBSERVATION AND GEOINFORMATION, 49, 10-23.
- Christensen, N. K., Christensen, S., & Ferre, T. (2016). Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models. HYDROLOGY AND EARTH SYSTEM SCIENCES, 20(5), 1925-1946.
- Kennedy, J. R., & Ferre, T. P. (2016). Accounting for time- and space-varying changes in the gravity field to improve the network adjustment of relative-gravity data. GEOPHYSICAL JOURNAL INTERNATIONAL, 204(2), 892-906.
- Kennedy, J., Ferre, T., & Creutzfeldt, B. (2016). Time-lapse gravity data for monitoring and modeling artificial recharge through a thick unsaturated zone. WATER RESOURCES RESEARCH, 52(9), 7244-7261.
- Naveed, M., Herath, L., Moldrup, P., Arthur, E., Nicolaisen, M., Norgaard, T., Ferre, P. A., & de Jonge, L. W. (2016). Spatial Variability of Microbial Communities and Relationships with Soil Organic Carbon, Texture and Structure across an Agricultural Field. Applied Soil Ecology, 103, 44-55.
- Naveed, M., Herath, L., Moldrup, P., Arthur, E., Nicolaisen, M., Norgaard, T., Ferre, T., & de, J. (2016). Spatial variability of microbial richness and diversity and relationships with soil organic carbon, texture and structure across an agricultural field. APPLIED SOIL ECOLOGY, 103, 44-55.
- Chellasamy, M., Ferre, T. P., & Greve, M. H. (2015). An Ensemble-Based Training Data Refinement for Automatic Crop Discrimination Using WorldView-2 Imagery. IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING, 8(10), 4882-4894.
- Groenendyk, D. G., Ferre, T. P., Thorp, K. R., & Rice, A. K. (2015). Hydrologic-Process-Based Soil Texture Classifications for Improved Visualization of Landscape Function. PLOS ONE, 10(6).
- Kikuchi, C. P., Ferre, T. P., & Vrugt, J. A. (2015). On the optimal design of experiments for conceptual and predictive discrimination of hydrologic system models. WATER RESOURCES RESEARCH, 51(6), 4454-4481.
- Pangle, L. A., DeLong, S. B., Abramson, N., Adams, J., Barron-Gafford, G. A., Breshears, D. D., Brooks, P. D., Chorover, J., Dietrich, W. E., Dontsova, K., Durcik, M., Espeleta, J., Ferre, T., Ferriere, R., Henderson, W., Hunt, E. A., Huxman, T. E., Millar, D., Murphy, B., , Niu, G., et al. (2015). The Landscape Evolution Observatory: A large-scale controllable infrastructure to study coupled Earth-surface processes. GEOMORPHOLOGY, 244, 190-203.
- Pangle, L. A., Delong, S. B., Abramson, N., Adams, J., Barron-Gafford, G. A., Breshears, D. D., Brooks, P. D., Chorover, J. D., Dietrich, W. E., Dontsova, K. M., Durcik, M., Espleta, J., Ferre, P. A., Ferriere, R. H., Henderson, W., Hunt, E. A., Huxman, T. E., Millar, D., Murphy, B., , Niu, G., et al. (2015). The Landscape Evolution Observatory: A large-scale controllable infrastructure to study Earth-surface processes.. Geomorphology, 244, 190-203.
- Pangle, L. A., Pangle, L. A., Delong, S. B., Delong, S. B., Abramson, N., Abramson, N., Adams, J., Adams, J., Barron-Gafford, G. A., Barron-Gafford, G. A., Breshears, D. D., Breshears, D. D., Brooks, P. D., Brooks, P. D., Chorover, J. D., Chorover, J. D., Dietrich, W. E., Dietrich, W. E., Dontsova, K. M., , Dontsova, K. M., et al. (2015). The Landscape Evolution Observatory: A large-scale controllable infrastructure to study Earth-surface processes.. Geomorphology, 244, 190-203.
- Pangle, L., DeLong, S., Abramson, N., Adams, J., Barron-Gafford, G. A., Breshears, D. D., Brooks, P. D., Chorover, J. D., Dietrich, W. E., Dontsova, K. M., Durcik, M., Espeleta, J., Ferre, P. A., Ferriere, R. H., Henderson, W., Hunt, E., Huxman, T. E., Millar, D., Murphy, B., , Niu, Y., et al. (2015). The Landscape Evolution Observatory: A large-scale controllable infrastructure to study coupled Earth-surface processes. Geomorphology, 244, 190-203.
- Pangle, L., DeLong, S., Abramson, N., Adams, J., Barron-Gafford, G. A., Breshears, D. D., Brooks, P. D., Chorover, J. D., Dietrich, W. E., Dontsova, K. M., Durcik, M., Espeleta, J., Ferre, P. A., Ferriere, R. H., Henderson, W., Hunt, E., Huxman, T. E., Millar, D., Murphy, B., , Niu, Y., et al. (2015). The Landscape Evolution Observatory: A large-scale controllable infrastructure to study coupled Earth-surface processes. Geomorphology.
- Paradelo, M., Norgaard, T., Moldrup, P., Ferre, T. P., Kumari, K. G., Arthur, E., & de Jonge, L. W. (2015). Prediction of the glyphosate sorption coefficient across two loamy agricultural fields. GEODERMA, 259, 224-232.
- Chellasamy, M., Ferre, P. A., Greeve, M. H., Larsen, R., & Chinnasamy, U. (2014). Ensemble Classification Approach for Improved Land Use/Cover Change Detection. The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 695-702.
- Chellasamy, M., Ferre, T., Greeve, M. H., Larsen, R., & Chinnasamy, U. (2014). AN ENSEMBLE CLASSIFICATION APPROACH FOR IMPROVED LAND USE/COVER CHANGE DETECTION. ISPRS TECHNICAL COMMISSION VIII SYMPOSIUM, 40-8, 695-701.
- Creutzfeldt, B., Troch, P. A., Guentner, A., Ferre, T. P., Graeff, T., & Merz, B. (2014). Storage-discharge relationships at different catchment scales based on local high-precision gravimetry. HYDROLOGICAL PROCESSES, 28(3), 1465-1475.More infoIn hydrology, the storage-discharge relationship is a fundamental catchment property. Understanding what controls this relationship is at the core of catchment science. To date, there are no direct methods to measure water storage at catchment scales (10(1)-10(3)km(2)). In this study, we use direct measurements of terrestrial water storage dynamics by means of superconducting gravimetry in a small headwater catchment of the Regen River, Germany, to derive empirical storage-discharge relationships in nested catchments of increasing scale. Our results show that the local storage measurements are strongly related to streamflow dynamics at larger scales (> 100km(2); correlation coefficient=0.78-0.81), but at small scale, no such relationship exists (similar to 1km(2); correlation coefficients=-0.11). The geologic setting in the region can explain both the disconnection between local water storage and headwater runoff, and the connectivity between headwater storage and streams draining larger catchment areas. More research is required to understand what controls the form of the observed storage-discharge relationships at the catchment scale. This study demonstrates that high-precision gravimetry can provide new insights into the complex relationship between state and response of hydrological systems. Copyright (c) 2012 John Wiley & Sons, Ltd.
- Creutzfeldt, B., Troch, P. A., Güntner, A., P., T., Graeff, T., & Merz, B. (2014). Storage-discharge relationships at different catchment scales based on local high-precision gravimetry. Hydrological Processes, 28(3), 1465-1475.More infoAbstract: In hydrology, the storage-discharge relationship is a fundamental catchment property. Understanding what controls this relationship is at the core of catchment science. To date, there are no direct methods to measure water storage at catchment scales (101-103km2). In this study, we use direct measurements of terrestrial water storage dynamics by means of superconducting gravimetry in a small headwater catchment of the Regen River, Germany, to derive empirical storage-discharge relationships in nested catchments of increasing scale. Our results show that the local storage measurements are strongly related to streamflow dynamics at larger scales (> 100km2; correlation coefficient=0.78-0.81), but at small scale, no such relationship exists (~ 1km2; correlation coefficients=-0.11). The geologic setting in the region can explain both the disconnection between local water storage and headwater runoff, and the connectivity between headwater storage and streams draining larger catchment areas. More research is required to understand what controls the form of the observed storage-discharge relationships at the catchment scale. This study demonstrates that high-precision gravimetry can provide new insights into the complex relationship between state and response of hydrological systems. © 2012 John Wiley & Sons, Ltd.
- Dickinson, J. E., Ferre, T. P., Bakker, M., & Crompton, B. (2014). A Screening Tool for Delineating Subregions of Steady Recharge within Groundwater Models. VADOSE ZONE JOURNAL, 13(6).More infoWe have developed a screening method for simplifying groundwater models by delineating areas within the domain that can be represented using steady-state groundwater recharge. The screening method is based on an analytical solution for the damping of sinusoidal infiltration variations in homogeneous soils in the vadose zone. The damping depth is defined as the depth at which the flux variation damps to 5% of the variation at the land surface. Groundwater recharge may be considered steady where the damping depth is above the depth of the water table. The analytical solution approximates the vadose zone diffusivity as constant, and we evaluated when this approximation is reasonable. We evaluated the analytical solution through comparison of the damping depth computed by the analytic solution with the damping depth simulated by a numerical model that allows variable diffusivity. This comparison showed that the screening method conservatively identifies areas of steady recharge and is more accurate when water content and diffusivity are nearly constant. Nomograms of the damping factor (the ratio of the flux amplitude at any depth to the amplitude at the land surface) and the damping depth were constructed for clay and sand for periodic variations between 1 and 365 d and flux means and amplitudes from nearly 0 to 1 x 10(-3) m d(-1). We applied the screening tool to Central Valley, California, to identify areas of steady recharge. A MATLAB script was developed to compute the damping factor for any soil and any sinusoidal flux variation.
- Ferre, P. A., Goode, T. C., & Hinnell, A. C. (2014). Tunnel Discrimination Using Mobile Geophysical Arrays. Fast Times, 19(2), 45-52.
- Kennedy, J., Ferre, T. P., Guentner, A., Abe, M., & Creutzfeldt, B. (2014). Direct measurement of subsurface mass change using the variable baseline gravity gradient method. GEOPHYSICAL RESEARCH LETTERS, 41(8), 2827-2834.More infoTime-lapse gravity data provide a direct, nondestructive method to monitor mass changes at scales from centimeter to kilometer. But, the effectively infinite spatial sensitivity of gravity measurements can make it difficult to isolate the signal of interest. The variable baseline gravity gradient method, based on the difference of measurements between two gravimeters, is an alternative to the conventional approach of individually modeling all sources of mass and elevation changes. This approach can improve the signal-to-noise ratio for many applications by removing the contributions of Earth tides, loading, and other signals that have the same effect on both gravimeters. At the same time, this approach can focus the support volume within a relatively small user-defined region of the subsurface. The method is demonstrated using paired superconducting gravimeters to make for the first time a large-scale, noninvasive measurement of infiltration wetting front velocity and change in water content above the wetting front.
- Norgaard, T., Moldrup, P., Ferre, T. P., Katuwal, S., Olsen, P., & de Jonge, L. W. (2014). Field-scale Variation in Colloid Dispersibility and Transport: Multiple Linear Regressions to Soil Physico-Chemical and Structural Properties. JOURNAL OF ENVIRONMENTAL QUALITY, 43(5), 1764-1778.More infoWater-dispersible soil colloids (WDC) act as carriers for sorbing chemicals in macroporous soils and hence constitute a significant risk for the aquatic environment. The prediction of WDC readily available for facilitated chemical transport is an unsolved challenge. This study identifies key parameters and predictive indicators for assessing field-scale variation of WDC. Samples representing three measurement scales (1-to 2-mm aggregates, intact 100-cm(3) rings, and intact 6283 cm(3) columns) were retrieved from the topsoil of a 1.69-ha agricultural field in a 15-m by 15-m grid to determine colloid dispersibility, mobilization, and transport. The amount of WDC was determined using (i) a laser diffraction method on 1- to 2-mm aggregates and (ii) an end-over-end shaking method on 100-cm(3) intact rings. The accumulated amount of colloids leached from 20-cm by 20-cm intact columns was determined as a measure of the integrated colloid mobilization and transport. The WDC and the accumulated colloid transport were higher in samples from the northern part of the field. Using multiple linear regression (MLR) analyses, WDC or amount of colloids transported were predicted at the three measurement scales from 24 measured, geo-referenced parameters to identify parameters that could serve as indicator parameters for screening for colloid dispersibility, mobilization, and transport. The MLR analyses were performed at each sample scale using all, only northern, and only southern field locations. Generally, the predictive power of the regression models was best on the smallest 1-to 2-mm aggregate scale. Overall, our results suggest that different drivers controlled colloid dispersibility and transport at the three measurement scales and in the two subareas of the field.
- Norgaard, T., Moldrup, P., Ferre, T. P., Olsen, P., Rosenbom, A. E., & de Jonge, L. W. (2014). Leaching of Glyphosate and Aminomethylphosphonic Acid from an Agricultural Field over a Twelve-Year Period. VADOSE ZONE JOURNAL, 13(10).More infoThe globally used herbicide glyphosate [N-(phosphonomethyl)glycine] and its most frequently detected metabolite, aminomethylphosphonic acid (AMPA), were studied in a unique 12-yr field-scale monitoring program. The leaching of glyphosate, AMPA, and soil particles was studied in a shallow drainage system beneath a 1.26-ha field. Five annual glyphosate applications were applied with different autumn application dates. Solute mass flux from the drain system following the five glyphosate applications were compared to determine how different factors affect the leaching of glyphosate, AMPA, and particles. Glyphosate and AMPA leaching were highly event driven, controlled by the time and intensity of the first rainfall event after glyphosate application. A high similarity in cumulative drainage and leached pesticide masses with time suggests near-constant drainage and leaching rates. There was no clear relationship between particle-facilitated transport and the transport of glyphosate or AMPA. However, soil particles, glyphosate, and AMPA all showed distinct, simultaneous concentration curves, indicating common dominant transport mechanisms. Also, soil-water content at the time of application and the level of the groundwater table relative to the drain depth exerted clear controls on detection of solutes in the drainage water. To summarize our findings, we present a leaching risk chart to illustrate the dependence of glyphosate, AMPA, and soil particle leaching based on rainfall intensity and the timing of rainfall events after glyphosate application.
- Walsh, D. O., Grunewald, E. D., Turner, P., Hinnell, A., & Ferre, T. P. (2014). Surface NMR instrumentation and methods for detecting and characterizing water in the vadose zone. NEAR SURFACE GEOPHYSICS, 12(2), 271-284.More infoA commercially available surface NMR instrument was modified to address the challenges of using earth's field surface NMR to detect and characterize water in the unsaturated (or vadose) zone. The modified instrument incorporates faster switching electronics to achieve an instrument dead time of 2.8 ms, and higher output power electronics to enable a maximum coil voltage of 8000 volts and coil current of 800 amps. The instrument was used to collect and interpret surface NMR data at several active vadose zone investigation sites in the western US. A 6-week surface NMR experiment was conducted at a managed aquifer storage and recovery facility in Arizona, to explore the measurement capabilities and limitations of the instrument, during a managed infiltration event. The resulting time lapse surface NMR data were used to map zones of held water prior to the flood event, image the influx of water through the top 15 metres of the subsurface during and after the event, quantify the spatial and temporal distribution of infiltrating water throughout the event, and characterize the distribution of water in different relative pore sizes throughout the event. Data obtained at pseudo-static vadose zone investigation sites indicate that the surface NMR instrument can detect and image some forms of water held in unconsolidated vadose zone formations, at depths up to 30 metres. Complementary NMR logging data indicate that the surface NMR instrument does not detect all of the water held in these pseudo-static formations, but that the non-invasive surface NMR data may yield valuable information nonetheless.
- Bakker, M., Bartholomeus, R. P., & Ferre, T. (2013). "Groundwater recharge: processes and quantification" Preface. HYDROLOGY AND EARTH SYSTEM SCIENCES, 17(7), 2653-2655.
- Bakker, M., Bartholomeus, R. P., & Ferré, T. (2013). Preface Groundwater recharge: Processes and quantification. Hydrology and Earth System Sciences, 17(7), 2653-2655.
- Blasch, K., Ferré, T. P., Hoffmann, J., Pool, D., Bailey, M., & Cordova, J. (2013). Processes Controlling Recharge Beneath Ephemeral Streams in Southern Arizona. Groundwater Recharge in a Desert Environment: The Southwestern United States, 9, 69-76.
- Desilets, S. L., Nijssen, B., Ekwurzel, B., & Ferre, T. P. (2013). Post-wildfire changes in suspended sediment rating curves: Sabino Canyon, Arizona. HYDROLOGICAL PROCESSES, 21(11), 1413-1423.
- Franz, T. E., Zreda, M., Ferre, T. P., & Rosolem, R. (2013). An assessment of the effect of horizontal soil moisture heterogeneity on the area-average measurement of cosmic-ray neutrons. Water Resources Research, 49(10), 6450-6458.More infoAbstract: The cosmic-ray neutron probe measures soil moisture over tens of hectares, thus averaging spatially variable soil moisture fields. A previous paper described how variable soil moisture profiles affect the integrated cosmic-ray neutron signal from which depth-average soil moisture is computed. Here, we investigate the effect of horizontal heterogeneity on the relationship between neutron counts and average soil moisture. Observations from a distributed sensor network at a site in southern Arizona indicate that the horizontal component of the total variance of the soil moisture field is less variably in time than the vertical component. Using results from neutron particle transport simulations we show that 1-D binary distributions of soil moisture may affect both the mean and variance of neutron counts of a cosmic-ray neutron detector placed arbitrarily in a soil moisture field, potentially giving rise to an underestimate of the footprint average soil moisture. Similar simulations that used 1-D and 2-D Gaussian soil moisture fields indicate consistent mean and variances of a randomly placed detector if the correlation length scales are short (less than ∼30 m) and/or the soil moisture field variance is small (
- Franz, T. E., Zreda, M., Ferre, T., & Rosolem, R. (2013). An assessment of the effect of horizontal soil moisture heterogeneity on the area-average measurement of cosmic-ray neutrons. WATER RESOURCES RESEARCH, 49(10), 6450-6458.
- Lloyd, R. A., Lohse, K. A., & Ferre, T. (2013). Influence of road reclamation techniques on forest ecosystem recovery. FRONTIERS IN ECOLOGY AND THE ENVIRONMENT, 11(2), 75-81.
- Lloyd, R. A., Lohse, K. A., & Ferré, T. (2013). Influence of road reclamation techniques on forest ecosystem recovery. Frontiers in Ecology and the Environment, 11(2), 75-81.More infoAbstract: Road reclamation has emerged as an integral part of ecological restoration strategies, particularly on public lands. However, there are no consistent techniques for how road reclamation should be implemented to restore ecosystem structure and function. Resource managers are hindered by critical research gaps regarding the linkages between, as well as the effects of different restoration actions on, above- and belowground ecological and hydrological properties. In the western US, we examined how two road reclamation methods (recontouring and abandonment) affect ecosystem properties relative to "never-roaded" areas. Recontoured and abandoned sites displayed similar aboveground properties but exhibited notable differences in belowground properties, including soil hydraulic conductivity, organic matter, total carbon, and total nitrogen, among others. Our findings suggest that recontouring can dramatically accelerate recovery of above- and belowground properties so they resemble never-roaded reference conditions. In contrast, abandoning roads generates above- and belowground properties that follow a different path to recovery. © The Ecological Society of America.
- Arthur, E., Razzaghi, F., Moldrup, P., Tuller, M., Ferre, T., & de, J. (2012). Simple Predictive Models for Saturated Hydraulic Conductivity of Technosands. SOIL SCIENCE, 177(3), 153-157.
- Arthur, E., Razzaghi, F., Moldrup, P., Tuller, M., P., T., & Wollesen, L. (2012). Simple predictive models for saturated hydraulic conductivity of technosands. Soil Science, 177(3), 153-157.More infoAbstract: Accurate estimation of saturated hydraulic conductivity (K s) of technosands (gravel-free, coarse sands with negligible organic matter content) is important for irrigation and drainage management of athletic fields and golf courses. In this study, we developed two simple models for predicting Ks of technosands based on either (i) the classic Kozeny-Carman (K-C) model modified by considering the content of finer particles (fines) less than 200 μm to estimate an immobile water fraction or (ii) the Revil-Cathles (R-C) model modified by using the characteristic particle diameter from the Rosin-Rammler particle size distribution (PSD) function. The Ks and PSD data of 14 golf course sands from literature as well as newly measured data for a size fraction of Lunar Regolith Simulant, packed at three different dry bulk densities, were used for model evaluation. The pore network tortuosity-connectivity parameter (m) obtained for pure coarse sand after fitting to measured Ks data was 1.68 for both models and in good agreement with m values obtained from recent solute and gas diffusion studies. Both the modified K-C and R-C models are easy to use and require limited parameter input, and both models gave comparable accuracy as more complex Ks models. The models are therefore recommended for preliminary assessment and design of technosand layers, for example, with regard to selecting sand PSD for optimal hydrological performance at athletic fields or golf courses. Copyright © 2012 by Lippincott Williams & Wilkins.
- Blasch, K. W., Ferre, T. P., Hoffmann, J. P., & Fleming, J. B. (2012). Relative contributions of transient and steady state infiltration during ephemeral streamflow. WATER RESOURCES RESEARCH, 42(8).
- Callegary, J. B., P., T., & Groom, R. W. (2012). Three-dimensional sensitivity distribution and sample volume of low-induction-number electromagnetic-induction instruments. Soil Science Society of America Journal, 76(1), 85-91.More infoAbstract: There is an ongoing effort to improve the understanding of the correlation of soil properties with apparent soil electrical conductivity as measured by low-induction-number electromagnetic-induction (LIN FEM) instruments. At a minimum, the dimensions of LIN FEM instruments' sample volume, the spatial distribution of sensitivity within that volume, and implications for surveying and analyses must be clearly defined and discussed. Therefore, a series of numerical simulations was done in which a conductive perturbation was moved systematically through homogeneous soil to elucidate the three-dimensional sample volume of LIN FEM instruments. For a small perturbation with electrical conductivity similar to that of the soil, instrument response is a measure of local sensitivity (LS). Our results indicate that LS depends strongly on the orientation of the instrument's transmitter and receiver coils and includes regions of both positive and negative LS. Integration of the absolute value of LS from highest to lowest was used to contour cumulative sensitivity (CS). The 90% CS contour was used to define the sample volume. For both horizontal and vertical coplanar coil orientations, the longest dimension of the sample volume was at the surface along the main instrument axis with a length of about four times the intercoil spacing (s) with maximum thicknesses of about 1 and 0.3 s, respectively. The imaged distribution of spatial sensitivity within the sample volume is highly complex and should be considered in conjunction with the expected scale of heterogeneity before the use and interpretation of LIN FEM for mapping and profiling. © Soil Science Society of America.
- Creutzfeldt, B., Ferré, T., Troch, P., Merz, B., Wziontek, H., & Güntner, A. (2012). Total water storage dynamics in response to climate variability and extremes: Inference from long-term terrestrial gravity measurement. Journal of Geophysical Research D: Atmospheres, 117(8).More infoAbstract: Terrestrial water storage is a basic element of the hydrological cycle and a key state variable for land surface-atmosphere interaction. However, measuring water storage in a comprehensive way for different storage compartments and beyond the point scale is a challenge. In this study, we explore a 10-year time series of total water storage changes derived from high-precision superconducting gravimeter observations in a headwater catchment in Southern Germany. In combination with hydro-meteorological data, we examine the relationship between gravity-derived water storage changes, climate, and river discharge. Distinct seasonal water storage dynamics observed by the gravimeter are strongly related to the meteorological forcing, in particular evapotranspiration. Intra-annual water storage variations demonstrate that the simplifying assumption of water storage averaging to zero at the annual scale is not valid for this catchment. At the event-scale, gravimeters provide a measure of the available subsurface water storage capacity, which can be useful for runoff prediction. During the Central European drought in 2003, the gravimeter data show a strong depletion of water storage and a long-term recovery that extended over a period of several years. In comparison to point measurements or different environmental indices, our findings suggest that depth-integrated gravimeter measurements give a more complete picture of the dynamics of a hydrologic system in response to climate variability and extremes. In view of the considerable costs of gravimeters concerning the infrastructure and measurements, we suggest the strategic deployment of gravimeters at selected sites of hydro-meteorological monitoring networks. Copyright 2012 by the American Geophysical Union.
- Franz, T. E., Zreda, M., Ferre, T. P., Rosolem, R., Zweck, C., Stillman, S., Zeng, X., & Shuttleworth, W. J. (2012). Measurement depth of the cosmic ray soil moisture probe affected by hydrogen from various sources. Water Resources Research, 48(8).More infoAbstract: We present here a simple and robust framework for quantifying the effective sensor depth of cosmic ray soil moisture neutron probes such that reliable water fluxes may be computed from a time series of cosmic ray soil moisture. In particular, we describe how the neutron signal depends on three near-surface hydrogen sources: surface water, soil moisture, and lattice water (water in minerals present in soil solids) and also their vertical variations. Through a combined modeling study of one-dimensional water flow in soil and neutron transport in the atmosphere and subsurface, we compare average water content between the simulated soil moisture profiles and the universal calibration equation which is used to estimate water content from neutron counts. By using a linear sensitivity weighting function, we find that during evaporation and drainage periods the RMSE of the two average water contents is 0.0070m 3 m-3 with a maximum deviation of 0.010m3 m-3 for a range of soil types. During infiltration, the RMSE is 0.011m3 m-3 with a maximum deviation of 0.020m3 m-3, where piston like flow conditions exists for the homogeneous isotropic media. Because piston flow is unlikely during natural conditions at the horizontal scale of hundreds of meters that is measured by the cosmic ray probe, this modeled deviation of 0.020m3 m-3 represents the worst case scenario for cosmic ray sensing of soil moisture. Comparison of cosmic ray soil moisture data and a distributed sensor soil moisture network in Southern Arizona indicates an RMSE of 0.011m3 m-3 over a 6month study period. © 2012. American Geophysical Union. All Rights Reserved.
- Franz, T. E., Zreda, M., Rosolem, R., & Ferre, T. P. (2012). Field validation of a cosmic-ray neutron sensor using a distributed sensor network. Vadose Zone Journal, 11(4).More infoAbstract: With continued refinement in land surface model resolution the need for accurate and continuous soil moisture datasets at intermediate spatial scales has become critical for improved meteorological and hydrological prediction. The current availability of such data is inadequate. Here, we present a comparison of two datasets that provide average soil moisture over an area hundreds of meters squared in a dryland ecosystem in southern Arizona. One dataset is from a high-resolution soil moisture network of 180 time-domain transmission probes; the other is from a cosmic-ray neutron sensor placed at the center of the study area. We find the cosmic-ray neutron counts correlate well with spatially aver- aged point measurements of soil moisture over a 6-mo period with an RMSE of 0.0165 m3 m-3 and percent error of less than 20%. Neutron transport simulations suggest our understanding of the effective sensor depth in the presence of vertical variations in water content is adequate. We find that daily evapotranspiration water fluxes inferred from cos- mic-ray measurements agree with previously published eddy-covariance measured values at the study site, suggesting that the cosmic-ray neutron sensor may be able to provide flux measurements of the near surface at intermediate spatial scales. © Soil Science Society of America.
- Harlow, R. C., Burke, E. J., & Ferre, T. P. (2012). Measuring Water Content in Saline Sands Using Impulse Time Domain Transmission Techniques. VADOSE ZONE JOURNAL, 2(3), 433-439.
- Huisman, J. A., Vrugt, J. A., & Ferre, T. (2012). Vadose Zone Model-Data Fusion: State of the Art and Future Challenges. VADOSE ZONE JOURNAL, 11(4).
- Huisman, J. A., Vrugt, J. A., & P., T. (2012). Vadose zone model-data fusion: State of the art and future challenges. Vadose Zone Journal, 11(4).More infoAbstract: Models are quantitative formulations of assumptions regarding key physical processes, their mathematical representations, and site-specific relevant properties at a particular scale of analysis. Models are fused with data in a two-way process that uses information contained in observational data to refine models and the context provided by models to improve information extraction from observational data. This process of model-data fusion leads to improved understanding of hydrological processes by providing improved estimates of parameters, fluxes, and states of the vadose zone system of interest, as well as of the associated uncertainties of these values. Notwithstanding recent progress, there are still numerous challenges associated with model-data fusion, including: (i) dealing with the increasing complexity of models, (ii) considering new and typically indirect measure-ments, and (iii) quantifying uncertainty. This special section presents nine contributions that address the state of the art of model-data fusion. © Soil Science Society of America.
- Kikuchi, C. P., Ferre, T., & Welker, J. M. (2012). Spatially telescoping measurements for improved characterization of ground water-surface water interactions. JOURNAL OF HYDROLOGY, 446, 1-12.
- Kikuchi, C. P., Ferré, T., & Welker, J. M. (2012). Spatially telescoping measurements for improved characterization of ground water-surface water interactions. Journal of Hydrology, 446-447, 1-12.More infoAbstract: The suite of measurement methods available to characterize fluxes between groundwater and surface water is rapidly growing. However, there are few studies that examine approaches to design of field investigations that include multiple methods. We propose that performing field measurements in a spatially telescoping sequence improves measurement flexibility and accounts for nested heterogeneities while still allowing for parsimonious experimental design. We applied this spatially telescoping approach in a study of ground water-surface water (GW-SW) interaction during baseflow conditions along Lucile Creek, located near Wasilla, Alaska. Catchment-scale data, including channel geomorphic indices and hydrogeologic transects, were used to screen areas of potentially significant GW-SW exchange. Specifically, these data indicated increasing groundwater contribution from a deeper regional aquifer along the middle to lower reaches of the stream. This initial assessment was tested using reach-scale estimates of groundwater contribution during baseflow conditions, including differential discharge measurements and the use of chemical tracers analyzed in a three-component mixing model. The reach-scale measurements indicated a large increase in discharge along the middle reaches of the stream accompanied by a shift in chemical composition towards a regional groundwater end member. Finally, point measurements of vertical water fluxes - obtained using seepage meters as well as temperature-based methods - were used to evaluate spatial and temporal variability of GW-SW exchange within representative reaches. The spatial variability of upward fluxes, estimated using streambed temperature mapping at the sub-reach scale, was observed to vary in relation to both streambed composition and the magnitude of groundwater contribution from differential discharge measurements. The spatially telescoping approach improved the efficiency of this field investigation. Beginning our assessment with catchment-scale data allowed us to identify locations of GW-SW exchange, plan measurements at representative field sites and improve our interpretation of reach-scale and point-scale measurements. © 2012 .
- Naveed, M., Moldrup, P., Tuller, M., Ferre, T. P., Kawamoto, K., Komatsu, T., & Wollesen, L. (2012). Prediction of the soil water characteristic from soil particle volume fractions. Soil Science Society of America Journal, 76(6), 1946-1956.More infoAbstract: Modeling water distribution and flow in partially saturated soils requires knowledge of the soil water characteristic (SWC). However, measurement of the SWC is challenging and time-consuming and, in some cases, not feasible. This study introduces two predictive models (FW-model and AW-model) for the SWC, derived from readily available soil properties such as texture and bulk density. A total of 46 undisturbed soils from different horizons at 15 locations across Denmark were used for model evaluation. The FW-model predicts the volumetric water content as a function of volumetric fines content (organic matter and clay). It performed reasonably well for the dry-end of SWC (above a pF value of 2.0; pF = log(|ψ|), where ψ is the matric potential in cm), but did not do as well closer to saturated conditions. The AW-model predicts the volumetric water content as a function of volumetric content of different particle size fractions (organic matter, clay, silt, and fine and coarse sands). The volumetric content of a particular soil particle size fraction was considered if it contributed to the pore size fraction still occupied with water at the given pF value. Hereby, the AW-model implicitly assumes that a given particle size fraction creates an analogue pore size fraction and further this pore size fraction filled with water is corresponding to a certain pF value according to the wellknown capillary rise equation. The A W-model was found to be quite robust, and it performed exceptionally well for pF values ranging from 0.4 to 4.2 for different soil types. For prediction of the continuous SWC, it is recommended to parameterize the van Genuchten model based on the SWC data points predicted by the A W-model. © Soil Science Society of America.
- Naveed, M., Moldrup, P., Tuller, M., Ferre, T., Kawamoto, K., Komatsu, T., & de, J. (2012). Prediction of the Soil Water Characteristic from Soil Particle Volume Fractions. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 76(6), 1946-1956.
- Zreda, M., Desilets, D., Ferre, T. P., & Scott, R. L. (2012). Measuring soil moisture content non-invasively at intermediate spatial scale using cosmic-ray neutrons. GEOPHYSICAL RESEARCH LETTERS, 35(21).
- Bechtold, M., Haber-Pohlmeier, S., Vanderborght, J., Pohlmeier, A., Ferre, T., & Vereecken, H. (2011). Near-surface solute redistribution during evaporation. GEOPHYSICAL RESEARCH LETTERS, 38.
- Bechtold, M., Haber-Pohlmeier, S., Vanderborght, J., Pohlmeier, A., Ferré, T., & Vereecken, H. (2011). Near-surface solute redistribution during evaporation. Geophysical Research Letters, 38(17).More infoAbstract: We present results from solute transport experiments in an evaporating composite porous medium consisting of a cylindrical inner core with coarse sand that was surrounded by a mantle with fine sand. Small volumes of dye and salt tracer were applied at the surface of the fine material of the evaporating column. The pressure head at the bottom boundary was kept constant using a hanging water table ensuring liquid phase continuity to top surface in both fine and coarse material, whereby the latter was hydraulically less conductive at these pressure conditions. Contrary to the expectation that solute accumulation at an evaporating surface is proportional to local cumulative evaporation, high concentration spots developed at the surface of the coarse material, for which IR surface temperature measurements did not indicate higher evaporation fluxes. 3D unsaturated flow and transport simulations and a second tracer experiment monitored with magnetic resonance imaging (MRI) demonstrated that preferential upward water flux in the fine sand deeper in the column and near-surface lateral water flow from the fine into the coarse sand in combination with a downward diffusive flux are responsible for the local solute accumulation. We propose that at the wet regions of a soil surface, solute accumulation is largely decoupled from local evaporation fluxes and strongly governed by relative differences of the hydraulic conductivities. The possible formation of high solute concentration spots at the surface of coarser regions usually representing preferential flow pathways during strong precipitation may have an accelerating effect on the leaching of solutes. Copyright 2011 by the American Geophysical Union.
- Chief, K., Ferre, T. P., & Nijssen, B. (2011). Correlation between Air Permeability and Saturated Hydraulic Conductivity: Unburned and Burned Soils. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 72(6), 1501-1509.
- Resurreccion, A. C., Moldrup, P., Tuller, M., Ferre, T. P., Kawamoto, K., Komatsu, T., & De Jonge, L. W. (2011). Relationship between specific surface area and the dry end of the water retention curve for soils with varying clay and organic carbon contents. WATER RESOURCES RESEARCH, 47.
- Resurreccion, A. C., Moldrup, P., Tuller, M., Ferré, T., Kawamoto, K., Komatsu, T., & Wollesen, L. (2011). Relationship between specific surface area and the dry end of the water retention curve for soils with varying clay and organic carbon contents. Water Resources Research, 47(6).More infoAbstract: Accurate description of the soil water retention curve (SWRC) at low water contents is important for simulating water dynamics and biochemical vadose zone processes in arid environments. Soil water retention data corresponding to matric potentials of less than -10 MPa, where adsorptive forces dominate over capillary forces, have also been used to estimate soil specific surface area (SA). In the present study, the dry end of the SWRC was measured with a chilled-mirror dew point psychrometer for 41 Danish soils covering a wide range of clay (CL) and organic carbon (OC) contents. The 41 soils were classified into four groups on the basis of the Dexter number (n = CL/OC), and the Tuller-Or (TO) general scaling model describing water film thickness at a given matric potential ( 10. A strong correlation between the ratio of the two surface area estimates and the Dexter number was observed and applied as an additional scaling function in the TO model to rescale the soil water retention curve at low water contents. However, the TO model still overestimated water film thickness at potentials approaching ovendry condition (about -800 MPa). The semi-log linear Campbell-Shiozawa-Rossi- Nimmo (CSRN) model showed better fits for all investigated soils from -10 to -800 MPa and yielded high correlations with CL and SA. It is therefore recommended to apply the empirical CSRN model for predicting the dry part of the water retention curve (-10 to -800 MPa) from measured soil texture or surface area. Further research should aim to modify the more physically based TO model to obtain better descriptions of the SWRC in the very dry range (-300 to -800 MPa). Copyright 2011 by the American Geophysical Union.
- Soto-López, C. D., Meixner, T., & P., T. (2011). Effects of measurement resolution on the analysis of temperature time series for stream-aquifer flux estimation. Water Resources Research, 47(12).More infoAbstract: From its inception in the mid-1960s, the use of temperature time series (thermographs) to estimate vertical fluxes has found increasing use in the hydrologic community. Beginning in 2000, researchers have examined the impacts of measurement and parameter uncertainty on the estimates of vertical fluxes. To date, the effects of temperature measurement discretization (resolution), a characteristic of all digital temperature loggers, on the determination of vertical fluxes has not been considered. In this technical note we expand the analysis of recently published work to include the effects of temperature measurement resolution on estimates of vertical fluxes using temperature amplitude and phase shift information. We show that errors in thermal front velocity estimation introduced by discretizing thermographs differ when amplitude or phase shift data are used to estimate vertical fluxes. We also show that under similar circumstances sensor resolution limits the range over which vertical velocities are accurately reproduced more than uncertainty in temperature measurements, uncertainty in sensor separation distance, and uncertainty in the thermal diffusivity combined. These effects represent the baseline error present and thus the best-case scenario when discrete temperature measurements are used to infer vertical fluxes. The errors associated with measurement resolution can be minimized by using the highest-resolution sensors available. But thoughtful experimental design could allow users to select the most cost-effective temperature sensors to fit their measurement needs. Copyright 2011 by the American Geophysical Union.
- Walsh, D. O., Grunewald, E., Turner, P., Hinnell, A., & Ferre, P. (2011). Practical limitations and applications of short dead time surface NMR. NEAR SURFACE GEOPHYSICS, 9(2), 103-111.
- Walsh, D. O., Grunewald, E., Turner, P., Hinnell, A., & Ferre, P. (2011). Practical limitations and applications of short dead time surface NMR. Near Surface Geophysics, 9(2), 103-111.More infoAbstract: There is increasing interest in the unique measurement capabilities of nuclear magnetic resonance (NMR) for hydrologie applications. In particular, the ability to quantify water content (both bound and free) and to infer the permeability distribution are critical to hydrologists. As the method has gained in acceptance, there has been growing interest in extending its range to near-surface and vadose zone applications and to measurement in finer grained and magnetic soils. All of these applications require improved resolution of early-time signals, which requires shorter measurement dead times. This paper analyses three physical/electrical processes that limit the minimum achievable measurement dead times in surface NMR applications: 1) inherent characteristics of electromechanical and semiconductor switching devices, 2) the effective bandwidth of the receiver and signal processing chain, 3) transient signals associated with induced eddy currents in the ground. We then describe two applications of surface NMR that rely on reduced measurement dead time: detection and characterization of fast decaying NMR signals in silt and clay and the detection of fast decaying NMR signals in magnetic geology. © 2011 European Association of Geoscientists & Engineers.
- Blasch, K. W., Ferre, T., & Vrugt, J. A. (2010). Environmental controls on drainage behavior of an ephemeral stream. STOCHASTIC ENVIRONMENTAL RESEARCH AND RISK ASSESSMENT, 24(7), 1077-1087.
- Blasch, K. W., Ferré, T. P., & Vrugt, J. A. (2010). Environmental controls on drainage behavior of an ephemeral stream. Stochastic Environmental Research and Risk Assessment, 24(7), 1077-1087.More infoAbstract: Streambed drainage was measured at the cessation of 26 ephemeral streamflow events in Rillito Creek, Tucson, Arizona from August 2000 to June 2002 using buried time domain reflectometry (TDR) probes. An unusual drainage response was identified, which was characterized by sharp drainage from saturation to near field capacity at each depth with an increased delay between depths. We simulated the drainage response using a variably saturated numerical flow model representing a two-layer system with a high permeability layer overlying a lower permeability layer. Both the observed data and the numerical simulation show a strong correlation between the drainage velocity and the temperature of the stream water. A linear combination of temperature and the no-flow period preceding flow explained about 90% of the measured variations in drainage velocity. Evaluation of this correlative relationship with the one-dimensional numerical flow model showed that the observed temperature fluctuations could not reproduce the magnitude of variation in the observed drainage velocity. Instead, the model results indicated that flow duration exerts the most control on drainage velocity, with the drainage velocity decreasing nonlinearly with increasing flow duration. These findings suggest flow duration is a primary control of water availability for plant uptake in near surface sediments of an ephemeral stream, an important finding for estimating the ecological risk of natural or engineered changes to streamflow patterns. Correlative analyses of soil moisture data, although easy and widely used, can result in erroneous conclusions of hydrologic cause-effect relationships, and demonstrating the need for joint physically-based numerical modeling and data synthesis for hypothesis testing to support quantitative risk analysis. © 2010 U.S. Government.
- Desilets, D., Zreda, M., & P., T. (2010). Nature's neutron probe: Land surface hydrology at an elusive scale with cosmic rays. Water Resources Research, 46(11).More infoAbstract: Fast neutrons are generated naturally at the land surface by energetic cosmic rays. These "background" neutrons respond strongly to the presence of water at or near the land surface and represent a hitherto elusive intermediate spatial scale of observation that is ideal for land surface studies and modeling. Soil moisture, snow, and biomass each have a distinct influence on the spectrum, height profile, and directional intensity of neutron fluxes above the ground, suggesting that different sources of water at the land surface can be distinguished with neutron data alone. Measurements can be taken at fixed sites for long-term monitoring or in a moving vehicle for mapping over large areas. We anticipate applications in many previously problematic contexts, including saline environments, wetlands and peat bogs, rocky soils, the active layer of permafrost, and water and snow intercepted by vegetation, as well as calibration and validation of data from spaceborne sensors. Copyright © 2010 by the American Geophysical Union.
- Dickinson, J., Hanson, R., Ferre, T., & Leake, S. (2010). Inferring time-varying recharge from inverse analysis of long-term water levels. WATER RESOURCES RESEARCH, 40(7).
- Ferre, T., & Thomasson, M. J. (2010). Understanding the Impacts of Anisotropy on the Extent of Drawdown. GROUND WATER, 48(4), 478-479.
- Ferré, T. P., & Thomasson, M. J. (2010). Understanding the impacts of anisotropy on the extent of drawdown. Ground Water, 48(4), 478-479.More infoPMID: 20015344;
- Selker, J., & P., T. (2010). The ah ha moment of measurement: Introduction to the special section on hydrologic measurement methods. Water Resources Research, 46(4).
- Soto-Lopez, C. D., Meixner, T., & Ferre, T. P. (2010). Effects of measurement resolution on the analysis of temperature time series for stream-aquifer flux estimation. WATER RESOURCES RESEARCH, 47.
- Ferré, T., Bentley, L., Binley, A., Linde, N., Kemna, A., Singha, K., Holuger, K., Huisman, J. A., & Minsley, B. (2009). Critical steps for the continuing advancement of hydrogeophysics. Eos, 90(23), 200-.
- Selker, J., & Ferre, T. (2009). The ah ha moment of measurement: Introduction to the special section on Hydrologic Measurement Methods. WATER RESOURCES RESEARCH, 45.
- Selker, J., & P., T. (2009). The ah ha moment of measurement: Introduction to the special section on Hydrologic Measurement Methods. Water Resources Research, 45(6).
- Chief, K., Ferré, T. P., & Hinnell, A. C. (2008). The effects of anisotropy on in situ air permeability measurements. Vadose Zone Journal, 7(3), 941-947.More infoAbstract: Previous research has established a correlation between air permeability (k a) and saturated hydraulic conductivity for agricultural soils based on ex situ air permeability (k ex situ). In situ air permeability (k in situ) measurements in nonagricultural soils, however, have shown a decrease in correlation that may be attributed to soil anisotropy. Our objectives were: (i) to examine the effects of anisotropy on k ex situ using a three-dimensional air flow model; (ii) to develop a method to identify anisotropy using k ex situ and k ex situ measurements; and (iii) to determine the sample volume of an air permeameter as a function of the permeameter design and the anisotropy ratio. Numerical results showed that the k a measured in situ in anisotropic media results in some average of the horizontal and vertical permeabilities. The averaging depends on the degree of anisotropy and the ratio of the diameter to the insertion depth of the permeameter. Therefore, a shape factor developed for an isotropic soil can give unreliable results. We determined that paired in situ and ex situ permeability measurements can be used to infer the anisotropy ratio. This approach is more accurate if the vertical permeability, k az, is higher than the horizontal, k ax. The sample volume does not extend outside of the air permeameter for high k ax/k az. It is stretched vertically for low k az/k az. A field experiment showed qualitative agreement with model predictions, but anisotropy alone was not able to fully explain the difference between k ex situ and k ex situ. © Soil Science Society of America.
- Chief, K., P., T., & Nijssen, B. (2008). Correlation between air permeability and saturated hydraulic conductivity: Unburned and burned soils. Soil Science Society of America Journal, 72(6), 1501-1509.More infoAbstract: Prior research has shown a log-log correlation between ex situ air permeability (ka) measured at a matric potential of -50 and -100 cm H2O and saturated hydraulic conductivity (Ksat) in agricultural soils. We examined the applicability of a previously established log ka vs. log Ksat predictive relation in unburned and burned woodland-chaparral and coniferous soils. Specifically, we measured in situ ka in the field using the soil corer air permeameter (SCAP) and measured laboratory Ksat on soil cores. To determine postfire soil physical changes, Ksat was transformed into water permeability, kw. Then ka and kw were compared in unburned and burned soils. The median ka was lower and median kw was higher in burned than unburned woodland-chaparral soils. The median k a and kw were both lower in burned than unburned coniferous soils. Despite these effects, the 95% prediction interval of the predictive relation includes 80% of the burned soils and 83% of all desert soils. The RMSE values of the predicted log Ksat and measured log Ksat were 0.371, 0.552, 0.588, and 0.511 m d-1 for unburned and burned woodland-chaparral and unburned and burned coniferous soils, respectively. In comparison, the RMSE for the predicted and measured log K sat was 0.654 m d-1 for an agricultural data set. The overall RMSE for unburned and burned soils including the agricultural soils was 0.551 m d-1. This suggests that the predictive relation is applicable for unburned and burned desert soils for in situ ka measurements. © Soil Science Society of America All rights reserved.
- Faust, A. E., Ferre, T. P., Schaap, M. G., & Hinnell, A. C. (2008). Can basin-scale recharge be estimated reasonably with water-balance models?. VADOSE ZONE JOURNAL, 5(3), 850-855.
- Ferre, T. P., Nissen, H. H., & Simunek, J. (2008). The Effect of the Spatial Sensitivity of TDR on Inferring Soil Hydraulic Properties from Water Content Measurements Made during the Advance of a Wetting Front. VADOSE ZONE JOURNAL, 1(2), 281-288.
- Franz, T. E., Zreda, M., Rosolem, R., & Ferre, T. P. (2008). A universal calibration function for determination of soil moisture with cosmic-ray neutrons. HYDROLOGY AND EARTH SYSTEM SCIENCES, 17(2), 453-460.
- Furman, A., Ferre, T. P., & Heath, G. L. (2008). Spatial focusing of electrical resistivity surveys considering geologic and hydrologic layering. GEOPHYSICS, 72(2), F65-F73.
- Furman, A., Ferre, T. P., & Warrick, A. W. (2008). A Sensitivity Analysis of Electrical Resistivity Tomography Array Types Using Analytical Element Modeling. VADOSE ZONE JOURNAL, 2(3), 416-423.
- Hinnell, A. C., & Ferre, T. (2008). Considerations for measuring pressure head and water content in inclined boreholes. WATER RESOURCES RESEARCH, 44(12).
- Hinnell, A. C., & Ferré, T. (2008). Considerations for measuring pressure head and water content in inclined boreholes. Water Resources Research, 44(12).More infoAbstract: Angled boreholes have been proposed to improve water content and pressure head monitoring in deep vadose zones by reducing the impact of the borehole on measurements by placing sensors below undisturbed soil. However, the borehole casing distorts the flow field, which may impact measurements made with sensors placed on or in the boreholes. We examined a wide range of soil types, background fluxes, and casing radii and angles of inclination to predict the error in water content and pressure head measurements that arise due to this flow disruption under unit gradient flow. We found that placing pressure head and water content sensors 110° and 120° from the top of the borehole, respectively, minimizes the effects of flow perturbation. Under some conditions, it may be possible to use the perturbation of the flow field caused by the casing to estimate hydraulic parameter values. Copyright 2008 by the American Geophysical Union.
- L., S., P., T., & Ekwurzel, B. (2008). Flash flood dynamics and composition in a semiarid mountain watershed. Water Resources Research, 44(12).More infoAbstract: Flash flood hydrographs were examined using water stable isotopes (deuterium and oxygen) and a plug-flow lumped catchment model to assess the origin and routing processes of flood water in a semiarid basin in southwestern United States. Precipitation and stream water were sampled during storm and flood conditions at high and low elevations. Isotope mixing relationships readily determined the predominance of three sources for the representative summer monsoon events: high elevation precipitation from two major subbasins and base flow. Each flood progressed through a series of source water contributions, as indicated by several segments of linear mixing between these end-members. We developed a plug-flow lumped catchment model to test possible governing processes for specific watershed and forcing conditions. Results suggest two main findings: First, these flood events were generated primarily from event water runoff in high elevations that mixed at the flood bore with pre-event base flow resident in the stream. The power, speed, and turbulence of the flood bore cause it to mix with, ride atop and push the resident in-stream water in the front of the rising limb. Second, the timing and volume of flood waves from subbasins are identified by their combined isotopic signature at the basin outlet; this approach may provide an effective mesoscale constraint for rainfall-runoff models. Copyright 2008 by the American Geophysical Union.
- L., S., P., T., & Troch, P. A. (2008). Effects of stream-aquifer disconnection on local flow patterns. Water Resources Research, 44(9).More infoAbstract: Disconnected stream-aquifer systems are becoming increasingly common because of lowering groundwater tables. This work focuses on the pathways and rates of infiltration and seepage as streams transition from fully connected to disconnected conditions. HYDRUS-2D simulations show for a connected stream, water infiltrates vertically then moves laterally below the top of the preflooding capillary fringe height, finally causing an upward displacement of antecedent water into the vadose zone. This contradicts the commonly held assumption that stream water moves laterally for some distance into the stream bank, forming a wedge above the antecedent water. Even for shallow disconnections (
- Robinson, D. A., Binley, A., Crook, N., Day-Lewis, F., Ferré, T., Grauch, V. J., Knight, R., Knoll, M., Lakshmi, V., Miller, R., Nyquist, J., Pellerin, L., Singha, K., & Slater, L. (2008). Advancing process-based watershed hydrological research using near-surface geophysics: A vision for, and review of, electrical and magnetic geophysical methods. Hydrological Processes, 22(18), 3604-3635.More infoAbstract: We want to develop a dialogue between geophysicists and hydrologists interested in synergistically advancing process based watershed research. We identify recent advances in geophysical instrumentation, and provide a vision for the use of electrical and magnetic geophysical instrumentation in watershed scale hydrology. The focus of the paper is to identify instrumentation that could significantly advance this vision for geophysics and hydrology during the next 3-5 years. We acknowledge that this is one of a number of possible ways forward and seek only to offer a relatively narrow and achievable vision. The vision focuses on the measurement of geological structure and identification of flow paths using electrical and magnetic methods. The paper identifies instruments, provides examples of their use, and describes how synergy between measurement and modelling could be achieved. Of specific interest are the airborne systems that can cover large areas and are appropriate for watershed studies. Although airborne geophysics has been around for some time, only in the last few years have systems designed exclusively for hydrological applications begun to emerge. These systems, such as airborne electromagnetic (EM) and transient electromagnetic (TEM), could revolutionize hydrogeological interpretations. Our vision centers on developing nested and cross scale electrical and magnetic measurements that can be used to construct a three-dimensional (3D) electrical or magnetic model of the subsurface in watersheds. The methodological framework assumes a 'top down' approach using airborne methods to identify the large scale, dominant architecture of the subsurface. We recognize that the integration of geophysical measurement methods, and data, into watershed process characterization and modelling can only be achieved through dialogue. Especially, through the development of partnerships between geophysicists and hydrologists, partnerships that explore how the application of geophysics can answer critical hydrological science questions, and conversely provide an understanding of the limitations of geophysical measurements and interpretation. Copyright © 2008 John Wiley & Sons, Ltd.
- Rucker, D., Warrick, A., & Ferre, T. (2008). Parameter equivalence for the Gardner and van Genuchten soil hydraulic conductivity functions for steady vertical flow with inclusions. ADVANCES IN WATER RESOURCES, 28(7), 689-699.
- Warrick, A. W., Hinnell, A. C., Ferre, T., & Knight, J. H. (2008). Steady state lateral water flow through unsaturated soil layers. WATER RESOURCES RESEARCH, 44(8).
- Warrick, A. W., Hinnell, A. C., Ferré, T., & Knight, J. H. (2008). Steady state lateral water flow through unsaturated soil layers. Water Resources Research, 44(8).More infoAbstract: The effects of gravity on flow through variably saturated soil layers are investigated quantitatively using two new analytical solutions and a numerical model. In all cases, steady state flow occurs laterally through a tilted, rectangular layer of soil with a constant hydraulic head on either end. The first solution is for gravity-driven flow through a tilted layer with sublayering parallel to the slope. As intuitively suggested by earlier investigators, flow occurs parallel to the floor of the layer and the pressure head is a simple function of the normal distance from the floor of the layer. The second analytical solution is for a tilted soil layer described by a Gardner soil model with both gravity and pressure head gradients. Flow velocities remain parallel to the layer floor, which is confirmed by numerical simulations. This is in contrast with chosen non-Gardner examples for which the flow does not necessarily remain parallel to the floor. Copyright 2008 by the American Geophysical Union.
- Zreda, M., Desilets, D., Ferré, T., & Scott, R. L. (2008). Measuring soil moisture content non-invasively at intermediate spatial scale using cosmic-ray neutrons. Geophysical Research Letters, 35(21).More infoAbstract: Soil moisture content on a horizontal scale of hectometers and at depths of decimeters can be inferred from measurements of low-energy cosmic-ray neutrons that are generated within soil, moderated mainly by hydrogen atoms, and diffused back to the atmosphere. These neutrons are sensitive to water content changes, but largely insensitive to variations in soil chemistry, and their intensity above the surface is inversely correlated with hydrogen content of the soil. The measurement with a portable neutron detector placed a few meters above the ground takes minutes to hours, permitting high-resolution, long-term monitoring of undisturbed soil moisture conditions. The large footprint makes the method suitable for weather and short-term climate forecast initialization and for calibration of satellite sensors, and the measurement depth makes the probe ideal for studies of plant/soil interaction and atmosphere/soil exchange. Copyright 2008 by the American Geophysical Union.
- Blainey, J. B., P., T., & Cordova, J. T. (2007). Assessing the likely value of gravity and drawdown measurements to constrain estimates of hydraulic conductivity and specific yield during unconfined aquifer testing. Water Resources Research, 43(12).More infoAbstract: Pumping of an unconfined aquifer can cause local desaturation detectable with high-resolution gravimetry. A previous study showed that signal-to-noise ratios could be predicted for gravity measurements based on a hydrologic model. We show that although changes should be detectable with gravimeters, estimations of hydraulic conductivity and specific yield based on gravity data alone are likely to be unacceptably inaccurate and imprecise. In contrast, a transect of low-quality drawdown data alone resulted in accurate estimates of hydraulic conductivity and inaccurate and imprecise estimates of specific yield. Combined use of drawdown and gravity data, or use of high-quality drawdown data alone, resulted in unbiased and precise estimates of both parameters. This study is an example of the value of a staged assessment regarding the likely significance of a new measurement method or monitoring scenario before collecting field data. Copyright 2007 by the American Geophysical Union.
- Callegary, J. B., Ferre, T. P., & Groom, R. W. (2007). Vertical spatial sensitivity and exploration depth of low-induction-number electromagnetic-induction instruments. VADOSE ZONE JOURNAL, 6(1), 158-167.
- Callegary, J. B., P., T., & Groom, R. W. (2007). Vertical spatial sensitivity and exploration depth of low-induction-number electromagnetic-induction instruments. Vadose Zone Journal, 6(1), 158-167.More infoAbstract: Vertical spatial sensitivity and effective depth of exploration (d e) of low-induction-number (LIN) instruments over a layered soil were evaluated using a complete numerical solution to Maxwell's equations. Previous studies using approximate mathematical solutions predicted a vertical spatial sensitivity for instruments operating under LIN conditions that, for a given transmitter-receiver coil separation (s), coil orientation, and transmitter frequency, should depend solely on depth below the land surface. When not operating under LIN conditions, vertical spatial sensitivity and de also depend on apparent soil electrical conductivity (σa) and therefore the induction number (β). In this new evaluation, we determined the range of σa and β values for which the LIN conditions hold and how de changes when they do not. Two-layer soil models were simulated with both horizontal (HCP) and vertical (VCP) coplanar coil orientations. Soil layers were given electrical conductivity values ranging from 0.1 to 200 mS m-1. As expected, de decreased as σa increased. Only the least electrically conductive soil produced the de expected when operating under LIN conditions. For the VCP orientation, this was 1.6s, decreasing to 0.8s in the most electrically conductive soil. For the HCP orientation, de decreased from 0.76s to 0.51s. Differences between this and previous studies are attributed to inadequate representation of skin-depth effect and scattering at interfaces between layers. When using LIN instruments to identify depth to water tables, interfaces between soil layers, and variations in salt or moisture content, it is important to consider the dependence of de on σa. © Soil Science Society of America.
- Chief, K., Ferre, T. P., & Hinnell, A. C. (2007). The effects of anisotropy on in situ air permeability measurements. VADOSE ZONE JOURNAL, 7(3), 941-947.
- Desilets, D., Zreda, M., & Ferre, T. P. (2007). Nature's neutron probe: Land surface hydrology at an elusive scale with cosmic rays. WATER RESOURCES RESEARCH, 46.
- Desilets, D., Zreda, M., & Ferré, T. (2007). Scientist water equivalent measured with cosmic rays at 2006 AGU fall meeting. Eos, 88(48), 521-522.
- Desilets, S. L., Nijssen, B., Ekwurzel, B., & Ferré, T. P. (2007). Post-wildfire changes in suspended sediment rating curves: Sabino Canyon, Arizona. Hydrological Processes, 21(11), 1413-1423.More infoAbstract: Wildfire has been shown to increase erosion by several orders of magnitude, but knowledge regarding short-term variations in post-fire sediment transport processes has been lacking. We present a detailed analysis of the immediate post-fire sediment dynamics a semi-arid basin in the southwestern USA based on suspended sediment rating curves. During June and July 2003, the Aspen Fire in the Coronado National Forest of southern Arizona burned an area of 343 km2. Surface water samples were collected in an affected watershed using an event-based sampling strategy. Sediment rating parameters were determined for individual storm events during the first 18 months after the fire. The highest sediment concentrations were observed immediately after the fire. Through the two subsequent monsoon seasons there was a progressive change in rating parameters related to the preferential removal of fine to coarse sediment. During the corresponding winter seasons, there was a lower supply of sediment from the hillslopes, resulting in a time-invariant set of sediment rating parameters. A sediment mass-balance model corroborated the physical interpretations. The temporal variability in the sediment rating parameters demonstrates the importance of storm-based sampling in areas with intense monsoon activity to characterize post-fire sediment transport accurately. In particular, recovery of rating parameters depends on the number of high-intensity rainstorms. These findings can be used to constrain rapid assessment fire-response models for planning mitigation activities. Copyright © 2006 John Wiley & Sons, Ltd.
- Ferre, T., & Selker, J. S. (2007). A glass always half full: Reconsideration of the Wales apparatus to apply constant head boundary conditions. WATER RESOURCES RESEARCH, 43(12).
- Fink, W., Dohm, J. M., Tarbell, M. A., Hare, T. M., Baker, V. R., Schulze-Makuch, D., Furfaro, R., Fairen, A. G., Ferre, T., Miyamoto, H., Komatsu, G., & Mahaney, W. C. (2007). Tier-scalable reconnaissance missions for the autonomous exploration of planetary bodies. 2007 IEEE AEROSPACE CONFERENCE, VOLS 1-9, 194-203.
- Franz, T. E., Zreda, M., Rosolem, R., & Ferre, T. P. (2007). Field Validation of a Cosmic-Ray Neutron Sensor Using a Distributed Sensor Network. VADOSE ZONE JOURNAL, 11(4).
- Furman, A., Ferré, T. P., & Heath, G. L. (2007). Spatial focusing of electrical resistivity surveys considering geologic and hydrologic layering. Geophysics, 72(2), F65-F73.More infoAbstract: Electrical resistivity tomography (ERT) has shown great promise for monitoring transient hydrologic processes. One advantage of ERT under those conditions is the ability of a user to tailor the spatial sensitivity of an ERT survey through selection of electrode locations and electrode combinations. Recent research has shown that quadripoles can be selected in a manner that improves the independent inversion of ERT data. Our ultimate interest lies in using ERT data along with measurements from other sensors, which typically can provide high-quality data from shallow regions of the subsurface, in a joint inversion. As a result, we do not consider the selection of quadripoles specifically for inde-pendent ERT inversion. Rather, we present an approach to focusthe spatial sensitivity of ERT surveys in specificsubsurface regions with the assumption that those data, when interpreted along with other measurements that are sensitive to those regions, will lead to more complete hydrologic characterization. Because we are interested in monitoring rapid processes, our approach is designed to efficiently identify optimal quadripoles. This is achieved by separating the optimization from the inversion grid, significantly reducing computational effort. We extend our previous work to consider the use of both surface and borehole ERT electrodes and to consider the impacts of horizontally layered electrical conductivity conditions. Results confirm the ability of the method to focus survey sensitivity while showing the importance of incorporation of prior knowledge of the subsurface electric conductivity structure in designing optimal ERT surveys. © 2007 Society of Exploration Geophysicists.
- P., T., & Selker, J. S. (2007). A glass always half full: Reconsideration of the Wales apparatus to apply constant head boundary conditions. Water Resources Research, 43(12).More infoAbstract: A new apparatus is presented that is capable of applying a constant fluid pressure at inflow and outflow boundaries. The apparatus can be refilled during operation and does not rely on an overflow mechanism. The device is constructed of two vessels, one that contains the delivered fluid and the other that contains a less dense fluid. By matching the fluid densities and the areas of the vessels the absolute elevation of the delivered fluid is maintained as the fluid is added to or removed from the system. The history of the development of the device, the underlying physical principles, and two demonstrations of the operation of a prototype device are shown. Copyright 2007 by the American Geophysical Union.
- Rucker, D., & Ferre, T. (2007). The effect of a dipping layer on the first-arrival traveltime from zero-offset and fixed-offset borehole radar. NEAR SURFACE GEOPHYSICS, 5(3), 151-159.
- Rucker, D., & Ferré, T. P. (2007). The effect of a dipping layer on the first-arrival traveltime from zero-offset and fixed-offset borehole radar. Near Surface Geophysics, 5(3), 151-159.More infoAbstract: The effect of a dipping layer on the first-arrival traveltime from single-offset profiling with borehole radar is investigated, including both zero-offset and fixed-offset profiling. In our study, offset refers to the vertical distance between bistatic radar antennae. Using forward modelling of electromagnetic wave travel, the traveltime of zero-offset and fixed-offset profiles through a dipping layer is compared to those of flat-lying layers. The model considers three distinct raypaths: direct, critically refracted and cross-dip refracted. Whereas critical refraction only occurs in a layer of low propagation velocity relative to an adjacent high-velocity layer, cross-dip refraction can occur in any velocity structure. The forward model demonstrated that the slope of the traveltime through the cross-dip portion of the profile is approximately half of that in the critically refracted portion. To obtain the electromagnetic wave propagation velocities above and below the dip, only one profile is necessary. However, to invert for the dip angle and position, two profiles with different offsets must be considered together. © 2007 European Association of Geoscientists & Engineers.
- Blainey, J. B., Ferre, T. P., & Cordova, J. T. (2006). Assessing the likely value of gravity and drawdown measurements to constrain estimates of hydraulic conductivity and specific yield during unconfined aquifer testing. WATER RESOURCES RESEARCH, 43(12).
- Blasch, K. W., Ferre, T. P., Christensen, A. H., & Hoffmann, J. P. (2006). New Field Method to Determine Streamflow Timing Using Electrical Resistance Sensors. VADOSE ZONE JOURNAL, 1(2), 289-299.
- Blasch, K. W., P., T., Hoffmann, J. P., & Fleming, J. B. (2006). Relative contributions of transient and steady state infiltration during ephemeral streamflow. Water Resources Research, 42(8).More infoAbstract: Simulations of infiltration during three ephemeral streamflow events in a coarse-grained alluvial channel overlying a less permeable basin-fill layer were conducted to determine the relative contribution of transient infiltration at the onset of streamflow to cumulative infiltration for the event. Water content, temperature, and piezometric measurements from 2.5-m vertical profiles within the alluvial sediments were used to constrain a variably saturated water flow and heat transport model. Simulated and measured transient infiltration rates at the onset of streamflow were about two to three orders of magnitude greater than steady state infiltration rates. The duration of simulated transient infiltration ranged from 1.8 to 20 hours, compared with steady state flow periods of 231 to 307 hours. Cumulative infiltration during the transient period represented 10 to 26% of the total cumulative infiltration, with an average contribution of approximately 18%. Cumulative infiltration error for the simulated streamflow events ranged from 9 to 25%. Cumulative infiltration error for typical streamflow events of about 8 hours in duration in is about 90%. This analysis indicates that when estimating total cumulative infiltration in coarse-grained ephemeral stream channels, consideration of the transient infiltration at the onset of streamflow will improve predictions of the total volume of infiltration that may become groundwater recharge. Copyright 2006 by the American Geophysical Union.
- Chief, K., Ferre, T., & Nijssen, B. (2006). Field testing of a soil corer air permeameter (SCAP) in desert soils. VADOSE ZONE JOURNAL, 5(4), 1257-1263.
- Chief, K., P., T., & Nijssen, B. (2006). Field testing of a Soil Corer Air Permeameter (SCAP) in desert soils. Vadose Zone Journal, 5(4), 1257-1263.More infoAbstract: Measurements of air permeability are useful both directly, to assess gas phase movement through soils, and indirectly as a proxy for soil hydraulic conductivity. Several designs have been presented for field-based air permeameters; however, none are suitable for use in gravelly desert soils. We designed an air permeameter compatible with a standard soil corer to facilitate insertion into desert soils. The soil corer air permeameter (SCAP) uses digital components to measure flow rates under low-pressure gradients to improve accuracy, ease of use, and portability. The SCAP allows the extraction of undisturbed soil samples for laboratory analysis, providing direct comparisons of air permeability (ka) with other soil physical and hydraulic properties. The soil sample can be extracted before measuring ka, thus removing the need for a shape factor to account for divergent flow. In an analysis of the SCAP's performance, field testing showed that digital components operate well under field conditions; however, spanner wrench insertion holes must be sealed to provide correct ka measurements. The Jalbert and Dane shape factor for in situ ka is applicable for tilled, unstructured soils. However, significant soil-specific variability exists in the shape factor, so we recommend measuring ex situ ka in the field, where possible. Ex situ field ka and laboratory hydraulic conductivity (Ksat) measurements were compared and air to water permeability ratios were calculated to determine structural changes due to water saturation. For soils that could be extracted with minimal structural change, we found good correlation between ka and Ksat and reasonable agreement with previously published results. © Soil Science Society of America.
- Desilets, S. L., Ferre, T. P., & Troch, P. A. (2006). Effects of stream-aquifer disconnection on local flow patterns. WATER RESOURCES RESEARCH, 44(9).
- Faust, A. E., P., T., Schaap, M. G., Hinnell, A. C., & Brown Jr., G. E. (2006). Can basin-scale recharge be estimated reasonably with water-balance models?. Vadose Zone Journal, 5(3), 850-855.More infoAbstract: We examine in-place recharge as an example of the complex, basin-scale hydrologic processes that are being represented with simplified numerical models. The rate and distribution of recharge depend on local meteorological conditions and hydrogeologic properties. The pattern of recharge is defined predominantly by the distribution of net precipitation (precipitation less evapotranspiration), but different pedotransfer functions (PTFs) predict different fractions of precipitation that become in-place recharge at a given location. At any single location, these differences can often be explained on the basis of the PTF characteristics, but because of the complex averaging that occurs across a basin, the combined effects of meteorological variation and soil textural variation on the basin-wide recharge rates cannot be predicted on the basis of the characteristics of different PTFs. In fact, we show that the same basin-scale numerical model, using identical inputs and modeling options, can produce almost an order of magnitude variation in predicted basin total recharge depending on the choice of PTF. This suggests that sensitivity analyses should be performed on the choice of constitutive relationship (e.g., PTF) when assessing the predictive capability of basin-scale hydrologic models. © Soil Science Society of America.
- Ferré, T., Hinnell, A. C., & Blainey, J. B. (2006). Inferring hydraulic properties using surface-based electrical resistivity during infiltration. Leading Edge (Tulsa, OK), 25(6), 720-723.More infoAbstract: Hydraulic conductivity and sorptivity are rock properties of primary importance for subsurface hydrologic analysis. Standard methods to determine these properties, such as ring infiltrometers, are based on adding water under constant pressure and monitoring the water flux into the ground. Ring infiltrometers are tens of centimeters in diameter. However, the concept of inferring hydraulic properties by monitoring infiltration beneath ponded water could be applied to hydrologic studies at larger scales. Two such cases, for which it may be useful to infer hydraulic properties, are artificial recharge facilities and ephemeral streams (Figure 1). © 2006 Society of Exploration Geophysicists.
- Hinnell, A. C., Ferre, T. P., & Warrick, A. W. (2006). The influence of time domain reflectometry rod induced flow disruption on measured water content during steady state unit gradient flow. WATER RESOURCES RESEARCH, 42(8).
- Hinnell, A. C., P., T., & Warrick, A. W. (2006). The influence of time domain reflectometry rod induced flow disruption on measured water content during steady state unit gradient flow. Water Resources Research, 42(8).More infoAbstract: Intrusive measurement techniques require placing a sensor within the sample, possibly changing the conditions under which the measurement is collected and thereby affecting the quality of the measurement. In this study we consider time domain reflectometry (TDR), which is an intrusive water content measurement method. TDR rods are impermeable, and thus water is forced to flow around the rods. In an unsaturated medium this changes the water content distribution in the vicinity of the rods, with the water content increased at the tops of the rods and decreased at the bottoms of the rods. TDR has nonuniform spatial sensitivity, with much higher sensitivity immediately adjacent to rods, in the regions that experience the greatest change in water content due to this flow disruption. Furthermore, the spatial sensitivity of TDR depends on the water content distribution within the sample volume. This raises the possibility that flow disruptions caused by TDR rods may affect the TDR-measured water content. In this study we are specifically interested in the effects of flow disruption due to TDR rods. Therefore we consider steady state unit gradient unsaturated flow in a homogeneous medium to eliminate spatial heterogeneity of water content due to soil heterogeneity and transient flow conditions. For common TDR probe designs in the wide range of soils examined, flow disruption gives rise to a water content measurement error that is less than 0.005 cm3 cm-3. This is smaller than the reported accuracy of the TDR method of 0.02 cm3 cm-3. As a result, we conclude that it is appropriate to ignore flow disruption caused by commonly used TDR probes when assessing sources of TDR measurement error. Copyright 2006 by the American Geophysical Union.
- Kawamoto, K., Moldrup, P., Ferre, T., Tuller, M., Jacobsen, O. H., & Komatsu, T. (2006). Linking the gardner and campbell models for water retention and hydraulic conductivity in near-saturated soil. SOIL SCIENCE, 171(8), 573-584.
- Kawamoto, K., Moldrup, P., P., T., Tuller, M., Jacobsen, O. H., & Komatsu, T. (2006). Linking the Gardner and Campbell models for water retention and hydraulic conductivity in near-saturated soil. Soil Science, 171(8), 573-584.More infoAbstract: Linking the classical Gardner and Campbell models for soil hydraulic properties yields a combined Gardner-Campbell (GC) relationship for predicting unsaturated hydraulic conductivity (K) from soil-water retention. The new GC water retention and hydraulic conductivity relationships are described by simple linearized expressions based on Campbell-b-scaled values of volumetric soil-water content (θ). The GC hydraulic properties models include four parameters, the pore connectivity parameter x (typically between 1 and 2), the Campbell pore size distribution parameter b, the Gardner macroscopic capillary length λ, and the air-entry soil-water matric potential (ψ)e. In the GC model for K(θ), these parameters are merged into a single dimensionless parameter, A. The GC models are applied to seven different undisturbed soils within a soil-water matric potential ψ with a range of 0 to -60 cm H2O. Results show that the simple GC ψ(θ) model adequately describes water retention data close to saturation, and that the GC K(θ) model performs well for predicting near-saturated hydraulic conductivity. The GC water retention and hydraulic conductivity parameters were incorporated into Wooding's equation for steady-state infiltration rate to examine the effects of variability in physical characteristics on infiltration. The steady-state infiltration rate was less sensitive to the GC water retention and hydraulic conductivity parameters than the saturated hydraulic conductivity. The GC models, which combine advantages of the Gardner model for linearization of the Richards' equation and the simple Campbell model for soil-water retention, seem useful for describing or predicting near-saturated soil hydraulic properties and for stochastic simulations of field-scale water infiltration. Copyright © 2006 by Lippincott Williams & Wilkins, Inc.
- P., M., Ferré, T., Nijssen, B., & Washburne, J. (2006). Design and testing of a low-cost soil-drying oven. Vadose Zone Journal, 5(3), 856-859.More infoAbstract: Measuring gravimetric soil water content is a relatively elementary laboratory procedure; however, the inaccessibility of a laboratory oven makes this activity impractical for K-12 students. The Soil Moisture Campaign (SMC) Project of the Global Learning and Observation to Benefit the Environment (GLOBE) Program was developed to use gravimetric water content measurement as an introduction to earth science research for K-12 students. We have designed and tested a low-budget, low-technology "light-bulb oven" that is affordable enough for use in a classroom. The light-bulb oven was tested by drying replicate samples of four different soil types in the light-bulb oven and in a traditional laboratory oven. The results showthat the performance of the light-bulb oven was comparable to that of a traditional laboratory oven. © Soil Science Society of America.
- Thomasson, M. J., Wierenga, P. J., & Ferre, T. (2006). A field application of the scaled-predictive method for unsaturated soil. VADOSE ZONE JOURNAL, 5(4), 1093-1109.
- Thomasson, M. J., Wierenga, P. J., & Ferré, T. (2006). A field application of the scaled-predictive method for unsaturated soil. Vadose Zone Journal, 5(4), 1093-1109.More infoAbstract: Unsaturated hydraulic conductivity is important to many vadose zone processes. However, there is uncertainty regarding how laboratory-and field-measured hydraulic property measurements can be combined with soil textural data to improve the description of the unsaturated hydraulic conductivity function at the field scale. In this investigation, we examine a scaled-predictive method for defining the hydraulic conductivity function. This approach uses field-measured data to adjust the hydraulic conductivity relationship developed using either laboratory measurements or soil textural data. In addition, both hydraulic property models were scaled using field-measured data collected during a controlled infiltration experiment. Data from a second controlled infiltration experiment were used to evaluate the hydraulic property models based on accuracy of prediction of the arrival time of a wetting front and the water content distribution with time. The unadjusted laboratory-derived parameters provide the best first approximation for predicting the wetting front arrival. Both hydraulic property models gave more accurate predictions of the wetting front arrival after adjustment with field-measured data. Both scaled models predicted the water content distributions poorly. These predictions were improved, especially for the pedotransfer model, if the scaling was applied to only the lower portion of the soil profile. © Soil Science Society of America.
- Whitaker, M., Ferre, P. A., & Washburne, J. C. (2006). Design and Testing of a Low-Cost Soil-Drying Oven. Vadose Zone J, 5, 856-859.
- Whitaker, M., Ferre, T., Nijssen, B., & Washburne, J. (2006). Design and testing of a low-cost soil-drying oven. VADOSE ZONE JOURNAL, 5(3), 856-859.
- Baker, V. R., Dohm, J. M., Fairén, A. G., Ferré, T. P., Ferris, J. C., Miyamoto, H., & Schulze-Makuch, D. (2005). Extraterrestrial hydrogeology. Hydrogeology Journal, 13(1), 51-68.More infoAbstract: Subsurface water processes are common for planetary bodies in the solar system and are highly probable for exoplanets (planets outside the solar system). For many solar system objects, the subsurface water exists as ice. For Earth and Mars, subsurface saturated zones have occurred throughout their planetary histories. Earth is mostly clement with the recharge of most groundwater reservoirs from ample precipitation during transient ice- and hot-house conditions, as recorded through the geologic and fossilized records. On the other hand, Mars is mostly in an ice-house stage, which is interrupted by endogenic-driven activity. This activity catastrophically drives short-lived hydrological cycling and associated climatic perturbations. Regional aquifers in the Martian highlands that developed during past, more Earth-like conditions delivered water to the northern plains. Water was also cycled to the South Polar Region during changes in climate induced by endogenic activity and/or by changes in Mars' orbital parameters. Venus very likely had a warm hydrosphere for hundreds of millions of years, before the development of its current extremely hot atmosphere and surface. Subsequently, Venus lost its hydrosphere as solar luminosity increased and a run-away moist greenhouse took effect. Subsurface oceans of water or ammonia-water composition, induced by tidal forces and radiogenic heating, probably occur on the larger satellites Europa, Ganymede, Callisto, Titan, and Triton. Tidal forces operating between some of the small bodies of the outer solar system could also promote the fusion of ice and the stability of inner liquid-water oceans. © Springer-Verlag 2005.
- Burke, E. J., Harlow, R. C., & Ferre, T. (2005). Measuring the dielectric permittivity of a plant canopy and its response to changes in plant water status: An application of Impulse Time Domain Transmission. PLANT AND SOIL, 268(1-2), 123-133.
- Burke, E. J., Harlow, R. C., & P., T. (2005). Measuring the dielectric permittivity of a plant canopy and its response to changes in plant water status: An application of Impulse Time Domain Transmission. Plant and Soil, 268(1), 123-133.More infoAbstract: Impulse Time Domain Transmission (ITDT) has been used to measure the complex dielectric permittivity of media such as ethanol, water and variably saturated sand. This paper applies ITDT to measurements of the complex dielectric permittivity of a vegetation canopy. The dielectric permittivity of a vegetation canopy is very close to that of air and only very small changes in its value will occur with changes in plant water status. This paper presents preliminary results demonstrating that ITDT can make repeatable measurements of the complex components of the dielectric permittivity of a plant canopy. Furthermore, ITDT is shown to be highly sensitive to the very small changes in dielectric that occur as a result of changes in plant water status. Based on these preliminary results, there are potential applications foreseen for ITDT in microwave remote sensing, irrigation scheduling, plant physiological ecology, and fire susceptibility. © Springer 2005.
- Delin, K. A., Jackson, S. P., Johnson, D. W., Burleigh, S. C., Woodrow, R. R., McAuley, J. M., Dohm, J. M., Felipe, I. p., P., T., Rucker, D. F., & Baker, V. R. (2005). Environmental studies with the sensor web: Principles and practice. Sensors, 5(1-2), 103-117.More infoAbstract: In 1997, the Sensor Web was conceived at the NASA/Jet Propulsion Laboratory (JPL) to take advantage of the increasingly inexpensive, yet sophisticated, mass consumer-market chips for the computer and telecommunication industries and use them to create platforms that share information among themselves and act in concert as a single instrument. This instrument would be embedded into an environment to monitor and even control it. The Sensor Web's purpose is to extract knowledge from the data it collects and use this information to intelligently react and adapt to its surroundings. It links a remote end-user's cognizance with the observed environment. Here, we examine not only current progress in the Sensor Web technology, but also its recent application to problems in hydrology to illustrate the general concepts involved. © 2005 by MDPI.
- Franz, T. E., Zreda, M., Ferre, T. P., Rosolem, R., Zweck, C., Stillman, S., Zeng, X., & Shuttleworth, W. J. (2005). Measurement depth of the cosmic ray soil moisture probe affected by hydrogen from various sources. WATER RESOURCES RESEARCH, 48.
- Hook, W. R., Ferre, T., & Livingston, N. J. (2005). The effects of salinity on the accuracy and uncertainty of water content measurement (vol 68, pg 47, 2004). SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 69(3), 931-931.
- Hook, W. R., Ferré, T., Livingston, N. J., Bassey, C. E., & Stuchly, S. S. (2005). Erratum: The effects of salinity on the accuracy and uncertainty of water content measurement (Soil Science Society of America Journal (January-Febuary 2004) 68 (47-56)). Soil Science Society of America Journal, 69(3), 931-.
- Hook, W., Ferre, T., & Livingston, N. (2005). The effects of salinity on the accuracy and uncertainty of water content measurement. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 68(1), 47-56.
- Rucker, D. F., & Ferre, T. (2005). Automated water content reconstruction of zero-offset borehole ground penetrating radar data using simulated annealing. JOURNAL OF HYDROLOGY, 309(1-4), 1-16.
- Rucker, D. F., & Ferré, T. P. (2005). Automated water content reconstruction of zero-offset borehole ground penetrating radar data using simulated annealing. Journal of Hydrology, 309(1-4), 1-16.More infoAbstract: The automated inversion of water content profiles from first arrival travel time data collected with zero-offset borehole ground penetrating radar is discussed. The inversion algorithm sets out to find the water content profile that minimizes a least-squares objective function representing the difference between the modeled and measured first arrival travel time. Ray-tracing analysis is used to determine the travel time for direct and critically refracted paths to identify the first arrival travel time. This automated method offers improvement over a previously presented graphical solution that considers both direct and critical refractions. Specifically, this approach can identify thinner layers and allow for the incorporation of uncertainty in the travel time measurements to determine the depth-specific uncertainty of the inferred water content profile through multiple simulations using a stochastic approach. © 2004 Elsevier B.V. All rights reserved.
- Rucker, D. F., Warrick, A. W., & Ferré, T. P. (2005). Parameter equivalence for the Gardner and van Genuchten soil hydraulic conductivity functions for steady vertical flow with inclusions. Advances in Water Resources, 28(7), 689-699.More infoAbstract: The analytic element method is well suited for the Gardner hydraulic conductivity function, but is limited in describing real soils. Therefore, parameter equivalence between the van Genuchten and Gardner hydraulic conductivity functions is explored for the case of steady vertical flow through a homogeneous medium with a single inclusion, i.e., a binary soil. The inclusion has different hydraulic parameters than the background medium. Equivalence is established using three methods: (1) effective capillary drive; (2) capillary length; (3) and a least-squares optimization method that aims to fit a Gardner function to a corresponding van Genuchten function by minimizing the difference in log conductivity over a specified pressure range. Comparisons between hydraulic models are made based on scatterplots of pressure head and the vertical Darcian flux obtained using a finite-element numerical solution with both constitutive relations. For applicability of an equivalent Gardner function over a broad range of pressure heads, the crossover pressure must be maintained between the two parametric functions. The crossover pressure is defined as the pressure in which the hydraulic conductivity of the inclusion is equal to the background. It can be shown that a hybrid methodology of preserving the crossover pressure exactly and using the effective capillary drive will result in hydraulic parameters that are easily obtained and provide good agreement between the conductivity functions of the GR model to the VG model. © 2005 Elsevier Ltd. All rights reserved.
- Rucker, D., & Ferre, T. (2005). Parameter estimation for soil hydraulic properties using zero-offset borehole radar: Analytical method. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 68(5), 1560-1567.
- Blasch, K. W., Ferre, T., & Hoffmann, J. P. (2004). A statistical technique for interpreting streamflow timing using streambed sediment thermographs. VADOSE ZONE JOURNAL, 3(3), 936-946.
- Blasch, K. W., Ferré, T., & Hoffmann, J. P. (2004). A statistical technique for interpreting streamflow timing using streambed sediment thermographs. Vadose Zone Journal, 3(3), 936-946.More infoAbstract: A moving standard deviation (MSD) technique is developed to infer the onset and cessation of ephemeral streamflow using temperature data from the upper 2.25 m of streambed sediments. During periods of streamflow, shifting of the predominant thermal-transport mechanism within the sediments from conduction to advection produced changes in the amplitude of the vertically propagating diurnal temperature waves. Analytical expressions describing propagation of conductive and advective diurnal temperature waves through streambed sediments are presented for identifying depths with the largest changes in the diurnal temperature wave amplitude between periods of flow and no flow. The MSD statistical technique was developed to identify the thermal amplitude changes from bed sediment thermographs and to infer streamflow timing. The accuracy of the MSD technique is quantified using direct streamflow and streambed water content measurements. Accuracy of the technique was most sensitive to the MSD window length and the threshold parameter separating periods of conductive and advective heat transport. An alternative calibration procedure was developed using temperature measurements alone. The average error for streamflow timing was approximately 400 min for each event. The results show that temperature sensors may be deployed at a range of sediment depths depending on streamflow stage and soil thermal and hydraulic properties, and that the MSD procedure can provide an objective and repeatable means to quantify streamflow timing. © Soil Science Society of America.
- Delin, K., Jackson, S., Johnson, D., Burleigh, S., Woodrow, R., McAuley, J., Dohm, J., Ip, F., Ferre, T., Rucker, D., & Baker, V. (2004). Environmental studies with the Sensor Web: Principles and practice. SENSORS, 5(1-2), 103-117.
- Dickinson, J. E., Hanson, R. T., Ferré, T., & Leake, S. A. (2004). Inferring time-varying recharge from inverse analysis of long-term water levels. Water Resources Research, 40(7), W074031-W0740315.More infoAbstract: Water levels in aquifers typically vary in response to time-varying rates of recharge, suggesting the possibility of inferring time-varying recharge rates on the basis of long-term water level records. Presumably, in the southwestern United States (Arizona, Nevada, New Mexico, southern California, and southern Utah), rates of mountain front recharge to alluvial aquifers depend on variations in precipitation rates due to known climate cycles such as the El Niño-Southern Oscillation index and the Pacific Decadal Oscillation. This investigation examined the inverse application of a one-dimensional analytical model for periodic flow described by Lloyd R. Townley in 1995 to estimate periodic recharge variations on the basis of variations in long-term water level records using southwest aquifers as the case study. Time-varying water level records at various locations along the flow line were obtained by simulation of forward models of synthetic basins with applied sinusoidal recharge of either a single period or composite of multiple periods of length similar to known climate cycles. Periodic water level components, reconstructed using singular spectrum analysis (SSA), were used to calibrate the analytical model to estimate each recharge component. The results demonstrated that periodic recharge estimates were most accurate in basins with nearly uniform transmissivity and the accuracy of the recharge estimates depends on monitoring well location. A case study of the San Pedro Basin, Arizona, is presented as an example of calibrating the analytical model to real data.
- Furman, A., Ferre, T., & Warrick, A. (2004). Optimization of ERT surveys for monitoring transient hydrological events using perturbation sensitivity and genetic algorithms. VADOSE ZONE JOURNAL, 3(4), 1230-1239.
- Furman, A., P., T., & Warrick, A. W. (2004). Optimization of ERT surveys for monitoring transient hydrological events using perturbation sensitivity and genetic algorithms. Vadose Zone Journal, 3(4), 1230-1239.More infoAbstract: A simple yet powerful algorithm is presented for the optimal allocation of electrical resistivity tomography (ERT) electrodes to maximize measurement quality. The algorithm makes use of a definition of the sensitivity of an ERT array to a series of subsurface perturbations. An objective function that maximizes the average sensitivity of a survey comprised of a large number of arrays is defined. A simple genetic algorithm is used to find the optimal ERT survey if there is a limited time allowed for survey. We further show that this approach allows for user definition of the sensitivity distribution within the targeted area. Results show clear improvement in the sensitivity distribution. The total sensitivity of the optimized survey compared with typically used surveys composed of one array type. This improved sensitivity will allow for more accurate monitoring of static and transient vadose zone processes. Furthermore, the algorithm presented may be fast enough to allow for real-time optimization during time- lapse surveys. © Soil Science Society of America.
- Hinnell, A. C., Ferre, T. P., Vrugt, J. A., Huisman, J. A., Moysey, S., Rings, J., & Kowalsky, M. B. (2004). Improved extraction of hydrologic information from geophysical data through coupled hydrogeophysical inversion. WATER RESOURCES RESEARCH, 46.
- Hook, W. R., Ferré, T., & Livingston, N. J. (2004). The Effects of Salinity on the Accuracy and Uncertainty of Water Content Measurement. Soil Science Society of America Journal, 68(1), 47-56.More infoAbstract: We used an automatic network analyzer (ANA) operated in both time and frequency domain modes to investigate the measurement accuracy of metallic time domain reflectometry (TDR) probes operated in sands saturated with NaCl solutions of varying electrical conductivity (EC). We chose to use time domain transmission (TDT) measurements for this investigation to separate the effect of the bulk soil-probe interaction from the effect of the large reflection typically found at the air-soil boundary for a TDR configuration. Pulse travel times and their variability increase with increasing pore-water EC. The source of travel time variability arises from the extreme variability in pulse shape, thereby introducing a high degree of uncertainty to curve fitting routines used to determine travel times. Pulse shape distortion is due primarily to attenuation of high frequency components through conductive loss rather than by dispersion. There is generally good correspondence between pulse rise time and the average water content measurement error over a 0- to 40-dS m-1 EC range. For rise times
- Huisman, J. A., Bouten, W., Vrugt, J. A., & Ferré, P. (2004). Accuracy of frequency domain analysis scenarios for the determination of complex dielectric permittivity. Water Resources Research, 40(2), W024011-W02401112.More infoAbstract: Frequency domain analysis of time domain reflectometry waveforms has been shown to be useful for more accurate water content determination, water content determination in saline soils, and determination of such difficult to measure soil properties as specific surface area and soil solution conductivity. Earlier frequency domain analysis approaches to determine frequency-dependent dielectric properties of soils have used a variety of methods. In this paper, these methods for the determination of dielectric permittivity were compared using the Shuffled Complex Evolution Metropolis algorithm (SCEM-UA). SCEM-UA is a global optimization method that allows the simultaneous determination of optimal Debye parameters, which describe the dielectric permittivity as a function of frequency, and their confidence intervals. The analysis of numerically generated measurements with added instrumental noise showed that analysis of network analyzer measurements in the frequency domain potentially has the highest accuracy for determination of dielectric permittivity. Furthermore, the analysis of time domain reflectometry waveforms in the time domain was found to be more accurate than analysis of these waveforms in the frequency domain. Analysis of real network analyzer measurements in the time and frequency domain showed that both analysis scenarios allowed reasonably accurate estimates of the Debye parameters with the SCEM-UA algorithm, even when the true value of a parameter falls beyond the limits of the frequency bandwidth. However, frequency domain analysis of ethanol measurements showed that results were susceptible to model errors caused by nonideal probe behavior. These errors were larger for three-wire probes than for seven-wire probes. This study shows that the accuracy of the dielectric permittivity determination can be improved by reducing the model error. This can be achieved by the use of more accurate models, such as multiscatter functions, and by using more advanced probes, such as coaxial cells. The results also imply that future research on dielectric properties of soils should focus more on the use of network analyzers instead of cable testers, since model errors are more obvious in the frequency domain. The SCEM-UA algorithm proved to be a valuable tool in frequency domain analysis because reported problems with parameter identification and initialization of the optimization are circumvented with this global optimization algorithm.
- Masbruch, K., & Ferre, T. P. (2004). A Time Domain Transmission Method for Determining the Dependence of the Dielectric Permittivity on Volumetric Water Content: An Application to Municipal Landfills. VADOSE ZONE JOURNAL, 2(2), 186-192.
- Rucker, D. F., & Ferre, T. (2004). BGPR_Reconstruct: A MATLAB((R)) ray-tracing program for nonlinear inversion of first arrival travel time data from zero-offset borehole radar. COMPUTERS & GEOSCIENCES, 30(7), 767-776.
- Rucker, D. F., & Ferre, T. (2004). Hydraulic parameter estimation with a constant water flux boundary using zero-offset borehole radar. PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON GROUND PENETRATING RADAR, VOLS 1 AND 2, 719-722.
- Rucker, D. F., & Ferré, P. (2004). Correcting water content measurement errors associated with critically refracted first arrivals on zero offset profiling borehole ground penetrating radar profiles. Vadose Zone Journal, 3(1), 278-287.More infoAbstract: Borehole ground penetrating radar (BGPR) operated in zero offset profiling (ZOP) mode has promise for monitoring rapidly changing water contents within the subsurface. However, the coexistence of multiple travel paths through the subsurface can give rise to measurement errors. Specifically, in layered systems with sharp changes in water content with depth, critically refracted waves may arrive before direct waves at some depths. Velocity profiles are determined based on analyses of the travel time of the first-arriving energy at each depth. Therefore, correct velocity analysis requires that these travel times be classified according to the path followed by the first-arriving energy. We establish criteria that can be used to identify first-arriving critically refracted waves from travel time profiles. Through hypothetical examples and a field experiment, we demonstrate that these criteria allow for more accurate determination of the water content profile. However, these corrections are limited if thin, high water content layers are present in the subsurface. © Soil Science Society of America.
- Rucker, D. F., & Ferré, T. P. (2004). BGPRconstruct: A MATLAB® ray-tracing program for nonlinear inversion of first arrival travel time data from zero-offset borehole radar. Computers and Geosciences, 30(7), 767-776.More infoAbstract: A MATLAB program was developed to invert first arrival travel time picks from zero offset profiling borehole ground penetrating radar traces to obtain the electromagnetic wave propagation velocities in soil. Zero-offset profiling refers to a mode of operation wherein the centers of the bistatic antennae being lowered to the same depth below ground for each measurement. The inversion uses a simulated annealing optimization routine, whereby the model attempts to reduce the root mean square error between the measured and modeled travel time by perturbing the velocity in a ray tracing routine. Measurement uncertainty is incorporated through the presentation of the ensemble mean and standard deviation from the results of a Monte Carlo simulation. The program features a pre-processor to modify or delete travel time information from the profile before inversion and post-processing through presentation of the ensemble statistics of the water contents inferred from the velocity profile. The program includes a novel application of a graphical user interface to animate the velocity fitting routine. © 2004 Elsevier Ltd. All rights reserved.
- Rucker, D. F., & Ferré, T. P. (2004). Hydraulic parameter estimation with a constant water flux boundary using zero-offset borehole radar. Proceedings of the Tenth International Conference Ground Penetrating Radar, GPR 2004, 2, 719-722.More infoAbstract: A ray tracing algorithm for first arrival travel times from zero-offset borehole radar is coupled with an analytical solution to the one dimensional unsaturated water flow equation with a constant flux top boundary condition to invert for soil hydraulic properties. The analytical solution for Richards' equation relies on a non dimensional form of Burger's equation using a Broadbridge and White (BW) soil. The BW soil is described with three parameters: saturated hydraulic conductivity (K s), sorptivity (S), and a dimensionless parameter (C). The ray tracing algorithm makes use of the the arrival time of first arriving waves (direct or critically refracted) to track the wetting front through the subsurface during infiltration. From the time series of first arrival travel time data collected from one depth, the K s can be determined, provided that the wetting front was sharp enough to cause critical refraction at its edge. To determine the other parameters uniquely, co-located pressure head data is needed from the dry range.
- Rucker, D. F., & P., T. (2004). Parameter estimation for soil hydraulic properties using zero-offset borehole radar: Analytical method. Soil Science Society of America Journal, 68(5), 1560-1567.More infoAbstract: Inverse methods to obtain soil hydraulic parameters are becoming increasingly popular, due to their more rapid, complete, and robust estimations of hydraulic parameters compared with traditional direct methods. We present a method to infer hydraulic parameters based on first arrival travel time measurements made with zero-offset borehole ground penetrating radar. (BGPR). Borehole ground penetrating radar offers many advantages for field-scale monitoring of transient processes including the ability to measure rapidly, over relatively large soil volumes, with high temporal resolution and to great depths. The BGPR measurements are used to infer the position of the wetting front during infiltration. The analysis makes use of critical refraction at the edge of the wetting front, which gives rise to a linear increase in BGPR travel time with time as the wetting front passes beneath the antennae. The slope of this response is used directly to calculate the hydraulic conductivity. We demonstrate that unique determination of the van Genuchten α and n parameter is not possible with BGPR data alone; at least one pressure head measurement in the dry range (early time) is required. We employ a nonlinear least squares parameter estimation code to obtain the optimal α and n parameters for synthetic data. The method could potentially be applied to areas of artificial recharge in an infiltration basin, natural recharge in an ephemeral stream, or agricultural settings where the surface is flooded with irrigated water.
- Rucker, D., & Ferre, T. (2004). Correcting water content measurement errors associated with critically refracted first arrivals on zero offset profiling borehole ground penetrating radar profiles. VADOSE ZONE JOURNAL, 3(1), 278-287.
- Vereecken, H., Hubbard, S., Binley, A., & Ferre, T. (2004). Hydrogeophysics: An introduction from the guest editors. VADOSE ZONE JOURNAL, 3(4), 1060-1062.
- Vereecken, H., Hubbard, S., Binley, A., & Ferré, T. (2004). Hydrogeophysics: An introduction from the guest editors. Vadose Zone Journal, 3(4), 1060-1062.
- Callegary, J. B., Ferre, T. P., & Groom, R. W. (2003). Three-Dimensional Sensitivity Distribution and Sample Volume of Low-Induction-Number Electromagnetic-Induction Instruments. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 76(1), 85-91.
- Creutzfeldt, B., Ferre, T., Troch, P., Merz, B., Wziontek, H., & Guentner, A. (2003). Total water storage dynamics in response to climate variability and extremes: Inference from long-term terrestrial gravity measurement. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 117.
- Dowman, C. E., Ferré, T. P., Hoffmann, J. P., Rucker, D. F., & Callegary, J. B. (2003). Quantifying ephemeral streambed infiltration from downhole temperature measurements collected before and after streamflow. Vadose Zone Journal, 2(4), 595-601.More infoAbstract: A constant flux infiltration experiment was conducted to determine the feasibility of using down hole temperature measurements to estimate infiltration flux. Temperatures measured using a down hole thermistor with in a 15.4-m-deep borehole compare well with temperatures measured with buried thermocouples in an adjacent borehole to 5 m depth. Numerical forward model simulations were conducted using VS2DI. A numerical sensitivity analysis showed that the temperature profile was most sensitive to the average temperature of the infiltrating water, the infiltration flux, and the specific heat capacity of dry soil. The high sensitivity of these variables allows for a simple sequential optimization to be used to estimate the average temperature of the infiltrating water, the water flux, and the specific heat capacity of dry soil from numerical inversion of temperature measurements. Down hole temperature measurements could be a useful complement to shallow streambed temperature methods, allowing for better quantification of the contribution of streambed infiltration to basin-scale recharge. © Soil Science Society of America.
- Dowman, C., Ferre, T., Hoffmann, J. P., Rucker, D. F., & Callegary, J. B. (2003). Quantifying Ephemeral Streambed Infiltration from Downhole Temperature Measurements Collected Before and After Streamflow. VADOSE ZONE JOURNAL, 2(4), 595-601.
- Ferre, T., & Kluitenberg, G. J. (2003). Advances in Measurement and Monitoring Methods: Preface from the Guest Editors. VADOSE ZONE JOURNAL, 2(4), 443-443.
- Ferre, T., Nissen, H. H., Knight, J. H., & Moldrup, P. (2003). Transverse sample area of two- and three-rod time domain reflectometry probes: Electrical conductivity. WATER RESOURCES RESEARCH, 39(9).
- Ferre, T., Rudolph, D. L., & Kachanoski, R. G. (2003). The electrical conductivity response of a profiling time-domain reflectometry probe. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 67(2), 494-496.
- Ferre, T., von, G. G., & Ferre, L. A. (2003). Monitoring the Maximum Depth of Drainage in Response to Pumping Using Borehole Ground Penetrating Radar. VADOSE ZONE JOURNAL, 2(4), 511-518.
- Ferré, T., Glinski, G. v., & Ferré, L. (2003). Monitoring the maximum depth of drainage in response to pumping using borehole ground penetrating radar. Vadose Zone Journal, 2(4), 511-518.More infoAbstract: There are many methods available for nondestructive measurement of volumetric water content. However, no current method can monitor rapidly to great depths with high spatial resolution over large sample volumes and with minimal need for medium-specific calibration. Borehole ground penetrating radar (BPGR) may provide this capability. It is well established that BGPR can make rapid measurements to great depth. Like time domain reflectometry (TDR), BGPR infers the water content from dielectric permittivity measurements, which show a robust correlation with volumetric water content. The goal of this investigation was to determine whether BGPR water content measurements made with a vertical sampling interval that is smaller than the antenna length could be used to measure the water content profile with high spatial resolution. Repeat water content profiles measured with BGPR during a pumping test and under static conditions 1 yr later are presented. The results show that BGPR measurements are highly repeatable, allowing for differencing of profiles to determine the water content change profile. However, this high repeatability required calibration over a depth range below the water table due to instrument drift and operator inconsistencies. Although critical refractions obscure the water content profile near the ground surface, there is no evidence that refracted waves have deleterious effects on travel time profiles collected across the water table, allowing for determination of the maximum depth of drainage from the water content change profiles. Thereis good agreement between the patterns of maximum depth of drainage and water table depth during pumping and recovery. However, the maximum depth of drainage, referenced to the middle of the BGPR antennae, is consistently 50 cm deeper than the water table. The results demonstrate that the primary limitation on the achievable resolution of water content monitoring with BGPR is the user-selected measurement sample interval, which can be much smaller than the antenna length. However, the cause of the near constant downward offsetof the BGPR measurements compared with the water table depth must be studied further to allow for direct use of BGPR to track water movement during pumping and recovery. © Soil Science Society of America.
- Ferré, T., Rudolph, D. L., & Kachanoski, R. G. (2003). The electrical conductivity response of a profiling time-domain reflectometry probe. Soil Science Society of America Journal, 67(2), 494-496.More infoAbstract: Direct measurements of changes in the electrical conductivity (EC) are made using the profiling time domain reflectometry (TDR) probe described in a previous work. This is the first demonstration of the ability of a TDR probe to measure EC through coatings or access tubes. Based on the ability of this probe to profile the water content, this suggests that a single instrument may be able to profile changes in water content and electrolytic solute concentration during transient flow through the unsaturated zone.
- Furman, A., P., T., & Warrick, A. W. (2003). A sensitivity analysis of electrical resistivity tomography array types using analytical element modeling. Vadose Zone Journal, 2(3), 416-423.More infoAbstract: The analytic element method is used to investigate the spatial sensitivity of different electrical resistivity tomography (ERT) arrays. By defining the sensitivity of an array to a subsurface location we were able to generate maps showing the distribution of the sensitivity throughout the subsurface. This allows us to define regions of the subsurface where different ERT arrays are most and least sensitive. We compared the different arrays using the absolute value of the sensitivity and using its spatial distribution. Comparison is presented for three commonly used arrays (Wenner, Schlumberger, and double dipole) and for one atypical array (partially overlapping). Most common monitoring techniques use a single measurement to measure a property at a single location. The spatial distribution of the property is determined by interpolation of these measurements. In contrast, ERT is unique in that multiple measurements are interpreted simultaneously to create maps of spatially distributed soil properties. We define the spatial sensitivity of an ERT survey to each location on the basis of the sum of the sensitivities of the single arrays composing the survey to that location. With the goal of applying ERT for time-lapse measurements, we compared the spatial sensitivities of different surveys on a per measurement basis. Compared are three surveys based on the typical Wenner, Schlumberger, and double dipole arrays, one atypical survey based on the partially overlapping array, and one mixed survey built of arrays that have been shown to be optimal for a series of single perturbations. Results show the inferiority of the double dipole survey compared with other surveys. On a per measurement basis, there was almost no difference between the Wenner and the Schlumberger surveys. The atypical partially overlapping survey is superior to the typical arrays. Finally, we show that a survey composed of a mixture of array types is superior to all of the single array type surveys. By analyzing the spatial sensitivity of the single array, and most significantly the sensitivity of the ERT survey, we set the basis for quantitative measurement of subsurface properties using ERT, with applications to both static and transient hydrologic processes. © Soil Science Society of America.
- Harlow, R. C., Burke, E. J., & P., T. (2003). Measuring water content in saline sands using impulse time domain transmission techniques. Vadose Zone Journal, 2(3), 433-439.More infoAbstract: This paper discusses two time domain transmission (TDT) electromagnetic methods for measuring soil water content in a sand and examines the impact of pore water salinity on the resulting measurements. The first technique calculates the time taken by an impulse traveling one way through the medium relative to its time taken in air. The second method converts this impulse to the frequency domain via a Fast Fourier Transform (FFT) and calculates the travel time from the difference in phase measured in air and that measured in the medium at each frequency, resulting in a measurement of the frequency-dependent travel time. The relationship between travel time and water content was determined for pore water electrical conductivities (EC) ranging from 0.5 to 40 dS m-1. At 0.5 dS m-1 the relationship was similar to that found by previous researchers using time domain reflectometry (TDR) measurements. At pore water EC ≥5 dS m-1 the travel time was faster than that found for 0.5 dS m-1 at the same water content, contradicting traditional thinking based on transmission line theory and differing from results of TDR methods. In addition, for pore water EC ≥5 dS m-1, the relationship determined between travel time and water content was shown to be independent of pore water EC, to the precision of the TDT measurement technique. As a result, the impulse TDT method and this calibration relationship may improve our ability to measure soil water content under natural field conditions and may encourage further investigation of the impact of salinity on the spectral dielectric response of porous media. © Soil Science Society of America.
- Harlow, R. C., Burke, E. J., Ferre, T., Bennett, J. C., & Shuttleworth, W. J. (2003). Measuring Spectral Dielectric Properties Using Gated Time Domain Transmission Measurements. VADOSE ZONE JOURNAL, 2(3), 424-432.
- Harlow, R. C., Burke, E. J., Ferré, T. P., Bennett, J. C., & Shuttleworth, W. J. (2003). Measuring spectral dielectric properties using gated time domain transmission measurements. Vadose Zone Journal, 2(3), 424-432.More infoAbstract: A method to measure the frequency-dependent dielectric permittivity of simple materials based on a time domain transmission technique is described. A vector network analyzer (VNA) was connected to a twin-rod transmission line via a coaxial cable. The complex dielectric permittivity was found from the difference in phase and magnitude between a reference line surrounded by air and the same line surrounded by the substance of interest. The spectral response showed periodic variations in the dielectric permittivity as a result of multiple reflections in the experimental setup. These multiple reflections can be removed by using a time domain gate that selects only the primary transmission and filters out any subsequent reflections. It is essential that the apparatus be designed so that the first reflection is well separated from the primary transmission. This requires a long transmission line and along coaxial cable. However, if the transmission line is too long, excessive conductive or dielectric losses make it hard to detect the primary transmission. The application of the gated time domain transmission technique to measure the frequency-dependent dielectric permittivity of water, ethanol, sand and saturated sand is demonstrated. This method does not have the typical limitations on sample volume. In addition, it does not require the assumptions necessary in previous time domain spectroscopy methods applied to open transmission lines where a probe model is used in conjunction with simple Debye relaxation and/or inverse methods.© Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA.
- Masbruch, K., & Ferré, T. (2003). A time domain transmission method for determining the dependence of the dielectric permittivity on volumetric water content: An application to municipal landfills. Vadose Zone Journal, 2(2), 186-192.More infoAbstract: A method for determining the dependence of the dielectric permittivity of municipal refuse on its volumetric water content is developed and tested. The method is based on time domain transmission (TDT) measurements collected with an automated network analyzer (ANA). Measurements in variably saturated sand were first made to test the method's ability to measure the apparent dielectric permittivity. The method was then extended to samples of municipal refuse to determine whether a single calibration can be used to describe the relationship between the dielectric permittivity and the volumetric water content of refuse. The results show that the relationship between the dielectric permittivity and the volumetric water content within the refuse shows significant spatial variability. The results do show, however, that a calibration based on multiple samples collected throughout the landfill can be used to measure the volumetric water content with a root mean square volumetric water content measurement error of
- Nissen, H. H., Ferre, T., & Moldrup, P. (2003). Sample area of two- and three-rod time domain reflectometry probes. WATER RESOURCES RESEARCH, 39(10).
- Nissen, H. H., Ferré, P. A., & Moldrup, P. (2003). Metal-coated printed circuit board time domain reflectometry probes for measuring water and solute transport in soil. Water Resources Research, 39(7), HWC21-HWC213.More infoAbstract: Metal-coated printed circuit board (PCB) time domain reflectometry (TDR) probes for simultaneous small-scale measurements of soil water content (θ) and bulk soil electrical conductivity (ECb) was developed and tested. To resolve corrosion problems associated with previous PCB probe designs, a nickel and gold plated copper waveguide is positioned at the surface of the PCB circuit laminate. In a numerical analysis the effect of PCB probe design parameters on the sample area distribution transverse to wave propagation was examined. The conclusions of the analysis were (1) two-rod PCB probes have a larger sample area compared to three-rod probes, (2) the probe rod separation has a larger effect on the sample area compared to rod width, and (3) if the thickness of the circuit laminate is 2/3 of the rod separation, a two-rod PCB probe is insensitive to the medium below the laminate. On the basis of the numerical analysis, 20 different metal-coated PCB probes were produced: five probe types on four laminates. Correct determination of PCB probe measured θ and ECb was ensured by calibration. The performance of the PCB probes in soil was tested in a water and solute transport experiment. Twenty PCB probes and five conventional two-rod TDR probes were positioned in five horizontal transects. Tap water was added to an air-dry soil and exchanged with a KCl solution. All probes registered changes in θ and ECb, but in some cases the level measured by the PCB probes differed significantly from the conventional probes. An EC b(θ) data analysis revealed that the differences was caused by local variations in θ rather than erroneous calibrations of the PCB probes. The metal-coated PCB probe is a useful new TDR probe design for simultaneous small-scale measurements of water and solute transport.
- Nissen, H. H., Ferré, P. A., & Moldrup, P. (2003). Time domain reflectometry developments in soil science: I. Unbalanced two-rod probe spatial sensitivity and sampling volume. Soil Science, 168(2), 77-83.More infoAbstract: The use of parallel two-rod time domain reflectometry (TDR) probes is widespread because the two-rod probe is the least destructive of the conventional TDR probes and has a larger sample volume than a three-rod probe of equal dimensions. However, in order to transform the electromagnetic signal from unbalanced to balanced at the point of connection with the cable, two-rod probes have been thought to require a balun, making the probe construction both more expensive and more complicated. In this study, a two-rod probe without a balun (unbalanced) was exposed to a rising air-water interface, creating a sharp dielectric permittivity boundary within the sample volume of the probe. The probes were horizontal, but they were located within a vertical plane, i.e., one rod was placed above the other. A shorting diode technique was used to improve the location of the end reflection on the TDR traces. Two experiments were carried out differing only in the connection of the coaxial cable to the probe rods. In one experiment, the conductor was connected to the lower rod and the shield was connected to the upper rod. In the second experiment these connections were reversed. Using a numerical model, the relative dielectric permittivity (K) responses of two-rod balanced and unbalanced TDR probes were predicted as a function of the fluid interface height. The measured and modeled responses of the unbalanced two-rod probe matched perfectly, and there was no observed increase in the spatial sensitivity of the probe adjacent to either rod. Furthermore, the modeled probe responses as well as the sample areas for the balanced and unbalanced probe configurations were identical. Based on these results, we suggest that baluns be omitted from two-rod TDR probe designs.
- Nissen, H. H., Ferré, P. A., & Moldrup, P. (2003). Time domain reflectometry developments in soil science: II. Coaxial flow cell for measuring effluent electrical conductivity. Soil Science, 168(2), 84-89.More infoAbstract: Time Domain Reflectometry (TDR) is a recognized and widely used technique for measuring electrical conductivity (EC) and volumetric water content (θ) in porous media. The ability of TDR to measure both EC and θ is especially appealing in solute transport in variably saturated media. It is commonly assumed that TDR measurements are representative of the EC and θ in the horizontal plane in which the probe is located. The problem is that it is difficult to recognize heterogeneous solute transport with TDR, especially if it occurs outside the sample volume or in regions where the solute is giving little weight to the TDR-measured EC. To determine the presence of heterogeneous solute transport effectively, there is a need for a device to monitor the EC boundary conditions. In this study, a simple and easy-to-make coaxial flow cell is designed and tested for this purpose. The flow cell is made primarily of cheap, prefabricated, and readily available components, and the construction requires only a hacksaw and some welding skills. The idea is to make the effluent from a solute transport experiment pass through the coaxial flow cell, thereby obtaining a measure of the effluent EC. In addition to providing detailed information on the solute transport through the entire sample of porous medium, it will also detect, for example, bypass flow. A solute transport experiment was carried out in a PVC pipe packed with coarse silica sand under saturated conditions to calibrate the flow cell and to demonstrate its potential use. Step input breakthrough and breakdown functions were created using tap water and a KCl solution. Highly detailed measurements of EC in the effluent were obtained, from which solute transport parameters can easily be inferred.
- Nissen, H. H., Ferré, P. A., & Moldrup, P. (2003). Time domain reflectometry developments in soil science: III. Small-scale probe for measuring bulk soil electrical conductivity. Soil Science, 168(2), 90-98.More infoAbstract: It is commonly believed that Time Domain Reflectometry (TDR) measures bulk soil electrical conductivity (EC) and volumetric water content within the same, well-defined sample volume. However, recent studies have shown that the sample volume is a function of the distribution of EC and dielectric permittivity near the probe. One result of this spatially distributed sensitivity is measurement-induced dispersion. That is, when TDR is used to measure a sharp advancing solute front, the measured EC is some average across the sharp front, leading to incorrect smoothing of the breakthrough curve. A reduction of the probe dimensions is the only solution to this artificial smoothing problem. In this study, a small scale TDR probe is presented and tested. The small probe dimensions produce a near point measurement of EC but make water content measurements unreliable. The small scale EC TDR (SEC-TDR) probe is simple, inexpensive, and made with readily available components. A solute transport experiment was carried out under saturated conditions in a plastic pipe packed with coarse silica sand. Five SEC-TDR probes were inserted, monitoring the EC at various positions along the column, and a coaxial flow cell was used to monitor the effluent EC. Step solute breakthrough and displacement breakthrough responses were created using tap water and a KCl solution. Highly detailed measurements of EC were obtained from which the dispersivity (λ) was inferred. The λ measured by the SEC-TDR probes was significantly lower than λ measured in the effluent by the coaxial flow cell, suggesting that the SEC-TDR probe can reduce the problem of TDR-induced dispersion under even the most challenging conditions.
- Nissen, H. H., P., T., & Moldrup, P. (2003). Sample area of two- and three-rod time domain reflectometry probes. Water Resources Research, 39(10), SBH91-SBH911.More infoAbstract: Recent advances in the application of numerical analyses to the spatial sensitivity of conventional two- and three-rod time domain reflectometry (TDR) probes allow for investigation of the response of TDR in spatially heterogeneous media. In this study, we present numerical analyses and laboratory measurements of the effects of steep gradients in relative dielectric permittivity (K) on the spatial sensitivity of TDR probes. Two- and three-rod probes were placed horizontally through the walls of an experimental box. These horizontal probes were placed either within the same horizontal plane (horizontal probes) or within the same vertical plane (vertical probes). Then, an air/liquid interface was raised upward from below and past the probe. Three liquids (sunflower oil, ethanol, and water) with varying K values were used. The same system was analyzed using a numerical model of the spatial sensitivity of TDR probes to lateral variations in K. There was good agreement between measured and modeled K, demonstrating that the spatial sensitivity of TDR probes is biased toward the area of lowest K. The sample areas of all of the probe designs depend strongly on the relative dielectric permittivity distribution in the plane transverse to the direction of wave propagation. Two-rod instead of three-rod probes should be used if sharp changes in K are expected in the direction transverse to the plane containing the probe rods, owing to separation of the traveling electromagnetic (EM) waves in the three-rod case. Generally, a horizontal probe orientation is more appropriate for monitoring across sharp vertical boundaries such as wetting fronts.
- P., T., & Kluitenberg, G. J. (2003). Advances in measurement and monitoring methods: Preface from the guest editors. Vadose Zone Journal, 2(4), 443-.
- P., T., Nissen, H. H., Knight, J. H., & Moldrup, P. (2003). Transverse sample area of two- and three-rod time domain reflectometry probes: Electrical conductivity. Water Resources Research, 39(9), SBH101-SBH109.More infoAbstract: Numerical models have been applied successfully to the analysis of the sensitivity and transverse spatial sample areas of time domain reflectometry (TDR) probes to lateral variations in dielectric permittivity (ε). However, no similar treatment has been presented for the spatial sensitivity of TDR to lateral variations in electrical conductivity (σ). The objective of this investigation was to examine the response of conventional two- and three-rod probes to sharp changes in σ within their sample areas. The spatial weighting, predicted numerically for probes of varying geometries with sharp ε boundaries and two different σ contrasts in the plane perpendicular to the direction of wave propagation, shows good agreement with the TDR-measured σ. For low-loss conditions the sensitivity distribution of TDR is shown to be independent of the value of σ. This demonstrates that the spatial sensitivities to dielectric permittivity and electrical conductivity are the same for these conditions and that TDR-measured water contents can be used to correct TDR-measured σ for water content effects.
- Rucker, D. F., & Ferre, T. P. (2003). Near-Surface Water Content Estimation with Borehole Ground Penetrating Radar Using Critically Refracted Waves. VADOSE ZONE JOURNAL, 2(2), 247-252.
- Rucker, D. F., & P., T. (2003). Near-surface water content estimation with borehole ground penetrating radar using critically refracted waves. Vadose Zone Journal, 2(2), 247-252.More infoAbstract: Zero-offset profiling (ZOP) with borehole ground penetrating radar (BGPR) is a promising tool for profiling water contents in the subsurface to great depths with high spatial and temporal resolution. The ZOP method relies on determining the velocity of an electromagnetic (EM) wave that follows a direct path from the transmitter to the receiver. However, near the ground surface, critically refracted energy that travels along the ground surface at the velocity of an EM wave in air may arrive before direct waves that travel through the subsurface. If the critically refracted waves are mistakenly interpreted to be direct waves, the water content will be underestimated. As a result, the water content near the ground surface cannot be determined using standard BGPR analysis. We refer to the depth below which direct waves are the first to arrive as the refraction termination depth. An alternative analysis is presented to determine the water content above the refraction termination depth using the slope of the travel time vs. depth profile. Additionally, guidelines are presented to predict the refraction termination depth for known near-surface water contents.
- Blasch, K. W., P., T., Christensen, A. H., & Hoffmann, J. P. (2002). New field method to determine streamflow timing using electrical resistance sensors. Vadose Zone Journal, 1(2), 289-299.More infoAbstract: Electrical resistance (ER) sensors were constructed to monitor streambed saturation to infer ephemeral streamflow timing. The sensors were evaluated in an ephemeral stream through comparison with temperature-based methods, a stream gauge, and soil water content sensors. The ER sensors were more accurate at estimating streamflow timing and the resultant data required less interpretation than data from temperature-based methods. Accuracy was equivalent to timing methods using stream gauge and soil water content measurements. The ER sensors are advantageous for use in ephemeral stream channels because they are inexpensive, deployable above or below the sediment surface, insensitive to depth, and do not require connecting wires to an external datalogger or power source. On the basis of these results, we conclude that ER sensors may be used to monitor changes in soil water content within the vadose zone. Additionally, the sensors can be used to infer the presence of surface water in diversion canals, storm-water sewers, and in the form of overland runoff.
- Desilets, S. L., Ferre, T. P., & Ekwurzel, B. (2002). Flash flood dynamics and composition in a semiarid mountain watershed. WATER RESOURCES RESEARCH, 44(12).
- Furman, A., Warrick, A. W., & Ferre, T. P. (2002). Electrical Potential Distributions in a Heterogeneous Subsurface in Response to Applied Current: Solution for Circular Inclusions. VADOSE ZONE JOURNAL, 1(2), 273-280.
- Furman, A., Warrick, A. W., & P., T. (2002). Electrical potential distributions in a heterogeneous subsurface in response to applied current: Solution for circular inclusions. Vadose Zone Journal, 1(2), 273-280.More infoAbstract: An analytic solution to the Laplace equation for potential distribution in response to current flow in a heterogeneous, two-dimensional semi-infinite domain is studied. Circular heterogeneities of varying sizes and electrical conductivities are considered. We investigate the response of the stream function, the potential field, and, in particular, the potential at the top boundary relative to the background as a function of the size, location, and electrical conductivity of circular inclusions taken singly or multiply. The analytic solution sets the basis for the application of sensitivity analysis to the electrical resistance tomography (ERT) method, as an initial step toward improving the application of the method to tracking rapid hydrological processes.
- P., T., Nissen, H. H., & Šimůnek, J. (2002). The effect of the spatial sensitivity of TDR on inferring soil hydraulic properties from water content measurements made during the advance of a wetting front. Vadose Zone Journal, 1(2), 281-288.More infoAbstract: Many measurement methods are considered to return point values of volumetric water content, water pressure, or other hydrologically relevant properties. However, many methods have spatially distributed measurement sensitivities, averaging a property of interest over some sample volume. In this investigation, we study the effects of the spatially distributed measurement sensitivity of time domain reflectometry (TDR) on the inversion of hydraulic properties from water content measurements. Specifically, a numerical analysis of the water breakthrough curves that would be measured by TDR probes of varying designs during the advance of a wetting front is presented. Numerical inversion of these water breakthrough curves is performed to estimate the soil hydraulic parameters. Time domain reflectometry probes with larger rod separations show less impact on the flow of water at the wetting front. However, these probes have more widely distributed spatial sensitivities, leading to more smoothing of the observed water breakthrough curve. The TDR-measured wetting front shape is more distorted for vertically emplaced probes than for horizontal probes. The optimal TDR probe configuration for inversion of hydraulic parameters from measurements recorded during the advance of a vertical wetting front has three closely spaced rods that lie in a common horizontal plane. The inversion results using this design show close agreement with known values and very small 95% confidence intervals of the inverted properties. This specific recommendation cannot be adopted generally for all TDR monitoring applications. Rather, we recommend that a similar analysis be performed for each specific monitoring application. While the results presented are specific to TDR responses, the same consideration should be given to all instruments with spatially distributed sensitivities.
- Rucker, D. F., & Ferre, T. (2002). A back propagation neural network for identifying first-break times on cross borehole ground penetrating radar traces. GPR 2002: NINTH INTERNATIONAL CONFERENCE ON GROUND PENETRATING RADAR, 4758, 630-634.
- Rucker, D. F., & Ferre, T. (2002). Measuring the advance of a wetting front using cross borehole GPR. GPR 2002: NINTH INTERNATIONAL CONFERENCE ON GROUND PENETRATING RADAR, 4758, 176-179.
- Rucker, D. F., & P., T. (2002). Measuring the advance of a wetting front using cross borehole GPR. Proceedings of SPIE - The International Society for Optical Engineering, 4758, 176-179.More infoAbstract: Two infiltration experiments were conducted to monitor an advancing wetting front at 2.25 m below ground surface with cross-borehole ground penetrating radar (XBGPR). The focus of the experiment was to understand how XBGPR responds to dielectric permittivities that vary on a scale that is smaller than the antenna length. To test this response, a sharp wetting front was formed by applying water evenly over a 5 m by 5 m area at a rate of 5×10-4 cm/s through porous hoses. The center of XBGPR antennae were placed at a depth of 2.25 m in a pair of vertical, PVC lined access tubes located within the irrigated area. The velocity of the first arrival was converted to moisture content using a standard calibration. The measured water content increased linearly with time during the advance of the wetting front. Through comparison with modeled results of flow in unsaturated media, we demonstrate how water contents are "averaged" along the antennae.
- Ferré, P., Knight, J. H., Rudolph, D. L., & Kachanoski, R. G. (2000). A numerically based analysis of the sensitivity of conventional and alternative time domain reflectometry probes. Water Resources Research, 36(9), 2461-2468.More infoAbstract: Conventional time domain reflectometry (TDR)probes are comprised of two or three parallel metal rods. Other probes have been designed for water content profiling [Hook et al., 1992; Ferre et al., 1998b; Redman and DeRyck, 1994], surface water content measurement [White and Zegelin, 1992; Selker et al., 1993], or measurement in electrically conductive media. We use the numerical approach of Knight et al.  to predict the responses of variants of these probes when surrounded by materials with different relative dielectric permittivities. These predictions are compared with published calibration curves and analytical solutions where available. Conventional rods are shown to be most sensitive to changes in the water content of the medium. The Hook et al.  probe shows the highest sensitivity of the alternative designs; both surface probes can be used to measure the water content at the soil surface nonintrusively with similar sensitivities. All of the alternative probes have sensitivities that vary with the soil water content, leading to incorrect averaging of the water content if the water content varies along the probes. However, those probes that place nonmetallic components in series with the soil have more pronounced errors than those that place these materials and the soil more nearly in parallel.
- Ferré, P., Rudolph, D. L., & Kachanoski, R. G. (2000). Erratum: Identifying the conditions amenable to the determination of solute concentrations with time domain reflectometry (Water Resources Research 36:12, 3767 (2000)). Water Resources Research, 36(12), 3767-.
- Ferré, P., Rudolph, D. L., & Kachanoski, R. G. (2000). Identifying the conditions amenable to the determination of solute concentrations with time domain reflectometry. Water Resources Research, 36(2), 633-636.More infoAbstract: On the basis of an analysis of the weighting of the bulk electrical conductivity along time domain reflectivity (TDR) probes we show theoretical limitations to the measurement of solute concentrations with TDR. Simple example calculations demonstrate that there will only be a unique relationship between the TDR-measured electrical conductivity and the average solute concentration in the pore water under one of two conditions. First, if the water content is spatially uniform throughout the sample volume of the probe, TDR may be used to determine solute concentrations. Second, if the water content is spatially variable but the spatial distribution is temporally constant and the solute concentration is spatially uniform throughout the probe's sample volume, solute concentrations can be inferred from the electrical conductivity response. Further complications arise in soils with spatially variable porosities or surface electrical conductivities, making TDR unsuited to determining solute concentrations even if one of these conditions is met.
- Ferré, P., Knight, J. H., Rudolph, D. L., & Kachanoski, R. G. (1998). The sample areas of conventional and alternative time domain reflectometry probes. Water Resources Research, 34(11), 2971-2979.More infoAbstract: We define the sample area in the plane perpendicular to the long axis of conventional and alternative time domain reflectometry (TDR) probes based on the finite element numerical analysis of Knight et al.  and the definition of spatial sensitivity of Knight . The sample area of conventional two- and three-rod probes is controlled by the rod separation. Two-rod probes have a much larger sample area than three-rod designs. Low dielectric permittivity coatings on TDR rods greatly decrease the sample area. The sample area of coated rod probes decreases as the relative dielectric permittivity of the surrounding medium increases. Two alternative profiling probes were analyzed. The separation of the metal rods of Hook et al.  probes controls the size of the sample area. Reducing the height or width of the rods improves the distribution of sensitivity within the sample area. The relative dielectric permittivity of the probe body does not affect the sample size. The sample size of the Redman and DeRyck  probe is also controlled by the rod separation. Two alternative surface probe designs [White and Zegelin, 1992; Selker et al., 1993] are shown to have similar sample areas.
- Ferré, P., Redman, J. D., Rudolph, D. L., & Kachanoski, R. G. (1998). The dependence of the electrical conductivity measured by time domain reflectometry on the water content of a sand. Water Resources Research, 34(5), 1207-1213.More infoAbstract: We present paired measurements of the water content and electrical conductivity collected in a laboratory column packed with a homogeneous, clean sand over a wide range of water content and pore water electrical conductivity (EC) conditions. The EC was determined using the method of Nadler et al.  from waveforms collected with two-rod time domain reflectometry (TDR) probes with and without baluns and with three-rod probes without baluns. Following Heimovaara et al. , we calibrated the probes in saline solutions to account for the series resistance of the cable and connectors. The calibrated EC shows a nonlinear dependence on the water content that is well described by a simple power relationship [Archie, 1942]. Recognizing that calibration in saline solutions is impractical for some TDR probes, we demonstrate that the EC response can be calibrated directly using the results of drainage events, incorporating only a separate calibration of the cable resistance. None of the probe designs shows any clear advantage for EC measurement.
- Ferré, P., Rudolph, D. L., & Kachanoski, R. G. (1998). Water content response of a profiling time domain reflectometry probe. Soil Science Society of America Journal, 62(4), 865-873.More infoAbstract: We designed a profiling time domain reflectometry (TDR) probe. The probe includes two short rods that measure through two parallel access tubes. Small diameter wires lead to the top of the measurement interval, limiting the sensitivity of the probe to the medium above the region of interest. Larger diameter target rods span the sample interval, leading to greater sensitivity of the probe to the medium surrounding the access tubes within the measurement interval. The probe sensitivity is further increased by sealing the access tubes and filling them with water. Six prototype probes built using readily available components showed a consistent sensitivity to the soil, receiving ≃25% of the total probe response from the medium around the access tubes in the sample interval. We tested three methods of field calibration of the probe. The calibrated profiling-probe responses produce water-content profiles comparable to those determined with a neutron probe during the advance of a wetting front.
- Knight, J. H., Ferré, P., Rudolph, D. L., & Kachanoski, R. G. (1997). A numerical analysis of the effects of coatings and gaps upon relative dielectric permittivity measurement with time domain reflectometry. Water Resources Research, 33(6), 1455-1460.More infoAbstract: Fluid-filled gaps or dielectric coatings around parallel-wire transmission lines affect the ability of time domain reflectometry (TDR) to measure the water content of soils and other porous materials. We use a steady state, two-dimensional, finite element numerical solution of Laplace's equation to analyze these effects. We prove that the numerically determined electrostatic potential distribution and boundary fluxes can be used to calculate the equivalent relative dielectric permittivity measured by TDR by comparing the results of the numerical model with those obtained using existing analytical solutions for special cases. We then analyze the effects of fluid-filled concentric gaps that completely or partially surround TDR rods. The results show that an analytical solution due to Annan [1977b] for nonconcentric gaps can be used as a good approximation to predict the effect of concentric gaps or coatings that completely surround the rods. Coatings or gaps filled with low relative dielectric permittivity materials have a greater impact on the measured relative dielectric permittivity than those filled with high dielectric media. An increase in the thickness of the gap or coating for given rod diameters and separations increases the impact of the coating. To a lesser degree, the impact of a coating of a given thickness decreases with an increase in the ratio of the rod diameter to the rod separation. A gap or coating of a given thickness and relative dielectric permittivity will have a greater impact on the response of a three-rod probe than on that of a two-rod probe with the same rod diameter and separation of the outermost rods. Partial air gaps surrounding less than 30°of the rod circumference are not likely to affect the probe response significantly.
- Ferré, P., Rudolph, D. L., & Kachanoski, R. G. (1996). Spatial averaging of water content by time domain reflectometry: Implications for twin rod probes with and without dielectric coatings. Water Resources Research, 32(2), 271-279.More infoAbstract: The averaging of apparent relative dielectric permittivities by time domain reflectometry (TDR) is examined for properties varying along TDR waveguides and in the plane perpendicular to a TDR probe. A square root averaging model with uniform weighting factors describes the measured apparent relative dielectric permittivity for axially varying materials; variations in the transverse plane are described by an inverse averaging model with nonuniform spatial weighting. We define the sensitivity of a TDR probe as the change in the measured travel time for a given change in the average soil water content for rods of a fixed length. For rods with dielectric coatings, this sensitivity increases with the dielectric permittivity of the coating and the rod radius and decreases with the soil dielectric permittivity. Due to the dependence of the sensitivity on the soil water content, coated rods will not measure the actual average water content for conditions of axially variable water contents.
- Dwivedi, R., Meixner, T., Mcintosh, J. C., Ferre, P. A., Eastoe, C. J., Minor, R., Barron-Gafford, G. A., & Chorover, J. D. (2017, December). Hydrologic functioning of the deep Critical Zone and contributions to streamflow in a high elevation catchment: testing of multiple conceptual models. In AGU Fall Meeting.
- Cassiani, G., Binley, A., Ferre, T. P., Vereecken, H., Binley, A., Cassiani, G., & Titov, K. (2002, 2006). Unsaturated zone processes. In APPLIED HYDROGEOPHYSICS, 71, 75-116.
- Chorover, J. D., Mcintosh, J. C., Meixner, T., Ferre, P. A., Sanchez, A., Olshansky, Y., Moravec, B., & White, A. (2018, Fall). THE INFLUENCE OF CRITICAL ZONE STRUCTURE ON ITS HYDROLOGIC FUNCTION: INSIGHTS INTO THE STORAGE AND ROUTING OF WATER THROUGH THE CRITICAL ZONE. Geological Society of America Conference. Indianapolis, IN.
- Chorover, J. D., Stanley, M., Mitra, B., Abramson, N., Barron-Gafford, G. A., Knowles, J., Minor, R., Niu, G., Wright, W., Castro, C. L., Eastoe, C., Ferre, P. A., Mcintosh, J. C., Meixner, T., & Dwivedi, R. (2018, Fall). An improved and practical approach for estimating catchment-scale response functions through power spectral analysis. American Geophysical Union Fall Meeting. Washington DC.
- Dwivedi, R., Meixner, T., Mcintosh, J. C., Ferre, P. A., & Chorover, J. D. (2016, Fall). A multi-tracer approach coupled to numerical models to improve understanding of mountain block processes in a high elevation, semi-humid catchment. Geological Society of America (GSA) Annual Meeting. Denver, CO.
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- Ferre, P. A., Rasmussen, C., Schaap, M. G., Crimmins, M. A., & McKellar, T. (2019, December). Using HYDRUS Soil Moisture Modeling to Improve Drought Index Usage on Arizona’s Rangelands. American Geophysical Union Annual Meeting. San Francisco, CA: American Geophysical Union.
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