ANNUAL REPORT OF REGIONAL RESEARCH PROJECT W-1188
January 1 to December 31, 2005
1. PROJECT:
W-1188 CHARACTERIZING MASS AND ENERGY TRANSPORT AT
DIFFERRENT SCALES
2. ACTIVE COOPERATING AGENCIES AND PRINCIPAL LEADERS:
Arizona
A.W. Warrick, Department of Soil, Water and Environmental Science,
University of Arizona, Tucson, AZ 85721
P.J. Wierenga, Department of Soil, Water and Environmental Science, University
of Arizona, Tucson, AZ 85721
W. Rasmussen, Department of Soil, Water and Environmental Science,
University of Arizona, Tucson, AZ 85721
P. Ferre, Department of Hydrology and Water Resources, University of Arizona,
Tucson, AZ 85721
California
S. A. Bradford, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA
92507
M. Ghodrati, Dept. of Env. Sci. Pol. Mgmt., University of California, Berkeley,
CA 94720-3110
J.W. Hopmans, Dept. of LAWR, Hydrologic Science, University of California
Davis, CA 95616
W.A. Jury, Dept. of Environmental Sciences, University of California, Riverside,
CA 92521
F. Leij, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507
D.R. Nielsen, Dept. of LAWR, Hydrologic Science, University of California
Davis, CA 95616
D.E. Rolston, Dept. of LAWR, Soil and BioGeochemistry, University of
California Davis, CA 95616
P.J. Shouse, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA
92507
J. Šimůnek, Dept. of Environmental Sciences, University of California, Riverside,
CA 92521
T. Skaggs, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507
M.Th. van Genuchten, George E. Brown, Jr. Salinity Lab - USDA-ARS,
Riverside, CA 92507
Z. Wang California State University, Fresno, CA
L.Wu, Dept. of Environmental Sciences, University of California, Riverside, CA
92521
Colorado
L.R. Ahuja, USDA-ARS, Great Plains System Research Unit Fort Collins, CO
80522
1
T. Green, USDA-ARS, Great Plains System Research Unit Fort Collins, CO
80522
G. Butters, Dept. of Agronomy, Colorado State University, Ft Collins, CO 80523
Connecticut
D. Or, Civil & Environmental Engineering, University of Connecticut, Storrs, CT
06269-2037
Delaware
Y. Jin, Dept. of Plant and Soil Sciences, Univ. of Delaware, Newark, DE 19716
Idaho
J.B. Sisson, Idaho National Engin. Lab., Idaho Falls, ID 83415-2107
J. Hubbel, Idaho National Engin. Lab., Idaho Falls, ID 83415-2107
Markus Tuller, Dept. of Plant, Soils & Environ. Sci. Univ. of Idaho, Moscow, ID
83844
Illinois
T.R. Ellsworth, University of Illinois, Urbana, IL 61801
Indiana
J. Cushman, Mathematics Dept., Purdue University, W. Lafayette, IN 47905
P.S.C. Rao, School of Civil Engineering, Purdue University, W. Lafayette, IN
47905
Iowa
R. Horton, Dept. of Agronomy, Iowa State University, Ames, IA 50011
D. Jaynes, National Soil Tilth Lab, USDA-ARS, Ames, IA 50011
Kansas
G. Kluitenberg, Dept. of Agronomy, Kansas State University, Manhattan, KS
66506
Minnesota
J. Nieber, Dept. Biosystems and Agricultural Eng., University of Minnesota,
St. Paul, MN 55108
T. Ochsner, USDA, Agricultural Research Services, St. Paul, MN 55108-6030
Montana
J. M. Wraith, Land Resources and Environ. Sciences, Montana State University,
Bozeman, MT 59717-3120
Nevada
S.W. Tyler, Hydrologic Sciences Graduate Program, University of Nevada, Reno,
NV 89532
M.H. Young, Desert Research Institute, University of Nevada, Las Vegas, NV
89119
New Mexico J.H.M. Hendrickx, New Mexico Tech, Dept. of Geoscience, Socorro, NM 87801
North Dakota F. Casey, Dept. of Soil Science, North Dakota State University, Fargo, ND
58105-5638
Tennessee
J. Lee, Biosys Engin & Envir SciUniversity of Tennessee, Knoxville, TN 37996
E. Perfect, Dept. of Geo. Sciences, Univ. Tennessee Knoxville, TN 37996-1410
Texas
S.R. Evett, USDA-ARS-CPRL, P.O. Drawer 10, Bushland, TX 79012
R.C. Schwartz, USDA-ARS-CPRL, P.O. Drawer 10, Bushland, TX 79012
2
Utah
S. Jones (and D. Or now in Connecticut), Dept. of Plants, Soils & Biomet., Utah
State University, Logan, UT 84322
Washington
M. Flury, Dept. of Crop & Soil Sciences, Washington State University, Pullman,
WA 99164
J. Wu, Dept. of Biological System Engineering, Washington State University,
Pullman, WA 99164
G. W. Gee, Battelle Pacific Northwest Division, Richland, WA 99352
P. D. Meyer, Battelle Pacific Northwest Division, Portland, OR 97204
M. Oostrom, Battelle Pacific Northwest Division, Richland, WA 99352
M. L. Rockhold, Battelle Pacific Northwest Division Richland, WA 99352
A. L Ward, Battelle Pacific Northwest Division, Richland, WA 99352
Z. F. Zhang, Battelle Pacific Northwest Division, Richland WA 99352
Wyoming
R. Zhang, Dept. of Renewable Resources, University of Wyoming, Laramie, WY
82071
CSREES
R. Knighton, USDA-CSREES, Washington, DC 20250-2200
Adm. Adv.
G.A. Mitchell, Palmer Research Center, 533 E. Fireweed, Palmer, AK 99645
3. PROGRESS OF WORK AND MAIN ACCOMPLISHMENTS:
OBJECTIVE 1: To develop and improved understanding of the fundamental soil physical
properties and processes governing mass and energy transport, and the biogeochemical
interactions these mediate.
Washington State University (WSU)
Researchers from Washington State University (WSU) focused on (1) elucidating mechanisms of
colloid fate and transport in unsaturated porous media, (2) colloid-facilitated contaminant transport, and
(3) sorption of the radionuclide Cs on mineral surfaces. They completed our studies on colloidal stability
in vadose zone pore waters and colloid-facilitated Cs transport under unsaturated flow conditions. The
combination of colloid stability determinations and transport experiments provides an improved
understanding of colloid fate and transport under unsaturated conditions. Colloids in pore water are often
in the slow aggregation regime, but will aggregate at time scales of months and years (Czigany et al.,
2005a). Typical subsurface colloids also do not likely attach to water-gas interfaces, but rather associate
to the water-solid interface near the gas-water-solid triple interface (Chen and Flury, 2005). Colloidfaciliated Cs transport experiments revealed an important mechanism: Cs was stripped of colloidal
carriers during transport through uncontaminated sediments (Chen et al., 2005).
WSU researchers have continued our studies on mineral transformations and colloid formation
due to contact of hyperalkaline solutions with subsurface sediments (Mashal et al., 2005a, 2005b). We
determined relative mineral labilities under alkaline conditions representative for Hanford tank farm
leaks. Cs sorption experiments on micaceous clays as affected by rhizosphere processes showed that
bacterial exudates can enhance Cs desorption from minerals and alter Cs availability (Wendling et al.,
3
2005a, 2005b). Certain minerals and colloids are microporous and can sorb contaminants inside the
microporous mineral framework. Sorption and diffusion are the major processes controlling contaminant
uptake and release. We have studied sorption and diffusion of Cs in microporous zeolites and
feldspathoids (Mon et al., 2005) and determined effective intraparticle diffusion coefficients.
The unique winter climatic conditions, steep topography, and winter wheat cropping with
conventional tillage combine to create massive winter runoff and erosion in the Palouse area of the
Northwestern Wheat and Range Region. WSU researchers conducted a study focusing on detailed field
monitoring and WEPP modeling of runoff and erosion under two drastically different management
practices at the PCFS near Pullman, WA, over the 2003–2004 winter season Greer et al., 2005). Two
main mechanisms causing runoff and erosion were observed in the field. First, runoff and erosion may
result solely from soil thawing and snowmelt. Without any precipitation input, the presence of frozen soil
layers could prevent infiltration of snowmelt, causing saturation-excess runoff and erosion. Second, when
rain fell on a snow-covered frozen ground, runoff would start as a consequence of the rain input and
snowmelt. Higher-rate erosion was evident when the additional rainfall caused substantial increase in soil
moisture and lowered soil erosion resistence. Such successive events may not happen frequently but are
very dynamic and can generate considerable amounts of sediment from uncovered surfaces. Although the
USDA’s WEPP model could reasonably reproduce certain winter processes (snow and thaw depths), it is
not yet able to represent all the complicated processes of winter erosion, as observed in the inland PNW.
Improved knowledge of heat and water migration during the freezing-thawing processes is needed to
better quantify soil strength changes, and thus soil erosion, over the winter season.
WSU Impact: Our results have revealed important processes in colloid and colloid-facilitated
contaminant transport, namely preferential colloid attachment to solid-water interfaces near the gas-solidwater interface and contaminant stripping from colloidal carriers. We have also demonstrated that over
long time scales of months to years, colloidal suspensions in the vadose zone are likely not stable.
Cal State Fresno (CSF)
Researchers for Cal State Fresno focused on: (1) theoretical re-analysis of unstable flow in the
upward and horizontal directions and the effect of soil water repellency, (2) design and construction of a
transparent permeameter for quick measurement of saturated conductivity Ks, (3) development of
Sequentially Activated Micro-Flood Irrigation System (SAMFIS) to reduce agricultural runoff, and (4)
development of geodatabase models for management of groundwater banks and watersheds in San
Joaquin Valley and Sierra Nevada Mountains.
CSF researchers have continued our studies on unstable flow in porous media. In an early paper by
Wang et al., (1998), theoretical derivations of fluid displacement involving immiscible oil, water and
air/gas in a porous medium by Chuoke et al. (1959) were generalized. Twenty-four specific criteria for the
onset of unstable flow were developed. The downward water flow displacing air in the vadose zone was
predicted to be unstable (producing fingers) when the infiltration rate I is < Vgrav -Vcap, where Vgrav is
fluid velocity driven by gravity (Vgrav = Ks|cos is the angle between the direction of flow and the
direction of gravity, Vcap is fluid velocity driven by the capillary forces [Vcap = (0.00015 ~ 5.7)Ks, the
coefficient value varies with soil texture ranging from coarse sand to silt clay]. The upward flow was
predicted to be unstable when the flow is too fast or if I is > Vgrav+Vcap. The horizontal flow was
predicted to be unstable if I is > Vcap. The last two criteria were inconsistent with predictions by John
Philip (Philip, 1975).
Reexamination of the complex derivations and parameter definitions by Chuoke et al. (1959) led to a
new set of 24 criteria (Javaux et al., 2005). For the upward and horizontal flow of water displacing air in
soils, the new criteria predicted unconditional stable flow (unstable only if infiltration rate is negative),
4
consistent with Philip’s prediction. Further more, we realized that the occurrence of unstable flow is only
related to two factors: (i) the position of the heavier fluid in the system (either above or blow the lighter
fluid), and (ii) the relative viscosity of the driving fluid (either more or less viscous than the displaced
fluid), see the specific criteria in Table 1. Soil water repellency was not a factor influencing the instability
criteria. Tests are still needed to verify some of the new criteria.
Table 1. Conditions for occurrence of unstable flow, derived from Javaux et al. (2005)
Viscosity
Relative position of the fluids
contrast
C
A
B
horizontal/capillary
Heavy over light
Light over heavy
1. driving>displaced
|V|<Vcrit-Vcap
2. driving<displaced
|V|>-Vcrit+Vcap
likely unstable
|V|< -Vcrit-Vcap
stable
|V|> Vcrit+Vcap
|V|< -Vcap
stable
|V|> Vcap
Impact: Our results have revealed important processes that may help identify unstable displacement during
water/oil flow and contaminant transport in the vadose zone and variably saturated aquifers.
North Dakota State University (NDSU)
Field and laboratory experiments included identification of fate, mobility, occurrence and
persistence of bioactive chemicals. 17-Estradiol and its primary metabolite estrone were evaluated to
identify the dynamic processes of fate and transport as 17-estradiol undergoes transformations in the
soil. First 17-estradiol was continuously applied to a soil column and effluent was collected from the
water moving through and out of the column (Casey et al., 2005). The metabolism of 17-estradiol was
identified as well as its simultaneous transformation. Second a series of incubation studies were done to
identify the degradation process of 17-estradiol and whether it is an aerobic and/or aerobic process and
whether microorganisms govern it (Fan et al., 2005b). 17-estradiol were only degraded under aerobic
conditions and only by microorganisms. A series of soil sorption and column transport experiments were
also done using non-toxic dioxins isomers of the most toxic dioxin, 2378-TCDD. TCDD dioxins were
strongly bound to the soil, but their transport was possibly facilitated by colloidal transport (Fan et al.,
2005a). Lastly, a field plot study was done where manure was applied to three different plots where
lysimeters were installed (60 cm below the surface) which were compared to a control (Thompson,
2005a; Thompson, 2005b). In all the lysimeter there were relatively high levels of 17-estradiol detected
in the leachate collected by the lysimeter and that there concentrations persisted throughout the collection
period. These results did not agree with laboratory results, where it was expected there would be little or
no mobility and very high metabolism rates.
Impact: The laboratory and field fate and transport studies on the various estrogens are important
because these hormones are highly potent and have the potential to be widespread in the environment.
When manures, which contain natural hormones, are applied to field soils, hormones can enter surface
and subsurface water. Our field and laboratory studies are the first to identify how hormones are bound,
transformed or transported in soils, and will help predict the potential of these potent substances entering
in surface or subsurface water.
Utah State University (USU)
USU contribution to W1188 included an ongoing NASA-funded flight experiment focused on
basic soil physics principles in reduced gravity. A flight experiment is scheduled to launch to the
International Space Station in the summer of 2006. Second, part of an Inland Northwest Research
5
Alliance (INRA)-funded Ph.D. fellowship project evaluated electromagnetic induction sensor
performance. Third, ongoing work is underway for development of a field-scale water content mapping
system.
NASA’s Advanced Life Support (ALS) program anticipates plant growth as part of any long-term, bioregenerative, life-support system in microgravity (e.g. ISS, Lunar or Mars mission). In order to insure
reliable plant-growth, the porous-media rooting environment needs to be well controlled and monitored to
support plant growth under the intense energy, mass, and volume constraints of space flight. Limited,
costly and infrequent opportunities for long-duration experiments on orbit and the cost and limitations of
short-term microgravity (g) opportunities on earth have limited progress toward quantifying unsaturated
hydraulic properties of porous media under reduced gravity conditions. Our objectives were to utilize
parabolic flight-induced variable gravity to (1) determine porous-medium hydraulic properties from
measurements of the spatial and temporal variations in hydraulic potential over a range of water contents,
and (2) use earth-based models to simulate sample-scale porous-medium hydraulic transport properties.
Measurement cells with different vertical extents and water addition/removal capability with the ability to
measure the vertical distribution of hydraulic potentials were developed and tested. Some of the cells
added the capability of measuring the vertical distribution of the water content using time domain
reflectometry (TDR). Effects of variable gravity on porous media hydraulic properties were measured and
modeled. Within the dynamic conditions of parabolic flight, we measured the transition of matric
potentials between 1.8g and microgravity (g). Experimental observations of measured hydraulic
potentials followed the dynamic parabolic flight behavior.
Figure 1 shows an example of the microgravity measured and modeled transition of hydraulic potentials.
The modeling, based on the Richards equation using 1g-based van Genuchten parameterization, was
conducted using a finite element model (HYDRUS-2D). The model provided reasonable agreement
between the predicted and measured transition of matric potentials in the g phase over a range of
saturation levels. Measured g matric potentials approached static equilibrium in saturated media with
dynamic readings increasing at reduced water contents in the 20s of g. Simultaneous wetting and
draining conditions were observed in the measurement cell where the vertical distribution of water
contents was found to be very inhomogeneous. Given the hysteretic nature of the porous media, we
attribute this to anomalous scanning retention curves that in the transition from 1.8g to g do not follow
the expected 1g scanning curves to produce the
uniform g distribution of matric potentials.
The substrate water retention characteristics of
porous ceramic aggregates were approximated for
microgravity from quasi-steady state conditions at
the end of the 20 s g phase. Data were compared
to 1g measured curves shown in Figure 2a taken
from 6-1cm thick replicate samples. As one
consequence of the parabolic flight, the
hypergravity draining state that always precedes
microgravity, appears to result in a reduction in
drainage (i.e., more negative) matric potentials
compared to the 1g reference curve for the case of
a 2 cm tall sample when using a cell averaged
water content. In the case of a 4 cm tall sample,
with the added capability of local TDR water
content measurements, we observed matric
Figure 1. Simulation using Hydrus-2D of hydraulic
potentials in the 7 cm cell during microgravity
following hypergravity. The results show the
measured and modeled distribution of matric
potentials in g for three observation heights at z=1,
3 and 5 cm and two water contents as a function of
time.
6
potentials that fell outside of the boundaries set by the 1g reference primary drying and wetting retention
curves (Figure 2b, Heinse et al. 2005).
Measurements of saturated flow in microgravity show the expected Darcian relationship between flux and
driving gradients (Figure 3). Within one standard deviation, all data formed a linear relationship between
flux and gradient. This suggests Darcy’s law is valid for conditions of short term g. The coefficient of
proportionality, the saturated hydraulic conductivity, for each medium is reported in (Heinse et al. 2005).
Measured saturated hydraulic conductivities for Profile and Turface were found to be comparable to
(Steinberg and Poritz, 2005).
Comparison of imbibition rates in the g phase of variable gravity with follow-up imbibition experiments
in 1g showed enhanced preferential flow and enhanced imbibition in pre-wetted media. Modeling
imbibition, using the dual porosity characteristic of the aggregates provided reasonable estimates of the
repeated imbibition (Jones, Tuller and Or, 2005). An updated experimental design using novel
measurements of imbibition and water retention has been prepared with anticipation of a follow-on
parabolic flight in February 2006.
Impact: These data and modeling efforts provide
valuable
insight
toward
advancing
our
understanding of porous media fluid physics in
extra-terrestrial gravity environments such as on
space craft orbiting the earth or traveling to the
Moon or Mars. Fundamental porous media fluid
physics research has been a key element of NASA’s
Advanced Life Support Program for designing plant
growth facilities that are part of bioregenerative life
support systems intended for microgravity.
0.35-0.5 mm GB
0.6-1 mm CA
0.6-1 mm GB
1-2 mm CA
2.5-3.5 mm GB
1-2 mm GB
Figure 2. Turface (1—2 mm aggregate) 1g
substrate-water retention curves a) solid lines were
fit to six replicate measurements of draining (filled
symbols) and wetting (empty symbols) data for
aggregate macro pores. Dashed/dotted lines
indicate the 95 percent confidence interval for the
fitted retention curves. b) Measured water
retention in a 4 cm tall sample with water contents
shown from TDR measurements.
Figure 3. Saturated porous medium flux and
hydraulic gradients measured in microgravity. The
proportionality between fluxes and gradients
provides evidence for applying Darcy’s law in
microgravity. Error bars indicate one standard
deviation.
7
USDA-ARS National Soil Tilth Laboratory and Iowa State University
Predicting Thermal Conductivity at Low Water Contents
Heat moves through soil in the solid, liquid, and gas phases, with the solid phase being composed of
quartz (high thermal conductivity ), other minerals and ice (medium ), and organic matter (low ).
Standard methods for predicting conductivity in composite materials are particularly inaccurate at low
water contents, because the presence of a small amount of water yields a large increase in . There is no
quantitative explanation for the large increase in  at low water contents.
Accomplishments. We hypothesized that the addition of small quantities of water to a dry soil increases
 by increasing the effective cross-sectional area of the contact between mineral grains. We tested this
hypothesis by modeling the soil as a chain of deformable spheres, with water forming capillary bridges at
the contact points (Fig. 1). The system has 3 degrees of freedom: the water content, the solid contact area
due to deformation of the spheres, and the ratio of the liquid to the solid thermal conductivity. Outcome.
In the special case of spheres touching at an infinitesimal point, with the liquid-phase conductivity w
equal to the solid-phase conductivity s, the thermal conductivity of the system is given by
1/ 4
s
More generally, the system’s conductivity is characterized by
     
    s  sb a
where s is the thermal conductivity of the dry system, i.e., the solid at porosity  and zero water, and a
and b are empirical coefficients which are functions of the ratio of the liquid to the solid conductivity
(Figs. 2 & 3). The value of the exponent a is independent of the extent of solid-solid contact (Fig. 4).
The scaling behavior described in these equations strictly applies only to a medium in which the capillary
bridges have not merged, generally below 10% water content. Impact. This work addresses up a longstanding puzzle in soil thermal conductivity as a function of water content, and will lead to improved
estimates of soil thermal regimes. Further work is underway to extend this analysis to higher water
contents and to different-sized spheres, and to compare this work with experimental data. The analysis
also applies to electrical conductivity for the case of a conducting solid; initial work on that scenario is
currently in review.
Figure 1: The problem domain.
Axis of symmetry
c
R
c
r
Plane of symmetry
Figure 2. Zero contact.
Figure 3. Solid to solid contact.
8
Case 1: contact singularity
Case 2: contact radius 0.5
0
log(- s )
0
log( )
-0.5
0.01
0.1
-1
1
-0.5
0.01
0.1
-1
1
10
10
100
100
-1.5
-1.5
-4
-3
-2
-1
0
-4
-3
-2
-1
0
log( )
log()
Figure 4: Exponent values across contacts and conductivity ratios.
Exponent a
0.3
0.2
0
0.01
0.1
0.1
0.5
0
0.01
0.1

1
water
/

10
100
solid
Measuring Coupled Heat and Water Transfer in Soil (Iowa and Minnesota):
Accomplishments. We have performed studies of coupled heat and water transfer in unsaturated soil for
a series of conditions including 2 soils, 2 water contents, 3 mean temperatures, 3 constant imposed
temperature gradients, and 3 oscillating temperature gradients. Thermo-TDR sensors (combined heatpulse and TDR) were installed within closed soil cells for observing transient temperature and moisture
conditions throughout the experiments. Boundary temperature gradients were applied using
programmable water baths and heat-exchangers. Temperature conditions approaching steady-state were
achieved within 4-5 days. The nondestructive techniques used in these experiments allow new insights
into coupled heat and water movement with repeated and transient measurements of moisture and
temperature for a given volume of soil under a variety of conditions. Preliminary work has been
conducted to measure thermal and hydraulic properties of hydrophobic soil materials for the next series of
experiments. Outcome. Results indicate increasing water redistribution with increasing mean
temperature and temperature gradient (Fig. 5). Little thermally-driven water redistribution was observed
for sand at high water contents. Experiments will continue in 2006, and will include similar imposed
boundary temperature conditions for hydrophobic soils. Impact. The results will provide a
comprehensive data set suitable for testing and developing coupled heat and water flow models.
9
Silt loam,  initial = 0.1 m3 m-3
40
0.30
35
0.25
HP (m3 m-3)
25
o
T ( C)
30
20
15
o
o
-1
mean ( C) / gradient ( C m )
15 / 50
15 / 100
15 / 150
22.5 / 150
30 / 150
0.20
0.15
0.10
0.05
10
5
0.00
0
2
4
6
8
10
0
Distance from warm end (cm)
2
4
6
8
10
Distance from warm end (cm)
35
0.35
30
0.30
HP (m3 m-3)
0.40
25
o
T ( C)
Silt loam,  initial = 0.2 m3 m-3
40
20
15
0.25
0.20
0.15
15 / 50
15 / 100
15 / 150
22.5 / 150
30 / 150
0.10
10
0.05
5
0.00
0
2
4
6
8
10
0
Distance from warm end (cm)
2
4
6
8
10
Distance from warm end (cm)
Figure 5. Selected results from coupled heat and water transfer experiments.
Balancing Soil Heat in the Near-surface Field Environment.
Accomplishments. Estimates of soil-water evaporation are commonly driven by micro-meteorological
models or by water balance. We performed a preliminary field study with the objective of determining
soil-water evaporation through near-surface soil heat balance. Heat-pulse probes were installed at
multiple depths in the upper 15 cm of a bare-surface field plot. The probes provided temporal
measurements of soil temperature, thermal properties, and water content. Independent estimates of
evaporation were obtained with mini-lysimeters. Data was collected for a series of naturally occurring
wetting and drying cycles. Outcome. Data analysis is currently on-going. Results will be used to direct
field efforts for further experiments in 2006. Impact. The results from this study will provide further
insight into coupled heat and water transfer in the near-surface field environment.
University of California Riverside
Nitrogen Leaching in Golf Course Fairways
Turfgrass is an intensively managed biota due to the high visual quality requirement. The high
nitrogen (N) fertilizer inputs in golf-course turfgrass have raised some concerns regarding the potential
for nitrate to leach into groundwater. This study was conducted to investigate the amount of nitrate
leaching on an overseeded bermudagrass fairway during the cool and warm seasons of 1994-1997 in a
sandy loam and a sand as affected by two irrigation treatments and two N fertilization programs
representing the typical resort turfgrass management practices in the semi-arid southern California. The
volume (R3-1) of leachate was collected from lysimeter assemblies each consisting of 5 metal cylinders.
Nitrate concentration of the leachate was determined by an Alpkem flow-through analyzer. Results
showed that nitrate concentration and mass of the leachate in the sand was lower than in the sandy loam.
The difference was attributed to N immobilization through plant uptake and clipping removal since both
10
clipping yield in the early stage and the root density after the completion of the 3-yr experiment in the
sand were significantly higher than in the sandy loam. The leaching volume was greater in the sand than
in the sandy loam that followed the same irrigation management practices due to the higher water holding
capacity of the latter. It was further shown that the average nitrate concentration of the leachate was
lower than that of the irrigation water in 5 out of the 6 seasons, implying that if the turfgrass is properly
managed, it may provide an opportunity to mitigate nitrate loading to surface and ground waters, even
when N application rate is high.
Nursery Runoff Study
Commercial nurseries generate large volumes of runoff. Water quality regulations require the growers to
take measures to reduce nutrients and pesticides runoff to the surface-water bodies. One of the best
management practices (BMPs) is to use retention ponds to recycle water in the production nurseries.
Waters in recycling ponds generally have high concentrations of nutrients, pesticides, dissolved organic
matter, as well as elevated salinity and turbidity. Little is known about pesticide degradation behaviors in
the unique environment of nursery recycling ponds. In this study, degradation of four commonly used
pesticides diazinon, chlorpyrifos, chlorothalonil, and pendimethalin in waters from two nursery recycling
ponds were investigated at an initial pesticide concentration of 50 g/L. Results showed the persistence
of diazinon and chlorpyrifos appeared to be prolonged in recycling pond waters as compared to surface
stream waters, possibly due to decreased contribution from biotic transformation, while degradation of
chlorothalonil and pendimethalin was enhanced. Activation energies of biotic degradation of all four
pesticides were lower than abiotic degradation, indicating microbial transformation was less affected by
temperature than chemical transformation. Overall, the pesticide degradation capacity of recycling ponds
was better buffered against temperature changes than in surface stream waters.
University of Idaho
Our contributions to the Multistate Research Project W-1188 in 2005 were primary focused on objectives
1 and 2; development and improvement of understanding of the fundamental soil physical properties and
processes governing mass and energy transport, and development and evaluation of instrumentation and
methods of analysis for characterizing mass and energy transport in soils at different scales.
We continued studies on hydraulic and swelling properties of clays. To gain better understanding
regarding initiation and evolution of surface crack networks in active clay soils we performed well
controlled dehydration experiments in conjunction with X-Ray Computed Tomography (CT)
observations. A collaborative project with the University of Connecticut yielded an analytical model for
prediction of seepage into subsurface tunnels and cavities. In addition we concluded a collaborative
NASA project (USU, UConn, UI, KSU, USRA, and NCSER) on liquid behavior in porous media under
reduced gravity conditions.
Hydraulic and Swelling Properties of Clays
To extend our knowledge regarding the effects of solution chemistry, concentration, clay mineralogy, and
clay content on hydraulic and swelling behavior of clay soils we conducted a series of experiments with
Na-bentonite – silica sand (F58) as well as Ca-montmorillonite – silica sand (F58) mixtures using
deionized water and different concentrated NaCl and CaCl2 solutions as permeant liquids. To investigate
effects of mono- and divalent ionic solutions without going through excessively time consuming ion
exchange processes we permeated mixtures with sodium saturated clay (Na-bentonite) with NaClsolutions and mixtures with calcium saturated clay (Ca-montmorillonite) with CaCl2-solutions. Dry
constituents were mixed on mass basis at clay-sand ratios of 0:100, 10:90, 20:80, 30:70, 40:60, and 50:50.
11
For measuring potential swelling we utilized a volume change device to monitor the volume of liquid
displaced by a swelling sample during slow gravity saturation (Fig.1). The water surrounding the sample
is hydraulically connected to a graduated stainless steel cylinder that is separated into two liquid-filled
compartments by a piston. As the sample swells, liquid is displaced and pushed into the lower
compartment thereby moving the piston upwards. The piston movement is detected by a high resolution
linear displacement transducer and recorded with a datalogger.
Fig.1: Experimental setup for volume change measurements.
Figure 2 shows measured maximum swelling expressed in terms of water ratios for NaCl as well as CaCl2
saturated clay samples. Results for Na-Bentonite mixtures saturated we deionized water and different
concentrated NaCl solutions (Fig.2a) reveal a distinct decrease in potential swelling when NaCl
concentrations are increased to 0.5M, which obviously is the cutoff concentration for osmotic swelling.
There is no further decrease in water ratios with further increase in NaCl concentration. Results for 0.5M
and 1.0M NaCl solutions are virtually the same. For CaCl2 and deionized water saturated Camontmorillonite mixtures we did not observe any distinct differences for all investigated solutions. This
indicates that the increase in water potential with increasing clay content is a result of crystalline rather
than osmotic swelling.
12
Fig.2: Observed water ratios for Na-bentonite and Ca-montmorillonite mixtures.
A fully automated Flexible Wall Permeameter system (Fig.3) was used to measure saturated hydraulic
conductivity. The system was operated in constant head pressure control mode. To assure sample
saturation we used a multistep sequential backpressure saturation procedure with intermittent flushing
phases. To assure steady state flow we measured and monitored permeability of each sample over a
period of at least 24 hours. Permeability measurements were generally conducted under nearly unconfined
conditions. An effective stress of 1 psi was introduced during backpressure saturation. For selected
samples and ionic solutions we conducted experiments with effective stress levels ranging from 1 to 50
psi.
Fig.3: (a) Sketch of the permeameter cell. (b) Photo showing the setup of the Flexible Wall Permeameter
System. Interface chambers prevent contamination of the flow pumps with permeant.
Figure 4 depicts measured permeability values for Na-bentonite as well as Ca-montmorillonite mixtures
permeated with deionized water and NaCl- and CaCl2-solutions respectively.
13
Fig.4: Effects of clay content and solution chemistry on intrinsic permeability
Results for Na-bentonite (Fig.4a) reveal that for all investigated solutions there is a sharp initial decrease
in permeability with increasing bentonite content until a critical value is reached. After this critical
bentonite content we see a slight increase. It is interesting to note that the critical clay content is highly
dependent on the permeant liquid concentration. Samples permeated with deionized water show lowest
permeability at around 20% bentonite content, whereas the critical bentonite content for 0.5 and 1.0M
NaCl-permeated samples is around 40%. We also observed a distinct decrease in permeability with
decreasing permeant liquid concentration.
Permeability values obtained for Ca-montmorillonite mixtures (Fig.4b) are generally higher and there is
no distinct difference between 0.5 and 1.0M CaCl2 solutions. Measurements obtained with deionized
water are slightly lower than values obtained for the CaCl2 solutions. While the critical clay content for
samples permeated with deionized water is around 30%, the critical clay content for samples permeated
with CaCl2 solutions seems to be beyond 50%.
Figure 5 shows effects of effective confinement stress on permeability for clay-sand mixtures permeated
with 0.5M NaCl and CaCl2 solutions. Measurements were conducted for stress levels ranging from 1 to
50 psi. Results for samples permeated with NaCl (Fig.5a) show that there is a distinct decrease in
permeability when the confinement stress is increased from 1 to 10 psi. Any further stress increase only
leads to a marginal decrease in permeability. CaCl2 permeated samples show a different behavior
(Fig.5b). Each increase in effective stress leads to a significant decrease in permeability. At the 50 psi
stress level observed permeabilities are within the range of permeabilities observed for NaCl permeated
samples.
Fig.5: Effects of solution chemistry and confinement stress on intrinsic permeability
14
As a preliminary test of predictive capabilities of a recently developed pore-scale model [Tuller and Or,
2003]1 we calculated saturated permeabilities across a range of clay contents for 0.5 and 1.0M NaCl as
well as CaCl2 solutions and compared predicted values with measurements. The ion valence and the
molarity of the solutions, a surface potential of 0 = -0.175 volts, a characteristic length of 
and an interaction energy of Kh = 20000 J, and a mean grain diameter of 400 m (silica sand F58) were
used for the calculations. Platelet dimensions and the number of platelets per tactoid were chosen in
accordance with values reported in literature. For Na-bentonite we used a platelet thickness of t=9Å, a
platelet length of L=1300Å, and 10 platelets per tactoid. For Ca-montmorillonite we used t=20Å,
L=8000Å, and 85 platelets per tactoid. Permeability calculations for expansive and reductive unit cells
were weighed by clay content in a fashion that expansive cells dominate at low clay contents, whereas
reductive cells dominate at high clay contents.
As shown in Fig.6, predicted values capture the trend of measurements quite well, though the predicted
critical clay contents are lower than the measured ones for NaCl (Fig.6a) as well as for CaCl 2 (Fig.6b)
permeated samples. Though it is clear that much more work is needed to study microstructural changes of
the clay fabric due to changes in solution chemistry to better bracket model input parameters, and to
develop upscaling strategies to predict sample and profile scale behavior, this preliminary model test
demonstrates the overall potential of our pore scale modeling approach.
Fig.6: Comparison of predicted and measured intrinsic permeabilities for (a) samples permeated with
0.5 and 1.0M NaCl solutions; and (b) samples permeated with 0.5 and 1.0M CaCl2 solutions.
Initiation and Evolution of Surface Crack Networks in Active Clay Soils Observed with X Ray Computed
Tomography
Swelling clay soils receive increasing attention as technical buffer materials in geological and engineered
barriers in order to isolate hazardous waste. However, swell-shrink dynamics of clay soils in response to
changes in soil water content and chemical composition of the soil solution can induce surface cracks,
which act as preferential transmission zones for pollutants and potentially lead to groundwater
contamination. Hence, the optimized use of such porous materials relies on reliable knowledge of their
hydraulic behavior. To facilitate development and refinement of physically based predictive models for
hydraulic conductivity a detailed quantitative description of the three dimensional crack network is
required [Tuller and Or, 2002]2. While traditional methods for analyzing pore networks are destructive
1
Tuller, M., and D. Or, 2003. Hydraulic functions for swelling soils: pore scale considerations. Journal of
Hydrology, 272:50-71.
2 Tuller, M., and D. Or, 2002. Unsaturated hydraulic conductivity of structured porous media: a review of
liquid configuration-based models. Vadose Zone Journal, 1:14-37.
15
and commonly limited to two-dimensional representations, we use X-ray Computed Tomography (CT) in
association with mathematical morphology functions to quantify the three-dimensional features of crack
networks.
X-Ray Computed Tomography is an advanced technique that allows visualization and quantification of
the internal structure of opaque objects by mapping the x-ray absorption through the sample. The linear
attenuation of x-rays through the sample is calculated based on Beer’s law as I/I0 = e-mx, where I/I0 is the
attenuation of x-ray intensity per unit length of a given material, x is the thickness of the material, and m
is the attenuation coefficient. The scanning process consists of three steps that include data acquisition,
data processing and volume reconstruction. The reconstruction process involves application of complex
mathematical algorithms that convert sinograms into two- and three-dimensional images. We apply a new
FLASHCT (Flat Panel Amorphous Silicon High-Resolution Computed Tomography) scanner (Fig.7)
available at Washington State University through collaboration with the Department of Geotechnical
Engineering. FLASHCT is an advanced high-speed industrial X-ray based 3-D scanning system that was
developed as an area detector scanner employing flat panel amorphous silicon arrays. FLASHCT is
suitable for applications requiring a wide spectrum of X-ray energies and geometric magnifications. The
WSU scanner incorporates both a 225 kV micro-focus X-ray source for material characterization at high
magnification that will be used for the proposed project and a 420 kV X-ray source for larger component
analysis.
Fig.7: WSU FLASHCT X-Ray Computed Tomography system.
Mathematical Morphology (MM) is a mathematical theory of image processing, which facilitates the
quantitative analysis and description of geometric image structures. Major MM operations include
nonlinear image transforms such as erosion, dilation, opening, closing, skeletonization, and watershed
transformations. Erosion and dilation operations are applied to extract aperture distributions, remove
noise and artifacts, and to quantify pore topology, which refers to the connectivity of pore spaces.
To investigate effects of clay content, clay type, and solution chemistry on initiation and evolution of
surface crack networks we performed well-controlled dehydration experiments. An infrared heater panel
in combination with thermocouples (Fig.8) is employed to control and monitor sample surface
temperature. Samples are isolated with high density foam to prevent horizontal thermal gradients.
16
Fig.8: Setup of the dehydration experiment.
Initial experiments were performed with bentonite - silica sand mixtures (10/90, 20/80, 30/70, 40/60, and
50/50) saturated with 0.05M and 0.5M NaCl solutions. Samples were dehydrated at a constant surface
temperature of 40oC and scanned on consecutive days over a period of several weeks. Crack porosity and
surface area (SA) were determined based on binary images (Fig.9).
Fig.9: Binarization of grayscale images. The grey level threshold is mathematically
the minimum between the two histogram peaks.
17
determined
as
Preliminary results (Fig.10) indicate that solution chemistry and bentonite content strongly influence
initiation and evolution of surface crack networks. Samples with low bentonite content (10% and 20%)
developed less cracks than high bentonite content mixtures both for 0.5M and 0.05M NaCl solutions.
Samples saturated with 0.05M NaCl show significantly higher crack porosities than samples saturated
with 0.5M NaCl.
Fig.10: Evolution of sample water ratios and crack porosities with time under dehydration.
We used MATLAB® to develop a code based on Mathematical Morphology (MM) dilation and erosion
operations to determine aperture distributions from 3-D reconstructed images. Preliminary results indicate
that high bentonite content samples saturated with 0.05M NaCl develop significantly larger cracks than
samples saturated with 0.5M NaCl. Figure 11 depicts the evolving aperture distribution for a 50/50
bentonite/sand mixture saturated with 0.05M NaCl solution.
18
Fig.11: Aperture distributions for a 50% bentonite mixture saturated with 0.05M NaCl after 2, 10, and 18
days of drying under 40oC.
Initial results reveal that X-ray CT in combination with mathematical morphology is a powerful tool to
quantify development and evolution of crack networks as a function of drying rate and physico-chemical
conditions. Current and future work includes well controlled experiments under different drying
conditions, varying clay content and pore water chemistry for both natural and artificial clay-sand
mixtures to provide comprehensive data for development of physically based models for crack evolution
and hydraulic properties.
Seepage into Drifts and Tunnels in Unsaturated Fractured Rock
Methods for obtaining estimates of seepage into drifts and tunnels excavated in unsaturated fractured rock
are of great interest for many engineering and environmental applications. For uniform porous media a
tunnel surface may present a capillary barrier promoting water diversion around the opening through the
porous matrix, hence reducing seepage into the opening. The presence of fractures intersecting the
opening complicates flow behavior and presents a challenge to seepage prediction. We developed a
simple and physically based model for seepage estimation that preserves key physical processes
associated with fracture flow, while avoiding complexity of detailed fracture network characterization [Or
et al., 2005]. The processes of film and capillary-driven flows are combined with a geometrically tractable
representation of the dual-continuum fractured rock with two disparate populations of matrix pores and
fracture apertures (Fig.12). The large disparity in capillary forces between matrix and fractures rules out
matrix seepage based on Philip’s theory. We obtain estimates of seepage fraction for a given percolation
flux from consideration of the hydraulic conductivity of the fracture domain only. Similar to previous
studies, the new model shows existence of a percolation threshold for onset of seepage. The new model
also exhibits a steep increase in seepage with increase in percolation flux that reflects the role of fracture
film flow (Fig.13). In addition to consideration of physically based flow processes, computations for the
proposed analytical model can be performed with common spreadsheet software, which is a distinct
19
advantage over numerical equivalent porous media approaches that require a powerful computational
environment, excessive computation time, and thorough characterization of the fracture domain.
Fig.12: Conceptual sketch for dual continuum pore space representation of a fractured porous medium.
Fractures may be represented by unit elements as depicted in the right upper corner, and matrix is
represented by angular pores connected to slits. Note (1) the pore size disparity between the two
domains; and (2) large fractures empty first.
20
Fig.13: Comparison of new model predictions assuming two values of matrix permeability with results
based on Monte Carlo simulations [Finsterle, 2000] using a fracture-only continuum model (line
represents mean values).
Flow and Distribution of Fluid Phases through Porous Plant Growth Media in Microgravity
During the reporting period we concluded a comprehensive collaborative NASA project with the
objective to enhance basic understanding of fluid behavior in porous media under reduced gravity
conditions. Plants are essential for NASA’s closed and regenerable life support systems. As mission
durations increase and colonial scenarios develop, resupply becomes impractical and the cost untenable.”
Even though plants/crops would be grown in a protected habitat in transit vehicles or on the surface of
Moon and Mars, the environment is hostile to growth unless conditions are carefully controlled. The
added complication that methods and procedures for water and nutrient management are necessarily
modified under micro- or reduced gravity conditions presents a unique challenge that has yet to be met.
The ability to predict and tailor water, air and nutrient transport in porous media under micro- or reduced
gravity conditions remains a critical constraint to development of reliable experimental and production
plant growth facilities. Successful plant growth during space missions is dependent on adequate control of
the rooting and canopy environments and understanding impact of micro- reduced gravity on plant
physiological functions. An especially critical area has been control of water and air in plant growth
media. Some of the key findings of this project include:
(1) Characterization of porous plant growth media – optimal set points for water delivery in any g
environment strongly depend on growth- media hydraulic properties. Although baked ceramic aggregates
have been used in space flight for over 10 years, we conducted the first rigorous characterization of
physical and hydraulic properties [Steinberg et al., 2005]. This work has enhanced the understanding of
aggregate dual porosity, pore size distribution, water conducting porosity, air entrapment, and air entry
that allows critical examination of water delivery set points that have been used in space.
21
(2) Small volumes and susceptibility to heterogeneous fluid distributions - limitations on mass and size of
on-board root modules accentuate the impact of inherently irregular wetting patterns in particulate media
and the role of root volume. Wetting front irregularities may span the entire root module depth used for
space flight promoting entrapment and discontinuous phase formation. Root proliferation modifies media
properties, especially with high root density where an entirely new porous medium is created with
different physical and hydraulic properties. Consequently, water management based on macroscopic
criteria (set points) may be constantly changing.
(3) Micro- and reduced gravity effects on water transport - water moves within porous media under the
influence of pressure, gravity and surface/capillary forces. Surface/capillary forces dominate in micro- or
low gravity environments when both water and air phases are present. Wetting front irregularities or
surface forces that cause water and air to segregate into wet and dry clusters are difficult to control or
predict. Irregularities in pore size distribution and expansion of capillary length scales enhance phase
entrapment in 0g. Once these clusters become established during initial infiltration they may be hard to
remove in 0g due to the combination of water-primed pathways and dominance of capillary forces.
Additionally infiltration into pre-wetted porous media occurs faster in 0g.
(4) Water content sensing and control - matric potential or water content sensors have been used to
control and schedule water delivery to plant growth media. Limited sensing volume of most sensors used
in root modules (<1 cm3) combined with discontinuous phases may result in “accurate” readings on the
mesoscale (several pores or particles), but an inaccurate assessment of water content in the bulk volume
of growth media.
For further details please see USU report.
Oregon State University
Our activities focused on elucidating the mechanisms that govern the movement of liquid and solutes
when cracks are present in a soil profile. In 2005 we completed the first stage toward the development of
a numerical model to simulate water and solute redistribution within a soil profile with cracks. The model
investigated the effect of the crack on (1) evaporative flux from the profile, (2) salt flux and salt
accumulation towards the crack surface, and (3) the effect of crack presence on net downward flux of
solute through the vadose zone.
Soil cracks can significantly enhance the amount of evaporation from agricultural soils. This understanding evolved
from an extensive series of field and laboratory experiments in the 1970’s. However, at the time, and since then, no
mechanisms were suggested for the processes governing the observed enhanced evaporative flux, limiting our ability
to predict flux quantities beyond the specific field conditions tested. As part of this project we proposed a
mechanism for enhanced evaporation consisting of thermally driven nighttime convective venting of the fractures.
Convective venting leads to evaporative fluxes that can be far greater than those driven by diffusive venting. Recent
work has demonstrated that this enhanced evaporative flux, caused by the presence of cracks, may be responsible for
the formation of salt crusts along fracture walls in semi-arid areas (Weisbrod and Dragila, 2006). During
precipitation events, these salts may dissolve and move further down the soil profile, affective soil chemical
development and providing a concentrated saline plume that may migrate to the water table. Being able to quantify
the salt redistribution will permit more accurate quantification of evaporative fluxes, infiltration rates, and solute
transport rates important for field scale water balance and contaminant migration calculations. During 2004 we
investigated the theoretical constraints of the mechanism and tested the concept of nighttime venting. The focus in
2005 was to begin development of a numerical model to predict downward salt flux and upward evaporative flux.
(Weisbrod and Dragila, et al. 2004, 2005).
A numerical model was constructed using TOUGH2, a multiphase, multicomponent flow and transport porous
media simulator [Pruess et al., 1999] with the EWASG module [Battistelli et al., 1997]. TOUGH2 has been shown
to be able to accurately model land-atmosphere relationships [Webb and Phelan, 2003] and is especially suited to
22
fractured media, while the EWASG module fully models (liquid and solid) salt reactions in three-phase systems.
Modeling evaporation of a saline solution required modifications to the standard grid-block connection scheme. The
improved model was validated against a controlled laboratory experiment using evaporation sand columns, and
verified by comparison with published field data [Ritchie and Adams, 1974]. The advantages of the improved gridblock connection scheme include: evaporation occurs from the fracture surface, salt does not clog the block
immediately, and the connection length between the surface of the matrix grid-block and the center of the aperture
grid-block, has physical significance, that of the thickness of the boundary layer in analytical solutions. This
modification allows for control of the evaporation rate without imposing unrealistic relative humidity values,
considerably increasing the accuracy and flexibility of the model. The model was then used to investigate
evaporation, saline flux, and solid-phase salt precipitation for three matrix permeabilities.
Relative humidity within pores is consistent with the local matric potential. Initial conditions for fracture air and
atmospheric grid blocks are set at a relative humidity less than 100%, creating a vapor pressure gradient, resulting in
water-vapor flux driven by Fickian diffusion. Processes included in the model are: liquid movement driven by
capillary and osmotic gradients; salt movement driven by advective and diffusive processes; thermal gradients were
not included in this first modeling stage; evaporation was controlled by vapor diffusion and boundary layer
thickness within the fracture aperture; atmosphere was an infinite sink for vapor (convective venting speed did not
limit evaporative potential).
Simulations were conducted for three permeabilities representing fine sandstone, an intermediate permeability
matrix, and the chalk matrix at the field site (Table 1).
Table 1. Matrix parameters used in numerical model
Physical model. The domain is based on field measurements taken from a fractured chalk aquifer in the
Negev Desert [Weisbrod et al., 2000], where collaborative field work is in progress. This field identified
vertical fractures in ranging in aperture from 5 mm to 5 cm (dissolution zones), at a density of ~1 fracture
per 1.2 m. Model parameters for the matrix are based on field measurements of permeability and
porosity. Water retention and relative permeability are modeled using the van Genuchten [1980]
formulations. Fitting parameters for the van Genuchten curves were obtained from soil textural classes of
loam and clay [Carsel and Parrish, 1988]. Fracture permeability is estimated assuming the cubic law.
Model domain. By assuming vertical symmetry for the fracture, only one-half of the fracture-rock system
was modeled (Figure 1). The two-dimensional domain was 120 cm deep by 60 cm wide. The leftmost
column represents the fracture, with 2-cm wide grid blocks. This column is only 50 cm deep in order to
limit evaporation and salt crust deposition to a depth of 50 cm. Column widths away from the fracture
increase from 1.0 to 10 cm. The same mesh design was used for the soil-atmospheric boundary, where
the upper row (atmospheric) is 5 cm high. All grid blocks are 5 cm thick (Figure 1).
Initial and boundary conditions. The boundary conditions are depicted in Figure 1. The right-hand
boundary is a noflow (Neumann) boundary, while the lower boundary is a (water table) constant pressure
(Dirichlet) boundary, which allows for gravity drainage. The upper boundary is also a constant pressure
boundary, representing the atmosphere and allowing for evaporation. The lower half of the fracture (50 <
z < 120 cm), exhibiting no evaporation, was modeled as a no-flow boundary. The upper half of the
fracture (0 < z < 50 cm) is a constant pressure boundary. Initial conditions used for all simulations were
matrix air and atmospheric temperature at 20°C, relative humidity of fracture air and atmosphere at 42%,
barometric pressure at 100 kPa, initial matrix liquid saturation of 99%, and an initial dissolved salt-mass
23
fraction of 6 g L−1 (commensurate with what was measured in the field-site pore water). Simulations
were run for 100 days. No thermal diurnal cycles were incorporated into any of the simulations.
Three simulations were run to test each of the three selected intrinsic permeabilities. Figures 2, 3 and
4 depict the results of 100 days of simulation. The simulations represents 100 days of arid conditions
during which the fracture walls evaporate continuously due to convective venting. The matrix is allowed
to evaporate and gravity drain, with salt solution consequently removed from the system via solution
drainage out the bottom boundary. In every situation, salt redistribution began rapidly and leveled off, in
response to matrix drying. Predictably, drainage was highest in the sandstone, and least in the chalk/clay
matrix (Table 2). During these simulations, evaporation redistributed salt in response to capillary, osmotic
and diffusive processes, relocating it to the surface of the fracture. It is important to note that the code
does not permit salt to deposit in an atmospheric block, thereby salt deposition within the outermost soil
grid-block is considered to be synonymous with a salt crust forming on the surface of the fracture. In the
1-cm zone nearest the fracture, solute levels increased 660% in the sandstone and 158% in the chalk
simulations (Figure 3 and 4). An increase in solute concentration near the soil surface in response to
evaporation is well documented in agricultural settings (e.g., Nakayama et al., 1973) but has not been
investigated for vertically oriented evaporative surfaces.
While salt crust formation (Figure 3) was also higher for the sandstone than the chalk, the important
relationship is the ratio of salt crust formation to drainage.
Matrix
Accumulation along the
fracture wall (outer 1-cm
gridblock)
Loss from profile due to
gravity drainage
Ratio
(g day-1 cm2)
Sandstone
Intermediate
Chalk /clay
(g day-1 cm2)
4.79
1.51
0.54
7.96
1.50
0.16
24
43%
100%
368%
Figure 1. Numerical model domain showing
dimensions, grid-block shapes, and boundary
conditions.
Figure 2. Cumulative Drainage of pore solution
as a function of time for three matrix permeabilities
Figure 3. Distribution of salt mass (solid and
dissolved) with distance from the fracture into the
matrix after 100 days of simulated evaporation and
drainage. Values are the sum of the salts for each
vertical column of grid blocks.
Figure 4. Mass of salt in the 1-cm column
of grid blocks nearest the fracture as a
function of simulation time, for three intrinsic
permeabilities.
Numerical model supports our collaborative laboratory observations that show significant portion of the
precipitated salt is deposited on the fracture surface, with some deposited within the porous matrix,
although the relative amount has yet to be quantified. At this stage the amount of salt deposition in the
first centimeter grid-block (nearest the fracture) is interpreted as the proportion of salt accumulated in the
fracture, capable of being dissolved and available for bypass flow to the water table. Results from this
first series of numerical model exercises suggests that while the sandstone accumulated a greater total
amount of salt along the fracture, the higher permeability also allowed for greater drainage of dissolved
solutes. Thus, the presence of the fracture under these circumstances does not dramatically enhance the
mass flux of dissolved solutes that drain downward to the aquifer. In fact, the ratio of salt accumulation
to drainage, and consequently the importance of fractures in solute transport, increases with decreasing
permeability. In these simulations, the sandstone exhibited only 43% as much accumulation of salt along
the fracture as that drained by gravity drainage, whereas the chalk accumulated 368% more salt along the
fracture than that drained to the water table through the matrix.
Numerical investigations demonstrated significant solute transport toward fracture surfaces, suggesting
that subsequent dissolution from near-surface fractures could increase net salt transport to the underlying
aquifer. The relative proportion of salt-crust accumulation and the magnitude of flushing via fractures are
strongly dependent on matrix permeability. Whereas all rocks, irrespective of permeability, exhibited
some salt precipitation along the fracture face, the ratio of salt accumulation along the fracture to drainage
through the matrix increased with decreasing permeability. Therefore, this mechanism for salt-crust
formation along near-surface fractures, with subsequent flushing to underlying aquifers, may be more
important in low-permeability media, where saline flux through the matrix is depressed, leaving the
fracture system as the main focusing and delivery mechanism for matrix solutes.
The actual functionality of this mechanism under natural conditions is still under examination and needs
to be directly quantified. The complexity of fracture structures, including irregular aperture, dissolution
holes and cavities in carbonate rocks, surface roughness, surface skin with different physical and chemical
properties, the host of filling materials that in some cases generate an effective “secondary porous media”
25
within the aperture, and variable water content around the fracture surfaces could significantly affect the
aforementioned mechanism.
This project has brought to light a very important mechanism of evaporation that has not previously been
considered in calculations of land-atmospheric water fluxes, or for the impact this has on salt
redistribution and transport within the vadose zone. The project has further developed a strong
infrastructure of expertise and tools, which provides a solid foundation for future theoretical, numerical,
laboratory and field investigations of the questions:
1. What are the physical mechanisms governing processes within the fractured vadose zone?
2. What is the role that these fractures play in earth processes?
Desert Research Institute and University of Nevada
Ongoing research in Nevada is investigating the extent of tritium diffusion in heterogeneous arid
soils. A large soil box (11 m long by 1.5 m high by 1.5 m wide) was constructed to evaluate uptake of
tritium by perennial desert shrubs, and the response time relative to distance to the tritium source. The
studies are being done in conjunction with UNLV researchers. The box contains two different materials
constructed in three layers (loam soils above and below a layer of pea gravel). The soil was installed at
air dry conditions during the Summer 2004. A carefully controlled volume of non-tritiated water was
applied to the soil in vapor form, at the opposite end of the tank to sustain a single wolfberry (Lycium
pallidum) shrub. Approximately 12 L of fluid has evaporated into the soil material. Tritium content in
the wolfberry leaves has been monitored for the last ca. 500 days. A slight increase in concentration
above background was detected. We coupled the field work with numerical simulation of tritium
diffusion using the TOUGH2 code (Transport of Unsaturated Groundwater and Heat) code [Zhu et al.,
2005b]. Our preliminary results show that tritium mass fraction distribution in the soil box stabilized over
time and irrigation at other end of the tank had virtually no effect on tritium mass distributions. The
controlled study of dispersive and diffusive transport of tritium, could provide a more process-based
explanation of tritium transport, and hence improve the predictions of future potential transport from the
disposal areas to surrounding soil. The measurement of tritium in shrub leaves could be used as an earlywarning of release of radioactive materials into the uncontrolled environment. Advancements made on
predicting surface runoff potential can be used by land managers who design and construct flood control
structures or who study potential erosion from surface flooding.
Nevada has been evaluating surface runoff processes on alluvial fan complexes in arid regions. The
overall goal of these studies (Grant and Young, 2005; Chen and Young, 2005) is to improve the
predictability of surface runoff potential while considering environmental factors such as temperature
changes, surface slope angle, and spatial variability of soil hydraulic properties. Grant and Young (2005)
presented a general analytic model of normalized infiltrability as a function of normalized time. They
included the effects of temperature and soil texture by modifying the capillary length scale as calculated
by the Brooks and Corey equation. This approach allows estimates of infiltration–model parameters of
soil texture and temperature. Calculations implementing this approach show that infiltrability is an
increasing function of increasing mean reciprocal particle radius and temperature. For very fine–textured
soils, the model predicts that infiltration increases with temperature to a maximum, then decreases with
increasing temperature due to the increasing importance, relative to hydraulic conductivity, of the
reduction in hydraulic gradient. Chen and Young (2005) evaluated the physical effects of slope angle on
infiltration and runoff generation by extending the Green-Ampt equation onto sloping surfaces. In this
study, which assumed homogeneous and isotropic soil, three infiltration scenarios were studied: ponded
infiltration, infiltration under steady rainfall events, and infiltration under unsteady rainfall events. All
theoretical and numerical results showed that infiltration increases with increasing slope angle. For
26
ponded infiltration, the slope effect was generally not significant for mild to moderate slopes. During
rainfall, the slope effect could be significant depending on the intensity level and duration of the rainfall
events. For steady rainfall events, time before ponding and cumulative infiltration increased by a factor
of cos2 on slopes with a slope angle . The slope effect was reduced for high intensity and long duration
events due to increases in runoff ratio. Unsteady rainfall events bring additional complexity to the system,
but did not change the basic trends.
Overland/litter interflow is also being investigated in Sierran ecosystems. It is now clear that surface
runoff via overland flow is an important hydro-geochemical watershed process (Miller et al. 2005). Such
runoff has been found to frequently contain exceedingly high concentrations of biologically available
NH4+-N, NO2-+NO3--N and PO43--P, and accumulating O horizon materials in heavily forested watersheds
have been identified as an apparent source. Indeed, greenhouse leaching of intact monoliths collected in
situ has identified a net discharge of both inorganic N (4 mg N kg-1; 0.45 kg N ha-1) and P (17 mg P kg-1;
2.0 kg ha-1) from O horizon materials (Loupe et al., submitted). Nitrogen demonstrated a fluctuating longterm discharge characteristic, which may explain why many investigators have reported early in situ peak
concentrations in snowmelt discharge, whereas others have identified late season peaks. Phosphorus
discharge, on the other hand, was very rapid and occurred primarily during early stage leaching. This
characteristic could explain why high PO43--P concentrations in tributaries of the Sierra Nevada are
seldom reported in the literature. These findings alone address an important gap in our understanding of
watershed hydrochemistry that is totally overlooked in the current literature; i.e., the presence of
previously undetected nutrient laden surface runoff is directly pertinent to hydrologic and nutrient
transport models being applied at the landscape scale. Additional research has shown wildfire to cause an
immediate and high intensity nutrient mobilization effect (Johnson et al., 2005; Murphy et al., In Press;
Miller et al., In Press), whereas the use of prescribed fire in combination with mechanical harvest for
fuels reduction appears to not only improve overall forest health, but also to reduce the nutrient content in
surface runoff without the effects of a wildfire induced nutrient “shock” (Loupe, 2005).
Another facet of our work focuses on improving our understanding of water flow through highly
structured arid soils. Specifically, we are investigating the hydraulic properties of soils found in desert
pavement environments. Laboratory studies using a modified evaporation experiment (Meadows et al.,
2005a) allow us to investigate the properties of individual soil peds. We can then compare average ped
values with tension disc infiltrometer tests over the same area. Because both methods are sampling the
same soil, with the exception of the interped regions that the infiltrometer samples, we can estimate the
impact of the interped region on hydraulic properties. This approach provides a novel means of
investigating flow through structured soils. We are applying this method to desert pavement surfaces of
differing age and pedologic development (Meadows et al., 2005b). This is potentially important because
it will help elucidate the transient nature of the mode of infiltration. Dye studies are currently underway
to more closely investigate the changing nature of infiltration as a function of surface age and soil
development. Preliminary results indicate that infiltration evolves from a matrix dominated process on
younger surfaces to a preferential-flow dominated process on the older more developed soils. These
results have implications regarding long-term predictive models of recharge and plant-available water.
Research in Nevada is being done to investigate water and nutrient cycling in near surface desert soils
and the relationship to root morphology of desert plants. Soil development and resulting morphology are
a function of time, and morphological features (petrocalcic and/or argillic horizons in particular) affect
the distribution of water in soil. We postulated that rooting patterns (both depth and lateral spread) would
be affected by increasing soil development (i.e. soil age). Soil morphology (below plant canopies and in
interspaces), soil hydrologic properties, Larrea tridentata root distributions, and canopy size were
measured at three Mojave Desert sites. Each site was located to represent a geomorphic chronosequence
containing a young (Holocene) weakly developed soil and an older (Pleistocene) strongly developed soil
(Caldwell et al., 2005a; Steveson et al., 2005). Larrea tridentata height, canopy volume, root numbers,
27
rooting depth, and canopy-to-interspace root ratio were all significantly greater in weakly developed
Holocene soils than older strongly developed Pleistocene soils (P<0.05). Root densities were greatest in
weakly cemented soil horizons (Bwk and Ck horizons in Holocene soils and Btk horizons in Pleistocene
soils) and rarely occurred in strongly cemented petrocalcic (Bkm) horizons. Soil hydraulic conductivity,
and mean annual water flux generally corresponded with rooting depth. We conclude that the soil age and
hydropedologic development exerts significant controls on Larrea root distribution and canopy size by
both the physical obstruction of root expansion and the modification of soil water distribution. Related to
the above-described research, Nevada is investigating practical and economical methodologies to estimate
plant-available soil moisture needed to facilitate revegetation practices under the extremely arid
conditions that typically prevail. Seedbed microclimate soil water content, soil water potential, and soil
temperature, were continuously monitored and used to calibrate the Simultaneous Heat And Water
(SHAW) and HYDRUS numerical models at three, large-scale, seeded restoration sites.
Furthermore, a collaborative effort with the Catalina Island Conservancy and DRI is serving as a pilot
project to demonstrate the importance of assessing the soil water balance for the purposes of revegetation
efforts and monitoring of this island ecosystem. Hydrologic characterization of both hillslope and valley
bottom alluvial deposits is needed to develop both conceptual and numerical models for oak restoration
work currently being conducted on Catalina Island, CA (Caldwell et al., 2005b). Models were
hierarchically parameterized to varying degrees of field data and modeling complexity (inverse solutions)
to determine output validity. Various surface treatments included ripping, use of tackifiers, straw mulch,
gravel mulch, and plastic sheeting. Several irrigation scenarios were also evaluated to determine effective
restoration practices to maximize revegetation success and minimize water use.
Military training exercises at the National Training Center (NTC), Ft. Irwin, California have led to the
degradation of large areas of the Mojave Desert. Ongoing research in Nevada is investigating soil
physical properties in areas subjected to low and high disturbance at interspace and plant (Larrea
tridentata) mound microsites. These areas were quantitatively compared to undisturbed surfaces of both
well-developed soils formed on Pleistocene age alluvial deposits and weakly developed soils formed on
Holocene age alluvial deposits to improve future restoration efforts (Caldwell et al., 2005c). Results from
multi-tension infiltrometers showed that young, coarser-textured surfaces had saturated conductivities
(Ksat) nearly twice that of older surfaces. Mound microsites were more sand-rich than interspace locations
although Ksat was not significantly different. After sites were subjected to low and high disturbance levels,
bulk density was significantly increased from 1.54 to 1.62 and 1.80 g cm-3, respectively. Similarly,
penetration resistance increased following low and high disturbance from 1.32 to 1.47 and 3.90 kg cm-2,
respectively. Although low disturbance increased Ksat, high disturbance resulted in a significant (P<0.05)
reduction in Ksat from 2.4 to 1.3 cm hr-1 and mean Gardner’s  from 0.20 to 0.10 (P<0.001) for all sites.
In general, interspaces microsites on young soils were less sensitive to disturbance, when compared to
older, well-developed interspace soils. Results showed that Ksat on these older surfaces was not
dramatically reduced, despite large losses of fines and increased bulk densities; however, the overall soil
morphology was dramatically impacted.
USDA-ARS, Bushland, TX
We initiated a study to investigate tillage effects on bare soil evaporation and near surface soil water and
temperature dynamics (Schwartz et al., 2005).Twelve field plots were divided equally between sweep
tillage and no tillage treatments. Soil temperatures and water contents were monitored on these plots from
August 2004 through December 2005. Soil bulk density, ambient air temperature, relative humidity, wind
speeds, net radiation and global irradiance were also monitored during the study. Higher water contents at
0.05 and 0.1 m under no tillage persisted throughout the summer despite greater rainfall infiltration
amounts under sweep tillage (Fig. 1). However, water contents at soil depths below 0.15 m were not
influenced by sweep tillage. Most water depletion near the surface under sweep tillage occurred
28
immediately after tillage and after rainfall occurring within ~30 d of tillage. Increased soil water depletion
under tillage was likely a result of a change in hydraulic properties accompanied with enhanced vapor
flow near the surface and greater absorption of radiation by a tilled surface with reduced albedo.
Numerical simulations that include vapor transport and tillage effects on surface albedo are currently
underway to model tillage effects on coupled heat and vapor transport and water flow near the soil
surface.
Impact: This data set represents one of the few high temporal resolution (half-hourly intervals) soil
water content measurements before and after tillage. The study demonstrated that tillage, independent of
residue cover, increases soil water depletion near the surface probably through accelerated vapor transport
and elevated surface heating via reduced surface albedo. Reduction of evaporation via decreased capillary
flow to the surface after shallow tillage is either unimportant or not operative in these soils.
OBJECTIVE 2: To develop and evaluate instrumentation and methods of analysis for characterizing
mass and energy transport in soils at different scales
Washington State University
Fiberglass wicks were tested for their suitability to sample colloids from vadose zone pore water. These
studies showed that under certain conditions (high pH, high flow rates, negatively charged colloids),
fiberglass wicks can be suitable for colloid sampling; however, under many other conditions quantitative
colloid sampling is not possible (Czigany et al., 2005b, Shira et al., 2005).
We have developed a technique to coat silica sand with aluminosilicate clays (Jerez et al., 2005, Jerez
and Flury, 2005). It has been possible so far to coat silica sand with aluminum and iron oxides and humic
acid, but no method for clay coating was available so far. Our methodology allows the generation of a
clay-based porous matrix, with hydraulic properties that can be varied by adjusting the grain size of the
inert silica support.
In an effort to find better dye tracers for vadose zone hydrology, we have developed a new technique
based on QSAR (Quantitative Structure Activity Relationships) to seek for optimal molecular structures
of dye tracers (Mon et al., 2005b, 2005c). We have proposed a new molecular structure of an optimal
vadose zone dye tracer (class of the triarylmethane dyes).
A principal task of evaluating a large wildfire is to assess its effects on the soil to predict the potential
watershed response. Two types of soil water repellency tests, the water drop penetration time (WDPT)
test and the mini-disk infiltrometer (MDI) test, were performed after the Hayman Fire in Colorado, in the
summer of 2002 to assess the infiltration potential of the soil (Lewis et al., 2005). Postfire ground cover
measurements were collected at these locations. Weak correlations were found between postfire
hyperspectral imagery and soil water repellency. Indirect relationships between water repellency
measurements, ground cover measurements, and the imagery were examined. Percent ash cover measured
on the ground was significantly correlated to WDPT and MDI rate. Mixture tuned matched filtering
(MTMF), a partial unmixing algorithm, was applied to the hyperspectral imagery which produced
fractional cover maps of ash, soil, and scorched and green vegetation. A comparison of a spatiallypredicted surface of soil water repellency to an imaged surface of ash suggested a correspondence
between these two surfaces, especially within the range of spatial autocorrelation of the water repellency
measurements.
Impact: Our efforts on testing fiberglass wicks for colloid sampling provide the first systematic data
on colloid sampling from vadose zone pore water. In situ colloid sampling in the subsurface is a
challenging, but important, endeavor. Good and reliable tools are needed to assess colloid transport in
29
situ. The technique developed to coat silica sand with aluminosilicate clays provides the tool to conduct
dynamic flow experiments with clays, something that has not been possible before, because clays have
such a low hydraulic permeability.
Cal State Fresno University
A transparent permeameter was designed and constructed for fast measurement of saturated hydraulic
conductivity Ks. As shown in the picture below, the system is composed of a transparent Plexiglas tank,
Plexiglas cells fixed on soil core samples, siphons and water collection bottles for each cell, two sliding
conduits on each side of the water tank, a water collection and storage tank at the bottom, and the
pumping and tubing system.
Measurement for a batch of up to 20 samples at a time starts with setting the cells in the transparent
tank first, then pumping water to the tank, setting the siphons to drain water from inside the cells to
achieve a steady state flow condition, and finally observing water levels inside and outside the transparent
walls for each cell, and collecting the volumes of drainage after a certain period of steady state flow. This
device allows direct reading of water levels from the side of the tank, quick start/stop of batch
measurements, and individual uses of the cells in a small tank or glass beak.
Impact: This new design and construction of permeameter provide convenient and fast measurement
of saturated hydraulic conductivity which is one of the most often needed parameters for characterizing
water flow and contaminant transport in variably saturated soils and other porous media.
North Dakota State University
A method for predicting field-scale transport was developed and evaluated (Lee and Casey, 2005). An in
situ method was used to estimate field soil preferential flow properties for a surface soil. These
preferential flow soil properties were then used to calibrate a mechanistic-stochastic stream tube model to
predict field-scale solute transport. To evaluate this prediction, a field-scale leaching study was done and
30
solute redistribution was monitored over a period of nearly 40 days. This method reasonably predicted the
field-scale transport over this time period.
Impact:The development of the field-scale model is a simplified means to identify how solute, such as a
pollutant, can transport through a soil and enter the groundwater. Future applications of this technique
may include the identification of aquifer vulnerability.
Utah State University
Electromagnetic Induction sensor comparison (Dualem-1S and EM38-DD)
Earth conductivity instruments based on the principle of electromagnetic induction (EMI) are extensively
used for mapping soil salinity and increasingly for mapping soil texture. Environmental variables such as
temperature can impact sensor response beyond the effect of soil solution electrical conductivity. This
study was conducted to determine the effect of variable temperature environments on instrumental drift as
well as to compare the bulk soil electrical conductivity (ECa) – depth relationship between the DUALEM
1-S and Geonics EM38-DD devices described in Table 1 and shown in Figure 4. Each instrument has two
sets of coils with orientations shown where each has a set of vertical coils (II) and one uniquely oriented
set each. The effect of temperature on both instruments was investigated under two salinity levels at two
sites. The relationship of ECa to the depth below ground was investigated by raising each instrument in
increments of 0.15 m up to 1.8 m above ground. The instruments correspond reasonably with theoretical
models describing the ECa – depth relationships which are primarily coil-orientation dependent. The
equations that relate the cumulative response of the different orientations to depth are (McNeill, 1980):
1
RV -V ( z)  1 - (4 z  1)
2
R H -V ( z )  1 -
1
(4 z 2  1)
1
[5]
2
2
2z
(4 z 2  1)
1
- 2z
[6]
[7]
EM-38 DD
RH - H ( z )  1 -
Transmitter
Receiver
І
Horizontal - Horizontal (H-H)
2
II
Data from moderate (3 dS/m) and low (0.5 dS/m)
electrical conductivity soils were used to determine
the ECa-depth relationship of the different
orientations of the two instruments. Raising the
instruments above the earth surface introduces an air
layer transforming the measurements into a duallayer system. The low EC soil with its small range
31
Vertical – Vertical (V-V)
DUALEM
The cumulative response graph (Figure 5) is a good
indicator of the depth of exploration (DOE) of the
different orientations. Below the DOE the
conductivity meter is insensitive to response from
the Earth. A 70% cumulative response for the V-V
orientation accrues at a DOE of 1.5 m, while the HH and V-H orientations achieve the same response
at a DOE of 0.75m and 0.5m respectively.
ІІI
Vertical - Horizontal (V-H)
Figure 4.
Transmitter and receiver dipole
orientations of the EM38-DD and DUALEM 1-S.
The loops of wire form a solenoid and a dipole is
created when current is driven through the
transmitter coil, the resulting magnetic field
generates soil EC-dependent current loops in the
subsurface. The ground current loops create a
secondary magnetic field causing a secondary field
driving current through the receiver coil.
of ECa response (0-20 mS m-1 in Fig. 6A and B)
does not correlate with the theoretical models as
well as the wide ranging (6-160 mS m-1) ECa
response in the moderate EC soils shown in
figures 6C and D. The perpendicular orientation
mode of the DUALEM 1-S achieves the best
results at both high and low ECa environments.
Under these test conditions, both instruments
were prone to a higher margin of error (10-40%)
at lower ECa readings while the error becomes
less significant (~5%) at higher ECa ( >100 mS
m-1).
The difference in response of the
instruments can be attributed to the temperaturedependent change in soil ECa due to a 20°C
diurnal temperature variation in addition to
instrumental temperature-induced effects on the
processing circuitry. The complete manuscript
documenting these results has been submitted
for review in SSSAJ.
70%
Figure 5. Cumulative response with respect to depth
of the three coil orientations of the DUALEM and
EM38-DD.
Soil mapping in water sheds using
electromagnetic
induction
for
electrical
conductivity measurements was also explored as
a means of characterizing soil properties.
Measurements are related to soil texture and
other properties of interest from distributed
sampling. A vertical 2m deep by 1x1m
instrumented plot was established with TDR
probes and thermocouples for characterization
of the vertical profile measurement character of
the EMI instrument.
Impact: The instrument comparison paper will
provide users with valuable information
regarding instrument and environmental factors
affecting measurement quality. Ongoing work is
utilizing EMI measurements for determination
of texture and other soil properties.
Figure 6. Normalized ECa – depth relationships for
the EM38-DD and DUALEM under low and moderate
salinity conditions.
Table 1. Technical specifications for the EM38-DD and Dualem-1S.
Operating frequency
Power Supply
Instrument dimensions
Instrument weight
Conductivity Range
Advantages
EM38-DD
DUALEM-1S
14.6 kHz / 17 kHz
2 internal 9 Volt batteries
1.06 x 0.15 x 0.18 m
6.8 kg
1000 mS m-1
LCD display, Carrying handle
9 kHz
External 12 V DC
1.41m long, 0.09 m diameter
5 kg
3000 mS m-1
Internal memory (50k), Precalibration
32
Approximate cost
$21,000
$14,000
University of Arizona
Results reported from last year were published. Included were the affect of variations in water heads on
infiltration in borders and basins (Warrick et al., 2005) and predominantly vertical flow through a
spherical inclusion using the analytic element method (Furman and Warrick, 2005). Also published were
results for effective unsaturated hydraulic conductivity through a repeating, 1-D layered system (Warrick,
2005). The system was described by a “cell length” L which is the length of the overall repeating pattern
and 1, 2… n describing the relative thickness of each sublayer. When L is small the effective
conductivity approaches the harmonic average of the unsaturated hydraulic conductivities and the
corresponding pressure head is constant in the profile; when L is large the pressure head varies in each
sub-layer and the hydraulic conductivity (equal to the background flux) corresponds to a pressure equal to
the arithmetic average of the pressures defined by the flux for each of the n sublayers. Results were
included for the limiting an intermediate L values for binary and tertiary systems.
New work include infiltration from two (x,z) and three-dimensional axially symmetric sources (r,z). The
basic approach is a generalization of results by Haverkamp, Ross, Smettem and Parlange (1994, WRR, p.
2931). They worked with a relationship for a tension disc infiltrometer for which the three-dimensional
cumulative infiltration per unit source area I3D [L] is the simple sum
I 3 D  I1D 
 S02
t
r0  0 -  n 
(1)
where I1D [L] is the one-dimensional cumulative infiltration,  a dimensionless “constant”, S0 [LT-0.5] the
sorptivity, 0 [-] the volumetric water content at the disc source,  n [-] the initial water content in the
profile and t [T] is time. The last term in (1) is based on linear diffusion from an edge of a onedimensional semi-infinite strip. Using alternate lines of reasoning, they established a“reasonable bounds”
on  of 0.6-0.8.
Our approach is to test the form of (1) directly using HYDRUS for a range of soils, disc radii, initial water
contents and source pressures. Results are that the final term in (1) is, for all practical purposes, linear
with respect to time but that  varies from 0.7 to 1.2, depending on the specific scenario. Figure 1 shows
I3D - I1D for the six soils used. Note the linear relationship with time. The corresponding values of  are
given in Figure 2.
33
Inspired by the success from the disc, we also looked at the analogous form for a strip (2D) source. If
cumulative flow due to a unit length of the edge is defined to be Qedge [L3L-1], inspection of the last term
in (1) reveals
Qedge 
 S02t
2( 0 -  n )
(2)
When Qedge is multiplied by the circumference and divided by the area of the circle the result is the last
term in (1). With x0[L] the semi-width, results for the strip are found by multiplying Qedge by 2 to
account for two sides of the strip and dividing by the area per unit length. The result in a form analogous
to (1) is
I 2 D  I1D 
 S02
t
2 x0  0 -  n 
(3)
with I2D[L] the cumulative infiltration per area of a strip of semi-width x0. A by-product is a “twodimensional” Wooding’s equation of the form

2 
qW ,2 D  K0 1 

  x0 
(4)
(Wooding’s equation for the disc has a “4” in place of the “2”). We are investigating whether alternative
values of the slope are superior (to 2/).
Repeating from last year, the variation in ponded water heads (depth hydrograph) measured for border
and basin irrigations was found to have a minimal impact on infiltration amounts compared to a constant
head at any given location. The solution for inclusions and structured heterogeneous profiles for
unsaturated flow are important in describing subsurface heterogeneity and its impact on flow of water and
solutes in the profile.
The new solutions for disc source are applicable to analysis of disc tensiometer which is widely used to
measure unsaturated hydraulic properties in the field. The parallel solution for the strip is relevant to
water entry from shallow furrows and from surface line sources.
Developments from the two solutions above for the disc and strip will be published. Use of these results
to define new strategies for measurements are being considered, including further techniques using small
heads of water in varying sizes of rings. These results will be extended for furrows and boreholes.
Preliminary results show these also result in a linear term accounting for the “edge” effects.
34
I3D - I2D (cm)
100
75
Sand
Loamy sand
Sandy loam
A
Loam
Silt loam
Clay
B
50
25
0
I3D - I2D (cm)
5
4
3
2
1
0
0
0.5
1
1.5
2
Time (h)
Figure 1. Results for disc. Relative source and initial water contents are 1 and 0.1, respectively. (The
hydraulic parameters are the same as the defaults in HYDRUS).
1.1

1.0
0.9
0.8
0.7
0
0.2
0.4
0.6
0.8
m
Figure 2. Values of  vs. m (=1 – 1/n) for the six soils from Figure 1.
USDA-ARS National Soil Tilth Laboratory and Iowa State University
Providing One-dimensional Temperature Distributions in Studies of Coupled Heat and Water Transfer
(Iowa, Minnesota, and North Dakota):
Accomplishments. The impetus for this work was to provide improved measurement techniques for
laboratory studies of coupled heat and water transfer. Laboratory studies are often confounded by radial
temperature gradients, from ambient temperature conditions, that interfere with imposed axial
temperature gradients. Our objective was to develop a closed soil cell capable of effectively eliminating
radial temperature gradients. We developed and tested several closed soil cells that made use of soil as
insulation for the control volume soil. Outcome. By insulating our control volume with material having
similar thermal properties, we were able to produce near one-dimensional temperature gradients. The
35
radial to axial temperature gradient ratio was < 0.02:1 for a 10 cm length, 10 cm diameter soil cell using
soil as an insulator. Impact. This new cell design will allow further improvement in studies aimed at
measuring coupled heat and moisture transfer.
University of California Riverside
Developing a potential hazard index for nitrate in the Southwest States
Surface and ground waters in southwestern states are often polluted by nutrient runoff and leaching from
irrigated agriculture. The objectives of the project are to develop an interactive, web-based system
where growers on irrigated lands in California, Arizona, or Nevada can assess their relative risk of
contaminating groundwater. The greatest attention and resource investment can be directed to areas with
a high hazard index (HI) rating, while less concern is given to areas with a low HI. To assess the
vulnerability of a site, a number of factors, each with their own hazard rating, are used. Factors
considered are: soil type, crop, and irrigation system. Soil type is rated on a scale of 1 to 5 and crops and
irrigation systems from 1 to 4. In each case, the relative hazard potential is lowest at 1. By multiplying
the values from each factor, the final HI can range from 1 to 80. A database of over 500 soils and 150
crops in the three states has been compiled. The soils and crops were ranked for their leaching potential
and the rankings were reviewed by experts. An interactive website that calculates nitrate leaching
potential and provides growers with best management practices was then developed. While much of the
above work was completed in 2004, our work in 2005 built the GIS function to the website so a grower in
the three Southwest States can click on the map to locate their soil and assess the nitrate leaching index
without knowing their soil names.
Soil and Water Management Research Unit, USDA-ARS, St. Paul, MN
Time domain reflectometry (TDR) and the heat pulse method are both used to measure soil water
content and track soil water movement. Changes in ambient temperature have been shown to affect TDR
measurements, but less is known about the behavior of heat pulse sensors in response to changes in
temperature. We have completed a study to directly measure and compare the temperature sensitivity of
the TDR and heat pulse methods. The resulting manuscript has been accepted for publication in Vadose
Zone Journal (Olmanson and Ochsner, 2006). A synopsis of the paper follows.
The TDR and heat pulse methods were used to estimate water content in silt loam and sand at two
fixed water contents across a wide temperature range. An increase in temperature led to an increase in
measured water content in most cases. Across the 40°C temperature range, changes in measured water
content were generally 0.04 m3m-3 or less for both methods. Weighted linear regression showed that in
these soils the heat pulse method exhibited greater temperature sensitivity than the TDR method, although
the differences were not statistically significant (Table 1).
Table 1. Weighted linear regression analysis of estimated water content versus ambient temperature for
heat pulse and TDR methods.
Soil type
Method
Silt loam
heat pulse
TDR
heat pulse
TDR
Sand
heat pulse
TDR
Water content
m3m-3
0.11
0.11
0.36
0.36
0.11
0.11
36
Slope
Uncorrected
Corrected
-3 3 -3
10 m m °C-1
1.05*
0.11
0.62*
-1.03*
1.01*
0.13
0.45
-0.41
0.32*
-0.15
-0.67*
-0.041
heat pulse
0.32
TDR
0.32
* Significant at the 0.05 probability level.
1.04*
0.46
-0.007
1.56
A previously proposed correction for the temperature sensitivity of the TDR method (Or and
Wraith, 1999) produced mixed results (Table 1 and Fig. 1).
0.42
0.42
Water Content (m3m-3)
uncorrected
corrected
uncorrected
corrected
0.38
0.38
0.34
0.34
0.3
0.3
0.26
0.26
Silt loam
0.22
5
15
25
Temperature C
35
Sand
0.22
45
5
15
25
Temperature C
35
45
Figure 1. Corrected and uncorrected water content estimates using the TDR method in Ida silt loam with
an actual water content of 0.36 m3m-3 and Hanlon sand with and actual water content of 0.32 m3m-3.
Lines represent weighted linear regression.
To correct the heat pulse data, the temperature dependence of the specific heat of dry soil was
estimated by applying the third law of thermodynamics. This law implies that the specific heat of a
crystalline solid should approach zero as the temperature approaches absolute zero (0 K) (Kay and Goit,
1975). Furthermore, the relationship is known to be linear (Kay and Goit, 1975; Kluitenberg, 2002). We
used the heat pulse method to measure the specific heat of the oven dry soils (Ren et al., 2003) and
divided the specific heat values by the temperature at which they were measured to obtain estimates of
0.00309 and 0.00327 MJ Mg-1 K-2 for the sand and silt loam respectively.
Heat pulse water content estimates were corrected accounting for the changes in the density and
specific heat of water and specific heat of soil with respect to temperature. When the changes in these
parameters were accounted for, the temperature sensitivity was eliminated in three out of four cases, the
exception being sand at low water content (Table 1 and Fig. 2).
0.42
0.42
Water Content (m3m-3)
uncorrected
corrected
uncorrected
corrected
0.38
0.38
0.34
0.34
0.3
0.3
0.26
0.26
Silt loam
0.22
5
15
25
Temperature C
35
Sand
0.22
45
37
5
15
25
Temperature C
35
45
Figure 2. Corrected and uncorrected water content estimates using the heat pulse method in Ida silt loam
with an actual water content of 0.36 m3m-3 and Hanlon sand with and actual water content of 0.32 m3m-3.
Lines represent weighted linear regression.
Desert Research Institute and University of Nevada
Activities in Nevada focused on developing methodologies to characterize vadose zone heterogeneity
and variability in soil hydraulic properties by incorporating “hard”-to-measure data and readily available
“soft” data, such as soil moisture measurements, topographic attributes, and remotely-sensed land cover
information. Based on the correlation of soil deposition and vegetation growth patterns across a
topographically heterogeneous landscape, we explored the use of topographic and vegetation attributes, in
addition to pedologic attributes, to develop pedology-topography-vegetation-transfer functions (PTVTFs)
for estimating soil hydraulic properties in the Southern Great Plains of the USA [Sharma et al., 2005]. A
total of eighteen models combining bootstrapping techniques with artificial neural networks were
developed in a hierarchical manner to predict the soil water contents at eight different soil water potentials
(θ at -5, -10, -333, -500, -1000, -3000, -8000 and -15000 cm H2O) and the van Genuchten hydraulic
parameters (θr, θs, α, n). We specifically explored the usefulness of topographic attributes from Digital
Elevation Models (DEM) and remotely-sensed Normalized Difference Vegetation Index (NDVI) in
addition to soil physical attributes in developing and improving catchment- or regional-scale pedotransfer functions. Improvements in prediction of water content were achieved with certain input
combinations of basic soil properties, topography, and vegetation information, when compared to using
only the basic soil properties as inputs. The findings in our studies will be useful for estimating pixelscale soil hydraulic parameters in Soil Vegetation Atmosphere Transfer (SVAT) schemes used in
regional-scale hydro-climatic models. Results from Nevada also indicate that including “soft” data can
greatly enhance characterization of formation heterogeneities and help to describe variability in soil
hydraulic properties. An integration of cokriging and neural network approaches resulted in an efficient
framework to incorporate the spatially correlated “soft” and “hard” data.
In a separate project, we also used cokriging a approach to estimate heterogeneous pedo-transfer
variables (bulk density and percentages of gravel, coarse sand, fine sand, silt, and clay) and a neural
network approach to generate heterogeneous soil hydraulic parameters (saturated hydraulic conductivity
and van Genuchten water retention parameters). We then simulated a field injection experiment and
compare simulated and observed water contents to evaluate the methodology [Ye et al., 2005].
Nevada completed work on a comprehensive effort to address landfill cover designs using numerical
estimation methods that combined site-specific data on soil properties, historical climatic conditions, and
native vegetation (Young et al., 2005a). These parameters and their levels of uncertainty were combined
into a method that quantified overall uncertainty in numerical predictions of deep flux (percolation below
the root zone), and provided information on the dependence of deep flux to incremental variations in
important design components. The method partitioned potential evapotranspiration into potential
evaporation and potential transpiration based on phenological characteristics of the local (Mojave Desert)
plant community. Results of nearly 1000 realizations for each of 72 different combinations of soil type,
cover thickness, and percent plant cover demonstrated that the presence of at least a 10% plant cover was
necessary to prevent excessive deep flux (e.g., > 0.5 cm/yr) regardless of the soil thickness. Threshold
values of cover thickness (76 cm) and percent plant cover (10%) were identified, beyond which
incremental additions had diminishing impact on the deep flux. The methods developed here demonstrate
innovative uses for numerical simulations, which can provide effective cover designs and contribute to
improved decision making.
Research is also underway to investigate the efficacy of surface based ground penetrating radar
(GPR) as a means of estimating the fine-grained component and Ks of surficial soils in desert pavement
environments (Meadows et al., 2005b). Because signal attenuation is proportional to electrical
38
conductivity, the degree of direct wave attenuation should be a useful diagnostic tool regarding nearsurface soil in certain cases. We investigated two surfaces in the Mojave Desert: a young surface of
sandier texture, and an old surface of silty/clayey texture. For each surface, we conducted 100-m long
linear transects to determine GPR direct wave attenuation, terrain electrical conductivity (via EM-38),
water content, soluble salt content, soil texture, and hydraulic properties. Neither surface contained
significant quantities of water or salts. However, the older pavement contained substantial amounts of silt
and clay in the surficial soil horizon. As expected, increases in clay content caused a reduction in signal
amplitude as more electromagnetic energy was dissipated in the form of conduction currents. Using
multivariate linear regression, which included a nominal measure of soil structure ascertained by visual
field inspection, we were able to show significant correlations between measured and predicted values of
both silt plus clay content (r=0.84, p=<0.0001) and Ks (r=0.73, p=<0.0001) for the older surface.
Including the metric of soil structure improved the predictive capabilities on the older surface. However,
no significant correlations were found on the younger surface. This is likely due to the low
concentrations of clays in the young soil. This approach has certain benefits over more traditional
techniques. The GPR method provides higher spatial resolution than EM measurements. In addition, the
results suggest that the GPR is not influenced by heterogeneities in lower soil horizons. We show that the
method can be used for reconnaissance surveys as a means of estimating the clay content, and in some
cases Ks, of surficial soils on certain well-developed desert pavements.
In Sierran ecosystems, Nevada researchers have developed an apparatus for the collection of slow
moving overland/litter interflow. It is generally held that surface runoff in heavily forested ecosystems is
minimal and therefore nutrient fluxes via runoff are unimportant. This is based in large measure on the
absence of direct observation or remnant physical evidence, the belief that protected forests with heavy
understory serve as a water and nutrient sink due to maximum uptake and interception, and the lack of
direct physical measurements. The recently developed collection device (Miller et al., 2005) consists of a
buried bucket container slightly larger than 8 L in volume fitted with a collection funnel, vent stack roof
flashing, screen, and a high-density polyethylene cover. The top of the collection funnel is located
approximately 5 cm below the soil surface and the roof flashing is aligned perpendicular to the slope
either at the soil surface of bare soil for the collection of overland flow, or at the litter/mineral surface
interface for the collection of litter interflow. The excavated hole is backfilled for insulation and to secure
the collection bucket assembly. A small V-notch equilateral triangular opening (length = 1.0 cm; area =
0.43 cm2) is cut into a 20x30 cm piece of high-density polyethylene (HDPE) and secured over the roof
flashing with the V-notch opening coincident to the opening in the flashing, which was screened to
prevent the entry of forest debris. A sufficient length of tubing was attached to the top of each sample and
vent bulkhead fittings to allow for sampling under a 1 m winter snowpack. The device appears to function
quite well and data thus far show that during rainfall precipitation and snowmelt, water is in fact seeping
downslope through the organic horizon within at least two Sierran watersheds, never gaining enough
momentum to cause much physical disturbance.
USDA-ARS, Bushland, TX
Work was completed and published on a method to calibrate conventional time domain reflectometry
(TDR) to estimate soil water content in terms of travel time, bulk electrical conductivity, and effective
frequency of the TDR pulse at the probe (Evett et al., 2005a). The effective frequency was calculated
from the maximum slope of the reflection caused by the ends of the TDR probe rods (Fig. 2).
39
Sweep Tillage
0.05 m
0.1 m
0.15 m
0.4
0.05 m
0.1 m
0.15 m
3
Volumetric Water Content, m m
-3
No Tillage
NT 0.15 m
0.3
ST 0.15 m
NT 0.1 m
0.2
ST 0.1 m
0.1
NT 0.05 m
ST 0.05 m
0.0
200
220
240
260
280
Day of Year
Figure 1. Mean volumetric water contents at three depths for no tillage (NT) and sweep tillage (ST) plots
in 2005. Number of observations: n = 12 for sweep tillage at 0.05 cm and n = 6 for all others.
fvi = 2π  109  ΔVt/[ tb(V0 – VI)]
ΔVt =
ΔVt changes with
water content…
Figure 2. (Left) Effective frequency, fvi, was calculated from the slope of the second rising limb of
the TDR waveform, which is caused by the reflection of the TDR pulse from the ends of the
probe rods. (Right) The slope, ΔVt, decreases as soil water content and bulk electrical
conductivity increase in the Pullman soil.
A common calibration equation provided estimates of water content with an accuracy of 0.01 m3 m-3
in three soils that varied in clay content from 17 to 48%, and that varied in bulk electrical conductivity at
the saturated end from 0.75 to 1.47 dS m-1. The soils were non-saline, but clays contained large
proportions of smectite/montmorillonite, with large surface area, and are known to contain large amounts
40
of inter-layer K+. Bulk electrical conductivity was strongly and positively dependent on soil temperature;
and effective frequency was strongly and negatively dependent on temperature (Fig. 3). The common
calibration virtually eliminated temperature dependency of estimated water contents, reducing it to
<0.0006 m3 m-3 ºC-1.
Figure 3. (Left) Bulk electrical conductivity, σa, increased most strongly with temperature for
soil B, which had the largest clay content (48%). (Right) Effective frequency decreased most
strongly with temperature for soil C, which had the smallest clay content (17%) and bulk
electrical conductivity, but which exhibited the largest effective frequencies.
Work was completed and submitted for publication on comparisons and calibrations of several soil
water sensors in laboratory soil columns (Evett et al., 2006). Accurate soil water content measurements to
considerable depth are required for investigations of crop water use, water use efficiency, irrigation
efficiency, and soil water and solute fluxes. Although the neutron moisture meter (NMM) has served this
need well, increasing regulatory burdens, including the requirement that the NMM not be left unattended,
limit the usefulness of the method. Newer methods, which respond to soil electromagnetic (EM)
properties, typically allow data logging and unattended operation, but with uncertain precision, accuracy,
and volume of sensitivity. In laboratory columns of three soils, we compared the Sentek EnviroSCAN3
and Diviner 2000 capacitance devices, the Delta-T PR1/6 Profiler capacitance probe, the Trime T3 tubeprobe, all called EM devices, with the NMM and conventional time domain reflectometry (TDR). All but
conventional TDR can be used in access tubes. Measurements were made before, during and after wetting
to saturation in triplicate re-packed columns of three soils: 1) a silty clay loam (30% clay, 53% silt), 2) a
clay (48% clay, 39% silt), and 3) a calcic clay loam (35% clay, 40% silt) containing 50% CaCO3. Each
75-cm deep, 55-cm diameter column was weighed continuously to 50-g precision on a scale.
Conventional TDR determinations of water content and thermocouple determinations of temperature were
made at depths of 2, 5, 15, 25, 35, 45, 55, and 65-cm in each column every 30 min. Depth resolution of
each device was investigated by lowering its probe from a height ~30-cm above the soil surface and
taking measurements at 2-cm increments until the probe was 30-cm below the soil surface.
Comparisons of soil water content reported by the devices vs. soil temperature showed that all of the
devices were sensitive to temperature except for conventional TDR and the NMM. The Trime T3 and
Delta-T PR1/6 devices were so sensitive to temperature (0.015 and 0.009 m3 m-3 C-1, respectively, at the
saturated end using soil-specific calibration) as to be inappropriate for routine field measurements of soil
profile water content. Soil-specific calibrations increased the temperature sensitivity for all except the
Trime sensor. Temperature sensitivity was up to 12 times larger at the saturated end compared with
3
The mention of trade or manufacturer names is made for information only and does not imply an
endorsement, recommendation, or exclusion by USDA-Agricultural Research Service.
41
values in air-dry soils, corresponding to the much larger bulk electrical conductivities of these soils when
saturated. All devices exhibited measurement precision better than 0.01 m3 m-3 as evidenced by repeated
measures through time under isothermal conditions. However, under non-isothermal conditions,
measurement precision decreased as the number of measurements (and time involved in taking readings)
increased, and as the soils became wetter, resulting in precision worse than (values greater than) 0.01 m3
m-3 for the Trime and Delta-T devices. Accuracy of the devices was judged by the root mean squared
difference (RMSD) between column mean water contents determined by mass balance and those
determined by the devices using factory calibrations. Smaller values of the RMSD metric indicated more
accurate factory calibration. The Delta-T system was least accurate, with an RMSD of 1.299 m3 m-3 on
the wet end. At the saturated end, the Diviner, EnviroSCAN and Trime devices all exhibited RMSD
values >0.05 m3 m-3, while the neutron probe and TDR exhibited RMSD <0.03 m3 m-3. Soil-specific
calibrations determined in this study resulted in RMSE of regression values (an indicator of calibration
accuracy) ranging from 0.016 to 0.058 m3 m-3. All of the devices would require separate calibrations for
soil horizons with widely different properties (e.g. Fig. 4). Of the EM devices, only the Delta-T PR1/6
exhibited axial sensitivity appreciably larger than the axial height of the sensor, indicating small
measurement volumes generally, and suggesting that these systems may be susceptible to small-scale
variations in soil water content (at scales smaller than the representative elemental volume for water
content) and to soil disturbance close to the access tube caused during installation.
Impact: The flexibility and accuracy of conventional TDR measurements using variable cable
lengths and in soils exhibiting appreciable bulk electrical conductivity may be much improved by the
proposed method of calibration in terms of travel time, bulk electrical conductivity and effective
frequency. Factory calibrations of some electromagnetic (EM) sensors, manufactured for use in access
tubes, were shown to be inaccurate in three soils of the Southern Great Plains, and by extension in many
soils. Soil-specific calibrations are required, greatly increasing the effort needed to successfully use these
sensors. The relatively small axial measurement sensitivity of the EM sensors increases the likelihood that
they will be overly sensitive to small-scale variations in soil water content, at scales smaller than the
representative elemental volume for soil water content. Temperature sensitivity of two of the EM sensors
is so large as to make them problematic in field contexts for near-surface soil water content estimation.
Measurement precision was shown to be dependent on temperature sensitivity and the period of time over
which measurements are averaged to obtain a mean value.
42
Figure 4. Calibration curves for the EnviroSCAN system for the combined data from soils A and B, and
for soil C, compared with the factory calibration (Factory E) and the calibration of Baumhardt et al.
(2000) in the Olton soil; and, calibration curves for the Diviner2000 system for the combined soils A and
B data, and for the C soil, compared with the factory calibration (Factory D).
Kansas State University
Characterization of Effective Measurement Scales for Thermal Sensors: Kansas, in collaboration with
John Knight (CSIRO Land & Water), has continued to investigate spatial weighting functions for a broad
class of methods involve heat pulse sensors. During the past year we completed our investigation of the
weighting function for volumetric heat capacity (C) as measured with the original DPHP method of
Campbell et al. (1991, SSSAJ 55:291-293). In this method, C is estimated from the maximum
temperature rise observed at the temperature probe after a pulse of heat is released from the heater probe.
Although our ultimate goal is to obtain a complete volumetric characterization of the spatial sensitivity of
the DPHP method, our work to date has focused on characterizing the spatial sensitivity of the DPHP
method in a plane normal to the line heat source that passes through the location at which temperature is
measured with the DPHP method (Fig. 1). Spatial integration of the weighting function within this plane
Figure 1. Sketch of a DPHP sensor with heater probe and temperature
probe. The plane passing through the heater and temperature probes
43
defines the area in which the spatial sensitivity of the DPHP method is
characterized.
has allowed us to calculate contours of equal fractional spatial sensitivity (Fig. 2) that characterize the
size and shape of the region sampled when measuring C. The dimensionless coordinates X and Y in Fig.
2 are defined as X = x/a and Y = y/a, respectively, where a is the distance between the heater and
temperature probes of the DPHP sensor and x and y are coordinates with units of length. The location of
the heater and temperature probes can be interchanged without affecting the results because the spatial
weighting function for C is symmetric about the Y axis. The number on each contour (Fig. 2) gives the
fraction of the total spatial sensitivity contained within the region bounded by that contour. It is clear
from Fig. 2 that the spatial sensitivity of the DPHP method for measuring C is not radially symmetric
about the heater probe. The temperature probe and heater probe are of equal importance in defining the
spatial sensitivity of the method. The spatial sensitivity is greatest in the small areas immediately left and
right of the two probes of the DPHP sensor, and it decreases exponentially with increasing distance from
the probes. Far from the probes of the sensor the contours of equal fractional spatial sensitivity become a
family of ellipses. Thus, the effective outer boundary of the DPHP method can be characterized by an
Figure 2. Contour lines representing selected values of the fractional spatial sensitivity
for a DPHP sensor with heater probe at (X,Y) = (-1/2,0) and temperature probe at (X,Y)
= (1/2,0). The dots show the location of the probes. The number on each contour
represents the fraction of the total spatial sensitivity contained within the region bounded
by that contour.
44
ellipse with foci at  X ,Y   - 1 2 ,0 and  X ,Y   1 2 ,0 . If we use 99% of the total spatial sensitivity as
our criteria for defining the effective outer boundary, this ellipse has a major axis of length ~2.6 times the
distance between the heater and temperature probes (Fig. 2). Table 1 contains the dimensionless areas for
the regions defined by the contours in Fig. 2. Multiplying the areas in Table 1 by a2 yields corresponding
areas with physical units. Thus, for a sensor with spacing a = 6 mm, the boundary capturing 99% of the
total spatial sensitivity has an area of 128 mm2.
The results presented in Fig. 2 are general inasmuch as they hold for any combination of probe spacing,
soil thermal properties, and sensor heat input. When the results are examined in terms of the coordinates
x and y having units of length, the scaling of the x and y axes become a function of a, the probe spacing,
but remain unaffected by soil thermal properties and the heat input. Thus, it does not appear possible to
manipulate the sampling area of a DPHP sensor by increasing or decreasing the amount of heat released
from the heater probe. The relative size of the sampling are can only be manipulated by altering the
distance between the heater and temperature probes. The results in Fig. 2 are also general in that they
hold for the measurement of volumetric water content () as determined from the measurement of C.
This follows from the fact that C varies linearly with .
Table 1. Values of dimensionless area for the
fractional spatial sensitivity contours in Fig. 2. The
dimensionless area is the area of the region bounded
by a particular contour of equal fractional spatial
sensitivity.
Fractional spatial
Dimensionless area
sensitivity
0.1
0.165
0.2
0.357
0.3
0.567
0.4
0.786
0.5
1.018
0.6
1.270
0.7
1.566
0.8
1.963
0.9
2.611
0.95
3.237
0.99
4.665
0.999
7.042
During the past year we have also initiated work on the spatial sensitivity of the multi-functional heat
pulse (MFHP) sensor of Mori et al. (2003, VZJ 2:561-571). Specifically, we have developed spatial
weighting functions for volumetric heat capacity (C) and soil water flux density (u) as measured with the
MFHP sensor. Figure 3 shows the five probes (subset of six total probes) of the MFHP sensor that are
used to measure these quantities. The soil water flux density u is uniform throughout the x-y plane, but
has arbitrary magnitude and direction. Preliminary analysis indicates that the spatial weighting function
45
y
= Temperature probes
= Heater probe
x
Water flux u
Figure 3. Sketch of the five probes of a multi-functional heat pulse
sensor used to measure volumetric heat capacity and soil water flux
(u). The spatial sensitivity of the sensor is characterized in the x-y
plane, which is oriented normal to the probes and passes through the
temperature probes at the locations where temperature is measured
with a thermistor or thermocouple.
for C in the x-y plane is affected by the spatial arrangement of the heater probe and temperature probes.
It is also affected slightly by the magnitude of u, but it is not affected by the direction of u. The spatial
arrangement of the heater probe and temperature probes also influences the spatial weighting function for
u in the x-y plane. As might be expected, the spatial weighting function for u also depends on the
magnitude and direction of u. The principle underlying development and evaluation of the MFHP sensor
is the measurement of multiple soil properties and processes in the same soil volume. Results of the
spatial sensitivity analysis described above, as well as similar analysis for other properties measured with
the MFHP sensor, will allow us to quantify the approximate sampling volume (size and shape of region
sampled) for each property and processes measured with the sensor. More importantly, we expect that
these results will yield insights that may allow for manipulation of the sampling volume for select
properties. That is, it may be possible to alter the design and operation of the MFHP sensor so that the
objective of equal and overlapping measurement volumes is better achieved.
46
Evaluation of PTF Approach for Estimation of Saturated Hydraulic Conductivity: Current methods for
measuring saturated hydraulic conductivity (Ks) are costly, time-consuming, require specialized
equipment, and are subject to numerous sources of uncertainty. An alternative approach is to use
pedotransfer functions (PTFs) to estimate Ks from surrogate data that are more easily measured, or are
already available. The primary purpose of this project is to collect data that will permit evaluation of PTF
approaches for estimating Ks. During the summer of 2005, in collaboration with a team of NRCS
scientists, field data were collected at sites representative of five benchmark soils. A pit was excavated at
each site to describe soil horizons. Samples from each horizon were sent to the NRCS National Soil
Survey Laboratory for detailed physical and chemical property determination. Large undisturbed soil
cores (25 cm diameter) were collected at each site for laboratory determination of Ks. At each site, three
cores were collected from each major soil horizon (three to four horizons per site) by sampling the face of
the pit. Field measurements of Ks were also obtained for the major soil horizons (five replicates per
horizon) at each site using the constant-head borehole permeameter method. Constant-head and fallinghead methods are being used for Ks measurements in the laboratory.
Field Assessment of a Method for Estimation of Groundwater Consumption of Phreatophytes:
Hydrographs from shallow wells in riparian zones with phreatophytes frequently display a distinctive
pattern of diurnal fluctuations. Kansas, in collaboration with scientists from the Kansas Geological
Survey, is using these small, diurnal water-table fluctuations to assess the amount and variability of
groundwater consumption. The method is being evaluated at a site (Larned Research Site, LRS) in the
riparian zone of the Arkansas River in south-central Kansas. The phreatophyte community at the LRS
consists primarily of cottonwood with lesser amount of mulberry and willow. During the past year we
have expanded this work to include a site (Ashland Research Site, ARS) located along the Cimarron
River in southwest Kansas near the border with Oklahoma. The major phreatophyte at the ARS is salt
cedar. There are also minor amounts of Russian Olive. At both sites, numerous wells (screened across
the water table) have been installed at locations within and outside of the riparian zone. Water-table
fluctuations are measured in each well with an ntegrated pressure-transducer and datalogger submerged in
the water column. Meteorological data are being collected at both sites, and the water status of the vadose
zone is monitored biweekly during summer using a neutron probe.
Estimates of specific yield (Sy) are needed in order to estimate consumptive water use from diurnal watertable fluctuations. We have obtained reasonable estimates of Sy at the LRS using the method of Skaggs et
al. (1978, Trans. ASAE 21:522-528). This is an in-situ method based on soil-moisture and water-level
changes. Inasmuch as the method assumes equilibrium conditions in the unsaturated zone, it implies that
Sy is equivalent to total drainable porosity. The method appears to be appropriate for the LRS because the
sediments (coarse sand and gravel) in the vadose zone are highly permeable. It appears unlikely that this
approach will yield reasonable Sy estimates at the ARS because the water table is close to the land surface
and the predominantly silty sediments at this site drain relatively slowly. Because of these issues, Sy must
be treated as a readily available specific yield rather than a total drainable porosity. Estimation of Sy at
the ARS will therefore require an approach similar to that implemented by Loheide et al. (2005, WRR
41:W07030). We are currently characterizing vadose zone hydraulic properties for the ARS so that this
approach can be implemented.
While the principle focus of this work is the estimation of groundwater consumption by phreatophytes,
we have also used our data – in conjunction with data from a number of additional sites – to assess the
major controls on phreatophytes-induced water-table fluctuations. This work has shown that spatial and
temporal variations in the amplitude of the fluctuations are primarily a function of variations in the
meteorological drivers of plant water (primarily global irradiance); vegetation type, density, and vitality;
and the specific yield of the sediments in the vicinity of the water table. Past hydrologic conditions
experienced by the riparian-zone vegetation, either in previous years or earlier in the same growing
47
season, are also an important control. A manuscript summarizing this work has been submitted to Water
Resources Research.
OBJECTIVE 3: To develop and evaluate scale-appropriate methodologies for the management of
soil and water resources
Washington State University
A study was carried out to investigate the effects of Digital elevation models (DEMs) on deriving
topographic and hydrologic attributes, and on predicting watershed erosion using WEPP v2005 (Zhang et
al., 2005). Six DEMs at three resolutions from three sources were prepared for two small forest
watersheds located in northern Idaho, USA. These DEMs were used to calculate topographic and
hydrologic parameters that served as inputs to WEPP. The model results of sediment yields and runoffs
were compared with field observations. For both watersheds, DEMs with different resolutions and
sources generated varied watershed shapes and structures, which in turn led to different extracted
hillslope and channel lengths and gradients, and produced substantially different erosion predictions by
WEPP.
A 3D-distributed watershed model was developed to simulate catchment-scale hydrological
process like runoff, infiltration, plant water uptake, and discharge. The model directly interfaces with GIS
data. We tested the model by comparing: (a) simulated and observed soil water contents for a laboratory
experiment on one-dimensional infiltration in a soil slab, (b) simulated and observed soil water contents
for a field experiment with one-dimensional flow, and (c) three-dimensional simulated and observed
stream flow data for a 0.75-km2 hilly catchment in Central Italy.
Cal State Fresno University
A preliminary study was carried out to develop a Sequentially Activated Micro-Flood Irrigation System
(SAMFIS). The practical purpose is to reduce agricultural runoff and deep percolation for ecosystem
restoration in Central Valley and the Bay-Delta area of California. Irrigation efficiency can be
significantly improved if control of water flow is engineered into the system and not left to human
control, such as in the center pivot sprinkler systems. Flood irrigation mechanization has met with limited
success, partly due to the complex physics involved in predicting the simultaneous surface sheet flow and
unsteady infiltration in the soil, and balancing hydraulic parameters and the volume of runoff and deep
percolation. We try to incorporate a computer program for surface irrigation simulation and design with
innovative water delivery system that results in an automated surface irrigation system in which a low
cost Sequential Irrigation Valve (SIV) will be used as the critical water-flow control device. The new
concept of surface irrigation will result in a scientifically designed and technically programmed system
that can be achieved without changing the existing field layouts and without arbitrary human intervention.
A GIS-aided watershed model (BASINS) was used to simulate hydrographs and water quality in
streams along the foothill areas of east Sierra Nevada. We started with Fresno River Watershed. The
model produced reasonable hydrographs when compared with historical and our own monitoring data.
However, it’s difficult to obtain the water quality predictions due to limited history of monitoring work
and complicated parameterization of various pollutant sources and sinks in the watershed.
We have also started building geodatabase models for assessment of watersheds in east Sierra Nevada
and groundwater banks in San Joaqin Valley. This includes the collection of digital elevation models
(DEM), land and water use data, meteorological and geological datasets, etc., for regional assessment of
48
water resources, water supply and water quality conditions. We used RockWork, ArcGIS and HYDRUS1D software programs to simulate the capacity of a groundwater bank in Bekersfield, CA. Results were
consistent with those obtained separately by Geomatrix company for the same project area.
University of California Riverside
We have developed a new comprehensive simulation tool HP1 (HYDRUS1D-PHREEQC) that was
obtained by coupling the HYDRUS-1D one-dimensional variably-saturated water flow and solute
transport model with the PHREEQC geochemical code. The HP1 code incorporates modules simulating
(1) transient water flow in variably-saturated media, (2) transport of multiple components, and (3) mixed
equilibrium/kinetic geochemical reactions. The program numerically solves the Richards equation for
variably-saturated water flow and advection-dispersion type equations for heat and solute transport. The
program can simulate a broad range of low-temperature biogeochemical reactions in water, soil and
ground water systems including interactions with minerals, gases, exchangers, and sorption surfaces,
based on thermodynamic equilibrium, kinetics, or mixed equilibrium-kinetic reactions. The program may
be used to analyze water and solute movement in unsaturated, partially saturated, or fully saturated porous
media. The graphical user interfaces of both HYDRUS-1D and PHREEQC can be used for easy input data
preparation and output display in the MS Windows environment.
We have further developed a multi-component reactive transport module CW2D (Constructed Wetlands
2D, Langergraber, 2001), as an extension of the HYDRUS-2D variably-saturated water flow and solute
transport program (Šimůnek et al., 1999). CW2D to model the biochemical transformation and
degradation processes in subsurface-flow constructed wetlands. The mathematical structure of CW2D is
based on the IWA Activated Sludge Models (Henze et al., 2000). Monod-type expressions are used to
describe the process rates. All process rates and diffusion coefficients are temperature dependent. The
biochemical components defined in CW2D include dissolved oxygen, three fractions of organic matter
(readily- and slowly-biodegradable, and inert), four nitrogen compounds (ammonium, nitrite, nitrate, and
dinitrogen), inorganic phosphorus, and heterotrophic and autotrophic micro-organisms. Organic nitrogen
and organic phosphorus are modelled as part of the COD. Heterotrophic bacteria are assumed to be
responsible for hydrolysis, mineralization of organic matter (aerobic growth) and denitrification (anoxic
growth). Autotrophic bacteria are assumed to be responsible for nitrification, which is modelled as a twostep process. All micro-organisms are assumed to be immobile. Lysis is considered to be the sum of all
decay and loss processes.
We have released a new version 3.0 of HYDRUS-1D, a software package for simulating water, heat and
solute movement in one-dimensional variably saturated media. The new features include a) flow equation
that may consider dual-porosity-type flow with a fraction of water content being mobile, and fraction
immobile, b) the transport equations that include provisions for kinetic attachment/detachment of solute to
the solid phase and it can be thus used to simulate transport of viruses, colloids, or bacteria, c) modules
for simulating carbon dioxide and major ion solute movement, d) new model of hysteresis, e) new
analytical models for the soil hydraulic properties, and f) compensated root water uptake.
We are close to releasing Version 1.0 of HYDRUS-3D. This completely new rewrite of the HYDRUS-2D
code will include, in addition to many improvements in the graphical user interface, the following new
features:
 Water flow in a dual-porosity system allowing for preferential flow in fractures or macropores
while storing water in the matrix (Šimůnek et al., 2003)
 Root water uptake with compensation
 Spatial root distribution functions of Vrugt et al. (2001, 2002)
 Soil hydraulic property models of Kosugi (1995) and Durner (1994)
 Transport of viruses, colloids, and/or bacteria using attachment/detachment model, filtration theory,
and blocking functions (Bradford et al., 2004, 2005, 2006)
 Constructed wetland module (only in 2D) (Langergraber and Šimůnek, 2005)
49

Hysteresis model of Lenhard et al. (1991) and Lenhard and Parker (1992) that eliminates
pumping by keeping track of historical reversal points
 New print management (printing at regular time intervals or after constant number of time steps)
 Dynamic system-dependent boundary conditions (e.g., switching between pressure head and
seepage face, zero flux or atmospheric boundary depending on position of water level)
Various applications of these programs can be found in many references given below.
University of California Riverside
Effects of Salinity, Sodicity, and Clay Mineralogy on Soil Physical and Hydraulic Properties
Understanding the relationship among soil properties, irrigation water quality, and soil
management practices is vital to the sustainability of irrigated agriculture. The objectives of this study
were to evaluate the interactive effects of clay mineralogy, prewetting rate (PWR), salinity, and sodicity
on soil aggregation, water infiltration rate, soil water characteristics, and bulk soil electrical conductivity
(ECa). Six soils with predominant clay minerals of smectite, vermiculite-smectite and kaolinite were
equilibrated with solutions of sodium adsorption ratio (SAR) = 0, 20, and 50 and electrical conductivity
(EC) = 3.0 dS m-1. After air-drying, the samples were sieved and repacked in brass or Plexiglas rings. The
soil columns were prewetted at rates of 2, 5, and 30 mm h-1, after which infiltration rates and aggregate
stabilities were determined. In other soil columns with similar treatment (except PWR), the soil water
characteristic curve and ECa were determined. When SAR increased from 0 to 50 (at EC = 0.6 dS m-1 and
low PWR), the aggregate stability decreased from 0.63 to 0.19. In addition, the steady-state infiltration
rate (i) in the vermiculitic and smectitic clay loam soils decreased by 87% and 92%, respectively. For a
given matric potential, the amount of water retained in the smectitic (except the Cotharin soil) and
vermiculitic soils increased when SAR increased from 0 to 50 (EC = 3.0 dS m-1). The air-entry value
decreased 678% for the smectitic silty-clay loam soil and 301% for the smectitic silty-clay soil, which
was attributed to a reduction in macroporosity due to high sodicity. The physical and hydraulic properties
of the kaolinitic loam soil were not significantly affected by SAR increase. The ECa of the smectitic clay
loam soil increased from 1.14 to 2.42 dS m-1 when SAR increased from 0 to 50 (soil solution EC ≤ 4 dS
m-1). At low EC, aggregate slaking by a fast PWR was the main cause of aggregate disruption and lower
infiltration capacities when SAR was low whereas swelling and dispersion become more important to
structural stability when SAR was  20.
Carbon Sequestration in Two California Soils under Native and Irrigated Cropping Conditions
Cultivation and irrigation may significantly alter the carbon (C) sequestration process in cropland soils
compared to native soil conditions. The degree of change due to human activity in irrigated soils,
however, is largely unknown. In this study, two soils were chosen to investigate the effect of irrigation
and cultivation on C sequestration. One soil is a Garces sandy loam located near Wasco in the San
Joaquin Valley, CA and the other is an Imperial clay loam located in the Imperial Valley, CA. Bulk soil
samples were collected from five field sites, representing a native soil and soils that have been
cultivated/irrigated for approximately 20, 25, 30, and 40 yr. for the Garces loam (Wasco soil), and from 3
other sites, representing a native soil and soils that have been cultivated/irrigated for 50 and 90 yr. for the
Imperial clay loam (Imperial soil). Within each field site, soil samples were taken from five locations
(replicates) approximately 10 m apart from each other at four depths (0-10, 10-25, 25-60, 60-100 cm).
The bulk soil samples were analyzed for total C, organic C, labile C, and organic N. Results showed that
conversion from native soils to irrigated cropland over a 10 to 30-year period increased the labile C
content, but the increase was not correlated to the length of cultivation. Organic C contents in cultivated
soils are higher than in the native soils in both of the areas, but the difference is not statistically significant
between cultivated and native soils in the Garces soil. No consistent trend was observed between
carbonate content and the length of irrigation and cultivation in the Garces soil, while the carbonate
content in the Imperial soil increases as the length of irrigation and cultivation increases.
50
North Dakota State University
A statistical study was done to identify the interactions of nitrogen, weather, soil type, and irrigation on
corn yield (Derby, 2005b). The significant interactions on yield were from nitrogen amounts and weather.
Several zone delineation methods for precision management of nitrogen at the field scale were also
compared (Franzen, 2005). Also, the six-year water quality history under irrigate corn production was
reported (Derby, 2005a), where there was strong evidence for in-situ nitrate reduction as a result of
denitrification.
The statistical study on the interactions of various factors on corn yield can help to develop methods that
conserve nutrient application. Potentially, in years that have poor growing weather, nutrient requirements
can be adjusted so that maximum yields can be achieved while minimizing economic inputs. The zone
management comparison study will lead to a more efficient use of nitrogen fertilizer and less
environmental impacts from its use.
Utah State University
Field-Scale Mapping of Soil Water Content Using On-The-Go TDR Measurements
We are continuing to develop and test TDR-based water content measurements in a mobile system that
can be integrated with agricultural machinery to provide mapping of soil water content, temperature, bulk
electrical conductivity and other key properties of field soils. The ability to obtain field scale water
content distribution maps is an important goal for improving management of irrigated and rain-fed
agriculture within watersheds as well as to rangeland and forestry. The goal is to develop field-scale water
content and soil property mapping approaches using statistical models that lead to linkages between infield measurements and remotely sensed data for improved resource management. The automation and
incorporation of this technology will facilitate improved monitoring and mapping of saline soils.
Diagnostic maps and surveys are needed for the root zone, where monitoring of salt accumulation and
leaching is critical for water management and reclamation activities. A prototype mobile sensor platform
was constructed previously, based around an all terrain vehicle, and this year we have made preliminary
measurements on a tractor mounted toolbar. We have submitted several proposals seeking funding for this
research.
USDA-ARS National Soil Tilth Laboratory and Iowa State University
Nitrate Loss In Subsurface Drainage From Mid-Season N Fertilizer Application:
Accomplishments. Whether in response to remotely sensed plant N status or as a rescue treatment when
previously applied N has been lost to denitrification or leaching, there is growing interest in applying N to
corn at mid-season. While the yield benefits of this practice are variable, little information is available as
to the impacts of mid-season N application on water quality. We compared grain yields and NO3 losses
in drainage water as a result of applying N either once at emergence or equally split between emergence
and mid-season. Nitrogen treatments consisted of 199 (H), 138 (M), and 69 (L) kg ha-1 applied postemergence and 69 kg ha-1 applied post-emergence and again at mid-season (R). Grain yield for corn and
soybean, grown in a 2-yr rotation, and drainage water NO3 concentrations were measured on replicated
tile-drained plots within a producer’s field from 2000 through 2004. Outcome. Mid-season application
of additional N (R treatment) increased corn yield every year from 0.9 to 2.5 Mg ha-1 compared to the L N
treatment. However, in only one of three years (2000) did the mid-season application increase yield
compared to the equivalent total N rate applied in the spring (M treatment). The yield advantages in 2000
may have been due in part to disease preferentially infesting the higher N treatments. There was no carry
over N-treatment effect on soybean yields. Nitrate concentrations in tile drainage were consistently
greater (0.3 – 2.5 mg L-1) for the R treatment than the M treatment and significantly greater when
51
averaged over all years. Residual soil NO3 at the end of the year also indicated that some of the midseason N application was not taken up by the crop and was available for leaching. Impact. Mid-season
N application may be beneficial for recovering some of the potential corn yield, but the practice does not
benefit water quality compared to a single application at emergence. This information will help Midwest
farmers make decisions on the use and timing of N fertilizers that maximize corn yields and minimize
effects on water quality.
Development and Application of SWAT to Landscapes with Tile Drains and Potholes:
Acccomplishments. SWAT (Soil and Water Assessment Tool) is a watershed model that has been
incorporated into USEPA’s modeling framework called BASINS used for total maximum daily load
(TMDL) analysis. It is thus important that SWAT realistically simulate tile flow and pothole landscapes
that are common in much of the Corn Belt and Great Lakes states. In this study, SWAT was modified to
simulate water table dynamics and linked with a simple tile flow equation. Algorithms were also added to
SWAT to include simulation of potholes (closed depressions), surface tile inlets, and aeration stress on
plants. Flow interaction between HRUs was introduced in order to simulate pothole water. The modified
SWAT model (SWAT-M) was evaluated using eight years of measured flow data from Walnut Creek
watershed (WCW), an intensively tile-drained watershed in central Iowa. The model was calibrated
during the period of 1992 to 1995 and validated during the period of 1996 to 1999. In addition,
comparisons between the enhanced version (SWAT-M) and older version (SWAT2000) of SWAT were
conducted. For assessing overall performance of the SWAT models, predictions were compared to data
measured at stream sites approximately at the midpoint of the watershed (site 310) and at the outlet (site
330). Outcome. Nash-Sutcliffe E values for the simulated monthly flows during the calibration/validation
periods were 0.88/0.82 and 0.84/0.72 at sites 310 and 330, respectively (Fig. 6). The relative mean errors
(RME) of the simulated monthly flows during the calibration/validation periods were −2%/ −1% and
−18% / 10%, respectively, for the same two sites. These statistical values indicate that SWAT-M
estimated both pattern and amount of the monthly flows reasonably well for the large flat landscape of
WCW containing tile drains and potholes. SWAT-M needs to improve in its daily prediction because of
its lower E values (−0.11 to 0.55), compared to the monthly results. In applying the model to a third site
(site 210) that was predominantly influenced by tile drainage, it was concluded that the pattern and
amount of simulated monthly subsurface flows (E values of 0.61 and 0.70 and RME values of 10% and
−9% for the calibration and validation periods, respectively) were relatively close to the measured values.
Nevertheless, SWAT-M simulation of daily subsurface flows was less accurate than monthly results.
Impact. The pattern and amount of monthly flow and subsurface tile drainage predicted by SWAT-M
Figure 6. Monthly flows at the mouth of Walnut Creek watershed simulated with the current (SWAT
2000) and modified (SWAT-M) versions of SWAT compared to measured for the calibration (a) and
validation (b) time periods.
52
has been greatly improved as compared to SWAT2000. The model is now better suited for predictions in
watersheds with pothole physiography having substantial artificial tile drainage.
Desert Research Institute and University of Nevada
Current research in Nevada is focusing on a multifaceted approach to investigating soil hydrology at a
variety of scales, from the micron to the landscape. At the meso-scale, we have developed a modified
evaporation experiment (Meadows et al., 2005c) to examine the hydraulic properties of individual soil
peds. Significant variability (2 orders of magnitude) in hydraulic properties was shown to exist at the
scale of tens of cm on older, well-developed desert pavements.
Research from Nevada seeks to define effective hydraulic parameters for various large scale
hydrologic processes in heterogeneous fields. The study of Zhu and Mohanty (2005a) investigated the
effective hydraulic parameters for transient infiltration in terms of the optimal averaging schemes for the
input fields of hydraulic and environmental parameters. The optimal effective p-norm derived for the
random (input) parameters defines an optimal averaging scheme for the random input fields. Zhu et al.
(2005a) examined the impact of the skewness (third-order moment) of hydraulic parameter distributions
on the schemes for effective averaging of soil hydraulic parameters on a flat landscape. The focus was to
study the influence of higher order moments of hydraulic parameter distributions on the effective
parameters that produce ensemble fluxes in the heterogeneous soils. They derived the effective parameter
values using three widely used unsaturated hydraulic conductivity functions and various types of
probability distribution functions to represent spatial variability for the nonlinear shape factor in the
hydraulic conductivity function. Zhu and Mohanty [2005b] studied effective soil hydraulic parameter
averaging schemes in heterogeneous soils. Assuming one-dimensional vertical moisture movement in
unsaturated soils, both scenarios of horizontal (across the land surface) and vertical (across the soil
profile) heterogeneities were investigated. The effects of hydraulic parameter statistics, surface boundary
conditions, domain scales and fractal dimensions in case of nested soil hydraulic property structure were
addressed.
In the study of Zhu and Young (2005), we examined (1) how the hydraulic parameters of Gardner and
van Genuchten models correspond based on the equivalence of important hydrologic processes; and (2)
the implication of correspondence in terms of averaging schemes of hydraulic properties when predicting
flux across land-atmosphere boundary and surface soil moisture in heterogeneous soils. In view of the
large range of hydraulic properties for silty clay and sand and the large variabilities of the scaling factor
considered in our study, a relatively small range in the p-norm values is somewhat encouraging with
respect to effective parameter estimation for large land areas encompassing various soil textures,
large/small topographic structures, and other hydrologic scenarios. Our results also reveal that distribution
skewness is also important in determining the upscaled effective parameters, in addition to the mean and
variance, and the optimal averaging schemes for different hydraulic property models can be quite
different.
Nevada has been examining whether an organic-based emulsion, used to stabilize environmental
contaminants near the soil surface, may produce undesired impacts on local desert ecosystems (Young et
al., 2005b). The examination included potential hydrologic impacts (changes in infiltration or surface
runoff characteristics) as well as its impact on dust emission potential. The “Encapco” emulsion used in
this study is a blend of organic esters, surfactants, water, and a proprietary chelating agent. The emulsion
was tested on desert alluvial soils at the Yuma Proving Ground (YPG), Yuma, AZ, USA, and on
controlled soil materials near Las Vegas, NV, USA. At YPG, triplicate tension infiltrometer
measurements and rainfall simulation experiments were conducted to examine the temporal dynamics (~0
mo, 3 mo, 6 mo, 12 mo), dilution ratio (control, 4:1, 6:1), geomorphic effects (young vs. old soils), and
surface disturbance (raked vs. natural) impact to the soil’s hydrologic properties. Results at YPG showed
that the emulsion significantly reduced (~1 order of magnitude) the saturated hydraulic conductivity of
53
the soil and decreased the time to ponding immediately following application. However, six months after
treatment, few plots differed statistically from the pretreatment values, indicating a relatively short-lived
hydrologic effect. The concentration of the applied emulsion did not affect the results, at least for the two
test dilutions used. The emulsion also appeared to have a larger impact on the younger soil, perhaps
because the older surface is naturally less permeable due to a fine-grained surface horizon.
USDA-ARS, Bushland, TX
A study of the spatial variability of soil profile water content as assessed by several sensors used in
access tubes was completed at a well-irrigated field site in the San Joaquin Valley, California. Sensors
included the Delta-T PR2/6, Sentek EnviroSCAN, and Sentek Diviner2000, all capacitance probes. Also
included were the Trime T3 tube probe, a quasi-TDR device, and the neutron moisture meter (Model 503
DR, Campbell Pacific Nuclear International, Inc.). The mean standard deviation of profile water content
(surface to 100-cm depth) was 3.3, 3.9, 5.6, 6.3 and 8.7 cm for the NMM, Trime T3, Diviner 2000,
EnviroSCAN, and Delta-T PR2/6, respectively (e.g. Fig. 5). This was the same order of ranking as found
in two seasons of field work at Bushland, Texas. However, values of SD found at Bushland varied over a
larger range because conditions there included dryland and severe deficit irrigation. Apparent variability
of profile water content was inversely proportional to apparent measurement volume as assessed in other
studies. California and Texas data will be combined for publication.
Impact: Capacitance sensors used in access tubes are of questionable suitability for assessment of
soil profile water content and its spatial variability. Numbers of access tubes required to assess the plot or
location mean water content to a given accuracy and probability level are much larger for capacitance
sensors than for either the NMM or soil coring.
54
Figure 5. Relative variability of soil profile water contents estimated by four devices used in
access tubes both earlier in the season when the crop was well-irrigated, and late in the season
after the field was allowed to dry for harvest. The crop was sweet peppers; and the twelve access
tubes were installed in plots that were irrigated to replenish 100% of crop water use in the San
Joaquin Valley, CA.
4. PUBLICATIONS DURING 2005:
Abdu, H., D.A. Robinson and S.B. Jones. 2005. A Complex Permittivity Model for a Coated
Coaxial TDR Probe in Saline Solutions. Agronomy Abstracts, ASA, Madison, WI.
Al-Jabri, S.A., J. Lee, A. Gaur, R. Horton, and D.B. Jaynes. 2006. A dripper-TDR method or in
situ determination of hydraulic conductivity and chemical transport properties of surface
soils. Adv. Water Resour. 29(2):239-249.
Bahaminyakamwe, L., J. Šimunek, J. Dane, J. F. Adams, and J. W. Odom, Copper mobility in
soils as affected by sewage sludge and low molecular weight organic acids, Soil Sci., (in
press).
Beresnev, I. A., R. D. Vigil, W. Li, W. D. Pennington, R. M. Turpening, P. Iassonov, and R. P.
Ewing. Elastic waves push organic fluids from reservoir rock. Geophys. Res. Lett. 32:
L13303, 2005
Blonquist, J.M., S.B. Jones and D.A. Robinson. 2005. A Low Cost Time Domain Transmission
Sensor with TDR Performance Characteristics for Determining Water Content in Soils. J.
Hydrology 314:235-245.
Blonquist, J.M., S.B. Jones, and D.A. Robinson. 2005. Standardizing Characterization of
Electromagnetic Water Content Sensors: Part II. Evaluation of Seven Sensing Systems.
Vadose Zone J. 4:1059-1069.
55
Blonquist, J.M.Jr., S.B. Jones, and D.A. Robinson. 2005. Precise Irrigation Scheduling Using a
Subsurface Electromagnetic Soil Moisture Sensor. Agronomy Abstracts, ASA, Madison,
WI.
Boivin, A., J. Šimunek, M. Schiavon and M. Th. van Genuchten, A comparison of pesticides
transport processes in three contrasting field soils using Hydrus-2D, Vadose Zone
Journal, (in press).
Bradford, S. A., and M. Bettahar. 2005. Straining, attachment, and detachment, of
Cryptosporidium oocysts in saturated porous media. Journal of Environmental Quality,
34, 469-478 (Log # 156114).
Bradford, S. A., and M. Bettahar. 2006. Concentration dependent colloid transport in saturated
porous media. Journal Contaminant Hydrology, 82:99-117.
Bradford, S. A., J. Šimunek, M. Bettahar, Yadata Tadassa, M. Th. van Genuchten, and S. R.
Yates, Straining of Colloids at Textural Interfaces, Water Resources Research, 41,
W10404, doi:10.1029/2004WR003675, 17 pp, 2005.
Bradford, S. A., M. Th. van Genuchten, and J. Simunek. 2005. Modeling of colloid transport
and deposition in porous media. Workshop on HYDRUS: Advanced modeling of water
flow and solute transport in the vadose zone, University of Utrecht, Utrecht, The
Netherlands, October 17-19, pp. 1-5.
Bradford, S. A., Y. F. Tadassa, and Y. Pachepsky. 2006. Transport of Giardia and manure
suspensions in saturated porous media. Journal of Environmental Quality, In Press.
Caldwell, T.G., E.V. McDonald, and M.H. Young, 2005b. Soil water balance, seedbed
microclimate, and the revegetation of arid lands in the Mojave Desert, In, The Mojave
Desert: Ecosystem Processes and Sustainability, (Eds) R.H. Webb, L.F. Fenstermaker,
J.S. Heaton, D.L. Hughson, E.V. McDonald, D.M. Miller, Submitted.
Caldwell, T.G., E.V. McDonald, and M.H. Young. 2005c. Soil disturbance and hydrologic
response at the National Training Center, Ft. Irwin, California, J. Arid Environs., revised.
Caldwell, T.G., E.V. McDonald, and T. Bullard. 2005a. Linking Soils, Landscape and
Geomorphology: Catalina Island, CA. Oak Researchers Workshop, Long Beach CA,
March 22.
Casey, F. X. M., J. Šimunek, J. Lee, G. L. Larsen, and H. Hakk, Sorption, mobility, and
transformation of estrogenic hormones in natural soil, J. of Environ. Quality, 34, 13721379, 2005.
Casey, F.X.M., J. Lee, and S. J. 2005. Sorption, Mobility, and Transformation of Estrogenic
Hormones in Natural Soil. J. Envrion. Qual. 34:1372-1379.
Chaplot, V.; A. Saleh, and D.B. Jaynes. 2005. Effect of the accuracy of spatial rainfall
information on the modeling of water, sediment, and NO3-N loads at the watershed level.
J.Hyrol. 312(1-4): 223-234.
Chen, G. and Flury, M., 2005. Retention of mineral colloids in unsaturated porous media as
related to their surface properties. Colloids Surf. Physicochem. Eng. Aspects, 256: 207216.
Chen, G., Flury, M., Harsh, J. B. and Lichtner, P. C., 2005. Colloid-facilitated transport of
cesium in variably-saturated Hanford sediments. Environ. Sci. Technol., 39: 3435-3442.
Chen, L. and M.H. Young. 2005. Green-Ampt model for sloping surfaces. Water Resour. Res.
Under revision.
56
Coquet, Y., C. Coutadeur, C. Labat, P. Vachier, M. Th. van Genuchten, J. Roger-Estrade, and J.
Šimunek, Water and solute transport in a cultivated silt loam soil: 1. Field Observations,
Vadose Zone Journal, 4, 573-586, 2005.
Coquet, Y., J. Šimunek, and J. Roger-Estrade, Modelling the effects of soil tillage on water and
solute transport: the HYDRUS-2D/SISOL coupling, In: S. Torkzaban and S. M.
Hassanizadeh (eds.), Proc. of Workshop on HYDRUS Applications, October 19, 2005,
Department of Earth Sciences, Utrecht University, The Netherlands, ISBN 90-39341125,
78-81, 2005.
Coquet, Y., J. Šimunek, C. Coutadeur, M. Th. van Genuchten, V. Pot, and J. Roger-Estrade,
Water and solute transport in a cultivated silt loam soil: 2. Numerical analyses, Vadose
Zone Journal, 4, 587-601, 2005.
Czigany, S., Flury, M. and Harsh, J. B., 2005a. Colloid stability in vadose zone Hanford
sediments. Environ. Sci. Technol., 39: 1506-1512.
Czigany, S., Flury, M., Harsh, J. B., Williams, B. C. and Shira, J. M., 2005b. Suitability of
fiberglass wicks to sample colloids from vadose zone pore water. Vadose Zone J., 4: 175183.
Das, B. S., J. M. Wraith, G. J. Kluitenberg, H. M. Langner, P. J. Shouse, and W. P. Inskeep.
2005. Evaluation of mass recovery impacts on transport parameters using least-squares
optimization and moment analysis. Soil Sci. Soc. Am. J. 69:1209-1216.
Decker, D. L., Ch. Papelis, S. W. Tyler, M. Logsdon, and J. Šimunek, Arsenate and arsenite
sorption on carbonate hosted precious metals ore, Vadose Zone Journal, (in press).
Decker, D. L., J. Šimunek, S. W. Tyler, Ch. Papelis, and M. Logsdon, Variably saturated reactive
transport of arsenic in heap leach facilities, Vadose Zone Journal, (in press).
Derby, N.E., and Casey, F.X.M. 2005a. Six-Year Water Quality History under Irrigated Corn
Production. In Annual Meetings Abstracts [CD-ROM]. ASA, CSSA, and SSSA,
Madison, WI.
Derby, N.E., Steele, D.D., Terpstra, J., Knighton, R.E. and Casey, F.X.M. 2005b. Nitrogen,
Weather, Soil and Irrigation Effects and Interactions on Corn Yield. Agron. J. 97:13421351.
Du, B., A. Saleh, D.B. Jaynes, and J.G. Arnold. 2005. Evaluation of SWAT in simulating
atrazine losses in stream discharge for Walnut Creek watershed (Iowa) [CD-ROM].
Watershed Management Conf. Proc. Atlanta, Georgia.
Du, B., J.G. Arnold, A. Saleh, and D.B. Jaynes. 2005. Development and application of SWAT to
landscapes with tiles and potholes. Trans. ASAE 48(3):1-13.
Evett, S.R. 2005. International Soil Moisture Sensor Comparison. In Irrigation Insights No. 1,
Second Edition, SOIL WATER MONITORING, P. Charlesworth (ed.). Land & Water
Australia, Braddon, Australia. Pp. 68-71. (Chapter)Evett, S.R., Howell, T.A. and Tolk,
J.A. 2005b. Time domain reflectometry calibration in terms of travel time, bulk electrical
conductivity, and effective frequency. ASA-CSSA-SSSA International Annual Meetings
(November 6-10, 2005) (Abstract)
Evett, S.R. and Parkin, G.W. 2005. Advances in Soil Water Content Sensing: The Continuing
Maturation of Technology and Theory. Vadose Zone J 2005 4: 986-991. Special Section:
Soil Water Sensing. doi:10.2136/vzj2005.0099
Evett, S.R., Tolk, J.A. and Howell, T.A. 2005a. TDR laboratory calibration in travel time, bulk
electrical conductivity, and effective frequency. Vadose Zone Journal 4:1020–1029
(2005). Special Section: Soil Water Sensing. doi:10.2136/vzj2005.0046
57
Evett, S.R., Tolk, J.A. and Howell, T.A. 2006. Sensors for Soil Profile Moisture Measurement:
Accuracy, Axial Response, Calibration, Precision and Temperature Dependence.
Submitted to the Vadose Zone Journal.
Fan, Z., F.X.M. Casey, G.L. Larsen, and H. Hakk. 2005a. Fate and transport of 1278-TCDD,
1378-TCDD, and 1478-TCDD in soil-water systems. Chemosphere (In review).
Fan, Z., F.X.M. Casey, G.L. Larsen, and H. Hakk. 2005b. Persistence and fate of 17ß-estradiol
and testosterone in agricultural soils. Environ. Sci. Technol. (In review).
Fares, A., J. Šimunek, L. R. Parsons, M. Th. van Genuchten, and K. T. Morgan, Effects of
Canopy Shading and Irrigation on Soil Water Content and Temperature, In: S. Torkzaban
and S. M. Hassanizadeh (eds.), Proc. of Workshop on HYDRUS Applications, October
19, 2005, Department of Earth Sciences, Utrecht University, The Netherlands, ISBN 9039341125, 6-10, 2005.
Franzen, D., Nanna, T., Gautam, R., Casey, F., Derby, N., Staricka, J., Panigrahi, S., Long, D.,
Sims, A. and Lamb, J. 2005. Evaluation and Effectiveness of Nitrogen Zone Delineation
Methods. In Annual Meetings Abastracts [CD-ROM]. ASA, CSSA, and SSSA, Madison,
WI.
French, C., L. Wu, T. Meixner, D. Haver, J. Kabashima and W. A. Jury. 2005. Modeling
nitrogen transport in the Newport Bay/San Diego Creek watershed of Southern
California. Agricultural Water Management. (in press).
Fuentes, J.-P. and Flury, M., 2005. Hydraulic conductivity of a silt loam soil as affected by
sample length. Trans. ASAE, 48: 191-196.
Furman, A. and A. W. Warrick. 2005. Unsaturated flow through spherical inclusions with
contrasting sorptive numbers.
Vadose Zone J., Vol. 4, 255-263.
doi:10.21.36/vzj2004.0076.
Gärdenäs, A., Hopmans, J. W., B. R. Hanson, and J. Šimunek, Two-dimensional modeling of
nitrate leaching for various fertigation scenarios under micro-irrigation, Agric. Water
Management, 74, 219-242, 2005.
Gaur, A., R. Horton, and D. B. Jaynes. 2006. Measured and predicted solute transport in a tile
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Kodešová, R., J. Kozák, J. Šimunek, and O. Vacek, Single and dual-permeability models of
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Pikul, J.L., Schwartz, R.C., Benjamin, J.B., Baumhardt, R.L. and Merrill, S.L. 2005. Cropping
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Ruiz, V.M. and L. Wu. 2005. Influence of sodicity and clay mineralogy on soil aggregation and
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Saito, H., J. Šimunek, and B. P. Mohanty, Numerical Analysis of One-Dimensional Coupled
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Shafer, D.S., M.H. Young, S.F Zitzer, T.G. Caldwell, E.V. McDonald. 2005. Impacts of coupled
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Šimunek, J. and J. R. Nimmo, Estimating soil hydraulic parameters from transient flow
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Šimunek, J., and M. Th. van Genuchten, Contaminant Transport in the Unsaturated Zone:
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Šimunek, J., D. Jacques, M. Th. van Genuchten, and D. Mallants, Multicomponent geochemical
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Šimunek, J., M. Th. van Genuchten, and M. Šejna, The HYDRUS-1D software package for
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Šimunek, J., M. Th. van Genuchten, S. A. Bradford, and R. J. Lenhard, New Features of
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5. SIGNATURES
Mart Oostrom, Chair
Technical Committee, W-1188
Date
G.A. Mitchell
Administrative Advisor, W-1188
Date
69