Development of multi-functional measurement devices for vadose zone characterization Jan Hopmans University of California, Davis, CA, USA Yasushi Mori Shimane University, Japan Annette Pia Mortensen Geological Institute, Copenhagen University, Denmark Gerard Kluitenberg Kansas State University Carlos Vaz EMBRAPA, Sao Carlos, Brazil Keith Bristow CSIRO, Townsville, Australia
SOIL PROPERTIES ARE NOTORIOUSLY HETEROGENEOUS, IN BOTH SPACE AND TIME QUESTIONS: Measurement Scale???? Measurement Types??? Measurement Instruments?? Measurement Locations??? Measurement Times??????
MULTI-FUNCTIONAL instruments, ensuring identical measurement volumes Rubber Septum Acrylic Tube Vent Tube Plug PVC Pipe Copper Tube Rubber Stopper Sample Bottle Sampling Tube PVC Dowel Porous Ceramic Cup
Combined tensiometer-solution sampling probe Rubber Acrylic Tube Vent Tube Plug PVC Pipe Copper Tube Rubber Tensiometer Sample Bottle Sampling Tube PVC Dowel Porous Ceramic Cup Soil Solution Sampling
Coiled Cone Penetrometer-TDR Probe o o o o o Two parallel copper wires are wrapped around inner core (as double helix); Wires are connected to conductor and ground of coaxial cable; Signal is analyzed by cable tester; Long wire length (about 30 cm) ensures accurate travel time measurement,and Narrow wire spacing ensure high depth resolution
Hammer penetrometer parallel wires (steel) tip (steel) 2.4 cm
Calibration ε coil 8 7 6 5 4 3 2 Columbia Yolo Sand Fit Columbia Fit Yolo Fit Sand Polynomial fit Yolo 0.0 0.1 0.2 0.3 0.4 θ (cm 3 cm -3 ) Penetration Resistance (MPa) 18 16 14 12 10 8 6 4 2-3 1.2 to 1.3 g cm-3 1.55 g cm 1.3 to 1.4 g cm -3 1.45 1.35 1.25 r 2 = 0.72 RMSE = 0.98 1.4 to 1.5 g cm -3 1.5 to 1.6 g cm -3 equation [3] 0 0.0 0.1 0.2 0.3 0.4 Water Content (cm 3 cm -3 )
Field development, Brazil
Combined Tensiometer-TDR Reflection Coefficient 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 dried glass beads sat. glass beads water 0 5 10 15 20 25 Time (ns)
Laboratory Calibration 24 Oso Flaco 22 Ottawa SRI Columbia 20 Lincoln 18 ε coil 16 14 12 10 8 0.0 0.1 0.2 0.3 0.4 0.5 Soil Water Content (cm 3 cm -3 )
A heat pulse probe? Instrumentation in the vadose zone TDR Time domain reflectometry Tensiometers Tracer experiments Heat pulse probe multifunctional Apply heat as tracer Heat, water and solute transport
Multifunctional heat pulse probe Temperature, T Thermal properties Heat capacity, C Heat conductivity, λ 0 Thermal diffusivity, κ Heat dispersion, D Hydraulic properties same time + same place + same scale Water flux, q w Water content, θ Electrical conductivity, EC a
Heat pulse probe design Heat pulse heater thermistor 6 needles 1 mm diameter 6 mm spacing 28 mm long 25 mm wide Electrical conductivity Wenner array
I. Multi-step outflow experiment Multiplexer AM416 MF-HPP Multi-plexer AM416 Heating Sensitometer Tensiometer and Outflow Four-electrode Datalogger CR10 Thermistor Datalogger CR10
I. Analytical solutions of heat transport De Vries (1952)- Thermal Conduction ( ) ( ) 0 2 0 2 ; 4 4 4 ', t t t r Ei t t r Ei C q t r T > κ κ κ π = Ren et al. (2000) Thermal Convection ( ) 0 2 1 0 4 4 t t ; ds s s V r exp s C q T t t t h d d > = κ κ π ( ) 0 2 1 0 4 4 t t ; ds s s V r exp s C q T t t t h u u > + = κ κ π
II. Experimental flow column pump rainmaking device multiplexer AM416 tensiometer and pressure transducer multiplexer AM416 HPP datalogger CR10
II. Numerical solution heat transport Heat conduction and convection Homogenoues and isotropic media Thermal equilibrium between phases x C V 2 2 T T T w T = κ + V 2 2 θ w t x z Cb z h Cq θcv = = C C w w w w bulk b z T U H Water flow r r Cbulk = Cs(1 φ) + C w θ D
Fitting of temperature response curve 0.7 Fitting 0.6 I. Analytical solution Temperature difference [C] 0.5 0.4 0.3 0.2 0.1 Downstream Upstream Transverse II. Numerical solution (HYDRUS 2D) Parameters Thermal conductivity λ Water content θ 0 Water flux q w 0 20 40 60 80 100 120 Time [s]
I and II: Calibration of MF-HPP Needle distance, r Calibration in agar solution heat capacity for water no convective heat transport Calibration in porous media heat capacity for material saturated conditions Wenner array Calibration in porous media varying EC and water content Temperature difference [K] 0.8 0.6 0.4 0.2 0.0 ECb (ds m -1 ) 3 2 1 0 20 40 60 80 100 0.03 M 0.06 M 0.10 M Fitted Time [s] 0 0 0.1 0.2 0.3 0.4 0.5 θ by MFHPP (m 3 m -3 )
I.Unsaturated hydraulic functions Cumulative outflow (cm 3 ) and -matric head (cm) 180 160 140 120 100 80 60 40 20 0 Cumulative outflow Matric head 0 20 40 60 80 Time (hours) -Matric head (cm) 100 80 60 40 20 0 0.03 M 0.06 M 0.10 M 0 0.1 0.2 0.3 0.4 0.5 Volumetric water content (m 3 m -3 ) -4-5 -6-7 -8-9 Log 10 Hydraulic conductivity (m s -1 ) Inverse Modeling of Multi-step Outflow
I and II. Estimation of thermal conductivity, λ ( heat conduction only) 2.0 Thermal conductivity λ [W/mK] 1.6 1.2 0.8 0.4 Mortensen et al. [2003] Mori et al [2003] Hopmans and Dane [1986] Thermal conductivity λ 0 = b + b θ + b θ 0 Thermal diffusivity κ = λ 0 1 /C bulk 2 0. 5 0.0 0.0 0.1 0.2 0.3 0.4 Water content [cm3/cm3]
II. Solute transport Electrical conductivity EC = θτ(θ) EC + bulk water EC solid v=0.0036 cm/s 2.5 θ=0.20 2.0 θ=0.22 θ=0.32 EC [ms/cm] 1.5 1.0 θ=0.37 0.5 Ψ=20 cm 0.0 0 10 20 30 40 50 60 Time [min]
I and II: Estimation of water content, θ (Heat conduction only) 0.40 0.40 Real water content 0.30 0.20 0.10 0.00 0.00 0.10 0.20 0.30 0.40 Estimated water content Real water content (m3m-3) 0.30 0.20 0.10 0.00 Static Transient 0.00 0.10 0.20 0.30 0.40 Estimated water content (m3m-3)
Water flux effect on temperature signature Temperature ( o C) 21.2 21.0 20.8 20.6 20.4 20.2 20.0 19.8 No Flow 1 m/d, downstream needle 1 m/d, upstream needle 10 m/d, downstream needle 10 m/d, upstream needle 0 25 50 75 100 Time (s) (B)
I and II: Estimation of water flux, q w (heat conduction and convection) Accurate range: 0.0001 to 0.01 cm/s or 10 to 1000 cm/day 8.E-5 7.E-5 6.E-5 Real flux [m/s] 5.E-5 4.E-5 3.E-5 2.E-5 1.E-5 Unsaturated Saturated 0.E+0 0.E+0 1.E-5 2.E-5 3.E-5 4.E-5 5.E-5 6.E-5 7.E-5 8.E-5 Estimated flux [m/s]
Water content error for high water fluxes However, these high water fluxes only occur under saturated conditions
Thermal dispersion effect on temperature signature (q w = 1 m d -1 ) 20.9 20.9 Temperature ( o C) 20.7 20.5 20.3 20.1 Dispersivity = 0 Downstream Upstream Transverse Temperature ( o C) 20.7 20.5 20.3 20.1 Downstream Upstream Transverse Dispersivity = 0.001 19.9 0 10 20 30 40 50 60 19.9 0 10 20 30 40 50 60 Time (s) Time (s) 20.9 20.9 Temperature ( o C) 20.7 20.5 20.3 20.1 Downstream Upstream Transverse Dispersivity = 0.01 Temperature ( o C) 20.7 20.5 20.3 20.1 Downstream Upstream Transverse Dispersivity = 0.1 19.9 0 10 20 30 40 50 60 19.9 0 10 20 30 40 50 60 Time (s) Time (s)
Conclusions Advantages Simultaneous measurement of water flow, solute and heat transport properties within the same sample volume Limitations In situ calibration of probe Sensibility to needle spacing Accurate water flux range is limited to 10-1000 cm/day Future work Compare heat and solute dispersivities Improve for water flux density < 10 cm/day Field applications
Multi-Functional Sensors: Are being developed, that Measure approximately same volumes, BUT Issues of probe-soil contact Measurement interferences What is real measurement volume, contributing to the measurement???
REV (Bear) or Relativist Concept (Baveye and Sposito, 1984)???? SENSOR Spatial weighting function, ω: ω = V ( xyzdv,, ) 1 θ ω θ mac ( xyz,, ) = ( xyz,, ) ( xyzdv,, ) mic V