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Direct Measurement Instruments for Estimation of Vertical Water Movement Pan Lysimeter
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ect Measurement Instruments for Estimat of Vertical Water Movement Pan Lysimeter Passive Capillary Sampler Tension Lysimeter Joel Hubbell AgE 558, Spring 2001
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Direct Measurement Instruments for Estimation of Vertical Water Movement Pan Lysimeter Passive Capillary Sampler Tension Lysimeter. Joel Hubbell AgE 558, Spring 2001. State Variables for Characterizing the Vadose Zone. Soil Water Potential Hydraulic gradient Water Content - PowerPoint PPT Presentation
Transcript of Direct Measurement Instruments for Estimation of Vertical Water Movement Pan Lysimeter
Direct Measurement Instruments for Estimationof Vertical Water Movement
Pan LysimeterPassive Capillary Sampler
Tension Lysimeter
Joel HubbellAgE 558, Spring 2001
State Variables for Characterizing the Vadose Zone
Soil Water PotentialHydraulic gradient
Water ContentMass of water-changes in time and space
Flux Rate Concentration of Solutes
Pan LysimeterPassive Capillary Sampler (PCAPS)
Tension Lysimeter
Theory of operation Construction, installation and operation Advantages and limitations
Comparison of devices
Pan Lysimeter
Intersect flow and route to sampling locationImpermeable layer beneath siteNumerous configurations
Pan, plastic, glass block, funnel
Pan Lysimeter
Pan Lysimeter
Pan Lysimeter
Pan Lysimeter
Pan Lysimeters
Advantages: “Simple” designLower costs Available materials
Limitations: Divergent flow (under sampling)Collect 0 to 36-45% of flow (optimum)Difficult to design to predict fluxSamples macropores-”wet” conditions
Passive Capillary Sampler
Intercepts flowCollects with a constant pressure
Wick fluid with fiberglass rope
PCAPS
Passive Capillary Sampler
Passive Capillary SamplerAssets:Passive design
Macro/micro pore flowBest in sandsMore representative flux
103, 80, 64 % of WBWell published-12+ articles
Limitations:Soil water potential <-150 cm “wet”Clay and silts lower recoveriesDesign/materials more complexInstallation more complex-undisturbed
Tension Lysimeter
Tension Lysimeter
Tension LysimeterAdvantages: Able to sample tensiometeric range
Good for sands, silts and claysMatches SWP in device with existing conditions
Could be automatedShould produce best estimate of flux
Limitations:Complex designSophisticated instrumentHigh cost of operationFew papers
Comparison of InstrumentsFlux representiveness
Pan/Gravity Lysimeter PCAPS Tension LysimeterOverall
Low Medium-High High
For Low water potential(dry) Low Low High
High water potential (wet)Best Good Good
Chemical representiveness of sampleHighest Good Fair
Comparison of InstrumentsPan/Gravity Lysimeter PCAPS Tension LysimeterPrimary pore size sampled
Macro pore Macro pore Macro and micro
Water Pressure range of operation 0-unk (Wet range only) 0 to about –80 cm 0 to -700cm
(up to –150 cm)
Vary tension range for sampling? (flexibility)No Limited 0 to -80 cm Yes, 0 to –700 cm
Best to SampleSand Sand Clay-course sand
Comparison of InstrumentsCost to install and construct tool
Medium-high Medium-high High Complexity of design
Low High Very high Ease of operation
Easy Medium Difficult Mode of operation
Passive Passive Active
Cost of operationLow Low High
Pan/Gravity Lysimeter PCAPS Tension Lysimeter
ConclusionsPan Lysimeter
Least accuracy/complexityPCAPS
More accurate/complexTension Lysimeter
Best/most complex
Problem is standard for comparisonAlso impedance match
Spatial variability in recharge Preferential flow-Finger, funnel flow, fast flow paths
Caution
Although the technique (flux meters) has worked well for those researchers that have perfected it subtleties,
it does not appear to be pragmatic on a large-area basis and should be used only for very localized
and specialized studies. (Wagenet, MOSA 1986)
