ASTM D3404-91(2004)
(Guide)Standard Guide for Measuring Matric Potential in Vadose Zone Using Tensiometers
Standard Guide for Measuring Matric Potential in Vadose Zone Using Tensiometers
SIGNIFICANCE AND USE
Movement of water in the unsaturated zone is of considerable interest in studies of hazardous-waste sites (1, 2, 3, 4) ; recharge studies (5, 6); irrigation management (7, 8, 9); and civil-engineering projects (10, 11). Matric-potential data alone can be used to determine direction of flow (11) and, in some cases, quantity of water flux can be determined using multiple tensiometer installations. In theory, this technique can be applied to almost any unsaturated-flow situation whether it is recharge, discharge, lateral flow, or combinations of these situations.
If the moisture-characteristic curve is known for a soil, matric-potential data can be used to determine the approximate water content of the soil (10). The standard tensiometer is used to measure matric potential between the values of 0 and -867 cm of water; this range includes most values of saturation for many soils (12).
Tensiometers directly and effectively measure soil-water tension, but they require care and attention to detail. In particular, installation needs to establish a continuous hydraulic connection between the porous material and soil, and minimal disturbance of the natural infiltration pattern are necessary for successful installation. Avoidance of errors caused by air invasion, nonequilibrium of the instrument, or pressure-sensor inaccuracy will produce reliable values of matric potential.
Special tensiometer designs have extended the normal capabilities of tensiometers, allowing measurement in cold or remote areas, measurement of matric potential as low as -153 m of water (-15 bars), measurement at depths as deep as 6 m (recorded at land surface), and automatic measurement using as many as 22 tensiometers connected to a single pressure transducer, but these require a substantial investment of effort and money.
Pressure sensors commonly used in tensiometers include vacuum gages, mercury manometers, and pressure transducers. Only tensiometers equipped with pressure transducers allow f...
SCOPE
1.1 This guide covers the measurement of matric potential in the vadose zone using tensiometers. The theoretical and practical considerations pertaining to successful onsite use of commercial and fabricated tensiometers are described. Measurement theory and onsite objectives are used to develop guidelines for tensiometer selection, installation, and operation.
1.2 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.4 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word“ Standard” in the title of this document means only that the document has been approved through the ASTM consensus process.
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Designation: D3404 − 91(Reapproved 2004)
Standard Guide for
Measuring Matric Potential in Vadose Zone Using
1
Tensiometers
This standard is issued under the fixed designation D3404; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope environmental changes. Parameters affecting pressure-sensor
hysteresis are temperature and measured pressure.
1.1 This guide covers the measurement of matric potential
2.1.3 precision (repeatability)—the variability among nu-
in the vadose zone using tensiometers. The theoretical and
practical considerations pertaining to successful onsite use of merous measurements of the same quantity.
commercial and fabricated tensiometers are described. Mea-
2.1.4 resolution—the smallest division of the scale used for
surement theory and onsite objectives are used to develop
a measurement, and it is a factor in determining precision and
guidelines for tensiometer selection, installation, and opera-
accuracy.
tion.
3. Summary of Guide
1.2 The values stated in SI units are to be regarded as the
standard. The inch-pound units given in parentheses are for
3.1 The measurement of matric potential in the vadose zone
information only.
can be accomplished using tensiometers that create a saturated
1.3 This standard does not purport to address all of the hydraulic link between the soil water and a pressure sensor.A
safety concerns, if any, associated with its use. It is the variety of commercial and fabricated tensiometers are com-
responsibility of the user of this standard to establish appro- monly used.Asaturated porous ceramic material that forms an
priate safety and health practices and determine the applica- interface between the soil water and bulk water inside the
bility of regulatory limitations prior to use. instrument is available in many shapes, sizes, and pore
1.4 This guide offers an organized collection of information diameters. A gage, manometer, or electronic pressure trans-
or a series of options and does not recommend a specific ducer is connected to the porous material with small- or
course of action. This document cannot replace education or large-diameter tubing. Selection of these components allows
experienceandshouldbeusedinconjunctionwithprofessional the user to optimize one or more characteristics, such as
judgment. Not all aspects of this guide may be applicable in all
accuracy, versatility, response time, durability, maintenance,
circumstances. This ASTM standard is not intended to repre- extent of data collection, and cost.
sent or replace the standard of care by which the adequacy of
a given professional service must be judged, nor should this
4. Significance and Use
document be applied without consideration of a project’s many
4.1 Movement of water in the unsaturated zone is of
unique aspects. The word“ Standard” in the title of this
considerable interest in studies of hazardous-waste sites (1, 2,
document means only that the document has been approved
2
3, 4) ; recharge studies (5, 6); irrigation management (7, 8, 9);
through the ASTM consensus process.
and civil-engineering projects (10, 11). Matric-potential data
alone can be used to determine direction of flow (11) and, in
2. Terminology
some cases, quantity of water flux can be determined using
2.1 Definitions of Terms Specific to This Standard:
multiple tensiometer installations. In theory, this technique can
2.1.1 accuracy of measurement—the difference between the
be applied to almost any unsaturated-flow situation whether it
value of the measurement and the true value.
is recharge, discharge, lateral flow, or combinations of these
2.1.2 hysteresis—that part of inaccuracy attributable to the
situations.
tendency of a measurement device to lag in its response to
4.2 If the moisture-characteristic curve is known for a soil,
matric-potentialdatacanbeusedtodeterminetheapproximate
watercontentofthesoil (10).Thestandardtensiometerisused
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ThisguideisunderthejurisdictionofASTMCommitteeD18onSoilandRock
and is the direct responsibility of Subcommittee D18.21 on Groundwater and
Vadose Zone Investigations.
CurrenteditionapprovedJuly1,2004.PublishedJuly2004.Originallyapproved
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in 1991. Last previous edition approved in 1998 as D3404-91 (1998). DOI: The boldface numbers in parentheses refer to a list of references at the end of
10.1520/D3404-91R04. the text.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D3404 − 91 (2004)
to measure matric potential between the values of 0 and-867 using Darcy’s
...
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