Further Developments on Apparatus for Field Moisture Studies

Richards, L. A.; Russell, M. B.; Neal, O. R.

doi:10.2136/sssaj1938.036159950002000c0008x

Cited by 29 publications

(9 citation statements)

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“…1) that are not completely free to expand or contract. This phenomenon is analogous to the widely observed pressure changes in tensiometers responding to diurnal temperature fluctuations (Richards et al, 1937; Butters and Cardon, 1998; Warrick et al, 1998).…”

supporting

confidence: 75%

Analysis of Temperature Effects on Tension Infiltrometry of Low Permeability Materials

Castiglione

Shouse

Mohanty

et al. 2005

Vadose Zone Journal

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disk having an air entry pressure of approximately Ϫ25 cm of water, contact material, and a ring for holding the Tension infiltrometers have become popular for in situ measurecontact material and leveling the supply disk ( Fig. 1). ment of the near-saturated hydraulic conductivity as a function of the soil water pressure head. Unfortunately, fluctuating ambient tempera-As water infiltrates across the soil surface, an equal voltures can cause dramatic pressure variations due to the presence of ume of air enters the reservoir through Tubes B and C. confined air inside the infiltrometer, thereby affecting the intended The procedure establishes a constant negative pressure pressure head to be applied to the soil surface and hence also the meaat the soil surface, which can be adjusted by manipulatsured infiltration rate. This is especially true for low infiltration rates ing Tube B in the Mariotte tower. The infiltration rate and long equilibration times typical of low permeability materials, is measured (often by means of a pressure transducer) including unsaturated fractured rock. We developed a model to anafrom water volume changes in the reservoir tower (Perlyze the effects of temperature changes on the static pressure of the conroux and White, 1988; Ankeny et al., 1988). fined air volume within tension infiltrometers. The model was tested An important feature of a well-designed infiltrometer using several prototype infiltrometer designs in a computer-controlled variable-temperature room. Experimental results confirmed the model temperature fluctuations on the Mariotte and reservoir Scoates Hall, Texas A&M Univ., College Station, TX 77843-2117. tower pressures. Received 17 Sept. 2004. *Corresponding author (pshouse@ussl.ars. Our objectives in this study were to analyze the effects usda.gov). of temperature and pressure fluctuations in both a single Published in Vadose Zone Journal 4:481-487 (2005). Mariotte tower and a complete tension infiltrometer sys-Original Research Paper tem during static (no-flow) conditions. We provided a rel-

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confidence: 75%

Analysis of Temperature Effects on Tension Infiltrometry of Low Permeability Materials

Castiglione

Shouse

Mohanty

et al. 2005

Vadose Zone Journal

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“…Air could be removed from Richards' tensiometer by removing a rubber bung at the top of the porous filter and refilling the system with de-aired water. Through the 1930s and 1940s Richards reported many improvements to tensiometers and covered many of the essential aspects of their design (Richards et al 1937;Richards 1942Richards , 1949.…”

Section: Pre 1950 Tensiometersmentioning

confidence: 99%

Field Measurement of Suction, Water Content, and Water Permeability

2008

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This paper presents a review of techniques for field measurement of suction, water content, and water hydraulic conductivity (permeability). Main problems in the use of field tensiometers are addressed and hints on how to improve tensiometer performance are given. Advantages and limitations of instruments for indirect measurement of suction including electrical conductivity sensors, thermal conductivity sensors, dielectric permittivity sensors, filter paper, and psychrometer are discussed. Techniques for water content measurement based on dielectric methods are then presented. These include time and amplitude domain reflectometry and capacitance. Finally, a brief overview of methods for measurement of water permeability in the field is presented.

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“…All tensiometers which operate near the soil surface are affected by temperature. Richards et al [1937] measured capillary tensions using a mercury column connected to a porous cup installed at the center of a sealed "one-quart" can. Tensions varied of the order of 140 cm of water over a day, corresponding to a soil temperature variation of-20øC [Richards et al, 1937, Figure 3].…”

Section: Introductionmentioning

confidence: 99%

Diurnal fluctuations of tensiometric readings due to surface temperature changes

Warrick

Wierenga

Young³

et al. 1998

Water Resources Research

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Abstract. Pressure fluctuations in tensiometers in response to temperature changes are examined. Mechanisms considered include temperature variation within an air gap at the top of the tensiometer, the air gap size, saturated water vapor pressure, and hydraulic conductivity of the soil. Pressures measured in a tensiometer generally fall between two simplified, limiting cases. The first limiting case assumes that the tensiometer cup is impermeable for water. This leads to very high fluctuations as air and soil temperatures change. For a cyclical temperature of 35 ___ 15øC, variations in water pressure inside the cup can be ___70 cm water head. For the second limiting case the water moves freely between the tensiometer and the soil, which leads to more stable readings, within _+ 1 cm for the above 15øC fluctuation. While cup impedance was found to be a negligible factor for all cases considered, the analysis presented here suggests that conductivity of the soil immediately around the cup is the main factor governing temperature-induced pressure fluctuations inside the cup. BackgroundTensiometers are widely used to evaluate soil water potentials in the wet range. Documentation and criteria for successful operation are extensive and well known [cf. Cassel and Klute, 1986]. An assumption for using tensiometers is that the soil water is in equilibrium with water inside of the device where the pressure is measured, either within standing water inside of the cup or in a gas phase existing at the upper end of the column. For the older style tensiometers the gas phase is minimized by servicing the device to remove gases which enter by leaking through the cup or coming out of solution in the water.The newer "puncture-type" tensiometer [Martbaler et al., 1983] is designed to include an air gap of ---2 cm at the top of the device to allow insertion of a needle to measure the pressure with a portable transducer. The air gap allows for a more gradual (seconds instead of milliseconds) change in pressure at the transducer membrane, and thus it eliminates membrane rupture. It also prevents the needle from filling with water and leads to a device which requires less servicing. An increase in air pressure due to insertion of the needle can be taken into account by a "double-puncture technique" [Greenwood and Daniel, 1996]. An intentional air gap can also be used for monitoring in the deep vadose zone by measuring the soil water pressure using a pressure transducer beiow the standing water level. In this case, a considerable air gap can be used, but the soil water pressure at the cup follows as long as the pressure transducer is below the standing water level.

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Further Developments on Apparatus for Field Moisture Studies

Cited by 29 publications

References 0 publications

Analysis of Temperature Effects on Tension Infiltrometry of Low Permeability Materials

Analysis of Temperature Effects on Tension Infiltrometry of Low Permeability Materials

Field Measurement of Suction, Water Content, and Water Permeability

Diurnal fluctuations of tensiometric readings due to surface temperature changes

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