Advances in Tensiometry for Long‐term Monitoring of Soil Water Pressures

Abstract

Soil water pressures, measured over space and time, are needed to predict the direction of water flow and chemical transport in the vadose zone. Advanced tensiometers (ATs), which utilize a water‐filled porous cup connected directly to a pressure transducer, can be installed at almost any location and depth using standard drilling techniques such as auger drilling, but these methods can significantly disturb the site. For sites where minimal disturbance is desired, alternate approaches for tensiometer placement have been sought. To test installation techniques and performance longevity, advanced tensiometers were placed into the ground at a test site near Richland, WA using two different installation methods, auger drilling and a drive‐cone push technique. The tensiometers were subsequently monitored for nearly 2 yr without refilling or recalibration. The data indicated that tensiometers placed by the auger technique took several months to equilibrate, while the cone push units came to equilibrium within 24 h following their installation. Soil water pressures always remained above −90 cm pressure head (−90 mbar) at depths >90 cm. At the greatest depth (730 cm), positive then negative pressures were observed as the water table was lowered and the soil drained. The results suggest that for our test conditions (coarse sandy soil, no vegetation), soil water pressures stay well within the tensiometer range and unit gradient conditions persist, indicating a draining profile. Advanced tensiometers, placed either by auger or cone penetrometer, provide a robust and reliable method for long‐term monitoring of soil water pressure profiles.

Comparison of methods for determining unsaturated hydraulic conductivity in the wet range to evaluate the sensitivity of wetting front detectors

“…1b). The deviations at 30 cm are possibly due to the effect of diurnal surface temperature fluctuations on the performance of the tensiometer (Sisson et al, 2002). The measured water contents also tended to be lower than the simulations, especially in the surface soil where the neutron probe is known to be less accurate.…”

Measuring Soil Water Potential for Water Management in Agriculture: A Review

“…The use of electric pressure transducers allow to obtain more precise reading and to collect the data through a datalogger, therefore allowing multiplexing and automation. Recently, advanced transducers are installed directly into the porous ceramic cup [18]. Another advancement proposed by a manufacturer (UMS, Munich, Germany) is to use a self-refilling tensiometers.…”

Compendium of Data for the Hanford Site (Fiscal Years 2004 to 2008) Applicable to Estimation of Recharge Rates

“…A series of lysimeters designed for water-balance studies and to simulate waste-burial-grounds with bare, coarse-4.4 grained surfaces was constructed at this site in 1978. Detailed descriptions of the site are provided by Gee and Jones (1985), Gee et al (1992), and Sisson et al (2002). Other instrumentation includes a Pronamic rain gage installed at the drainage outlet in the bottom of the lysimeter in August 2000.…”

“…Water content and matric potential profiles within the south caisson lysimeter are also monitored, as is matric potential outside the lysimeter at the 7.5 m depth. Additional information about the 300N Lysimeter Site and instrumentation can be found in Phillips et al (1979) and Sisson et al (2002).…”