| There is a need for an improved understanding of unsaturated flow and transport in deep vadose zones. Ten years of tensiometeric measurements over a 39 ha site reveals the temporal and spatial water potential distribution in response to drying and wetting events at land surface. The Darcian approach was used with laboratory derived soil hydraulic properties and field water potential measurements this approach produced flux estimates from 0.2 to 10,000 cm yr-1 compared to 22 cm of annual precipitation. We conclude that tensiometer data are sensitive indicators of in situ conditions, but laboratory derived hydraulic properties used for flux estimation can introduce uncertainties up to several orders of magnitude.A laboratory method was developed as a part of this investigation to directly measure unsaturated conductivity on core samples. The technique replicates in situ field conditions using the ambient water potential under a unit hydraulic gradient, while allowing precise measurement of water mass moving into and out of the sample. Samples were evaluated from -258 to -6 cm equivalent water potential pressure with mean hydraulic conductivity measurements (flux) from 2.0E-8 to 9.4E-6 cm sec-1 (1 to 300 cm yr-1). This unsaturated hydraulic conductivity, at an applied water potential, can be used to better compute the entire unsaturated hydraulic conductivity curve using standard empirical equations.This knowledge from the field measurements and laboratory test development is used to evaluate a monitoring systems' suitability to verify that an evaporation cap will be effective in reducing infiltration. The tensiometer monitoring system is sensitive to variations in flux rates, with rapid response times (days) to recharge events. The system is scalable to very large areas with the addition of new instruments and can have an operational life nearing 100 years, by using portable tensiometers. Sites can have low flux rates for years which then increases orders of magnitude in a short time period (weeks) in response to infiltration events at land surface. These tensiometers can detect subsurface trends not predicted from surface based observations and indicate areas within a site where infiltration is occurring. |
