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Unsaturated Hydraulic Conductivities of Fiberglass Wicks and Designing Capillary Wick Pore‐Water Samplers
Author(s) -
Knutson John H.,
Selker John S.
Publication year - 1994
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1994.03615995005800030012x
Subject(s) - hydraulic conductivity , capillary action , soil water , pressure head , water content , vadose zone , hydraulic head , exponential function , flux (metallurgy) , capillary pressure , moisture , suction , soil science , materials science , analytical chemistry (journal) , chemistry , geotechnical engineering , thermodynamics , environmental science , porosity , porous medium , mathematics , chromatography , geology , composite material , physics , mathematical analysis , metallurgy
Passive capillary samplers (PCAPS) use the capillary potential of fiberglass wicks to draw pore water from unsaturated soils. The sampling suction of a wick should be matched to the pressure head, h , in the soil in which the PCAPS will be installed. Currently there is no theoretically based procedure for matching wicks to soils, a problem this study solves. When matched, the top of a wick has approximately the same h as the soil across multiple fluxes. Unsaturated hydraulic conductivities, K ( h ), were measured in wicks. These data exhibited exponential behavior, and estimates of wick saturated conductivities, K sat , ranged from 220 to 1380 cm/h. The K sat values were compared with predictions from a capillary tube model ( R 2 = 0.85). Moisture contents, θ( h ), were measured in wicks. Hysteresis was observed, and the draining curves were used to predict K ( h ) using the van Genuchten equation coupled with the Mualem conductivity model. The van Genuchten equation fit the draining θ( h ) data well ( R 2 > 0.953), but Mualem's K ( h ) values did not reproduce the exponential predictions. A solution for unsaturated flow was used to calculate h in wicks given the flux, q , and length. Calculated values of h were within 25% of the measured values for high fluxes and within 5% of the measured values for low fluxes. A least‐squares procedure for matching the h vs. q curve of a wick to a soil was used to design PCAPS for application in two soils.