HR: 1330h
AN: H32A-0518    [PDF]
TI: Implementation of Automated Infiltration Soil Water Sampler: Application to Unsaturated Soil in Dune Fields
AU: * Higashi, N
EM: higashi@alrc.tottori-u.ac.jp
AF: Arid Land Research Center, Tottori University, 1390 Hamasaka, Tottori, 680-0001 Japan
AU: Inoue, M
EM: mainoue@alrc.tottori-u.ac.jp
AF: Arid Land Research Center, Tottori University, 1390 Hamasaka, Tottori, 680-0001 Japan
AU: Mori, Y
EM: yasushim@life.shimane-u.ac.jp
AF: Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue, 690-8504 Japan
AB: Accurate measurement and sampling of infiltration water from root zone are necessary to understand soil and groundwater contamination processes. The traditional instruments for sampling water leaching below the root zone cause divergence or bypass of the water flow around the instrument itself. That results in undesired soil water profile and inaccurate sampling. A suction controlled lysimeter, which consists of porous plate connected to an automated vacuum system and tensiometers has developed. Soil matric pressure heads are measured just above the porous plate that installed horizontally and at the same depth in the natural soil profile. The vacuum system is automatically controlled so that the readings of the matric pressure heads match each other. This instrument does not disturb the water flow and the water sampling flux (qe) is almost similar to that of natural infiltration flux (qd). However, for sandy soils, porous plate would show some resistance to flow and soil water could easily accumulate above the porous plate. We improved the existing automated water sampler in order to measure the unsaturated zone in dune fields. High flow rate glass filters with different pore size; 0.02 to 0.03 mm (G3), 0.005 to 0.01 mm (G4), and 0.002 to 0.005 mm (G5) were studied in laboratory instead of the traditionally used porous plate. In the unsaturated steady-state water flow experiment, the value of vacuum pressure was set manually in reference to retention curve of dune sand. The water sampling flux measured by these samplers corresponded well with the irrigation flux (qi) when a suction of 60 cm H$_{2}$O was applied to G4 and G5 filters. Four different irrigation fluxes were studied. The average water collecting efficiency (WCE = qe divided by qi) was 118 percent for G4 and 147 percent for G5. We concluded that glass filter, especially, G4 filter was suitable as soil water sampler in dune fields. Finally, the improved sampler using G4 filter was buried into a lysimeter (120 cm high and 80 cm in diameter) to estimate WCE and compared qe with qd. Because most of the soil water in sandy soils is under the gravity force, relatively large suction brought over water sampling. Therefore, it is critical to reduce the over pumping. The quality of measurements and sampling will be determined by the design of the suction differences, release of excess suction and suction duration.
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting