Tuesday, November 14, 2006
182-2
Measuring Dynamic Water Entry Suctions With Microtensiomters During Non-ponding Infiltration In Various Soil Materials.
Hiroyuki Cho, Dept. of Agric. Science, Saga University, Honjou 1, Saga, 840-8502, Japan, Gerrit De Rooij, Dep. Environmental Sciences, Soil Physics, Ecohydrology, and Groundwater Management Group, Wageningen Univ., Nieuwe Kanaal 11, Wageningen, 6709 PA, Netherlands, and Mitsuhiro Inoue, Tottori University, 1390 Hamasaka, Tottori, 680-0001, Japan.
Fingered flow rapidly moves water and pollutants from the root zone to the groundwater through a limited fraction of the unsaturated zone, limiting the possibilities for decay and adsorption. We developed a Green-Ampt based expression for the pressure head in a developing induction zone (from which fingers protrude) for the time before fingers developed. The equation excellently fits data from 2D fingered flow experiments if the dynamic water entry suction is treated as a fitting parameter, but we could not compare the fitted values to independent measurements of the water-entry suction. We therefore carried out one-dimensional infiltration experiments by applying three non-ponding water fluxes to the surface of soil packed homogeneously in an acrylic tube. We filled the tubes with different sieve fractions of sand, glass beads, loam, and silt, and installed microtensiometers. Even in silt, our model equation was valid during the early stage of infiltration. The independently observed dynamic water entry values were in good agreement with earlier fits from fingered flow trials. The results showed that this equation could provide the dynamic water entry suction and the hydraulic conductivity at that value if the quantity of water flux supplied at soil surface and pressure values for at least one point close to the surface were measured.