Tuesday, 11 July 2006

Hood Infiltrometer - A New Type of Tension Infiltrometer.

Jürgen Punzel, UGT Environmental Measuring Techniques Ltd., Eberswalder Str. 58, Muencheberg, 15374, Germany and Kai Schwärzel, Instiute of Soil Science and Site Ecology, Faculty of Forest-, Geo- and Hydro Science, Dresden University of Technology, Piener Strasse 19, Tharandt, 01737, Germany.

Tension Infiltrometer (TI) are widely used for determination of saturated and near saturated soil hydraulic properties. The complete contact between disc and soil is essential for reliable data. Any vegetation wihtin the sample should be trimmed to ground level. In vast majority soils are uneven. Hence, contact material should be placed over the undisturbed soil surface and this new surface is to level and to smooth (Perroux & White 1988). The characteristic of the contact material should have a hydraulic conductivity higher than that of the soil at the pressure head applied to the infiltrometer. In general, using of contact materials effects the infiltration. Furthermore, applying pressure heads near saturation might cause that mobile fine-textured particles of the contact material clog the macropores. Resulting is a decrease of the original near saturated conductivity. Finally, preparing the soil surface for TI measurement could lead to alterations of the primal properties of the soil surface. A new type of TI a so called Hood Infiltrometer (HI) is presented which could overcome the critical aspects mentioned. In contrast to the TI no preparation of soil surface is required. A hood connected to a Mariotte bottle is placed on the undisturbed infiltration surface. Inside of the hood water is ponded. An additionally negative pressure compensates the depth of water ponding and hence water can be supplied at different pressure heads. Our experimental setup allows the measurement of hydraulic properties from saturation up to the bubble point of the soil. The effective pressure head on the soil surface can be measured by an additionally U-tube manometer with a precision of +/- 1mm. Tension infiltrometer and Hood Infiltrometer measurements were carried out to evaluate the effects of contact material and soil surface preparation on the saturated and near saturated conductivity. Additionally soil cores were taken to analyze the hydraulic properties using lab methods.

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