Bemerkungen zur Ermittlung der ungesättigten Wasserleitfähigkeit unter nichtstationären Bedingungen

Abstract

On the Determination of Capillary Conductivity at Unsteady‐State Conditions. Therefore it is stated that for obtaining the effective ku‐values. Considering the importance of capillary conductivity for the soil water regime the large differences up to 2 orders of magnitude between determinations on core samples from the same soil using the double‐membrane‐method (Henseler and Renger 1969) and the evaporation‐method (Becher 1971a) initiated a study concerning the error caused by a possible nonlinearity of suction changes between two measuring levels using the latter method. The study was carried out on disturbed and undisturbed core samples from the three textural classes sand, silt and clay and with modified evaporation method. Comparing the geometric means of the obtained ku‐values calculated at unsteady‐state and quasisteady‐state conditions for different suctions resulted in that with usual application of the method the measured ku‐values must be diminished for obtaining the effective ku‐values. This correction factor increased with suction and is considered to be more important in laboratory than in field use. For sandy soils a correction factor of 2 at 150 cmH2O increasing to 6 at 1000 cm H2O must be applied. The coarser the sand would be, at the lower suction nonlinearity will start and the more rapidly the correction factor will increase;. For silty soils a correction factor of 2–4 must be applied for suctions > 300 cm H2O;. For clayey soils a correction factor of 2 rapidly increasing to 10 must be applied for suctions > 150 cm H2O, but depending on soil cracks. . The overestimation of water through‐put resulting from the uncorrected ku‐values amounts to 1.5–4.0 [l/m2 · d] at 100 cm H2O, but these values are within the variation of the effective ku‐values. For 800cm H2O the overestimation amounts to 0.002–0.065 [l/m2 · d], but this makes up 300–1000 % of the effective water through‐put.

A new laboratory method to quickly determine the unsaturated hydraulic conductivity of undisturbed soil cores within a wide range of textures

“…The error involved in linear extrapolation can be considerable, especially in sandy and clayey soils, where the relation between Y and z is nonlinear, leading to an overestimation of unsaturated hydraulic conductivity. Becher (1974) introduced correction factors, but this procedure does not seem suitable.…”