Field determination of unsaturated hydraulic conductivity of forest soils
This study introduces a field method to determine unsaturated hydraulic conductivity which is applicable to sloping terrain with a limited water supply. A single steel ring infiltrometer and an artificial rainfall simulator are used in this method to reduce the amount of water required to attain a steady-state flux condition. Six tensiometers and a time domain reflectometry (TDR) are employed as the soil capillary pressure head and the volumetric soil water content measurement devices, respectively. Water contents measured by the TDR are corrected using a simple calibration method suggested by Hook and Livingston (1996). Unsaturated hydraulic conductivities are computed based on the instantaneous profile method using capillary pressure head and water content changes measured during a drainage process. The proposed method was applied to a forest soil profile in Rokko Mountain range. Results showed that the relationships between the unsaturated hydraulic conductivity and capillary pressure head developed by the proposed method coincide well with those measured by the conventional steady-state laboratory experiment. The proposedin-situ method is the effective simple means to determine unsaturated hydraulic conductivities of forest soils, since this method is enough accurate and consuming less amount of water and time.
The effect of the shape parameters of a sample on the hydraulic conductivity
Summary The present study is a complement to the research investigating a laboratory method for measuring the saturated hydraulic conductivity of mountain forest soils, the results of which were presented in a paper by Ilek and Kucza (2014). The aim of the study is to analyse the influence of variation of particular cross-sections of samples and their enlarged side surface on the hydraulic conductivity measurement. The results show that a narrowing in the upper section of the sample results in an approximately twice lower disturbance of the laminar water flow than the narrowing occurring inside the sample. For that reason, the extent of the effect of the cross-section narrowing on the hydraulic conductivity measurement error is dependent on the location of the narrowing. An enlarged side surface of a sample, as described by the coefficient of side surface development, is on average 30% larger than the surface of a sample having the same volume and the same average cross-sectional area but a regular shape. The values of the coefficient of side surface development for a given sample were adopted in the range of 1.10–1.56. Among the shape parameters of the analysed irregular soil samples, the greatest impact on the measurement error is exerted by their enlarged lateral surface, which almost entirely explains the whole error of hydraulic conductivity measurement. The variability of successive cross-sectional areas of samples appears to be of marginal importance for the occurrence of this error, whose mean value was 1.15%.
Some Effects of Rain Intensity, Erosion, and Sedimentation on Infiltration-Capacity 1
INFILTRATION-CAPACITY JOHN L. AREND AND ROBERT E. HoRTON THE concept of infiltration-capacity as the maximum rate at which a given soil surface, when in a given condition, can absorb rain as it falls, was introduced by Horton in 1933 (3). Infiltration-capacity determines the portion of a given rain which, respectively, (a) enters the soil and becomes available for plant use or to provide ground-water, and (b) runs 'off from the surface and may produce destructive soil erosion. It has been found by various experiments (2) that the infiltration-capacity is generally controlled at and close to the soil surface and Horton has shown (4) that for continuous uniform rain intensity the infiltration-capacity decreases during rain until it attains a constant value designated as fc. The march of infiltration-capacity during continuous uniform rain can be represented by the equation f = fc + (f0 f c) e~ft I where t =.time, in minutes or hours, from a given chosen initial point, as the beginning of rain or the beginning of runoff; f = infiltration-capacity, inches per hour, at time t ; f0 = initial infiltration-capacity at the initial point; fc = final constant infiltration-capacity, which is approached asymptotically as t -» oo; e = base of Napierian logarithms; kf = a factor, constant for a given experiment, governing the rate of change of infiltration-capacity with time. This equation gives results in good agreement with experimental data and it has been shown by Horton (5) that it may be derived rationally from the simple assumption that the reduction of infiltration-capacity during rain is the result of the action of the energy of falling rain on the surface of the soil. The infiltration characteristics of a given soil-cover condition are therefore determined by three constants : f0, fc, and k(, and the results of experiments with different soil-cover conditions or different rain intensities can be most conveniently and accurately described and discussed in terms of the relative values or differences of value of these constants as derived from the different experiments. This method will be pursued in discussing the series of experiments described in this paper. EXPERIMENTAL PROCEDURE