Soil hydraulic conductivity is a mandatory input for determining water and solute transport through soils. There are several well-established infiltrometers and permeameters for measuring in situ hydraulic conductivity. Infiltrometers measure hydraulic conductivity based on water entry into an unsaturated soil at the soil-atmosphere boundary, whereas permeameters measure the flow of water from one point to another within the soil mass. This difference in measurement philosophy, along with the methods of analysis involved in the measurement, may result in varying estimates of in situ hydraulic conductivity. This study performs an evaluation among three infiltrometers (double ring infiltrometer [DRI] and two disc infiltrometers) and two permeameters (Guelph permeameter [GP] and laboratory permeameter) for measuring hydraulic conductivity. The primary objective of this study is to appraise the variability in the measurement of in situ hydraulic conductivity for identical field conditions using different infiltrometers and permeameters. The study indicated that all the permeameters and infiltrometers exhibited reasonably good repeatability in measurements. Unlike infiltrometers, the hydraulic conductivity determined from permeameters was found to exhibit similar values for two different seasons. Infiltrometers were found to be highly sensitive to alteration in the surface pore structure due to the soil-atmosphere interaction. The statistical evaluation indicated a negative bias of disc infiltrometers when compared with DRI, whereas the comparison of disc infiltrometers has shown a bias close to zero. The results of the GP closely compared with laboratory permeameter. Both the disc infiltrometers exhibited a negative bias and weak correlation with GP measurements. In the absence of parity between infiltrometer and permeameter, the former may be a better choice for including the effect of soil surface alteration on hydrological modeling, whereas the latter can be handy for modeling water redistribution within the soil mass.
Soil erosion is a very common phenomenon encountered at many sloped earthen geotechnical structures. For instance, the surface soil of an inclined landfill cover system undergoes the erosion due to various adverse atmospheric variants. This is one of the major causes for performance failure in the cover system. However, previous researchers have rarely conducted the study for field assessment of soil erosion in high rainfall tropical regions such as northeast India. The literature advocates the utilization of vegetation for erosion management. This study investigated the impact of vegetation growth on soil erosion of a cover surface layer under both natural and controlled artificial rainfall. The soil erosion was monitored by collecting the soil loss due to rainfall. Vegetation growth was evaluated based on photographic image analyses. The study clearly indicates that the vegetation growth can contribute to reduction of soil erosion from the landfill cover surface.
The mini disk infiltrometer (MDI) is used for measuring near-saturated infiltration rates (kh0) of soils. Because of its compact size, ease of use, and requirement for only a small volume of water, the MDI is handy for laboratory soil specimens (especially in column soil studies). In order to obtain representative infiltration characteristics of laboratory soil specimens, it is necessary to ensure negligible boundary effects on the three-dimensional wetting front propagation beneath the MDI. However, there is no existing study that suggests suitable column dimensions that would be devoid of kh0 variability because of boundary effects. Moreover, the current approaches in estimating the kh0 do not adopt measured van Genuchten (vG) soil parameters and rely on empirical vG values. Based on experiments carried out on ten different soils (with varying fine fractions), the current study explores the possible variability in determining a suitable soil specimen diameter to perform an MDI test with no boundary effects. This study is based on 123 infiltrometer experiments conducted on the selected soils and recommends using soil specimen diameters greater than 3.5 times the MDI base diameter for alleviating boundary effects. A power relationship is drawn between kh0, measured using the MDI, and the fine fractions of soils (percentage finer than 75 microns). The reliability of the current approach in estimating kh0 using the MDI was evaluated using measured vG parameters.
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