Effects of Measurement Method, Scale, and Landscape Features on Variability of Saturated Hydraulic Conductivity

Abstract

Knowledge of soil saturated hydraulic conductivity (Ks) and its spatial variation is important to characterize hydrological proc- esses. The objective was to quantify three important variability components, i.e., measurement technique, spatial arrangement in sampling, and differing landscape features (sloped surfaces and gullies), to map Ks distribution in eroded watersheds, such as the Chinese Loess Plateau. Classic and geostatistics were employed to explore the effects of measurement method, sampling scale, and landscape position on the Ks and its spatial variation. In a small watershed with an area of 0.2 km 2 , three techniques, including the soil core (SC), tension infiltration (TI), and Guelph permeameter (GP) methods, were employed to determine the surface Ks at 124 positions on the sloped landscape (minimum sampling space of approximately 10 m). Furthermore, the SC method was applied at 204 positions along four 100-m transects (minimum sampling space of 2 m), and 200 positions along four 10-m transects (minimum sampling space of 0.2 m) on the sloped landscape and 45 positions in the gully areas to determine the surface Ks. The results showed that no significant differences of mean logarithmic value of Ks (Log10 Ks) existed for SC and GP, and the spatial patterns behaved the same for TI and GP. The spatial dependence decreased with a decrease in sampling extent. Structured variability was not observed at the 10-m transect scale. When the minimum sampling space changed from 10 to 2 m, the nugget variance decreased, whereas the structured variance, sill variance, and spatial dependence increased. When minimum sampling space changed from 2 to 0.2 m, the changes in spatial pattern of Ks were negligible, implying that a minimum sampling space of 2 m is needed to capture the spatial pattern of Ks. Ks in the gully areas was significantly less than on the sloped positions. The spatial pattern of Ks changed when the gully positions were included. Gully areas, therefore, should be considered for characterizing the spatial pattern of Ks for watersheds in the Chinese Loess Plateau. DOI: 10.1061/(ASCE)HE.1943-5584.0000630. © 2013 American Society of Civil Engineers. CE Database subject headings: Spatial analysis; Infiltration; Hydraulic conductivity; Measurement. Author keywords: Spatial variability; Gully; Scale; Soil core method; Tension infiltration method; Guelph permeameter method.