Water infiltration underneath single-ring permeameters and hydraulic conductivity determination

A single-ring permeameter is suitable for measurement of soil hydraulic conductivity at a large-field scale because of its simple structure, easy operation, portability, small amount of recharging water and particularly because of its variable radius. The authors established a simple single-ring permeameter which consists of a hollow cylinder that is simply inserted into the top soil. Based on the theories of the Philip and Nestingen methods for single-ring permeameter tests, this paper presents new equations for describing 1-D infiltration within the inserted depth of the single-ring infiltrometer and 3-D flow beyond the depth under both gravity and soil suction forces. The soil hydraulic parameters of hydraulic conductivity and soil suction were optimized based on the declines of the ponded water depth within the single-ring cylinder. The new method was validated using numerical simulations of the declines of the water column within the cylinder through the variably saturated flow MODFLOW (VSF-MODFLOW). The new method was then successfully applied in laboratory troughs and on a hillslope in Huanjiang County, northwest Guangxi in southwest China. The results demonstrate that the hydraulic conductivity determined by the new method is more accurate than those from the 1-D Green-Ampt method and the 3-D Nestingen method.