Measurement and simulation of infiltration rates into undrained and subsurface drained soils

Abstract

Abstract. Infiltration is an important process in the hydrological cycle and the main source of water for crop production. Though infiltration occurs at the soil surface, it is affected by the soil properties below the ground surface, such as soil water content and hydraulic conductivities. Accurate measurement of infiltration rate is possible when accurate soil properties within the infiltration zone (up to 30 cm below soil surface) are determined. In this study, infiltration rates were measured using a Cornel Sprinkler Infiltrometer during spring, summer and fall of 2014 in undrained and subsurface drained (i.e. tile drained) fields in Clay County, Minnesota. Because of the soil moisture difference between the undrained and tile drained fields, the measured infiltration rates were also different. Soil moisture contents were measured at 5, 15 and 30 cm depths below the soil surface in both fields using soil moisture sensors. Soil water retention curves (SWRC) were developed from soil core samples collected in both fields using Hyprop and WP4 Dewpoint Potentiometer methods. Important parameters used in infiltration modeling, including saturated water content, residual water content and van Genuchten curve fitting parameters, were also determined from the SWRC. Two models, HYDRUS 1D and HYDROL-INF, were used to simulate infiltration rates using the measured soil properties. The measured and simulated infiltration rates were compared and analyzed in order to estimate the infiltration difference between undrained and tile drained soils. Average infiltration rate was greater in tile drained soil (0.0041 cm/min) compare to undrained soil (0.0023 cm/min) from HYDROL-INF model simulations. HYDRUS 1D model simulation indicated that tile drained soil had four times greater hydraulic conductivity (0.015 cm/min) and three times greater cumulative infiltrating water amount (2.04 cm) than those of undrained soil (0.0034 cm/min and 0.62 cm, respectively). The comparison between the undrained and tile drained soils suggested that due to better soil physical conditions, subsurface drained soil had higher hydraulic conductivity as well as higher infiltrating water amount and infiltration rate than those of undrained soil.