A study on unsaturated hydraulic conductivity of hill soil of north-east India

Abstract

Hill slope hydrology in terms of surface drainage and infiltration is important for analysing its stability and understanding the possibility of landslides. The infiltrating water during rainfall is found to cause instability to the slope. The location of water table will be low in such hill slopes and the soil will be mostly unsaturated. Therefore, the subsurface drainage of infiltrating water in a slope is influenced by the unsaturated hydraulic conductivity (ku ) of soil. The hill slopes of north-east India mainly constitute unsaturated red soil. There are not many studies related to the determination of unsaturated hydraulic conductivity of this soil. Direct experimental determination of ku is a challenging task and requires costly and skilled experimentation. Therefore, the normal practice is to obtain ku based on water retention characteristic (WRC) and saturated hydraulic conductivity (ks ) of the soil. In this study, an equitensiometer, a matric potential sensor and a relative humidity sensor have been used to measure WRCs of hilly red soil. The study indicates that the measurement methodologies have significant influence on the uniqueness of WRC of red soil and, hence, the estimation of ku .