COMPARISON OF UNSATURATED HYDRAULIC CONDUCTIVITY OF DIFFERENT SOILS THROUGH INVERSE MODELLING USING HYDRUS-1D

Abstract

Soil hydraulic conductivity is simply the ability of a soil to transmit water impacts almost every soil application. It is critical for understanding the complete water balance and is also used for estimating groundwater recharge through the vadose zone. Agricultural decisions are based on hydraulic conductivity for determining irrigation rates or to predict erosion or nutrient leaching. And it is used to determine landfill cover efficacy. Hydraulic conductivity is defined as the ability of a porous medium to transmit water under saturated or nearly saturated conditions. Unsaturated soil hydraulic conductivity is a main parameter in agricultural and environmental studies, necessary for predicting and managing water and solute transport in soils which refers to a measure of soil's water-retaining ability when soil pore space is not saturated with water. The objective of this study was to compare unsaturated hydraulic conductivity of different soils. Double ring infiltrometer experiment were conducted at KCAET, Tavanur campus. It comes under Malappuram District of Kerala state in India. Two sets of infiltration readings were collected from two different locations coming under different soil groups. HYDRUS 1-D software is used to calculate unsaturated hydraulic conductivity of soil by inverse modelling. The HYDRUS program numerically solves the Richards equation for variably saturated water flow and advection-dispersion type equations for heat and solute transport. The cumulative infiltration flux across a boundary at different time was used as the input variable to optimise the soil hydraulic parameters. Hydrus-1D software is used for inversion of six soil hydraulic parameters including saturated water content (θ s ), residual water content (θ r ), saturated hydraulic conductivity (K s ), soil water retention parameter (n), inverse of air entry value (α) and pore connectivity parameter (l) which is further optimized using Marquardt-Levenberg optimization algorithm. The optimised parameters were fitted to the empirical models proposed by van Genuchten (1980) for finding the unsaturated hydraulic conductivity (K) of the proposed soils. The study gives the conclusion that unsaturated hydraulic conductivity of sandy loam soil is greater than the clay soil.