Numerical and Experimental Analyses of Soil Wetting Patterns Under Drip Irrigation Using Pore Network Modeling

In multiphase flow systems of two immiscible fluids like air and water in a porous medium, e.g. an unsaturated soil, the flow properties depend on the amount and the spatial distribution of the phases within the pore spaces. At the pore scale, the phase distribution is controlled by the capillary forces depending on the pore size, surface tension, and wettability. For that reason, the relationship between the capillary pressure and liquid saturation (Pc–Sw relationship) is of high importance for the simulation of water flow in unsaturated soils. In this regard, dynamic pore network models can play a valuable role in predicting capillary pressure-saturation relationship. In the present study, numerical results from a dynamic pore network model which represents the void spaces of an unsaturated soil by a lattice of pores connected by throats are used to determine macroscopic relationships between capillary pressure and fluid saturations. Then using the resulted relationships from the pore network modeling and solving the partial differential Richard's equation using finite difference scheme, wetting patterns of drip irrigation have been simulated. Also, soil wetting patterns resulted from drip irrigation were investigated in laboratory experiments in a sandy soil with three dripper discharges rates of 2, 4 and 6 L.h-1 and different time intervals of 20, 40,… and 360 min. The performance of pore network model was evaluated by comparing the simulated wetting patterns with those of observed and simulated by HUDRUS software package. The results of current research showed that the pore network model for each of above-mentioned discharge rates had higher precision in comparison to HYDRUS model estimates of wetted pattern’s depth. With the exception of discharge rate of 2 L.h1, observed trend has been similar for estimation of wetted pattern’s radius and pore network model showed less error in comparison to HYDRUS model in estimation of wetted pattern’s radius.