UC Riverside

For optimal water and fertilizer management under furrow irrigation, it is important to understand the water and solute dynamics on the land surface and in the subsurface. An efficient mathematical tool is required to describe these dynamic processes. We propose a coupled model in which surface water flow and solute transport are described using the zero-inertia equation and the average cross-sectional convection-dispersion equation, respectively, while the two-dimensional Richards equation and the convection-dispersion equation are used to simulate water flow and solute transport in soils, respectively. Solutions are computed numerically using finite differences for surface water flow and finite volumes for solute transports in furrow. Subsurface water flow and solute transport equations are solved using the CHAIN_2D code. An iterative method is used to couple computations of surface and subsurface processes. Both surface and subsurface water flow and solute transport modules are coded in program subroutines and functions in the Intel FORTRAN environment. The coupled model was validated by comparing its simulation results with measured data. Results showed that simulated water front advances in the furrow and water contents in the soil agreed with the observations reasonably well. Good simulations can be achieved with a relatively fine temporal resolution. Numerical oscillations can be eliminated by adopting appropriate time steps. As compared with the traditional furrow irrigation model, the proposed model can better quantify soil water and solute dynamics by considering interactions between surface and subsurface water flow and solute transport processes. The proposed model can be used as a decision tool to design and manage furrow irrigation.