HYDRODYNAMIC FURROW IRRIGATION MODEL WITH SPECIFIED SPACE STEPS

A complete hydrodynamic furrow irrigation model was developed that solves for time of advance as a function of distance. Solution of the system of finite-difference equations is obtained with a shooting algorithm. After completion of advance, the model uses fixed time increments to compute storage and recession phases. The specified space step solution allows different infiltration functions along the furrow to be assigned and simulates irrigations with both uniform and stochastic infiltration. Infiltration is computed with a modified version of the extended Kostiakov equation that allows intake to vary with opportunity time and depth of flow. Numerical experiments have shown that the specified space step solution is computationally more efficient during advance than traditional specified time solutions. The specified space step solution cannot revert, however, to small time increments for storage and recession calculations, which hamper its ability to simulate rapid changes in boundary conditions. Comparison of simulation results with different space and time step combinations indicate that the consequent loss of accuracy is relatively small.