Numerical analysis of the effect of the different lower boundary conditions on water drainage in irrigated field

The effect of three different lower boundary conditions(free drainage,pressure head and fixed ground water table) on water drainage in irrigated field is studied using the numerical simulations based on the field data in Quzhou County on North China Plain.The water drainage in 2 m soil profile is calculated by the HYDRUS-1D model from October 1998 to September 2001 When the fixed ground water table is selected as the lower boundary condition,the soil water content at different depth in 2m soil profile is calculated by the HYDRUS-1D model,which agreeds well with the measured values,however,when taking free drainage and pressure head as the lower boundary condition,the difference exists between the measured and the simulated values. In comparison with the result of dynamic water drainage and accumulated water drainage estimated by using the Darcy law,we found that their dynamic process of water drainage by using the fixed ground water table agreed well with that of the Darcy Law.Therefore,the fixed ground water table being selected as the lower boundary condition is suit-able for the local conditions.