NUMERICAL SIMULATION OF THREE DIMENSIONAL SOIL WATER CONTENT DISTRIBUTION IN WATER STORAGE PIT IRRIGATION

Water storage pit irrigation (WSPI) provides a new method that is suitable for orchard irrigation in gully areas in northern China. Using WPSI can reduce the evaporative loss and increase water use efficiency. Realizing the full potential of WSPI requires optimizing the layout parameters of water storage pits, such as pit depth, spacing and diameter. These parameters depend on the distribution of soil water during WSPI. The present study involved development of a three-dimensional water movement model (WSPI-model) based on the theory of soil water dynamics and the characteristics of soil moisture movement during WSPI. The finite element method was used to drive the modeling. A mathematical model was also established to confirm the process of changing water depth in each pit based on the principle of conservation of mass. The simulated soil water content and water depth in the pit were compared with the measured value for two irrigation amount trials (80 L and 120 L per pit). The root mean square error (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE) of water depth in pits for the WSPI-model were less than 1.71 cm, 1.31 cm and 7.31%, respectively. The RMSE, MAE and MAPE of soil water content for the WSPI-model was less than 0.021 cm(3)/cm(3), 0.018 cm(3)/cm(3), and 6.64%, respectively. These findings indicated that appropriate soil water content and water depth in the pit can be successfully estimated by using the WSPI-model.