Simulating the changes of water table depth in coastal saline land with agro-subsurface drainage system

Agricultural subsurface drainage is an important measure for preventing waterlogging disaster, reducing soil salinity and promoting crop growth in coastal saline areas. This study was conducted in the coastal saline area of Cangzhou City, Hebei Province. The DRAINMOD model was used to simulate the changes of groundwater depths under subsurface drainage system (drain depth was 1.2 m deep and drain spacing 30 m) for the period from June to September of 2011. Groundwater depth changes under subsurface drainage system with different controlled drainage schemes were also predicted. The DRAINMOD model parameters included soil property data, climatological data, crop data and drainage system parameters. The parameters were collected either in laboratory or field observations. Based on the simulation results, the coefficient of efficiency of the model was 0.67, with a relative error of 6.15%, which showed that the DRAINMOD model simulation was reasonably favorable. The study showed that agro-subsurface drainage systems obviously reduced the occurrence of waterlogging. Water table depths were controlled to below 60 cm in 2 days by the subsurface drainage system. Also groundwater table depths were controlled to below 60 cm in 15 days in filed without subsurface drainage system. Four drainage schemes (natural drainage, controlling groundwater depth to 50 cm, 80 cm and 100 cm) were designed and the simulations indicated that it was appropriate to control water table depths to below 80 cm at low cost and no waterlogging. In conclusion, the DRAINMOD model proved to perform well for the hydrology of agro-surface drainage systems and was therefore a useful tool for designing drainage and water management systems. Thus the DRAINMOD model was as well usable in simulating future groundwater table depths in saline coastal areas. It then provided better solutions for subsurface drainage system optimization and water management selection.