Modeling shallow water table dynamics under subsurface irrigation and drainage

We develop conceptual and numerical models of water table dynamics under a subsurface irrigation and drainage system. The numerical model is implemented with distinct drainable and fillable porosity parameters that are estimated by accounting for the unsaturated zone fluxes to and from the shallow water table. The model was applied to two field sites under subsurface irrigation and drainage system in northeast Florida to simulate water table dynamics during potato growing seasons in 2010 and 2011. Simulated water table elevations showed a close agreement with the observed water table dynamics in the fields during both growing seasons. Furrows that act as shallow drains in the field facilitated rapid drawdown of the water table after rainfall events, while the outer, deeper ditches provided little drainage of water from the root-zone. Intermittent irrigation regimes, although could substantially reduce surface runoff from the fields, resulted in relatively deeper water tables during the growing season, suggesting a potential trade-off between water deliveries and root-zone soil moisture availability.