Integration of SWAP and MODFLOW-2000 for modeling groundwater dynamics in shallow water table areas

SummaryReasonable estimates of groundwater recharge and discharge through evapotranspiration is critical for sustainable water resources management in shallow water table areas. The hydrologic processes are highly interactive between the vadose zone and groundwater under shallow water table conditions. In traditional groundwater flow models, the recharge and evapotranspiration fluxes are often oversimplified as a simple sink/source term. However, the recharge and evapotranspiration are observed to vary with topography, soil type, land use, and water management practices. Additionally, they are known to vary temporally and spatially and are difficult to estimate, especially in arid and semi-arid regions. Thus, it is important to devise an appropriate method to estimate the recharge and evapotranspiration fluxes in groundwater modeling. In this study, a Soil–Water–Atmosphere–Plant (SWAP) package was integrated into a groundwater flow model (MODFLOW) in such a way that the SWAP package calculates vertical flux for MODFLOW, while MODFLOW provides averaged water table depth to determine the bottom boundary condition for SWAP zones. The SWAP zones in MODFLOW are derived from a combination of topology, soil type, land use, water management practices using geographic information systems (GIS). Then the MODFLOW with SWAP package was tested using a two-dimensional saturated–unsaturated water table recharge experiment. Results showed that the simulated water table elevations matched well with the observed ones except at the early period during which they were slightly higher than the observed ones, probably due to neglecting lateral diffusion in the unsaturated zone. Finally, we applied MODFLOW with SWAP package to simulate a regional groundwater flow problem in Hetao Irrigation District, upper Yellow River basin of North China. The simulation results validated the applicability of the developed MODFLOW with SWAP package for practical regional groundwater modeling.

► A coupled model for groundwater and regional unsaturated flow was developed.
► The model was on the basis of SWAP package and MODFLOW.
► The model was validated using laboratory data and regional field data.