Note: linking WEAP to MODFLOW is an advanced feature.
For situations where the built-in WEAP groundwater model is not sufficiently complex, there is the option to link a WEAP model to a MODFLOW model. MODFLOW is a three-dimensional finite-difference groundwater model created by the U.S. Geological Survey (USGS). When properly linked, data and results flow back and forth between WEAP and MODFLOW for each calculation timestep. With this tight coupling between the models, it is possible to study how changes in local groundwater levels affect the overall system (e.g., groundwater-stream interactions, pumping problems due to drawdown, lateral groundwater recharge) and vice versa (e.g., infiltration and abstraction). However, be advised that building and calibrating a MODFLOW model is not a trivial task, and the linkage to WEAP requires creating a GIS shape file to connect the WEAP elements to the MODFLOW cells. The versions of MODFLOW that WEAP is designed to link to are MODFLOW 2000, MODFLOW 2005 and MODFLOW-NWT.
For more information, please see the Appendix on linking WEAP to MODFLOW.