In HEC-FIA an alternative is a combination of an inundation configuration (includes watershed configurations), emergency planning zones, structure inventory, critical infrastructure, impact response curves, agricultural data, and computation settings. An alternative describes the data used during an HEC-FIA compute and the computations HEC-FIA performs.
In addition to defining the internal data HEC-FIA needs, an alternative is also a mechanism for defining the external data elements that are required to fully define a hydraulic event. HEC-FIA alternatives are important for linking HEC-FIA to other models through the HEC-WAT (Watershed Analysis Tool) software and the CWMS (Corps Water Management System) software.