The FHM is a fully integrated hydrologic model that simulates the full water budget of the surface water and ground water systems. This
tool allows hydrologic modelers to accurately simulate the interaction between the surface water system and the ground water system. Basically
the FHM is made of two off-the-shelf components; HSPF and MODFLOW. HSPF (Hydrological Simulation Program - FORTRAN), supported by United States
Environmental Protection Agency and US Geological Survey, simulates the surface water system including basin water budget and reach resevoir water budget. MODFLOW, supported by the USGS, computes
the aquifer water budget. Integration codes were written to link the two models together. Basin recharge is determined through the
analysis of the surface water budget. This recharge is then used by the ground water model which in turn calculates the baseflow to the
reaches. The baseflow combined with stormwater runoff allows the reach reservoir budget.