BAS specify the grid dimensions, the computational time steps, and an array identifying which packages are to be used
OUT Controls what and when information is to be output
GAGE generates time-series output for selected cell(s), as if a piezometer (gage) was installed there
BCF6 = Block Centered Flow Package
Performs the cell by cell flow calculations. input to this package includes layer types and cell attributes such as storage coefficients and transmissivity
LPF = Layer Propery Flow Package (an alternative to the BCF Package)
Performs the cell by cell flow calculations. The input to this package includes layer types and cell attributes such as storage coefficients and transmissivity
HUF = Hydrogeologic Unit Flow Package
Defines the model stratigraphy in a grid independent fashion (in the vertical direction)
RIV1 = River Package
Simulates river type boundary conditions (water source or sink, depending on head difference between river and aquifer)
RCH = Recharge Package
Simulates areal recharge
WEL = Well Package
Simulates injection/extraction wells
MNW = Multi-Node Well
Well that spans multiple layers
DRN = Drain Package
Simulates drain-type conditions (water extraction when head rises above specified elevation)
EVT = Evapotranspiration package
Simulates the effect of evapotranspiration from the vadose zone
GHB = General Head Boundary Package
Simulates a general purpose head-dependent source /sink. Commonly used to simulate lakes
STR = Stream/Aquifer Interaction Package
Simulates the exchange of water between the aquifer and surficial streams. Includes routing and automatic computation of stage (i.e. like River package but accounting for effect of aquifer on river, and along-stream surface water flow). Parameters for sensitivity analysis or parameter estimation are NOT supported.
CHD = Time Variant Specified Head Package
Simulates specified head boundary conditions where the head is allowed to vary with time (e.g. a fluctuating lake level)
HFB = Horizontal Flow Barrier Package
Simulates the effect of horizontal flow barriers such as faults/fractures (or engineered structures like sheet piles and slurry trenches)