Prepared in cooperation with the U.S. Geological Survey Water Availability and Use Science Program MODFLOW 6 – Description of Input and Output Version mf6.2.0—October 22, 2020 U.S. Department of the Interior U.S. Geological Survey Cover. Binary computer code illustration. Contents Introduction.......................................................................................1 Running a Simulation...............................................................................1 Form of Input Instructions...........................................................................2 Block and Keyword Input.......................................................................2 Specification of Block Information in OPEN/CLOSE File............................................4 File Name Input...............................................................................4 Lengths of Character Variables.................................................................4 Integer and Floating Point Variables.............................................................5 Simulation Name File...............................................................................6 Structure of Blocks............................................................................6 Explanation of Variables........................................................................6 Example Input File.............................................................................8 Temporal Discretization (TDIS) Package..............................................................9 Structure of Blocks............................................................................9 Explanation of Variables........................................................................9 Example Input File............................................................................. 10 Groundwater Flow (GWF) Model Input............................................................... 11 Information for Existing MODFLOW Users........................................................ 11 Array Input (READARRAY)...................................................................... 16 READARRAY Control Line.................................................................. 16 READARRAY Variable Descriptions.......................................................... 17 READARRAY Examples..................................................................... 18 List Input..................................................................................... 19 Units of Length and Time....................................................................... 20 Steady-State Simulations...................................................................... 20 Volumetric Budget............................................................................. 21 Cell-By-Cell Flows............................................................................. 22 GWF Model Name File......................................................................... 24 Structure of Blocks........................................................................ 24 Explanation of Variables................................................................... 24 Example Input File......................................................................... 26 Structured Discretization (DIS) Input File........................................................ 27 Structure of Blocks........................................................................ 27 Explanation of Variables................................................................... 27 Example Input File......................................................................... 28 i Discretization by Vertices (DISV) Input File....................................................... 29 Structure of Blocks........................................................................ 29 Explanation of Variables................................................................... 30 Example Input File......................................................................... 31 Unstructured Discretization (DISU) Input File..................................................... 33 Structure of Blocks........................................................................ 33 Explanation of Variables................................................................... 34 Example Input File......................................................................... 36 Initial Conditions (IC) Package.................................................................. 38 Structure of Blocks........................................................................ 38 Explanation of Variables................................................................... 38 Example Input File......................................................................... 38 Output Control (OC) Option..................................................................... 39 Structure of Blocks........................................................................ 39 Explanation of Variables................................................................... 39 Example Input File......................................................................... 40 Observation (OBS) Utility for a GWF Model....................................................... 42 Structure of Blocks........................................................................ 42 Explanation of Variables................................................................... 42 Example Observation Input File............................................................. 43 Node Property Flow (NPF) Package............................................................. 44 Structure of Blocks........................................................................ 44 Explanation of Variables................................................................... 44 Example Input File......................................................................... 47 Horizontal Flow Barrier (HFB) Package.......................................................... 48 Structure of Blocks........................................................................ 48 Explanation of Variables................................................................... 48 Example Input File......................................................................... 49 Storage (STO) Package........................................................................ 50 Structure of Blocks........................................................................ 50 Explanation of Variables................................................................... 50 Example Input File......................................................................... 51 Skeletal Storage, Compaction, and Subsidence (CSUB) Package................................... 52 Structure of Blocks........................................................................ 52 Explanation of Variables................................................................... 53 Example Input File......................................................................... 57 Available observation types................................................................ 58 Example Observation Input File............................................................. 60 Buoyancy (BUY) Package...................................................................... 62 Stress Packages.......................................................................... 62 Structure of Blocks........................................................................ 63 Explanation of Variables................................................................... 64 Example Input File......................................................................... 65 ii Constant-Head (CHD) Package................................................................. 66 Structure of Blocks........................................................................ 66 Explanation of Variables................................................................... 66 Example Input File......................................................................... 68 Available observation types................................................................ 68 Example Observation Input File............................................................. 69 Well (WEL) Package........................................................................... 70 Structure of Blocks........................................................................ 70 Explanation of Variables................................................................... 70 Example Input File......................................................................... 72 Available observation types................................................................ 73 Example Observation Input File............................................................. 73 Drain (DRN) Package.......................................................................... 74 Structure of Blocks........................................................................ 74 Explanation of Variables................................................................... 74 Example Input File......................................................................... 76 Available observation types................................................................ 76 Example Observation Input File............................................................. 77 River (RIV) Package..........................................................................